Discussion:
Inverter AM Interference
(too old to reply)
SOLARPRO
2009-07-15 00:48:39 UTC
Permalink
Hello:

Has anybody got a fix or a way to filter out inverter generated AM (
520-700 kHz MW) noise? I guess it's never been a problem in the past because
our customers must not have been fans of AM radio. Plus, I always approved
of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not very
ambulatory, sits in the same spot most of the day and just loves talk
radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there anything
we can do?

Patrick Redgate
Ameco Solar
**************Can love help you live longer? Find out now.
(http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweu
slove00000001)
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Dave Click
2009-07-15 01:26:01 UTC
Permalink
Weird! I was looking through the list archive for info on lightning
arrestors earlier this afternoon and coincidentally, this email may
help, from Aaron Wellendorf on 2006/4/12:
http://lists.re-wrenches.org/htdig.cgi/re-wrenches-re-wrenches.org/2006/019214.html

"I have used a different brand of AC surge arrestor with noise filtering to
quiet the AC line into a grid-tied Trace SW4048 back in 1999. It didn't
completely filter out all noise, but it did make my customer's favorite
680AM radio station listenable vs. a totally static roar. I put them on all
my systems after that, SW or not."

He doesn't say what surge arrestor he uses, but hopefully this helps
your customer.

DKC

-------- Original Message --------
Subject: [RE-wrenches] Inverter AM Interference
From: SOLARPRO at aol.com
To: re-wrenches at lists.re-wrenches.org
Date: 2009/7/14 20:48
Has anybody got a fix or a way to filter out inverter generated AM
( 520-700 kHz MW) noise? I guess it's never been a problem in the past
because our customers must not have been fans of AM radio. Plus, I
always approved of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not
very ambulatory, sits in the same spot most of the day and just loves
talk radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there
anything we can do?
Patrick Redgate
Ameco Solar
------------------------------------------------------------------------
Can love help you live longer? Find out now
<http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweuslove00000001>.
------------------------------------------------------------------------
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Dan Fink
2009-07-15 01:48:16 UTC
Permalink
Ouch! From a brand-new SMA? I thought AM interference was mostly
banished when the Trace SW series was introduced.

My checklist when I consult (and this question is fairly common), these
are in no particular order:

1) Be absolutely sure it's the inverter causing the problem; I've seen
lots of interference from BOS components, especially amp-hour meters.
1.5) Find out if the problem is conducted RFI in your wires, or radiated
RFI picked up by the AM antenna, or both. IE, try a battery-powered AM
radio.
2) Replace your 15-year old modified square wave inverter with a true
sine wave model. (OUCH! It's really a new SMA?)
3) Twist the battery --> inverter main +/- cables together. Tough if you
are in conduit.
4) Consider a filter capacitor across the inverter input.
5) Use an external AM antenna for the radio, and locate it well away
from the house.
6) Double check that the main system ground connection is excellent, and
those of all equipment and boxes.
7) Some inverters are just plain noisy on AM!
8) Some AM radios, especially modern ones, just plain suck on RFI
rejection. They don't make 'em like they used to. Try a better AM radio,
or even an old-school one.

I have a notoriously noisy inverter, but it's been "on" for 15 years now
without a hitch and I like that. For late-night baseball games on AM, I
take a battery-powered radio, and place it in a coal scuttle for
shielding. By placing the coal scuttle in *exactly* the right spot in
the middle of the room, and orienting it in the right direction so that
the RFI blocked, it works great.

AM interference is tricky stuff. Ask your customer if they can get a
simulcast of their favorite AM station on Fm anywhere?

DAN FINK
http://www.otherpower.com/
Has anybody got a fix or a way to filter out inverter generated AM
( 520-700 kHz MW) noise? I guess it's never been a problem in the past
because our customers must not have been fans of AM radio. Plus, I
always approved of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not
very ambulatory, sits in the same spot most of the day and just loves
talk radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there
anything we can do?
Patrick Redgate
Ameco Solar
jay peltz
2009-07-15 02:30:02 UTC
Permalink
Anybody heard of any interference from a Magnum or a magnum meter?

thanks,

jay
peltz power
robert ellison
2009-07-15 13:11:30 UTC
Permalink
I will try the AM on the Magnum 4024 and on the generator when i get to the
shop, much later today.
I must admit that I have not tried it in the last few years, I just accepted
it would not work well !

Bob
Post by jay peltz
Anybody heard of any interference from a Magnum or a magnum meter?
thanks,
jay
peltz power
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Howie Michaelson
2009-07-15 14:51:38 UTC
Permalink
Hi Jay,

About 18 months age (?) I inquired on the list about radio interference
from a somewhat early version of the Magnum MS4024 which I put in my
off-grid home (replacing an SW4024 which was fried by an amazing lightning
strike). Never had any radio interference that I noticed with the SW.
Magnum had no real advice or thoughts about it, and said noone else had
complained about it - they mostly thought it was something I was doing (or
not doing). It might be a slight change in the routing of the conductors
(it is siting on an E-Panel). It also interferes with the phone, both
wired and cordless. I did try a little shielding around the wiring, and
switched cordless phones, so things are a little better, but FM radio
stations are certainly harder to get cleanly now (haven't tried AM). I
never was able to change it significantly, although I haven't tried some
of the electronic solutions that were suggested, that I'd have to dig back
through my notes to find at this point.

Wish I could be of more help,
Howie
--
Howie Michaelson
NABCEP Certified Solar PV Installer?

Sun Catcher, LLC
Renewable Energy Systems Sales and Service
VT Solar & Wind Incentive Program Partner
http://www.SunCatcherVT.com
(cell) 802-272-0004
(home) 802-439-6096
Post by jay peltz
Anybody heard of any interference from a Magnum or a magnum meter?
thanks,
jay
peltz power
robert ellison
2009-07-15 13:11:30 UTC
Permalink
I will try the AM on the Magnum 4024 and on the generator when i get to the
shop, much later today.
I must admit that I have not tried it in the last few years, I just accepted
it would not work well !

Bob
Post by jay peltz
Anybody heard of any interference from a Magnum or a magnum meter?
thanks,
jay
peltz power
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Howie Michaelson
2009-07-15 14:51:38 UTC
Permalink
Hi Jay,

About 18 months age (?) I inquired on the list about radio interference
from a somewhat early version of the Magnum MS4024 which I put in my
off-grid home (replacing an SW4024 which was fried by an amazing lightning
strike). Never had any radio interference that I noticed with the SW.
Magnum had no real advice or thoughts about it, and said noone else had
complained about it - they mostly thought it was something I was doing (or
not doing). It might be a slight change in the routing of the conductors
(it is siting on an E-Panel). It also interferes with the phone, both
wired and cordless. I did try a little shielding around the wiring, and
switched cordless phones, so things are a little better, but FM radio
stations are certainly harder to get cleanly now (haven't tried AM). I
never was able to change it significantly, although I haven't tried some
of the electronic solutions that were suggested, that I'd have to dig back
through my notes to find at this point.

Wish I could be of more help,
Howie
--
Howie Michaelson
NABCEP Certified Solar PV Installer?

Sun Catcher, LLC
Renewable Energy Systems Sales and Service
VT Solar & Wind Incentive Program Partner
http://www.SunCatcherVT.com
(cell) 802-272-0004
(home) 802-439-6096
Post by jay peltz
Anybody heard of any interference from a Magnum or a magnum meter?
thanks,
jay
peltz power
Drake Chamberlin
2009-07-15 22:00:56 UTC
Permalink
Post by Dan Fink
2) Replace your 15-year old modified square wave inverter with a
true sine wave model. (OUCH! It's really a new SMA?)
The SMA Sunny Island requires metal conduit for the battery cables, for RFI.


Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648
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Wind-sun.com
2009-07-16 14:42:55 UTC
Permalink
In some cases we have had good luck with Ferrite filters. But not always, and not always easy to find the source of the noise.

..................................................................................................
Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
..................................................................................................
----- Original Message -----
From: Drake Chamberlin
To: Dan Fink ; RE-wrenches
Sent: Wednesday, July 15, 2009 3:00 PM
Subject: Re: [RE-wrenches] Inverter AM Interference


At 09:48 PM 7/14/2009, you wrote:

2) Replace your 15-year old modified square wave inverter with a true sine wave model. (OUCH! It's really a new SMA?)


The SMA Sunny Island requires metal conduit for the battery cables, for RFI.


Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648



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Wind-sun.com
2009-07-16 14:42:55 UTC
Permalink
In some cases we have had good luck with Ferrite filters. But not always, and not always easy to find the source of the noise.

..................................................................................................
Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
..................................................................................................
----- Original Message -----
From: Drake Chamberlin
To: Dan Fink ; RE-wrenches
Sent: Wednesday, July 15, 2009 3:00 PM
Subject: Re: [RE-wrenches] Inverter AM Interference


At 09:48 PM 7/14/2009, you wrote:

2) Replace your 15-year old modified square wave inverter with a true sine wave model. (OUCH! It's really a new SMA?)


The SMA Sunny Island requires metal conduit for the battery cables, for RFI.


Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648



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jay peltz
2009-07-15 02:30:02 UTC
Permalink
Anybody heard of any interference from a Magnum or a magnum meter?

thanks,

jay
peltz power
Drake Chamberlin
2009-07-15 22:00:56 UTC
Permalink
Post by Dan Fink
2) Replace your 15-year old modified square wave inverter with a
true sine wave model. (OUCH! It's really a new SMA?)
The SMA Sunny Island requires metal conduit for the battery cables, for RFI.


Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648
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Jeff Yago
2009-07-15 03:07:06 UTC
Permalink
We see the most AM radio interference with Fronius inverters, but the distance must be close. I listen to AM talk radio most of day and it is usually on in the car when I leave the office. My car is parked right next to our office on the exterior side of the garage that has the Fronius Inverter. When I get in a car or any of our trucks, the AM band is totally trashed until I back about 30 feet away, then it goes away. Seems to affect all radios, but the distance is limited. It does not affect the AM radios in the office area, which is about 40 feet and 2 walls away. I have not found this to be a problem with Outback equipment.

Jeff Yago

_____________________________________________________________
Netscape. Just the Net You Need.
robert ellison
2009-07-15 10:27:15 UTC
Permalink
I am a fan of talk radio and have always had a problem when the car gets
within 30' of the inverter, the brand seems to make no difference. The house
radio never had a chance.
I don't know if it applies to grid tie only inverters or not but suspect it
might be the same.

Interested in an easy cure also,

Bob
Has anybody got a fix or a way to filter out inverter generated AM
( 520-700 kHz MW) noise? I guess it's never been a problem in the past
because our customers must not have been fans of AM radio. Plus, I
always approved of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not very
ambulatory, sits in the same spot most of the day and just loves talk
radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there anything
we can do?
Patrick Redgate
Ameco Solar
------------------------------
Can love help you live longer? Find out now<http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweuslove00000001>
.
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David G Katz
2009-07-15 15:11:05 UTC
Permalink
I have always had problems with AM radio in my remote home. I have more
problems when it is connected to AC or DC for power. Try running it on
batteries. I switched to a CCrane internet radio and now I get 1000s of
stations very clear, but you need broadband internet.
David

David Katz

President

AEE Solar

1155 Redway Drive

P.O. Box 339

Redway, CA 95560

Tel (707) 825-1200

Fax (707) 825-1202

david at aeesolar.com <mailto:david at aeesolar.com>

www.aeesolar.com <http://www.aeesolar.com>



DISCLAIMER:
This communication, along with any documents, files or attachments, is
intended for the use of only the addressee and contains privileged and
confidential information. If you are not the intended recipient, you are
hereby notified that any dissemination, distribution or copying of any
information contained in or attached to this communication is strictly
prohibited. If you have received this message in error, please notify
the sender immediately by e-mail reply and destroy the original
communication and its attachments without reading, printing or saving in
any manner.

P Please consider the environment before printing this e-mail.
Has anybody got a fix or a way to filter out inverter generated AM
( 520-700 kHz MW) noise? I guess it's never been a problem in the
past because our customers must not have been fans of AM radio. Plus,
I always approved of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not
very ambulatory, sits in the same spot most of the day and just loves
talk radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there
anything we can do?
Patrick Redgate
Ameco Solar
Can love help you live longer? Find out now
<http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweuslove00000001>.
------------------------------------------------------------------------
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Chris Schaefer
2009-07-15 15:49:47 UTC
Permalink
To All,

I also tried changing to a CCrane radio and external antenna with no real
change. The radio was/is the Sangean and it doesn't matter if I use the AC
adapter or battery power. My Bose has no issues with FM but forget AM. Same
deal with the truck when parked next to the twin SW5548. Pull out and then I
can listen to my Ditto Heads with a smile:). David, thanks for the tip on
the internet radio.





Chris Schaefer

Solar and Wind FX Inc.

5115 South Hill Road

Canandaigua(Bristol Center) New York 14424

585.229.2083

Cell 748.1870

chris at solarandwindfx.com

http://www.solarandwindfx.com/

Where Knowledge Equals Power Independence





***CONFIDENTIALITY NOTICE***

The information in this email may be confidential and/or privileged. This
email is intended to be reviewed by only the individual or organization
named above. If you are not the intended recipient or an authorized
representative of the intended recipient, you are hereby notified that any
review, dissemination or copying of this email and its attachments, if any,
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_____

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of David G Katz
Sent: 15 July, 2009 11:11
To: RE-wrenches
Subject: Re: [RE-wrenches] Inverter AM Interference



I have always had problems with AM radio in my remote home. I have more
problems when it is connected to AC or DC for power. Try running it on
batteries. I switched to a CCrane internet radio and now I get 1000s of
stations very clear, but you need broadband internet.
David

David Katz

President

AEE Solar

1155 Redway Drive

P.O. Box 339

Redway, CA 95560

Tel (707) 825-1200

Fax (707) 825-1202

david at aeesolar.com

www.aeesolar.com



DISCLAIMER:
This communication, along with any documents, files or attachments, is
intended for the use of only the addressee and contains privileged and
confidential information. If you are not the intended recipient, you are
hereby notified that any dissemination, distribution or copying of any
information contained in or attached to this communication is strictly
prohibited. If you have received this message in error, please notify the
sender immediately by e-mail reply and destroy the original communication
and its attachments without reading, printing or saving in any manner.

P Please consider the environment before printing this e-mail.



SOLARPRO at aol.com wrote:


Hello:



Has anybody got a fix or a way to filter out inverter generated AM ( 520-700
kHz MW) noise? I guess it's never been a problem in the past because our
customers must not have been fans of AM radio. Plus, I always approved of
the fact that it wiped out reception for ditto-heads.

We called SMA and they are in a state of denial. Our customer is not very
ambulatory, sits in the same spot most of the day and just loves talk radio.
The inverter is more than 30 feet away from the radio.

Other than relocating the inverter (grid-tie, no battery) is there anything
we can do?



Patrick Redgate

Ameco Solar


Can love help you live longer? Find out now
<http://personals.aol.com/articles/2009/02/18/longer-lives-through-relations
hips/?ncid=emlweuslove00000001> .







_____




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Chris Schaefer
2009-07-15 15:49:47 UTC
Permalink
To All,

I also tried changing to a CCrane radio and external antenna with no real
change. The radio was/is the Sangean and it doesn't matter if I use the AC
adapter or battery power. My Bose has no issues with FM but forget AM. Same
deal with the truck when parked next to the twin SW5548. Pull out and then I
can listen to my Ditto Heads with a smile:). David, thanks for the tip on
the internet radio.





Chris Schaefer

Solar and Wind FX Inc.

5115 South Hill Road

Canandaigua(Bristol Center) New York 14424

585.229.2083

Cell 748.1870

chris at solarandwindfx.com

http://www.solarandwindfx.com/

Where Knowledge Equals Power Independence





***CONFIDENTIALITY NOTICE***

The information in this email may be confidential and/or privileged. This
email is intended to be reviewed by only the individual or organization
named above. If you are not the intended recipient or an authorized
representative of the intended recipient, you are hereby notified that any
review, dissemination or copying of this email and its attachments, if any,
or the information contained herein is prohibited. If you have received this
email in error, please immediately notify the sender by return email and
delete this message from your system.





_____

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of David G Katz
Sent: 15 July, 2009 11:11
To: RE-wrenches
Subject: Re: [RE-wrenches] Inverter AM Interference



I have always had problems with AM radio in my remote home. I have more
problems when it is connected to AC or DC for power. Try running it on
batteries. I switched to a CCrane internet radio and now I get 1000s of
stations very clear, but you need broadband internet.
David

David Katz

President

AEE Solar

1155 Redway Drive

P.O. Box 339

Redway, CA 95560

Tel (707) 825-1200

Fax (707) 825-1202

david at aeesolar.com

www.aeesolar.com



DISCLAIMER:
This communication, along with any documents, files or attachments, is
intended for the use of only the addressee and contains privileged and
confidential information. If you are not the intended recipient, you are
hereby notified that any dissemination, distribution or copying of any
information contained in or attached to this communication is strictly
prohibited. If you have received this message in error, please notify the
sender immediately by e-mail reply and destroy the original communication
and its attachments without reading, printing or saving in any manner.

P Please consider the environment before printing this e-mail.



SOLARPRO at aol.com wrote:


Hello:



Has anybody got a fix or a way to filter out inverter generated AM ( 520-700
kHz MW) noise? I guess it's never been a problem in the past because our
customers must not have been fans of AM radio. Plus, I always approved of
the fact that it wiped out reception for ditto-heads.

We called SMA and they are in a state of denial. Our customer is not very
ambulatory, sits in the same spot most of the day and just loves talk radio.
The inverter is more than 30 feet away from the radio.

Other than relocating the inverter (grid-tie, no battery) is there anything
we can do?



Patrick Redgate

Ameco Solar


Can love help you live longer? Find out now
<http://personals.aol.com/articles/2009/02/18/longer-lives-through-relations
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_____




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SOLARPRO
2009-07-15 23:57:44 UTC
Permalink
Hello again:

This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it must be AC
related.
I found out today that roam (or freedom) phones do not work at this home.
Since it was built with wire mesh in the walls - this was a transition
method used after plaster and before drywall...sometime in the late 40's early
50's - we are all supposing that this is the reason that the phones do not
work.
But could living in a modified Faraday cage have something to do with it?
I am taking my job site tested boom box over there tomorrow to see if
running unplugged helps. Maybe we can rig up an antenna for the BOSE....a
metal coat hanger in a vent pipe should do it.
I'll let you know....

Patrick Redgate
Ameco Solar



In a message dated 7/15/2009 2:52:50 P.M. Pacific Daylight Time,
drake.chamberlin at redwoodalliance.org writes:

At 09:48 PM 7/14/2009, you wrote:

2) Replace your 15-year old modified square wave inverter with a true sine
wave model. (OUCH! It's really a new SMA?)


The SMA Sunny Island requires metal conduit for the battery cables, for
RFI.

Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648



**************Can love help you live longer? Find out now.
(http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweu
slove00000001)
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boB Gudgel
2009-07-16 00:11:47 UTC
Permalink
Post by SOLARPRO
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?

boB
boB Gudgel
2009-07-16 00:11:47 UTC
Permalink
Post by SOLARPRO
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?

boB
SOLARPRO
2009-07-16 00:14:00 UTC
Permalink
It disappears when the breaker is thrown.
Pat Redgate


In a message dated 7/15/2009 5:11:58 P.M. Pacific Daylight Time,
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?

boB

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boB Gudgel
2009-07-16 00:30:11 UTC
Permalink
Post by SOLARPRO
It disappears when the breaker is thrown.
Pat Redgate
OK, is that the AC breaker or the PV input breaker ?

How about when you throw the PV input breaker (when not MPPTing) ? Does
that help ?

i.e. We know now that it's the inverter's auxiliary power supply, but
is the signal also getting
out (radiating) through the PV lines ? It could also come out the PV
negative so throwing just the PV input
positive breaker, by itself, may not tell the whole story.

If it's coming through the AC line, then a line filter, or running all
of the AC side wires through
a ferrite toroid may help.

boB
Post by SOLARPRO
In a message dated 7/15/2009 5:11:58 P.M. Pacific Daylight Time,
Post by SOLARPRO
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?
boB
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jay peltz
2009-07-17 04:36:02 UTC
Permalink
HI all,

I've got a different issue here with FM interference.

I replaced an old Trace DR with a Magnum 4024 pure sine wave.
The radio in question, or location is within 15' from the inverter.
The interference is there on a portable FM unit as well.
There is no interference with just the generator, but is there if the
inverter is charging.

So any help on this?

thanks,

jay
peltz power
Post by SOLARPRO
It disappears when the breaker is thrown.
Pat Redgate
In a message dated 7/15/2009 5:11:58 P.M. Pacific Daylight Time, boB at midnitesolar.com
Post by SOLARPRO
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?
boB
_______________________________________________
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boB Gudgel
2009-07-16 00:30:11 UTC
Permalink
Post by SOLARPRO
It disappears when the breaker is thrown.
Pat Redgate
OK, is that the AC breaker or the PV input breaker ?

How about when you throw the PV input breaker (when not MPPTing) ? Does
that help ?

i.e. We know now that it's the inverter's auxiliary power supply, but
is the signal also getting
out (radiating) through the PV lines ? It could also come out the PV
negative so throwing just the PV input
positive breaker, by itself, may not tell the whole story.

If it's coming through the AC line, then a line filter, or running all
of the AC side wires through
a ferrite toroid may help.

boB
Post by SOLARPRO
In a message dated 7/15/2009 5:11:58 P.M. Pacific Daylight Time,
Post by SOLARPRO
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?
boB
_______________________________________________
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jay peltz
2009-07-17 04:36:02 UTC
Permalink
HI all,

I've got a different issue here with FM interference.

I replaced an old Trace DR with a Magnum 4024 pure sine wave.
The radio in question, or location is within 15' from the inverter.
The interference is there on a portable FM unit as well.
There is no interference with just the generator, but is there if the
inverter is charging.

So any help on this?

thanks,

jay
peltz power
Post by SOLARPRO
It disappears when the breaker is thrown.
Pat Redgate
In a message dated 7/15/2009 5:11:58 P.M. Pacific Daylight Time, boB at midnitesolar.com
Post by SOLARPRO
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?
boB
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches at lists.re-wrenches.org
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Exeltech
2009-07-16 17:02:01 UTC
Permalink
Interference from inverters will always be an issue. It's a difficult topic for many to understand .. and equally difficult to reduce. Note you can reduce .. but not eliminate the interference.

To complicate things, the farther a radio is from the transmitter, the more difficult this issue will be to resolve.

Here's why...

To achieve the highest efficiency possible, inverter power circuits today transition from off to on in an extremely short time, as in totally off to totally on in microseconds .. or even nanoseconds. Internally, within the inverter, even "sine" wave models use square waves at various points. Why? Solid state devices operate with the least energy loss when they're completely off .. or turned on in a strongly "saturated" mode - meaning turned on to their maximum possible level with the least possible resistance. The transition from off to on is commonly done in one step, from zero to max .. then back again.

Micro-processor clocks also operate in this fashion, as do the signals within the processor, and any related communications circuits.

Square waves are a composite of a sine wave, plus all odd harmonics (odd integer multiples) of the original sine wave frequency. To create a 100 kHz square wave, we start with a 100 kHz sine wave and add sine waves of 300 kHz, 500 kHz, 700 kHz .. and so forth, up into the many Mhz region. The number of harmonics added is astonishing.

As a consequence, these harmonics radiate into the AM broadcast band .. and far beyond. To make matters worse, the circuits in inverters are not "linear", which is to say they don't faithfully reproduce the exact waveform put into them. It's done by intent, but with a side-effect. This non-linearity turns the circuits into "mixers". Mixers are a part of every radio and television. We use mixer circuits to combine two frequencies and obtain others. When non-linear circuits are fed a large number of signals, they add and subtract all the various combinations of signals to create still other frequencies .. and so it goes.

Radio frequency interference ("RFI") originates from many different aspects of an inverter. If the inverter is battery-based, you'll have many hundreds of amps being switched on and off very rapidly by the inverter "front end". To handle the hundreds of amps, the input resistance ("impedance") of the inverter must be very low .. on the order of a few milliohms.

String inverters connected to a series array of PV operate on the same principals, but at lower currents and higher voltages than their battery-based counterparts.

RFI filters work on the basis of a voltage divider, posing a very high impedance to the interference (blocking it), but a very low impedance to the DC that must flow, minimizing loss at DC. This is a very difficult challenge due to the high amperages involved.

The same is true of inverter AC output circuits. AC output is more easily addressed because the current is much lower than the DC input (battery based systems only). Conversely, inverters connect to AC circuits in the home, turning every inch of the house wiring into an antenna that radiates the interference.

As mentioned earlier in this thread, it's best to reduce the interference at the source - in this case, the inverter.

First step is to try to determine where the bulk of the interference is originating. The DC leads? AC leads? Inverter case? All the above? Each has its own set of possible steps to reduce RFI. Leads are the most likely culprit. A battery-operated shortwave radio with a signal strength indicator can be an invaluable tool here. If you have one, you're ahead of the game. If you consider buying one .. ensure it also receives the AM broadcast band. Most do.


Basic rules:

1) Keep the DC leads from the battery to the inverter as short as practicable.


2) Twist the DC leads together if possible. If not possible, keep them as close together as you can. The goal is to have the RFI magnetic energy from each lead cancel the RFI magnetic energy in the other. As was also pointed out, it may be helpful to run each DC leg in metal conduit and then GROUND the conduit to an earth ground - the shorter the better. Failure to ground the conduit will simply turn the conduit into another antenna. An RFI ground is separate from the earth "protective" ground. If you use the AC "ground", it too becomes an antenna unless it's kept short, and you've got a good connection to the grounding electrode conductor with highly conductive earth. It's tough to achieve all three together, but it can be done in some locations.

Someone suggested a "filter capacitor" be connected across the DC leads. This won't hurt, but isn't likely to be effective given the very low impedance of inverter input circuits.


3) Ferrite cores may be slipped over the length of each cable, and placed at the point where the cables exit the inverter. Toroid cores or similar may be of help, but you'll need many of them, and they'll need to extend at least two to three feet starting at the inverter. More is better, and keep in mind .. when many are used .. they're heavy.

Do not install them at the battery end. Installing at the battery end, and leaving some cable exposed at the inverter allows the exposed conductors at the inverter to act as antennas.

Select the proper type of ferrite. Surprisingly, various formulations of ferrite react differently depending on the frequency range in which they're used. For example, some ferrites are good for 100-500 Mhz, and would not do a good job blocking RFI that interferes with AM radio. For AM radio RFI, select ferrite that's rated to work from 250 kHz up to 2 Mhz or more.


4) AC EMI/RFI filters are also available, and may be installed on the AC output circuit at the inverter. These are made by Corcom, Tyco, and others. Select a unit rated for the output voltage AND current of the inverter. RFI filters will be UL/ETL/CSA recognized. If you find some that aren't .. don't buy them.


5) As was suggested, a radio with external antenna may help, especially if the antenna is fed with coaxial cable, which can act as a shield until the cable is well away from the house and/or inverter. Keep the radio antenna as far from the inverter and house wiring as you can.


6) A battery-operated radio is also an option. This too was mentioned earlier in this thread. Even well-filtered inverter AC output always carries with it some level of interference. A weak radio signal will still be affected by a weak source of interference.


7) Ground the inverter housing in accordance with the manufacturer's instructions. All inverters today are required to meet certain levels of FCC interference criteria. Actions of internal RFI filtering circuits may be improved if the inverter is properly grounded.


8) Ever drive into a parking garage while listening to the radio, and the radio station gets very weak or disappears altogether?? Same thing happens when we drive through long highway tunnels.

We can make use of that trait. It's caused by the reinforcing steel bars ("re-bar") acting to block the radio signals from getting to the antenna on your vehicle. The same characteristic that keeps signals from getting to your radio, also works to keep interference IN.

In addition to all the above, you may have to construct a screen around the entire inverter, then connect the screen itself to earth ground. This screen should NOT come into contact with the inverter housing. To do so would defeat the purpose of the screen. However, properly filtered DC and AC leads may pass through it.

In this case, you'll be constructing a "Faraday shield", which will keep interference inside. Surprisingly, this can be ferrous or non-ferrous metal. I'd recommend ferrous (such as chicken wire with small openings), for ease of soldering. Build a "box" around the inverter, including the back of the inverter. To do this, you'll need a board or other means to keep the inverter enclosure from contacting the wire.

Once you've constructed the box .. connect the box to its own "RFI" earth ground. This will be similar to a standard protective ground.

Next, add a bond wire from the RFI ground to the system protective earth for the system. This RFI-ground to safety ground bond wire should be outside if you can .. and buried in the soil if at all possible. Adding this bond wire avoids opportunity for AC ground loops or other issues. Keeping it in the soil also slightly reduces the opportunity it will become an antenna for the interference. If all the above are done properly, they won't impact the effectiveness of the box you've just constructed.


Reducing radio frequency interference is, at best, a snipe hunt. The strength of the radio/TV station signal itself can and will vary, and is dependant on a variety of variables. This can give the impression something you've done had an effect on the interference level from the inverter, where in fact you didn't change a thing. The weaker the radio signal, the more difficult it will be to reduce the interference from the inverter to make the radio signal listenable.


The best thing to do is keep the inverter and all of its wiring as far from the radios as you can. If this simply isn't possible .. see steps 1-8.

I wish you well.


Dan Lepinski
Sr. Engineer
Exeltech


Hunting and smothering RFI for more than 40 years ...
Larry Crutcher, Starlight Solar
2009-07-16 19:01:07 UTC
Permalink
Excellent Dan! The first thing I would do in most cases is your #5.
Increasing the RF signal to the receiver will usually overcome the
relatively low level RFI. As an amateur operator (KB5HMU) I sometimes
have to deal with close RFI at 160 meters, 1.8 to 2kHz. I have a
tunable dipole with preamp and simply tuning the preamp to the
frequency, which increases gain, the RFI can be eliminated. So try
improving the AM reception first. For sure it will make an improvement.

Larry
Post by Exeltech
Interference from inverters will always be an issue. It's a
difficult topic for many to understand .. and equally difficult to
reduce. Note you can reduce .. but not eliminate the interference.
To complicate things, the farther a radio is from the transmitter,
the more difficult this issue will be to resolve.
Here's why...
To achieve the highest efficiency possible, inverter power circuits
today transition from off to on in an extremely short time, as in
totally off to totally on in microseconds .. or even nanoseconds.
Internally, within the inverter, even "sine" wave models use square
waves at various points. Why? Solid state devices operate with the
least energy loss when they're completely off .. or turned on in a
strongly "saturated" mode - meaning turned on to their maximum
possible level with the least possible resistance. The transition
from off to on is commonly done in one step, from zero to max ..
then back again.
Micro-processor clocks also operate in this fashion, as do the
signals within the processor, and any related communications circuits.
Square waves are a composite of a sine wave, plus all odd harmonics
(odd integer multiples) of the original sine wave frequency. To
create a 100 kHz square wave, we start with a 100 kHz sine wave and
add sine waves of 300 kHz, 500 kHz, 700 kHz .. and so forth, up into
the many Mhz region. The number of harmonics added is astonishing.
As a consequence, these harmonics radiate into the AM broadcast
band .. and far beyond. To make matters worse, the circuits in
inverters are not "linear", which is to say they don't faithfully
reproduce the exact waveform put into them. It's done by intent,
but with a side-effect. This non-linearity turns the circuits into
"mixers". Mixers are a part of every radio and television. We use
mixer circuits to combine two frequencies and obtain others. When
non-linear circuits are fed a large number of signals, they add and
subtract all the various combinations of signals to create still
other frequencies .. and so it goes.
Radio frequency interference ("RFI") originates from many different
aspects of an inverter. If the inverter is battery-based, you'll
have many hundreds of amps being switched on and off very rapidly by
the inverter "front end". To handle the hundreds of amps, the input
resistance ("impedance") of the inverter must be very low .. on the
order of a few milliohms.
String inverters connected to a series array of PV operate on the
same principals, but at lower currents and higher voltages than
their battery-based counterparts.
RFI filters work on the basis of a voltage divider, posing a very
high impedance to the interference (blocking it), but a very low
impedance to the DC that must flow, minimizing loss at DC. This is
a very difficult challenge due to the high amperages involved.
The same is true of inverter AC output circuits. AC output is more
easily addressed because the current is much lower than the DC input
(battery based systems only). Conversely, inverters connect to AC
circuits in the home, turning every inch of the house wiring into an
antenna that radiates the interference.
As mentioned earlier in this thread, it's best to reduce the
interference at the source - in this case, the inverter.
First step is to try to determine where the bulk of the interference
is originating. The DC leads? AC leads? Inverter case? All the
above? Each has its own set of possible steps to reduce RFI. Leads
are the most likely culprit. A battery-operated shortwave radio
with a signal strength indicator can be an invaluable tool here. If
you have one, you're ahead of the game. If you consider buying
one .. ensure it also receives the AM broadcast band. Most do.
1) Keep the DC leads from the battery to the inverter as short as practicable.
2) Twist the DC leads together if possible. If not possible, keep
them as close together as you can. The goal is to have the RFI
magnetic energy from each lead cancel the RFI magnetic energy in the
other. As was also pointed out, it may be helpful to run each DC
leg in metal conduit and then GROUND the conduit to an earth ground
- the shorter the better. Failure to ground the conduit will simply
turn the conduit into another antenna. An RFI ground is separate
from the earth "protective" ground. If you use the AC "ground", it
too becomes an antenna unless it's kept short, and you've got a good
connection to the grounding electrode conductor with highly
conductive earth. It's tough to achieve all three together, but it
can be done in some locations.
Someone suggested a "filter capacitor" be connected across the DC
leads. This won't hurt, but isn't likely to be effective given the
very low impedance of inverter input circuits.
3) Ferrite cores may be slipped over the length of each cable, and
placed at the point where the cables exit the inverter. Toroid
cores or similar may be of help, but you'll need many of them, and
they'll need to extend at least two to three feet starting at the
inverter. More is better, and keep in mind .. when many are used ..
they're heavy.
Do not install them at the battery end. Installing at the battery
end, and leaving some cable exposed at the inverter allows the
exposed conductors at the inverter to act as antennas.
Select the proper type of ferrite. Surprisingly, various
formulations of ferrite react differently depending on the frequency
range in which they're used. For example, some ferrites are good
for 100-500 Mhz, and would not do a good job blocking RFI that
interferes with AM radio. For AM radio RFI, select ferrite that's
rated to work from 250 kHz up to 2 Mhz or more.
4) AC EMI/RFI filters are also available, and may be installed on
the AC output circuit at the inverter. These are made by Corcom,
Tyco, and others. Select a unit rated for the output voltage AND
current of the inverter. RFI filters will be UL/ETL/CSA
recognized. If you find some that aren't .. don't buy them.
5) As was suggested, a radio with external antenna may help,
especially if the antenna is fed with coaxial cable, which can act
as a shield until the cable is well away from the house and/or
inverter. Keep the radio antenna as far from the inverter and house
wiring as you can.
6) A battery-operated radio is also an option. This too was
mentioned earlier in this thread. Even well-filtered inverter AC
output always carries with it some level of interference. A weak
radio signal will still be affected by a weak source of interference.
7) Ground the inverter housing in accordance with the manufacturer's
instructions. All inverters today are required to meet certain
levels of FCC interference criteria. Actions of internal RFI
filtering circuits may be improved if the inverter is properly
grounded.
8) Ever drive into a parking garage while listening to the radio,
and the radio station gets very weak or disappears altogether??
Same thing happens when we drive through long highway tunnels.
We can make use of that trait. It's caused by the reinforcing steel
bars ("re-bar") acting to block the radio signals from getting to
the antenna on your vehicle. The same characteristic that keeps
signals from getting to your radio, also works to keep interference
IN.
In addition to all the above, you may have to construct a screen
around the entire inverter, then connect the screen itself to earth
ground. This screen should NOT come into contact with the inverter
housing. To do so would defeat the purpose of the screen. However,
properly filtered DC and AC leads may pass through it.
In this case, you'll be constructing a "Faraday shield", which will
keep interference inside. Surprisingly, this can be ferrous or non-
ferrous metal. I'd recommend ferrous (such as chicken wire with
small openings), for ease of soldering. Build a "box" around the
inverter, including the back of the inverter. To do this, you'll
need a board or other means to keep the inverter enclosure from
contacting the wire.
Once you've constructed the box .. connect the box to its own "RFI"
earth ground. This will be similar to a standard protective ground.
Next, add a bond wire from the RFI ground to the system protective
earth for the system. This RFI-ground to safety ground bond wire
should be outside if you can .. and buried in the soil if at all
possible. Adding this bond wire avoids opportunity for AC ground
loops or other issues. Keeping it in the soil also slightly reduces
the opportunity it will become an antenna for the interference. If
all the above are done properly, they won't impact the effectiveness
of the box you've just constructed.
Reducing radio frequency interference is, at best, a snipe hunt.
The strength of the radio/TV station signal itself can and will
vary, and is dependant on a variety of variables. This can give the
impression something you've done had an effect on the interference
level from the inverter, where in fact you didn't change a thing.
The weaker the radio signal, the more difficult it will be to reduce
the interference from the inverter to make the radio signal
listenable.
The best thing to do is keep the inverter and all of its wiring as
far from the radios as you can. If this simply isn't possible ..
see steps 1-8.
I wish you well.
Dan Lepinski
Sr. Engineer
Exeltech
Hunting and smothering RFI for more than 40 years ...
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches at lists.re-wrenches.org
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
www.re-wrenches.org/etiquette.htm
www.members.re-wrenches.org
Wind-sun.com
2009-07-16 19:25:17 UTC
Permalink
Excellent article that sums it all up.

The one thing I would add is that ferrite filters don't actively "do"
anything - they just act like a high resistance to EMI/RFI and swamp it out,
so you can put as many as you want, anywhere, and it won't hurt anything
(but it may also not do anything) - limited only by your budget.

We have used them for years to reduce AM interference from 12 volt
flourescent lights.

..................................................................................................
Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
..................................................................................................
----- Original Message -----
From: "Exeltech" <exeltech at yahoo.com>
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Sent: Thursday, July 16, 2009 10:02 AM
Subject: [RE-wrenches] Inverter AM Interference - The Basics
Post by Exeltech
Interference from inverters will always be an issue. It's a difficult
topic for many to understand .. and equally difficult to reduce. Note you
can reduce .. but not eliminate the interference.
To complicate things, the farther a radio is from the transmitter, the
more difficult this issue will be to resolve.
Here's why...
To achieve the highest efficiency possible, inverter power circuits today
transition from off to on in an extremely short time, as in totally off to
totally on in microseconds .. or even nanoseconds. Internally, within the
inverter, even "sine" wave models use square waves at various points.
Why? Solid state devices operate with the least energy loss when they're
completely off .. or turned on in a strongly "saturated" mode - meaning
turned on to their maximum possible level with the least possible
resistance. The transition from off to on is commonly done in one step,
from zero to max .. then back again.
Micro-processor clocks also operate in this fashion, as do the signals
within the processor, and any related communications circuits.
Square waves are a composite of a sine wave, plus all odd harmonics (odd
integer multiples) of the original sine wave frequency. To create a 100
kHz square wave, we start with a 100 kHz sine wave and add sine waves of
300 kHz, 500 kHz, 700 kHz .. and so forth, up into the many Mhz region.
The number of harmonics added is astonishing.
As a consequence, these harmonics radiate into the AM broadcast band ..
and far beyond. To make matters worse, the circuits in inverters are not
"linear", which is to say they don't faithfully reproduce the exact
waveform put into them. It's done by intent, but with a side-effect.
This non-linearity turns the circuits into "mixers". Mixers are a part of
every radio and television. We use mixer circuits to combine two
frequencies and obtain others. When non-linear circuits are fed a large
number of signals, they add and subtract all the various combinations of
signals to create still other frequencies .. and so it goes.
Radio frequency interference ("RFI") originates from many different
aspects of an inverter. If the inverter is battery-based, you'll have
many hundreds of amps being switched on and off very rapidly by the
inverter "front end". To handle the hundreds of amps, the input
resistance ("impedance") of the inverter must be very low .. on the order
of a few milliohms.
String inverters connected to a series array of PV operate on the same
principals, but at lower currents and higher voltages than their
battery-based counterparts.
RFI filters work on the basis of a voltage divider, posing a very high
impedance to the interference (blocking it), but a very low impedance to
the DC that must flow, minimizing loss at DC. This is a very difficult
challenge due to the high amperages involved.
The same is true of inverter AC output circuits. AC output is more easily
addressed because the current is much lower than the DC input (battery
based systems only). Conversely, inverters connect to AC circuits in the
home, turning every inch of the house wiring into an antenna that radiates
the interference.
As mentioned earlier in this thread, it's best to reduce the interference
at the source - in this case, the inverter.
First step is to try to determine where the bulk of the interference is
originating. The DC leads? AC leads? Inverter case? All the above?
Each has its own set of possible steps to reduce RFI. Leads are the most
likely culprit. A battery-operated shortwave radio with a signal strength
indicator can be an invaluable tool here. If you have one, you're ahead
of the game. If you consider buying one .. ensure it also receives the AM
broadcast band. Most do.
1) Keep the DC leads from the battery to the inverter as short as practicable.
2) Twist the DC leads together if possible. If not possible, keep them as
close together as you can. The goal is to have the RFI magnetic energy
from each lead cancel the RFI magnetic energy in the other. As was also
pointed out, it may be helpful to run each DC leg in metal conduit and
then GROUND the conduit to an earth ground - the shorter the better.
Failure to ground the conduit will simply turn the conduit into another
antenna. An RFI ground is separate from the earth "protective" ground.
If you use the AC "ground", it too becomes an antenna unless it's kept
short, and you've got a good connection to the grounding electrode
conductor with highly conductive earth. It's tough to achieve all three
together, but it can be done in some locations.
Someone suggested a "filter capacitor" be connected across the DC leads.
This won't hurt, but isn't likely to be effective given the very low
impedance of inverter input circuits.
3) Ferrite cores may be slipped over the length of each cable, and placed
at the point where the cables exit the inverter. Toroid cores or similar
may be of help, but you'll need many of them, and they'll need to extend
at least two to three feet starting at the inverter. More is better, and
keep in mind .. when many are used .. they're heavy.
Do not install them at the battery end. Installing at the battery end,
and leaving some cable exposed at the inverter allows the exposed
conductors at the inverter to act as antennas.
Select the proper type of ferrite. Surprisingly, various formulations of
ferrite react differently depending on the frequency range in which
they're used. For example, some ferrites are good for 100-500 Mhz, and
would not do a good job blocking RFI that interferes with AM radio. For
AM radio RFI, select ferrite that's rated to work from 250 kHz up to 2 Mhz
or more.
4) AC EMI/RFI filters are also available, and may be installed on the AC
output circuit at the inverter. These are made by Corcom, Tyco, and
others. Select a unit rated for the output voltage AND current of the
inverter. RFI filters will be UL/ETL/CSA recognized. If you find some
that aren't .. don't buy them.
5) As was suggested, a radio with external antenna may help, especially if
the antenna is fed with coaxial cable, which can act as a shield until the
cable is well away from the house and/or inverter. Keep the radio antenna
as far from the inverter and house wiring as you can.
6) A battery-operated radio is also an option. This too was mentioned
earlier in this thread. Even well-filtered inverter AC output always
carries with it some level of interference. A weak radio signal will
still be affected by a weak source of interference.
7) Ground the inverter housing in accordance with the manufacturer's
instructions. All inverters today are required to meet certain levels of
FCC interference criteria. Actions of internal RFI filtering circuits may
be improved if the inverter is properly grounded.
8) Ever drive into a parking garage while listening to the radio, and the
radio station gets very weak or disappears altogether?? Same thing
happens when we drive through long highway tunnels.
We can make use of that trait. It's caused by the reinforcing steel bars
("re-bar") acting to block the radio signals from getting to the antenna
on your vehicle. The same characteristic that keeps signals from getting
to your radio, also works to keep interference IN.
In addition to all the above, you may have to construct a screen around
the entire inverter, then connect the screen itself to earth ground. This
screen should NOT come into contact with the inverter housing. To do so
would defeat the purpose of the screen. However, properly filtered DC and
AC leads may pass through it.
In this case, you'll be constructing a "Faraday shield", which will keep
interference inside. Surprisingly, this can be ferrous or non-ferrous
metal. I'd recommend ferrous (such as chicken wire with small openings),
for ease of soldering. Build a "box" around the inverter, including the
back of the inverter. To do this, you'll need a board or other means to
keep the inverter enclosure from contacting the wire.
Once you've constructed the box .. connect the box to its own "RFI" earth
ground. This will be similar to a standard protective ground.
Next, add a bond wire from the RFI ground to the system protective earth
for the system. This RFI-ground to safety ground bond wire should be
outside if you can .. and buried in the soil if at all possible. Adding
this bond wire avoids opportunity for AC ground loops or other issues.
Keeping it in the soil also slightly reduces the opportunity it will
become an antenna for the interference. If all the above are done
properly, they won't impact the effectiveness of the box you've just
constructed.
Reducing radio frequency interference is, at best, a snipe hunt. The
strength of the radio/TV station signal itself can and will vary, and is
dependant on a variety of variables. This can give the impression
something you've done had an effect on the interference level from the
inverter, where in fact you didn't change a thing. The weaker the radio
signal, the more difficult it will be to reduce the interference from the
inverter to make the radio signal listenable.
The best thing to do is keep the inverter and all of its wiring as far
from the radios as you can. If this simply isn't possible .. see steps
1-8.
I wish you well.
Dan Lepinski
Sr. Engineer
Exeltech
Hunting and smothering RFI for more than 40 years ...
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches at lists.re-wrenches.org
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
www.re-wrenches.org/etiquette.htm
www.members.re-wrenches.org
Larry Crutcher, Starlight Solar
2009-07-16 19:01:07 UTC
Permalink
Excellent Dan! The first thing I would do in most cases is your #5.
Increasing the RF signal to the receiver will usually overcome the
relatively low level RFI. As an amateur operator (KB5HMU) I sometimes
have to deal with close RFI at 160 meters, 1.8 to 2kHz. I have a
tunable dipole with preamp and simply tuning the preamp to the
frequency, which increases gain, the RFI can be eliminated. So try
improving the AM reception first. For sure it will make an improvement.

Larry
Post by Exeltech
Interference from inverters will always be an issue. It's a
difficult topic for many to understand .. and equally difficult to
reduce. Note you can reduce .. but not eliminate the interference.
To complicate things, the farther a radio is from the transmitter,
the more difficult this issue will be to resolve.
Here's why...
To achieve the highest efficiency possible, inverter power circuits
today transition from off to on in an extremely short time, as in
totally off to totally on in microseconds .. or even nanoseconds.
Internally, within the inverter, even "sine" wave models use square
waves at various points. Why? Solid state devices operate with the
least energy loss when they're completely off .. or turned on in a
strongly "saturated" mode - meaning turned on to their maximum
possible level with the least possible resistance. The transition
from off to on is commonly done in one step, from zero to max ..
then back again.
Micro-processor clocks also operate in this fashion, as do the
signals within the processor, and any related communications circuits.
Square waves are a composite of a sine wave, plus all odd harmonics
(odd integer multiples) of the original sine wave frequency. To
create a 100 kHz square wave, we start with a 100 kHz sine wave and
add sine waves of 300 kHz, 500 kHz, 700 kHz .. and so forth, up into
the many Mhz region. The number of harmonics added is astonishing.
As a consequence, these harmonics radiate into the AM broadcast
band .. and far beyond. To make matters worse, the circuits in
inverters are not "linear", which is to say they don't faithfully
reproduce the exact waveform put into them. It's done by intent,
but with a side-effect. This non-linearity turns the circuits into
"mixers". Mixers are a part of every radio and television. We use
mixer circuits to combine two frequencies and obtain others. When
non-linear circuits are fed a large number of signals, they add and
subtract all the various combinations of signals to create still
other frequencies .. and so it goes.
Radio frequency interference ("RFI") originates from many different
aspects of an inverter. If the inverter is battery-based, you'll
have many hundreds of amps being switched on and off very rapidly by
the inverter "front end". To handle the hundreds of amps, the input
resistance ("impedance") of the inverter must be very low .. on the
order of a few milliohms.
String inverters connected to a series array of PV operate on the
same principals, but at lower currents and higher voltages than
their battery-based counterparts.
RFI filters work on the basis of a voltage divider, posing a very
high impedance to the interference (blocking it), but a very low
impedance to the DC that must flow, minimizing loss at DC. This is
a very difficult challenge due to the high amperages involved.
The same is true of inverter AC output circuits. AC output is more
easily addressed because the current is much lower than the DC input
(battery based systems only). Conversely, inverters connect to AC
circuits in the home, turning every inch of the house wiring into an
antenna that radiates the interference.
As mentioned earlier in this thread, it's best to reduce the
interference at the source - in this case, the inverter.
First step is to try to determine where the bulk of the interference
is originating. The DC leads? AC leads? Inverter case? All the
above? Each has its own set of possible steps to reduce RFI. Leads
are the most likely culprit. A battery-operated shortwave radio
with a signal strength indicator can be an invaluable tool here. If
you have one, you're ahead of the game. If you consider buying
one .. ensure it also receives the AM broadcast band. Most do.
1) Keep the DC leads from the battery to the inverter as short as practicable.
2) Twist the DC leads together if possible. If not possible, keep
them as close together as you can. The goal is to have the RFI
magnetic energy from each lead cancel the RFI magnetic energy in the
other. As was also pointed out, it may be helpful to run each DC
leg in metal conduit and then GROUND the conduit to an earth ground
- the shorter the better. Failure to ground the conduit will simply
turn the conduit into another antenna. An RFI ground is separate
from the earth "protective" ground. If you use the AC "ground", it
too becomes an antenna unless it's kept short, and you've got a good
connection to the grounding electrode conductor with highly
conductive earth. It's tough to achieve all three together, but it
can be done in some locations.
Someone suggested a "filter capacitor" be connected across the DC
leads. This won't hurt, but isn't likely to be effective given the
very low impedance of inverter input circuits.
3) Ferrite cores may be slipped over the length of each cable, and
placed at the point where the cables exit the inverter. Toroid
cores or similar may be of help, but you'll need many of them, and
they'll need to extend at least two to three feet starting at the
inverter. More is better, and keep in mind .. when many are used ..
they're heavy.
Do not install them at the battery end. Installing at the battery
end, and leaving some cable exposed at the inverter allows the
exposed conductors at the inverter to act as antennas.
Select the proper type of ferrite. Surprisingly, various
formulations of ferrite react differently depending on the frequency
range in which they're used. For example, some ferrites are good
for 100-500 Mhz, and would not do a good job blocking RFI that
interferes with AM radio. For AM radio RFI, select ferrite that's
rated to work from 250 kHz up to 2 Mhz or more.
4) AC EMI/RFI filters are also available, and may be installed on
the AC output circuit at the inverter. These are made by Corcom,
Tyco, and others. Select a unit rated for the output voltage AND
current of the inverter. RFI filters will be UL/ETL/CSA
recognized. If you find some that aren't .. don't buy them.
5) As was suggested, a radio with external antenna may help,
especially if the antenna is fed with coaxial cable, which can act
as a shield until the cable is well away from the house and/or
inverter. Keep the radio antenna as far from the inverter and house
wiring as you can.
6) A battery-operated radio is also an option. This too was
mentioned earlier in this thread. Even well-filtered inverter AC
output always carries with it some level of interference. A weak
radio signal will still be affected by a weak source of interference.
7) Ground the inverter housing in accordance with the manufacturer's
instructions. All inverters today are required to meet certain
levels of FCC interference criteria. Actions of internal RFI
filtering circuits may be improved if the inverter is properly
grounded.
8) Ever drive into a parking garage while listening to the radio,
and the radio station gets very weak or disappears altogether??
Same thing happens when we drive through long highway tunnels.
We can make use of that trait. It's caused by the reinforcing steel
bars ("re-bar") acting to block the radio signals from getting to
the antenna on your vehicle. The same characteristic that keeps
signals from getting to your radio, also works to keep interference
IN.
In addition to all the above, you may have to construct a screen
around the entire inverter, then connect the screen itself to earth
ground. This screen should NOT come into contact with the inverter
housing. To do so would defeat the purpose of the screen. However,
properly filtered DC and AC leads may pass through it.
In this case, you'll be constructing a "Faraday shield", which will
keep interference inside. Surprisingly, this can be ferrous or non-
ferrous metal. I'd recommend ferrous (such as chicken wire with
small openings), for ease of soldering. Build a "box" around the
inverter, including the back of the inverter. To do this, you'll
need a board or other means to keep the inverter enclosure from
contacting the wire.
Once you've constructed the box .. connect the box to its own "RFI"
earth ground. This will be similar to a standard protective ground.
Next, add a bond wire from the RFI ground to the system protective
earth for the system. This RFI-ground to safety ground bond wire
should be outside if you can .. and buried in the soil if at all
possible. Adding this bond wire avoids opportunity for AC ground
loops or other issues. Keeping it in the soil also slightly reduces
the opportunity it will become an antenna for the interference. If
all the above are done properly, they won't impact the effectiveness
of the box you've just constructed.
Reducing radio frequency interference is, at best, a snipe hunt.
The strength of the radio/TV station signal itself can and will
vary, and is dependant on a variety of variables. This can give the
impression something you've done had an effect on the interference
level from the inverter, where in fact you didn't change a thing.
The weaker the radio signal, the more difficult it will be to reduce
the interference from the inverter to make the radio signal
listenable.
The best thing to do is keep the inverter and all of its wiring as
far from the radios as you can. If this simply isn't possible ..
see steps 1-8.
I wish you well.
Dan Lepinski
Sr. Engineer
Exeltech
Hunting and smothering RFI for more than 40 years ...
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches at lists.re-wrenches.org
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
www.re-wrenches.org/etiquette.htm
www.members.re-wrenches.org
Wind-sun.com
2009-07-16 19:25:17 UTC
Permalink
Excellent article that sums it all up.

The one thing I would add is that ferrite filters don't actively "do"
anything - they just act like a high resistance to EMI/RFI and swamp it out,
so you can put as many as you want, anywhere, and it won't hurt anything
(but it may also not do anything) - limited only by your budget.

We have used them for years to reduce AM interference from 12 volt
flourescent lights.

..................................................................................................
Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
..................................................................................................
----- Original Message -----
From: "Exeltech" <exeltech at yahoo.com>
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Sent: Thursday, July 16, 2009 10:02 AM
Subject: [RE-wrenches] Inverter AM Interference - The Basics
Post by Exeltech
Interference from inverters will always be an issue. It's a difficult
topic for many to understand .. and equally difficult to reduce. Note you
can reduce .. but not eliminate the interference.
To complicate things, the farther a radio is from the transmitter, the
more difficult this issue will be to resolve.
Here's why...
To achieve the highest efficiency possible, inverter power circuits today
transition from off to on in an extremely short time, as in totally off to
totally on in microseconds .. or even nanoseconds. Internally, within the
inverter, even "sine" wave models use square waves at various points.
Why? Solid state devices operate with the least energy loss when they're
completely off .. or turned on in a strongly "saturated" mode - meaning
turned on to their maximum possible level with the least possible
resistance. The transition from off to on is commonly done in one step,
from zero to max .. then back again.
Micro-processor clocks also operate in this fashion, as do the signals
within the processor, and any related communications circuits.
Square waves are a composite of a sine wave, plus all odd harmonics (odd
integer multiples) of the original sine wave frequency. To create a 100
kHz square wave, we start with a 100 kHz sine wave and add sine waves of
300 kHz, 500 kHz, 700 kHz .. and so forth, up into the many Mhz region.
The number of harmonics added is astonishing.
As a consequence, these harmonics radiate into the AM broadcast band ..
and far beyond. To make matters worse, the circuits in inverters are not
"linear", which is to say they don't faithfully reproduce the exact
waveform put into them. It's done by intent, but with a side-effect.
This non-linearity turns the circuits into "mixers". Mixers are a part of
every radio and television. We use mixer circuits to combine two
frequencies and obtain others. When non-linear circuits are fed a large
number of signals, they add and subtract all the various combinations of
signals to create still other frequencies .. and so it goes.
Radio frequency interference ("RFI") originates from many different
aspects of an inverter. If the inverter is battery-based, you'll have
many hundreds of amps being switched on and off very rapidly by the
inverter "front end". To handle the hundreds of amps, the input
resistance ("impedance") of the inverter must be very low .. on the order
of a few milliohms.
String inverters connected to a series array of PV operate on the same
principals, but at lower currents and higher voltages than their
battery-based counterparts.
RFI filters work on the basis of a voltage divider, posing a very high
impedance to the interference (blocking it), but a very low impedance to
the DC that must flow, minimizing loss at DC. This is a very difficult
challenge due to the high amperages involved.
The same is true of inverter AC output circuits. AC output is more easily
addressed because the current is much lower than the DC input (battery
based systems only). Conversely, inverters connect to AC circuits in the
home, turning every inch of the house wiring into an antenna that radiates
the interference.
As mentioned earlier in this thread, it's best to reduce the interference
at the source - in this case, the inverter.
First step is to try to determine where the bulk of the interference is
originating. The DC leads? AC leads? Inverter case? All the above?
Each has its own set of possible steps to reduce RFI. Leads are the most
likely culprit. A battery-operated shortwave radio with a signal strength
indicator can be an invaluable tool here. If you have one, you're ahead
of the game. If you consider buying one .. ensure it also receives the AM
broadcast band. Most do.
1) Keep the DC leads from the battery to the inverter as short as practicable.
2) Twist the DC leads together if possible. If not possible, keep them as
close together as you can. The goal is to have the RFI magnetic energy
from each lead cancel the RFI magnetic energy in the other. As was also
pointed out, it may be helpful to run each DC leg in metal conduit and
then GROUND the conduit to an earth ground - the shorter the better.
Failure to ground the conduit will simply turn the conduit into another
antenna. An RFI ground is separate from the earth "protective" ground.
If you use the AC "ground", it too becomes an antenna unless it's kept
short, and you've got a good connection to the grounding electrode
conductor with highly conductive earth. It's tough to achieve all three
together, but it can be done in some locations.
Someone suggested a "filter capacitor" be connected across the DC leads.
This won't hurt, but isn't likely to be effective given the very low
impedance of inverter input circuits.
3) Ferrite cores may be slipped over the length of each cable, and placed
at the point where the cables exit the inverter. Toroid cores or similar
may be of help, but you'll need many of them, and they'll need to extend
at least two to three feet starting at the inverter. More is better, and
keep in mind .. when many are used .. they're heavy.
Do not install them at the battery end. Installing at the battery end,
and leaving some cable exposed at the inverter allows the exposed
conductors at the inverter to act as antennas.
Select the proper type of ferrite. Surprisingly, various formulations of
ferrite react differently depending on the frequency range in which
they're used. For example, some ferrites are good for 100-500 Mhz, and
would not do a good job blocking RFI that interferes with AM radio. For
AM radio RFI, select ferrite that's rated to work from 250 kHz up to 2 Mhz
or more.
4) AC EMI/RFI filters are also available, and may be installed on the AC
output circuit at the inverter. These are made by Corcom, Tyco, and
others. Select a unit rated for the output voltage AND current of the
inverter. RFI filters will be UL/ETL/CSA recognized. If you find some
that aren't .. don't buy them.
5) As was suggested, a radio with external antenna may help, especially if
the antenna is fed with coaxial cable, which can act as a shield until the
cable is well away from the house and/or inverter. Keep the radio antenna
as far from the inverter and house wiring as you can.
6) A battery-operated radio is also an option. This too was mentioned
earlier in this thread. Even well-filtered inverter AC output always
carries with it some level of interference. A weak radio signal will
still be affected by a weak source of interference.
7) Ground the inverter housing in accordance with the manufacturer's
instructions. All inverters today are required to meet certain levels of
FCC interference criteria. Actions of internal RFI filtering circuits may
be improved if the inverter is properly grounded.
8) Ever drive into a parking garage while listening to the radio, and the
radio station gets very weak or disappears altogether?? Same thing
happens when we drive through long highway tunnels.
We can make use of that trait. It's caused by the reinforcing steel bars
("re-bar") acting to block the radio signals from getting to the antenna
on your vehicle. The same characteristic that keeps signals from getting
to your radio, also works to keep interference IN.
In addition to all the above, you may have to construct a screen around
the entire inverter, then connect the screen itself to earth ground. This
screen should NOT come into contact with the inverter housing. To do so
would defeat the purpose of the screen. However, properly filtered DC and
AC leads may pass through it.
In this case, you'll be constructing a "Faraday shield", which will keep
interference inside. Surprisingly, this can be ferrous or non-ferrous
metal. I'd recommend ferrous (such as chicken wire with small openings),
for ease of soldering. Build a "box" around the inverter, including the
back of the inverter. To do this, you'll need a board or other means to
keep the inverter enclosure from contacting the wire.
Once you've constructed the box .. connect the box to its own "RFI" earth
ground. This will be similar to a standard protective ground.
Next, add a bond wire from the RFI ground to the system protective earth
for the system. This RFI-ground to safety ground bond wire should be
outside if you can .. and buried in the soil if at all possible. Adding
this bond wire avoids opportunity for AC ground loops or other issues.
Keeping it in the soil also slightly reduces the opportunity it will
become an antenna for the interference. If all the above are done
properly, they won't impact the effectiveness of the box you've just
constructed.
Reducing radio frequency interference is, at best, a snipe hunt. The
strength of the radio/TV station signal itself can and will vary, and is
dependant on a variety of variables. This can give the impression
something you've done had an effect on the interference level from the
inverter, where in fact you didn't change a thing. The weaker the radio
signal, the more difficult it will be to reduce the interference from the
inverter to make the radio signal listenable.
The best thing to do is keep the inverter and all of its wiring as far
from the radios as you can. If this simply isn't possible .. see steps
1-8.
I wish you well.
Dan Lepinski
Sr. Engineer
Exeltech
Hunting and smothering RFI for more than 40 years ...
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Tump
2009-07-17 01:51:37 UTC
Permalink
I see that this install is using EMT, are you using a bonding bushings on
the EMT? If so, I had interference on a large PV powered refrigeration unit
that used an electronic expansion valve. The wires were installed inside EMT
causing all kinds of weird problems. When I removed bonding at both ends & I
bonded only one end, similar to when one connects the "drain" conductor on
"shielded w/ drain" cat 5 cable, This took care of the problem! Who knows
.....tump


-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of boB Gudgel
Sent: Wednesday, July 15, 2009 8:12 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Inverter AM Interference
Post by SOLARPRO
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?

boB

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SOLARPRO
2009-07-15 00:48:39 UTC
Permalink
Hello:

Has anybody got a fix or a way to filter out inverter generated AM (
520-700 kHz MW) noise? I guess it's never been a problem in the past because
our customers must not have been fans of AM radio. Plus, I always approved
of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not very
ambulatory, sits in the same spot most of the day and just loves talk
radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there anything
we can do?

Patrick Redgate
Ameco Solar
**************Can love help you live longer? Find out now.
(http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweu
slove00000001)
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Dave Click
2009-07-15 01:26:01 UTC
Permalink
Weird! I was looking through the list archive for info on lightning
arrestors earlier this afternoon and coincidentally, this email may
help, from Aaron Wellendorf on 2006/4/12:
http://lists.re-wrenches.org/htdig.cgi/re-wrenches-re-wrenches.org/2006/019214.html

"I have used a different brand of AC surge arrestor with noise filtering to
quiet the AC line into a grid-tied Trace SW4048 back in 1999. It didn't
completely filter out all noise, but it did make my customer's favorite
680AM radio station listenable vs. a totally static roar. I put them on all
my systems after that, SW or not."

He doesn't say what surge arrestor he uses, but hopefully this helps
your customer.

DKC

-------- Original Message --------
Subject: [RE-wrenches] Inverter AM Interference
From: SOLARPRO at aol.com
To: re-wrenches at lists.re-wrenches.org
Date: 2009/7/14 20:48
Has anybody got a fix or a way to filter out inverter generated AM
( 520-700 kHz MW) noise? I guess it's never been a problem in the past
because our customers must not have been fans of AM radio. Plus, I
always approved of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not
very ambulatory, sits in the same spot most of the day and just loves
talk radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there
anything we can do?
Patrick Redgate
Ameco Solar
------------------------------------------------------------------------
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<http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweuslove00000001>.
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Dan Fink
2009-07-15 01:48:16 UTC
Permalink
Ouch! From a brand-new SMA? I thought AM interference was mostly
banished when the Trace SW series was introduced.

My checklist when I consult (and this question is fairly common), these
are in no particular order:

1) Be absolutely sure it's the inverter causing the problem; I've seen
lots of interference from BOS components, especially amp-hour meters.
1.5) Find out if the problem is conducted RFI in your wires, or radiated
RFI picked up by the AM antenna, or both. IE, try a battery-powered AM
radio.
2) Replace your 15-year old modified square wave inverter with a true
sine wave model. (OUCH! It's really a new SMA?)
3) Twist the battery --> inverter main +/- cables together. Tough if you
are in conduit.
4) Consider a filter capacitor across the inverter input.
5) Use an external AM antenna for the radio, and locate it well away
from the house.
6) Double check that the main system ground connection is excellent, and
those of all equipment and boxes.
7) Some inverters are just plain noisy on AM!
8) Some AM radios, especially modern ones, just plain suck on RFI
rejection. They don't make 'em like they used to. Try a better AM radio,
or even an old-school one.

I have a notoriously noisy inverter, but it's been "on" for 15 years now
without a hitch and I like that. For late-night baseball games on AM, I
take a battery-powered radio, and place it in a coal scuttle for
shielding. By placing the coal scuttle in *exactly* the right spot in
the middle of the room, and orienting it in the right direction so that
the RFI blocked, it works great.

AM interference is tricky stuff. Ask your customer if they can get a
simulcast of their favorite AM station on Fm anywhere?

DAN FINK
http://www.otherpower.com/
Has anybody got a fix or a way to filter out inverter generated AM
( 520-700 kHz MW) noise? I guess it's never been a problem in the past
because our customers must not have been fans of AM radio. Plus, I
always approved of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not
very ambulatory, sits in the same spot most of the day and just loves
talk radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there
anything we can do?
Patrick Redgate
Ameco Solar
Jeff Yago
2009-07-15 03:07:06 UTC
Permalink
We see the most AM radio interference with Fronius inverters, but the distance must be close. I listen to AM talk radio most of day and it is usually on in the car when I leave the office. My car is parked right next to our office on the exterior side of the garage that has the Fronius Inverter. When I get in a car or any of our trucks, the AM band is totally trashed until I back about 30 feet away, then it goes away. Seems to affect all radios, but the distance is limited. It does not affect the AM radios in the office area, which is about 40 feet and 2 walls away. I have not found this to be a problem with Outback equipment.

Jeff Yago

_____________________________________________________________
Netscape. Just the Net You Need.
robert ellison
2009-07-15 10:27:15 UTC
Permalink
I am a fan of talk radio and have always had a problem when the car gets
within 30' of the inverter, the brand seems to make no difference. The house
radio never had a chance.
I don't know if it applies to grid tie only inverters or not but suspect it
might be the same.

Interested in an easy cure also,

Bob
Has anybody got a fix or a way to filter out inverter generated AM
( 520-700 kHz MW) noise? I guess it's never been a problem in the past
because our customers must not have been fans of AM radio. Plus, I
always approved of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not very
ambulatory, sits in the same spot most of the day and just loves talk
radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there anything
we can do?
Patrick Redgate
Ameco Solar
------------------------------
Can love help you live longer? Find out now<http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweuslove00000001>
.
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David G Katz
2009-07-15 15:11:05 UTC
Permalink
I have always had problems with AM radio in my remote home. I have more
problems when it is connected to AC or DC for power. Try running it on
batteries. I switched to a CCrane internet radio and now I get 1000s of
stations very clear, but you need broadband internet.
David

David Katz

President

AEE Solar

1155 Redway Drive

P.O. Box 339

Redway, CA 95560

Tel (707) 825-1200

Fax (707) 825-1202

david at aeesolar.com <mailto:david at aeesolar.com>

www.aeesolar.com <http://www.aeesolar.com>



DISCLAIMER:
This communication, along with any documents, files or attachments, is
intended for the use of only the addressee and contains privileged and
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P Please consider the environment before printing this e-mail.
Has anybody got a fix or a way to filter out inverter generated AM
( 520-700 kHz MW) noise? I guess it's never been a problem in the
past because our customers must not have been fans of AM radio. Plus,
I always approved of the fact that it wiped out reception for ditto-heads.
We called SMA and they are in a state of denial. Our customer is not
very ambulatory, sits in the same spot most of the day and just loves
talk radio. The inverter is more than 30 feet away from the radio.
Other than relocating the inverter (grid-tie, no battery) is there
anything we can do?
Patrick Redgate
Ameco Solar
Can love help you live longer? Find out now
<http://personals.aol.com/articles/2009/02/18/longer-lives-through-relationships/?ncid=emlweuslove00000001>.
------------------------------------------------------------------------
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SOLARPRO
2009-07-15 23:57:44 UTC
Permalink
Hello again:

This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it must be AC
related.
I found out today that roam (or freedom) phones do not work at this home.
Since it was built with wire mesh in the walls - this was a transition
method used after plaster and before drywall...sometime in the late 40's early
50's - we are all supposing that this is the reason that the phones do not
work.
But could living in a modified Faraday cage have something to do with it?
I am taking my job site tested boom box over there tomorrow to see if
running unplugged helps. Maybe we can rig up an antenna for the BOSE....a
metal coat hanger in a vent pipe should do it.
I'll let you know....

Patrick Redgate
Ameco Solar



In a message dated 7/15/2009 2:52:50 P.M. Pacific Daylight Time,
drake.chamberlin at redwoodalliance.org writes:

At 09:48 PM 7/14/2009, you wrote:

2) Replace your 15-year old modified square wave inverter with a true sine
wave model. (OUCH! It's really a new SMA?)


The SMA Sunny Island requires metal conduit for the battery cables, for
RFI.

Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648



**************Can love help you live longer? Find out now.
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SOLARPRO
2009-07-16 00:14:00 UTC
Permalink
It disappears when the breaker is thrown.
Pat Redgate


In a message dated 7/15/2009 5:11:58 P.M. Pacific Daylight Time,
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?

boB

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slove00000001)
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Exeltech
2009-07-16 17:02:01 UTC
Permalink
Interference from inverters will always be an issue. It's a difficult topic for many to understand .. and equally difficult to reduce. Note you can reduce .. but not eliminate the interference.

To complicate things, the farther a radio is from the transmitter, the more difficult this issue will be to resolve.

Here's why...

To achieve the highest efficiency possible, inverter power circuits today transition from off to on in an extremely short time, as in totally off to totally on in microseconds .. or even nanoseconds. Internally, within the inverter, even "sine" wave models use square waves at various points. Why? Solid state devices operate with the least energy loss when they're completely off .. or turned on in a strongly "saturated" mode - meaning turned on to their maximum possible level with the least possible resistance. The transition from off to on is commonly done in one step, from zero to max .. then back again.

Micro-processor clocks also operate in this fashion, as do the signals within the processor, and any related communications circuits.

Square waves are a composite of a sine wave, plus all odd harmonics (odd integer multiples) of the original sine wave frequency. To create a 100 kHz square wave, we start with a 100 kHz sine wave and add sine waves of 300 kHz, 500 kHz, 700 kHz .. and so forth, up into the many Mhz region. The number of harmonics added is astonishing.

As a consequence, these harmonics radiate into the AM broadcast band .. and far beyond. To make matters worse, the circuits in inverters are not "linear", which is to say they don't faithfully reproduce the exact waveform put into them. It's done by intent, but with a side-effect. This non-linearity turns the circuits into "mixers". Mixers are a part of every radio and television. We use mixer circuits to combine two frequencies and obtain others. When non-linear circuits are fed a large number of signals, they add and subtract all the various combinations of signals to create still other frequencies .. and so it goes.

Radio frequency interference ("RFI") originates from many different aspects of an inverter. If the inverter is battery-based, you'll have many hundreds of amps being switched on and off very rapidly by the inverter "front end". To handle the hundreds of amps, the input resistance ("impedance") of the inverter must be very low .. on the order of a few milliohms.

String inverters connected to a series array of PV operate on the same principals, but at lower currents and higher voltages than their battery-based counterparts.

RFI filters work on the basis of a voltage divider, posing a very high impedance to the interference (blocking it), but a very low impedance to the DC that must flow, minimizing loss at DC. This is a very difficult challenge due to the high amperages involved.

The same is true of inverter AC output circuits. AC output is more easily addressed because the current is much lower than the DC input (battery based systems only). Conversely, inverters connect to AC circuits in the home, turning every inch of the house wiring into an antenna that radiates the interference.

As mentioned earlier in this thread, it's best to reduce the interference at the source - in this case, the inverter.

First step is to try to determine where the bulk of the interference is originating. The DC leads? AC leads? Inverter case? All the above? Each has its own set of possible steps to reduce RFI. Leads are the most likely culprit. A battery-operated shortwave radio with a signal strength indicator can be an invaluable tool here. If you have one, you're ahead of the game. If you consider buying one .. ensure it also receives the AM broadcast band. Most do.


Basic rules:

1) Keep the DC leads from the battery to the inverter as short as practicable.


2) Twist the DC leads together if possible. If not possible, keep them as close together as you can. The goal is to have the RFI magnetic energy from each lead cancel the RFI magnetic energy in the other. As was also pointed out, it may be helpful to run each DC leg in metal conduit and then GROUND the conduit to an earth ground - the shorter the better. Failure to ground the conduit will simply turn the conduit into another antenna. An RFI ground is separate from the earth "protective" ground. If you use the AC "ground", it too becomes an antenna unless it's kept short, and you've got a good connection to the grounding electrode conductor with highly conductive earth. It's tough to achieve all three together, but it can be done in some locations.

Someone suggested a "filter capacitor" be connected across the DC leads. This won't hurt, but isn't likely to be effective given the very low impedance of inverter input circuits.


3) Ferrite cores may be slipped over the length of each cable, and placed at the point where the cables exit the inverter. Toroid cores or similar may be of help, but you'll need many of them, and they'll need to extend at least two to three feet starting at the inverter. More is better, and keep in mind .. when many are used .. they're heavy.

Do not install them at the battery end. Installing at the battery end, and leaving some cable exposed at the inverter allows the exposed conductors at the inverter to act as antennas.

Select the proper type of ferrite. Surprisingly, various formulations of ferrite react differently depending on the frequency range in which they're used. For example, some ferrites are good for 100-500 Mhz, and would not do a good job blocking RFI that interferes with AM radio. For AM radio RFI, select ferrite that's rated to work from 250 kHz up to 2 Mhz or more.


4) AC EMI/RFI filters are also available, and may be installed on the AC output circuit at the inverter. These are made by Corcom, Tyco, and others. Select a unit rated for the output voltage AND current of the inverter. RFI filters will be UL/ETL/CSA recognized. If you find some that aren't .. don't buy them.


5) As was suggested, a radio with external antenna may help, especially if the antenna is fed with coaxial cable, which can act as a shield until the cable is well away from the house and/or inverter. Keep the radio antenna as far from the inverter and house wiring as you can.


6) A battery-operated radio is also an option. This too was mentioned earlier in this thread. Even well-filtered inverter AC output always carries with it some level of interference. A weak radio signal will still be affected by a weak source of interference.


7) Ground the inverter housing in accordance with the manufacturer's instructions. All inverters today are required to meet certain levels of FCC interference criteria. Actions of internal RFI filtering circuits may be improved if the inverter is properly grounded.


8) Ever drive into a parking garage while listening to the radio, and the radio station gets very weak or disappears altogether?? Same thing happens when we drive through long highway tunnels.

We can make use of that trait. It's caused by the reinforcing steel bars ("re-bar") acting to block the radio signals from getting to the antenna on your vehicle. The same characteristic that keeps signals from getting to your radio, also works to keep interference IN.

In addition to all the above, you may have to construct a screen around the entire inverter, then connect the screen itself to earth ground. This screen should NOT come into contact with the inverter housing. To do so would defeat the purpose of the screen. However, properly filtered DC and AC leads may pass through it.

In this case, you'll be constructing a "Faraday shield", which will keep interference inside. Surprisingly, this can be ferrous or non-ferrous metal. I'd recommend ferrous (such as chicken wire with small openings), for ease of soldering. Build a "box" around the inverter, including the back of the inverter. To do this, you'll need a board or other means to keep the inverter enclosure from contacting the wire.

Once you've constructed the box .. connect the box to its own "RFI" earth ground. This will be similar to a standard protective ground.

Next, add a bond wire from the RFI ground to the system protective earth for the system. This RFI-ground to safety ground bond wire should be outside if you can .. and buried in the soil if at all possible. Adding this bond wire avoids opportunity for AC ground loops or other issues. Keeping it in the soil also slightly reduces the opportunity it will become an antenna for the interference. If all the above are done properly, they won't impact the effectiveness of the box you've just constructed.


Reducing radio frequency interference is, at best, a snipe hunt. The strength of the radio/TV station signal itself can and will vary, and is dependant on a variety of variables. This can give the impression something you've done had an effect on the interference level from the inverter, where in fact you didn't change a thing. The weaker the radio signal, the more difficult it will be to reduce the interference from the inverter to make the radio signal listenable.


The best thing to do is keep the inverter and all of its wiring as far from the radios as you can. If this simply isn't possible .. see steps 1-8.

I wish you well.


Dan Lepinski
Sr. Engineer
Exeltech


Hunting and smothering RFI for more than 40 years ...
Tump
2009-07-17 01:51:37 UTC
Permalink
I see that this install is using EMT, are you using a bonding bushings on
the EMT? If so, I had interference on a large PV powered refrigeration unit
that used an electronic expansion valve. The wires were installed inside EMT
causing all kinds of weird problems. When I removed bonding at both ends & I
bonded only one end, similar to when one connects the "drain" conductor on
"shielded w/ drain" cat 5 cable, This took care of the problem! Who knows
.....tump


-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of boB Gudgel
Sent: Wednesday, July 15, 2009 8:12 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Inverter AM Interference
Post by SOLARPRO
This is a brand new 5000 US. EMT on all dc runs. The radio is a
BOSE...and is 27 feet away. The interference is runs 24/7... so it
must be AC related.
Does the radio noise go away when you completely disconnect the SMA
inverter ?

boB

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List sponsored by Home Power magazine

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