AM Radio noise from SW inverter

icarus · July 2007

Newbie here, apologies for any misposts.

I have a 150 watt panel system with 700amp amp hours of battery. We run a parallel 12vdc and 120vac system in out remote cabin. I have a Morningstar 300 pure sine inverter. It all works famously with one exception. When the inverter is on it induces a very loud howl on the AM radio. We are in a very remote location, so the only radio we get is after sunset. It is a automobile type radio with a very large outdoor antenna. The FM band is unaffected. (It also picks up a bad buzz from the cfl light bulbs near it). Any suggestions,

Thanks

Icarus

BB. · July 2007

Re: AM Radio noise from SW inverter

On my Grid Tie inverter, I get AM noise too... But it only goes about 10'...

Try:

Moving antenna farther from inverter/AC wiring, make sure antenna braid is well grounded to radio, try grounding antenna braid to earth ground.

Use a small AM radio and try to figure out where the noise is coming from (experiment with low/high AM frequency, on-station/off-station and see which setting gives you repeatable results)...

If it is the input wiring, make sure that the DC wiring runs parallel and is twisted, at least, a couple times per foot or is installed in metal conduit (grounded to the inverter case, earth ground).

If it is the output wiring, make sure that the AC wiring runs close together, and twist a couple times per foot, or run in metal conduit, grounded to inverter and earth ground.

Keep "noisy wires/equipment" away from those things you need to keep quiet (AC wires separated from DC wires, control wires separate from AC wires).

If it is the inverter body, make sure that all screws in case are tight. Try placing a grounded piece of sheetmetal over the inverter to block radio waves.

You can try aluminum foil (with edges folded/crimped/stapled--for electrical connection instead of conduit/metal shield) for a temporary fix to see it shielding will help. As always, hazardous voltages and currents are present--so be very careful with the foil/shielding.

AM radio noise can be very hard to control.

-Bill

PS: Different manufacturer's equipment will have different "noise" profiles. Try taking the same little AM radio to your neighbors (if you have any) and see if their's is quieter than your system. Trying different CFL's, or converting to DC LED lighting could help too.

icarus · July 2007

Re: AM Radio noise from SW inverter

Bill,

Thanks for the help. My nearest neighbor is 25km away! The howl is clearly a 60hrz buzz. One question is, you suggest that the ac wiring be "close together" I don't understand what you mean. I also don't know how you can twist nmb cable very effectivly.

Once again thanks for the help. I'll keep trying,

Icarus

BB. · July 2007

Re: AM Radio noise from SW inverter

A lot of old AC wiring was knob and tube--something like 6"-12" apart between hot and return... Basically, any differential noise gets radiated because the wires are so far apart. Running the wires close together (next to each other in Romex type should be fine)--the differential signals cancel each other out.

Twisting also tends to help keep differential noise radiation low (look at twisted pairs--used in almost every signaling type cable from microphones to Ethernet).

Keeping cable runs apart (avoiding long parallel runs, don't bundle AC/DC runs together, don't run AC/DC cables in the same conduit, crossing AC and DC cables at right angle, etc.), like between the DC battery for the automotive radio and the AC house wiring.

You might try moving the radio and attaching it directly to the DC battery bank--perhaps, running a dedicated pair of shielded power wires from the batteries to the radio may help (assuming 12 VDC radio).

Try to figure out where the noise is getting in to the radio... Disconnect the antenna, bring the car battery in and connect directly to the radio, wrap foil around the radio, etc...

Try an AC radio (good portable radio with ferrite AM antenna, rotate to avoid noise, pickup stations). Does a portable battery radio have the AM noise?

Common mode noise from the inverter, only shielding, or other filtering techniques (on the input/output will work).

Short of a new inverter (that works better than your current one), you may not have great success in fixing the problem (use Internet stations?)

-Bill

niel · July 2007

Re: AM Radio noise from SW inverter

as to the 12vdc battery i have to ask this, is the radio on the same battery as the inverter is on? if yes, then try it on another battery and see if the interference goes away for although the 60hz can radiate, most of the time it will follow a lower resistive path through the wires. in any case i'd obtain some ceramic disc capacitors with a value of about .47uf or higher to place at the dc input to the inverter. the caps can be paralleled to obtain higher values from smaller valued caps. example: 5 .1uf caps all paralleled across the + and - leads of the inverter would give a value of .5uf. these will handle 12vdc voltages fine as no ac is supposed to be present on a 12vdc line it will short some of the ac out of the 12vdc inputs. the higher voltages on the ac side of the inverter could be filtered with a cap of the correct value, but care must be taken here that the caps are rated at least 250vdc when on a 120vac inverter output. also, the higher values may not be appropriate on the ac side of the inverter and i ask that you do not try that without asking for further advice first.
the radio is obviously a sensitive one, so placing the antenna farther away from the inverter and any of the 120vac wiring will help some with any of the radiated interference it might be picking up, if radiated interference is the case here. i believe the interference may be being fed backwards from the inverter and through the 12v wiring. also, make sure ALL of your connections are good for bad connections anywhere could lead to 1> radiated interference and 2> pickup of interference. as said, if the radio is using the same battery that the inverter is using, putting the radio on a different battery would determine if the interference is being radiated or is being sent through the dc wires so try a different battery for the radio while the inverter uses its normal setup and battery. a smaller antenna would also decrease the pickup of radiated interference as well as the desired signal you wish to listen to. if the signal is always strong then some reduction of the incoming signals can be done by the smaller antenna.

icarus · July 2007

Re: AM Radio noise from SW inverter

Hey guys,,,It is nice to know that there are people out there who know way more about this stuff than I!

Here is the set up. The 6vdc batterys (parallel/series) are located in a different building about 75" away. ( I am currently building a new building which will house the batterys as well as the load, so I don't have such a long run of wire on the 12vdc load). The 12vdc runs through #4 solid copper wire.
After the wire enters the building, the load splits for the dc loads and the inverter. The inverter mounts on the wall. The ac loads are currently fed through simple outlet strips and #16 lamp extension cords. The only ac loads are 15watt cfl and the satelite internet modem.

The radio is a 4 year old Pioneer cd/ipod type. The model excapes me now. the antenna is a large "Fanfare" vertical, mounted on a 15' pole mounted on the side of the house. This antenna is specificly cut for the lower portion of the fm band, great fringe area antenna by the way. It feeds through rg59 type coax. There is one point whre the 12vdc and the 120ac parallel themselfs in the building.

In all of this, this is really more a solution in search of a problem, since as I said I rarely listen to the am anyway. I guess what I am looking to do is make the installation in the new building as "quiet" as I can.

Your information is appreciated. I am currently away from the cabin now, but I will return in mid august and try any and all suggestions. (I'm not sure about the capaciter wiring however!)

Once again, thanks for the help.

PS, the batterys are earth grounded, as is the inverter, the ac neutral , the antenna mast and the internet dish system. (grounding did nothing for the noise)

crewzer · July 2007

Re: AM Radio noise from SW inverter

Icarus,

It might be worth contacting Morningstar about this issue. Here's a link to their technical support request page:

http://www.morningstarcorp.com/forms/tech_support_request.shtml

HTH,
Jim / crewzer

icarus · July 2007

Re: AM Radio noise from SW inverter

Great minds think alike,,,I wrote to them last night,

Once again, thanks for the input, I'll keep in touch

Icarus

niel · July 2007

Re: AM Radio noise from SW inverter

it is quite a bit of work separating cables so try to determine the interference source by disconnecting (physically disconnecting both wires) the ac wires at the inverter and turn on the inverter while listenning to the radio. if you hear interference it is probably not being radiated by or picked up because of the ac wires, but is backfeeding through the dc. you could firstly try disconnecting each ac load (cfl as you indicated) to see if they are the culprits while having the ac line connected to the inverter and turned on of course. in the case of no ac line connected to the inverter with the inverter on and it still is emitting interference is when we can discuss putting in the capacitors.
as to the grounding of everything, that is a good thing provided it all goes to the same ground rod. if not to the same rod you could make things worse. if you can't get it to the same rod you can use multiple ground rods if you run a bare copper wire between them underground to interconnect them. i recommend using #6, but you could use #8 if the distance is more than 50ft between them. i still do officially still recommend #6 or better, for the wire will deteriorate in the moist ground over time.

icarus · July 2007

Re: AM Radio noise from SW inverter

Niel,

Once again thanks for the good idea(s) The idea of issolating the loads makes great sense.

As to the grounding, all the systems share a common ground wire, except the batterys. Because we are on Canadian Shield granite, with very little soil, the grounding system is directed into the cold lake as a earth ground rather than the earth itself. Driving a ground rod in the soil is a non starter, 6" would be deep. The lake provides as good a (earth) ground as I can get.

As I said earlier, I will try these ideas in a couple of weeks when I return home.

Icarus.

BB. · July 2007

Re: AM Radio noise from SW inverter

Tying grounds together is more of safety/lightening issue. In my testing for computer interference, earth grounding never made any difference (but, then again, I normally only worried/tested for noise above 30MHz-1GHz and above).

However, grounding a shield back to the source of the noise (such as 10' cable shield back to the inverter chassis) can be a very good thing. However, it really only helps in the mid-range frequencies (30-200MHz)--probably not near as much in the lower frequency spectrum (like AM band). But the good thing is that low frequency radiation, usually, does not propagate too far. Hence the recommendations for moving the radio/antenna/etc. away (by a couple ten's of feet) from the source of the noise.

-Bill

Vic · July 2007

Re: AM Radio noise from SW inverter

Hi Icarus,

There have been a number of good suggestions already. In addition, you might try disconnecting the antenna input to the radio, and note if the noise goes away. If the noise is completely gone with the ant. disconnected, then all of the noise is radiated from the inverter into the antenna/coax feed line. This means that you can focus on the antenna and feedline. If the noise is mostly gone then you have two approaches to take, and so on.

MorningStar makes good products, but this inverter is small, and probably intended for occasional or task type loads ... it may lack crucial EMI/RFI suppression inside the inverter. Such suppression would normally be ferrite (or powdered iron) cores, which can be a bit large and a bit expensive ... they may have been left out. MS might be able to supply some such cores to you if deemed necessary or lacking.

Most AM/FM receivers expect a short vertical whip to be used as the antenna. It is customary for the feedline from the antenna to the radio to be of the "low capactance" variety. Standard RG-59 is NOT such a feedline. If the intended feedline is low capacitance type, much of the received signal might be attenuated by the RG-59. Altho, one might expect the inverter noise to also be attenuated if the interference is only radiated noise.

If your primary radio interest is FM, then perhaps you could find an FM Yagi (directional, gain antenna), which would allow you to point the antenna in the direction of interest, and provide the radio with a much larger signal. It might be that if the interference mode is radiated, that the direction of interest could be away from the noise source. If such a Yagi antenna were used, there could still be in issue of matching the feedline from the Yagi to the radio. For AM, perhaps a longwire (random length of horizontal wire) could be used. Perhaps you could switch between the two antennas depending on your needs. These things are seldom simple.

Good luck, and MorningsStar is probably your best next step. Vic

icarus · July 2007

Re: AM Radio noise from SW inverter

Vic,

Once again, thank you for your good input.

As a matter of fact, I do have a Yagi antenna and I do switch between that and the vertical. Of course the problem with the Yagi is that it is very directional. Different times of the year the vertical has too much gain and I end up getting stations 1000km away instead of 250km. The directional solves this quite well, with the added aggravation of having to go out and rotate it when needed. (Who said channel surfing was restricted to T.V!). Un plugging the antenna is a good idea, I will try it,

Icarus

niel · July 2007

Re: AM Radio noise from SW inverter

when you finish the testing, please let us know what you have found. i also understand about your ground circumstance as many places do not have lots of soil to use as a ground. i myself hit bedrock after so many feet down which is unusual for most of the area i'm in, but not rare.

AM Radio noise from SW inverter

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