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Re: [RFI] Solar Inverter.

To: "Neil & Heather" <neil.goodell@myfairpoint.net>, rfi@contesting.com
Subject: Re: [RFI] Solar Inverter.
From: "Dale Svetanoff" <svetanoff@earthlink.net>
Reply-to: svetanoff@earthlink.net
Date: Mon, 19 Mar 2012 22:49:56 -0500
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>

Considering the cost of cleaning up "dirty" inverters, my first thought is
to ask your local ham friend if he had stipulated anything in the contract
with the solar system provider to make them responsible for not interfering
with his radio operation.  If he did not, he may be in for a very expensive
cure to the problem.

As in any RFI situation, you have a source (which appears to be the
inverter) and a victim (the antenna(s) feeding his radio receivers).  The
first thing to do would be to determine the coupling mechanism, as in is it
via the low voltage/high current input wiring of the inverter or via the
120/240 VAC house wiring that is attached to the output.  One way to do
that would be to place a dummy load (lots of incandescent light bulbs) on
the output side of the inverter with the leads to the house wiring
disconnected, and then power up the inverter.  If the noise is gone or
reduced, then he knows that the house wiring is a major part of the
coupling mechanism and filters on the inverter output should be beneficial.
If the noise level hardly changes, then it would seem to be the input
wiring to be the culprit.  In reality, I expect that both wiring systems
may be radiating.

I am not familiar with this particular brand of power filters, but they do
appear to be "real" industrial grade filters.  Having worked for more than
13 years at a company that had a filter product line similar to these, I
can tell you that yes, they will be pricey.  Do not be surprised if the
filter costs exceed $1500 or more.  At that price point, it may be worth
looking at what else could be done.  One suggestion is to increase the
distance between source and victim - in this case, get the antennas further
away from the house.  It may be necessary to move them by several hundred
feet or to re-orient their position relative to the house and its wiring. 
Another suggestion, of course, is to open up the inverter to see how it is
wired and constructed, and then plan a method of applying internal chokes
and by-pass capacitors to knock down the offending hash.  Of course, this
path is liable to void any warranty on the unit.  

Remember, the best cure for reducing RFI from a specific source is to
reduce or eliminate the emissions either within the source itself or as
close to the source device as possible.  So, if he ends up buying the
filters, he needs to install then directly adjacent to the inverter and
connected with the shortest possible leads.  He must also ensure that there
is a proper, low impedance ground path between the filter case and the
inverter case (assuming metal cases).  Note that while the inverter should
be grounded to meet codes and for safety, that grounding path is likely to
be long.  No matter, because we are talking common mode radiated emissions,
what matters most is the path between filter and inverter because that is
where the circulating currents will be located.

Finally, an obvious question:  Is the inverter in a metal case or chassis? 
One would hope so.  If not, it needs to be.

I really hope that your friend can throw this whole mess back at the
installer or equipment manufacturer, where it belongs.  I hope I am wrong,
but this could become a very costly fix.

73, Dale
Sr. EMC Engineer       

> [Original Message]
> From: Neil & Heather <neil.goodell@myfairpoint.net>
> To: <rfi@contesting.com>
> Date: 3/19/2012 9:10:57
> Subject: [RFI] Solar Inverter.
> Good Evening all.
> I received a call from a local ham who is experiencing serious RFI from
> a 3500kwH system he has just tied in at his house.
> He reports S-9+ when the inverter is on,shut off the inverter,noise is
> He also forwarded this link :
>   http://www.radiuspower.com/inverter-emi-filters.html
> Has anyone on the list had any experience with theses filters?
> There are a bit pricey,but,at this point, the fellow ham is only 
> concerned that they work.
> Any information on these filters,or others who may have tackled Solar 
> power Inverter RFI, are welcome.Thank you.
> 73
> Neil
> AE1P
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