Power converter too close to radio?

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Power converter too close to radio?

Postby Tommy2tone_1999 » Sat Jan 23, 2016 1:58 pm

I have a PD4045 converter in my teardrop with my car stereo installed just underneath it. When I plug into shore power, I lose my ability to pick up radio stations. I'm thinking I need to shield the radio from the converter, but not sure of the best way to go about doing that. Can you guys/gals same me some unnecessary labor?
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Re: Power converter too close to radio?

Postby Tommy2tone_1999 » Mon Jan 25, 2016 5:05 pm

...crickets
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Re: Power converter too close to radio?

Postby kludge » Mon Jan 25, 2016 6:16 pm

Where is the antenna?

The radio (I'm assuming it's a fairly standard car/marine radio) should be in a steel box. If so it should provide fairly good shielding. Also the antenna cable should also be a shielded cable. Try moving the antenna to a different location - as far as possible from the converter.

The other thing to remember is the inverse square law. Radio signals (it sounds like the converter is generating some) are attenuated according to the "inverse square law". Meaning every time you double the distance the amplitude of the signal is 1/4 what it was.

i.e. distance is your friend.

Does the converter have an FCC mark? Many types of household electronics have to pass FCC testing, but since the product is not really intended for household use they may be able to bypass the testing. If it's a "smart" converter or an "off-line" (transformerless) converter with MOSFET switches to control the charging voltage and current it would have to pass FCC for household use.

If the radio is already in a steel box, the next step may be to put a steel box around the converter. Or at least on the under side. Or move the converter.

Another possibility - since I don't know how your electrical is wired - is to give your radio a "clean" power and ground - i.e. run the radio off dedicated power and ground wires all the way back to the battery/fuse panel with nothing else on the circuit. You could have a situation similar to "alternator whine" if there is noise on these cables. The battery makes for a really good filter.

But beware, those dedicated cables can also pick up noise from the converter cables if they are run together. A lot of people like to bundle wires together because it's neat and pretty, but this can cause big problems for audio systems.
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Re: Power converter too close to radio?

Postby Tommy2tone_1999 » Tue Jan 26, 2016 3:25 pm

Great suggestions. The antenna is externally mounted, but the cable runs right next to the converter. I'll try to box in the converter and it that doesn't work, I'll go for the dedicated ground.
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Re: Power converter too close to radio?

Postby kludge » Wed Jan 27, 2016 10:44 pm

I had another thought, in addition to dedicated power and ground, one thing we always do with long runs is to twist the power and ground wires together.

A "twisted pair" is a concept used for long wire runs, like CAT5 Ethernet cable and other types of cables that would be sensitive to noise pickup.

The theory basically goes like this: whatever stray signal is picked up on one wire will be picked up on the other wire equally, and when you get to the other end the noise gets cancelled out.

In audio the notion that "any ground will work" (or any point you can get power from) doesn't work. Glitches on the power or ground (especially the ground) usually end up coming out the speakers.
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Re: Power converter too close to radio?

Postby drshoe » Thu Jan 28, 2016 9:14 am

What do you hear on the radio instead of the music? Would you know a 60 Hz hum if you heard it? Do your AC and DC systems share a common ground - if not I would expect your AC system is generating noise in your DC system via electromagnetic induction.

You could try shielding your radio as Kludge suggested. Steel is not a great choice, you want a metal with lots of free electrons in it's outer orbital. Copper or aluminum are the reasonably priced options. Also, you will likely have to ground the shielding (the point is for the shield material to collect the EM interference and dispose of it to ground).
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Re: Power converter too close to radio?

Postby kludge » Thu Jan 28, 2016 12:12 pm

Actually copper and aluminum don't work as well as steel.

Copper and aluminum can shield the electric part of the EM waves but does nothing for the magnetic component of the EM waves.

Steel being ferrous and therefore magnetic turns BOTH electric and magnetic waves into eddy currents which are then dissipated as heat.
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Re: Power converter too close to radio?

Postby Tommy2tone_1999 » Thu Jan 28, 2016 11:23 pm

There is no hum at all reception just goes bye bye
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Re: Power converter too close to radio?

Postby Dale M. » Fri Jan 29, 2016 10:48 am

Are you sure radio is not losing power when you switch to shore power.... Does it share fuse/breaker with other DC devices that stay powered?

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Re: Power converter too close to radio?

Postby H.A. » Fri Jan 29, 2016 7:54 pm

kludge wrote:Actually copper and aluminum don't work as well as steel.

Copper and aluminum can shield the electric part of the EM waves but does nothing for the magnetic component of the EM waves.

Steel being ferrous and therefore magnetic turns BOTH electric and magnetic waves into eddy currents which are then dissipated as heat.



Double check that...Of course in context of Radio signals being modulated...
Any conductive metal will capture modulated magnetic waves, creating eddycurrents...
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Re: Power converter too close to radio?

Postby kludge » Mon Feb 01, 2016 2:26 pm

While true, ferromagnetic metals do a much better job shielding at the frequencies of interest - where the converter is operating - probably in the neighborhood of tens of kHz up to maybe a couple hundred kHz. For effective shielding in this range you need higher magnetic permeability, and for the price low-carbon cold-rolled steel is the best choice. Once you get to the "radio" frequencies, especially a few MHz and above, copper starts winning.
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Re: Power converter too close to radio?

Postby drshoe » Tue Feb 02, 2016 10:03 am

Kludge, I'm quite interested. Can you point me towards a reliable source for this information? Experience tells me copper screen is enough to seriously attenuate the interference from 60Hz AC in very sensitive equipment (recording DC signals of a couple hundred nA).
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Re: Power converter too close to radio?

Postby kludge » Tue Feb 02, 2016 10:18 am

Here's one article.

http://www.ets-lindgren.com/pdf/emctd_1293_weibler.pdf

See especially the center of page 3 and all of page 4.
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Re: Power converter too close to radio?

Postby drshoe » Tue Feb 02, 2016 10:21 am

Tommy any update? Thinking about Dale's comment I am wondering if you have a voltmeter you can use to check the power output of the converter. Perhaps it is putting out enough to run lights but not the radio. I know the PD4045 was designed with possible dead converter replacements in mind.
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Re: Power converter too close to radio?

Postby Tommy2tone_1999 » Sun Feb 14, 2016 5:42 pm

No updates, I haven't done any changes yet. The radio in on it's own breaker.
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