[RE-wrenches] Inverter AM Interference

[Dan Fink]

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/





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