AM radio noise

colderthan
colderthan Registered Users Posts: 20 ✭
in Advanced Solar Electric Technical Forum #1
I get a lot of noise from my inverter when I listen to AM and SW radio. The inverter is an old Trace DR 2412. I've decided it would be worth the expense of a new one just to get rid of the irritation. Is there a model that is particularly good at eliminating noise, or is there a cheaper solution? When I listen at night my wife is getting real tired of me shutting the juice off in the rest of the house (I know, I should have checked if she was in the shower first:blush:)

Paul
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #2
    Re: AM radio noise

    The newer inverters that meet FCC regulations will probably be quieter... But would it fix your issue--can't guarantee it.

    AM radio waves are relatively low frequency and most electronic equipment has little ability to radiate radio waves at these frequencies.

    However, if the AM receiver is relatively close (within 10-20 feet or so), enough coupling can take place and still mess up AM reception.

    Moving the radio away from the inverter (and AC/DC wiring) and/or using a radio with a shielded cable and whip antenna (like a car radio) where you can move the antenna away from the source of RFI may help also.

    In any case, I would see if you can "borrow" a new inverter to test at your place, or use a portable AM radio (test at your home first) and try it next to the inverter you want to purchase and see if it is quieter.

    I have a two year old Xantrex GT 3.0 Grid Tied inverter (meets FCC requirements) and my car's AM radio picks up a "whine" when the car is within about 10-20 feet of the inverter.

    You might also try another radio--I have another (cheap) AM/FM radio mounted right behind the same Xantrex and it does not whine at all (although, the audio quality is not that good).

    We have tried many suggestions to others here that have had various AM radio (and VHF too) interference problems--and there have been few successes (one person did what you have done--just turns off the offending controller while listening to the radio).

    I would suggest that you see how you can best protect your cash such that if the new inverter is not quiet enough--see if you can get your money back.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Telco
    Telco Solar Expert Posts: 201 ✭✭✭✭✭
    #3
    Re: AM radio noise

    This page may help. Looks like if your radio allows an external antenna, you could probably set up an antenna on the far side of the house from the inverter. Or, it states that a shortwave radio makes an excellent AM receiver. If nothing else, you might try grounding the case of the inverter, or perhaps try putting a grounded metal screen between the inverter and the house, next to the inverter. Something like a window bug screen, so long as it is made of metal, would do the trick. Don't ground it to the same point the inverter is though, or it might become an antenna for the inverter interference instead of a shield.

    Hope this helps, unfortunately with radio interference what works for one guy will make it worse for another.
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  • System2
    System2 Posts: 6,290 admin
    #4
    Re: AM radio noise

    I've been struggling with the same thing. Several different inverters, all cause problems to a greater, or lesser extent. Basically had to give up using AM :(

    My system? Panels, controller, and inverters, all are inside a metal building, about 100 feet from the house, AND all the cables between that metal building and the house, are buried underground.
    Still the AM radios are unusable.
    Good luck and if you find a cure, please let us know,
    Peace
    Wayne
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  • SolarJohn
    SolarJohn Solar Expert Posts: 202 ✭✭
    #5
    Re: AM radio noise

    I'm not surprised by the reports of am radio noise when using a MSW inverter. When I switched to a true sine wave inverter those problems went away. The streaks in my TV picture were cured as well.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #6
    Re: AM radio noise

    I find in my limited experience that portable AM radios with Ferrite Rod antennas seem to be less sensitive to the AM hash from my GT inverter vs my AM car radios with the whip (or in-glass) aerials.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: AM radio noise

    you would think that most sinewave type inverters would be better, but that may not always be the case as both are derived the same way except that the sinewave inverter uses more of these steps to derive the better waveform from. more steps could lead to more interference possibilities and may totally depend on design parameters and the use of quality parts to help reduce this possibilty. at no time can any of them say there will not be any interference, but with fcc certification you will know it will not exceed a certain strength potential. if it lands on the radio signal you desire to hear it still may be strong enough to stop you from hearing it especially when the station is not close by.
    one possible help may be to have the wires in grounded conduit to help reduce the radiation of the interference. this would be difficult to do with the dc input if that is where it radiates from. there are many other possible ways of reducing this, but it can get quite involved. they won't add this extreme degree of protection from radiating rf as it would escalate costs far above the point of staying competitive. i must say the costs incurred to xantrex to get fcc class b certification were enormous and to stay competitive they swallowed those extra costs. it's not foolproof even at that, but odds are the extra effort they made will show or should i say not show as much?
    to the original poster paul please determine if the ac wiring is radiating the interference by disconnecting all ac loads hooked up to the inverter (ie no wires to radiate from). odds are this will eliminate it, but won't do you much good except to know where it comes from. we will discuss more after that step is done.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #8
    Re: AM radio noise

    A modified squarewave inverter (MSW) has those sharp edges and has almost no hope of having a cure for AM radio noise, where at least a sinewave inverter has a lot of hope... Although as Neil points out, still can have problems. They're made from smaller steps at a higher frequency so the spectrum of the noise is especially changed over that of a MSW type.
    boB
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  • colderthan
    colderthan Registered Users Posts: 20 ✭
    #9
    Re: AM radio noise

    Thank you all for the responses. Per Niel's suggestion I shut the ac breakers off and turned the inverter on, still noise but not as bad. Turned ac breakers back on one at a time, this doubled the interference. No one curcuit seemed to be the culprit. A load on the inverter didn’t seem to make a difference. When the generator is running thru the same curcuits, no noise.
    About half my loads are 12 volt (some lights, computer, telephone ant. booster and water pump). None of these affect the radio except the water pump (not surprised there)
    I'm about 180 miles from the nearest station, so AM is about my only choice for radio.
    Again , thank you for the help and thanks Telco for the link.

    Paul
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: AM radio noise

    that's not good news as that may indicate both the inputs and the outputs are radiating. you may try placing some ceramic capacitors on the inverter's input and output, but this may work some or not at all and should be a stop gap measure if you're serious of getting another inverter. these caps i'd recommend around 250v-300v ratings or higher with values of around .01uf to .001uf. these could be placed carefully across both of the dc input leads and then also across both of the ac output leads. do note that you may see the caps warm up to the touch or even pop if there's too much harmonic content in the modified waveform. another alternative would be ferrite chokes if you can get some to fit the wires you have with availability from within your area and are probably the safest thing you could do when the wires have insulation. i'm not sure if radio shack still sells the ferrites or not. now if you can fit the wire into the ferrite more than once, and this depends on the size and type you get be it torroidal (circle) or snap type then please do so as this increases its effectiveness. also, it has been shown that getting the radio antenna and possibly the radio itself as far from the inverter and its wiring as is physically possible could also reduce the interference potential somewhat. i also mentioned conduit being run and grounded, but even after doing all of this you may still see interference from the inverter and great care does need to be made in not created shorts if you do any of this. their would be other things that could be tried, but is not worth this much effort especially from somebody unfamiliar with what needs to be done. if you are unclear on any of these things, but wish to pursue any then please let me know.
    i think this may be a good time for some to chime in on their experiences with any interferences they have experienced with some sinewave inverters.
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #11
    Re: AM radio noise

    We sell a lot of these (also see the link on that page for noise problems) http://store.solar-electric.com/nosufefi.html

    Results, to be honest, are mixed - varying from almost total noise suppresion, to only a small reduction. The problem often seems to be to find out how it is actually getting into all the circuits and wiring and being radiated. One inverter installed in an ambulance that had to have lower noise took around 15 of them to get it down.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
    Re: AM radio noise

    sorry windsun as i didn't know you carried the ferrites. my mistake. :cry: live and learn.:cool::D
    colderthan,
    for the record, i mentioned toroidal types and these from naws are not that type that you could make loops to increase the effectiveness, but as windsun had said you just clamp more of the snap on types to the wires making these easier to use for most consumers. if doing the ac output for example, you will buy in multiples of 2 because there are 2 wires to cover. if doing the dc input wires the same thing applies there too as it should be in multiples of 2. 1 on the + and 1 on the - to start with in the latter example. most of the reduction should be seen on the first ferrite installed on each wire with diminishing returns afterwards.
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  • colderthan
    colderthan Registered Users Posts: 20 ✭
    #13
    Re: AM radio noise

    I will try the ferrites and give an update on the results.
    Thank you

    Paul
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  • System2
    System2 Posts: 6,290 admin
    #14
    Re: AM radio noise

    Sounds like grounding problems, to Me.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #15
    Re: AM radio noise

    "Grounding" to earth ground either will not make any difference, or could even make it worse... When testing for RFI emissions we did everything on a ground screen--but that was to create stable and repeat measurements (ground screen makes all sites "the same" so that we can go to different labs and get the same results).

    I played a few times on an FCC site with using 1" copper braid from the system to the local ground screen ground and never found any changes at all (measured with appropriate antenna and spectrum analyzer)...

    Grounding on a device is when we "shorted" gaps and RFI signals to local case ground--keeping the circulating currents as small (in areas) and short as possible.

    AM radio wavelengths are very long (~1,000 feet)... There is no local grounding/shorting that will "cripple" the antenna effect that would limit noise transmission (or ~250 feet for 1/4 wave length radiators).

    You can try just wrapping aluminum foil around the the device you suspect of radiating the AM noise (be careful of shorts and overheating). But I am not sure that it would help.

    Regarding Ferrite beads, they are frequency dependent so finding those that are compounded for the frequency desired can help too...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #16
    Re: AM radio noise

    Bill-I've had the opposite experience. My portable 12V and AC radios experience severe interference. The closer to the inverter, the worse the interference. However, the AM radio in my truck, with a whip antenna, experiences little or no interference even within 30' of the inverter. I've walked around my house with a portable 12V radio and I still get the high pitch whine over 100' from the inverter. I'm a little concerned about when the guy next door builds his house and experiences radio interference.

    Don
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