Inverter Interference

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Inverter Interference

Postby arcen1k » Sat Jan 19, 2013 9:08 pm

I have an DC - AC inverter for EL wire. I know that they release a certain amount of an audio frequency that we can hear. My inverter is setup next to a speaker and amp, and the amp is picking up the frequency emitted and amplifying it. Is there any straight forward way to dampen the signal? Or if it cannot easily be done, is there a cheap (within reason) inverter that could be used (12V DC - 110V AC)?
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Re: Inverter Interference

Postby BBadger » Sat Jan 19, 2013 10:26 pm

First try stuffing the inverter in a metal box, or wrapping it in aluminum foil.
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Re: Inverter Interference

Postby The CO » Sat Jan 19, 2013 10:59 pm

Seperate the audio electrical circuit from the lighting circuit, or try a ground lift.
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Re: Inverter Interference

Postby arcen1k » Sat Jan 19, 2013 11:19 pm

Thanks for the posts guys! I have tried wrapping it in aluminum foil to no avail. I have some older lead lined camera cases (lead is unexposed) that I may give a shot at. When you say separate the lighting circuit, what exactly do you mean? Right now my project is setup so that audio gets split half to a programmable EL wire sequencer, the other half to my amp and speakers. The amp and the sequencer both run off of the same 12V DC battery. Even when the audio jack to the sequencer is unplugged, the sound is still audible over the speakers. It is a bit odd that the sound is most noticeable and all of a sudden plays louder 1.5 - 2 seconds after the music stops, when there are also no lit EL wires.
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Re: Inverter Interference

Postby BBadger » Sun Jan 20, 2013 12:30 am

Do you have any ground loops in your circuit? All your grounds should be connected at a single point, and not form loops. That can cause oscillations.

Also, you may try opto-isolating the two.

Really, you should draw up a diagram of the setup so we can see how things are connected.
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Re: Inverter Interference

Postby arcen1k » Sun Jan 20, 2013 1:38 am

I've drawn up a quick diagram. I apologize ahead of time about the size... Battery is a 12V DC, 12 amp hour battery.

Image
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Re: Inverter Interference

Postby Roark » Sun Jan 20, 2013 7:12 am

Two things to try:
1). Twist the cables on the low-voltage side (input, from batteries) together in a helix. The tighter the better. ("Twisted pair")

2). Do the above then put a cap on the power cables right where they hit the case. Tantalum, polarized, starting about 10uF and going-up from there. My 1500/3000 watt unit took a 100 uF and a 22uF before the output was *silent*.

3). Do the above and then try running the output through a choke/cap filter. I didn't need to get this far, but if you google it the values for creating a "brickwall" for anything above 100 hz are on the net).

4). Throw away the inverter, cannibalize a 1968 VW Bug, invest in a torch, scrap metal, much beer, and steal your kids hamsters. WhaLAA! You now have an organically-powered generator set that has exactly the SAME PROBLEM! (And you'll have a headache to boot!). :mrgreen:
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Re: Inverter Interference

Postby Elorrum » Sun Jan 20, 2013 9:18 am

Roark wrote:Two things to try:
1). Twist the cables on the low-voltage side (input, from batteries) together in a helix. The tighter the better. ("Twisted pair")

2). Do the above then put a cap on the power cables right where they hit the case. Tantalum, polarized, starting about 10uF and going-up from there. My 1500/3000 watt unit took a 100 uF and a 22uF before the output was *silent*.

3). Do the above and then try running the output through a choke/cap filter. I didn't need to get this far, but if you google it the values for creating a "brickwall" for anything above 100 hz are on the net).

4). Throw away the inverter, cannibalize a 1968 VW Bug, invest in a torch, scrap metal, much beer, and steal your kids hamsters. WhaLAA! You now have an organically-powered generator set that has exactly the SAME PROBLEM! (And you'll have a headache to boot!). :mrgreen:


oooh, I love it when you talk techinical. 8) Welcome, Roark!!!!
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Re: Inverter Interference

Postby arcen1k » Sun Jan 20, 2013 4:45 pm

Loving these suggestions. :D

I'll give them a shot, thanks!
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Re: Inverter Interference

Postby The CO » Sun Jan 20, 2013 8:21 pm

The transformer for the EL wire is creating 'noise' that runs through the power cable and bleeds over to the amplifier. The amp, in turn, amplifies all the signal it gets, including the noise coming from the transformer. You'll be hard pressed to make it go away entirely without a seperate power source for each.

It's the reason audio at rock shows is isolated from pretty much every other electrical circuit. Any sort of transformer will have that effect.
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Re: Inverter Interference

Postby EspressoDude » Mon Jan 21, 2013 7:51 am

remember also that the el wire is a wire antenna broadcasting the RF hash out of the little inverter.

If it is coming through the power circuit, test this by using a second battery.

If it is through the audio side a small audio isolation transformer may fix it...Radio Shack, or rent a good one from a pro audio shop for testing. you may have to use 600 ohm balanced line audio as opposed to consumer single ended audio, dxf, or fiber optic audio coupling.

try some aluminum foil as a shield between the el wire and cases.

shield all cables as pairs ( +,-) audio twisted shielded pair and ground all shields to one point
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Re: Inverter Interference

Postby arcen1k » Mon Jan 21, 2013 5:59 pm

The CO wrote:The transformer for the EL wire is creating 'noise' that runs through the power cable and bleeds over to the amplifier. The amp, in turn, amplifies all the signal it gets, including the noise coming from the transformer. You'll be hard pressed to make it go away entirely without a seperate power source for each.

It's the reason audio at rock shows is isolated from pretty much every other electrical circuit. Any sort of transformer will have that effect.
EspressoDude wrote:remember also that the el wire is a wire antenna broadcasting the RF hash out of the little inverter.

If it is coming through the power circuit, test this by using a second battery.

If it is through the audio side a small audio isolation transformer may fix it...Radio Shack, or rent a good one from a pro audio shop for testing. you may have to use 600 ohm balanced line audio as opposed to consumer single ended audio, dxf, or fiber optic audio coupling.

try some aluminum foil as a shield between the el wire and cases.

shield all cables as pairs ( +,-) audio twisted shielded pair and ground all shields to one point


I did attach it to a separate battery and I did get the same results as I have been getting. It does appear to be transferred over RF. For which the EL wires are acting like giant antennae. It does appear to be more on the audio side, and an audio transformer may work... I still need to get my hands on a choke, the only one I have is on my camera cable, but I can probably get one online for a $1 or 2. Again, thank you so much for the help guys!
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Re: Inverter Interference

Postby arcen1k » Tue Jan 22, 2013 6:37 pm

EspressoDude wrote:remember also that the el wire is a wire antenna broadcasting the RF hash out of the little inverter.

If it is coming through the power circuit, test this by using a second battery.

If it is through the audio side a small audio isolation transformer may fix it...Radio Shack, or rent a good one from a pro audio shop for testing. you may have to use 600 ohm balanced line audio as opposed to consumer single ended audio, dxf, or fiber optic audio coupling.

try some aluminum foil as a shield between the el wire and cases.

shield all cables as pairs ( +,-) audio twisted shielded pair and ground all shields to one point


I bought an audio transformer, http://www.radioshack.com/product/index.jsp?productId=2103254. However I have no clue how to use it... Any advice?
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Re: Inverter Interference

Postby EspressoDude » Wed Jan 23, 2013 9:16 am

the radio shack transformer is an output transformer / step down to drive speakers. note the 1000 ohm primary and 8 ohm secondary.

you can try this for isolation but the volume level/signal strength will be reduced. You might try connecting the speaker side of the transformer to a speaker, then the higher resistance side of the transformer to the sequencer

edit to add:
post the data sheet(it is not avail online) so we can add to the confused suggestions
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Re: Inverter Interference

Postby oscillator » Wed Jan 23, 2013 2:21 pm

EDude nailed it. The wire itself radiates the audio frequency drive signal. I've struggled with this for years. Even tried solutions on the audio side (grounded enclosure) before giving up.

I did find that larger- than-rated El AC drivers seemed to improve things slightly.

My solution was to use only short lengths of EL, or switch to nice quite LEDs.
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Re: Inverter Interference

Postby arcen1k » Thu Jan 24, 2013 1:01 am

EspressoDude wrote:the radio shack transformer is an output transformer / step down to drive speakers. note the 1000 ohm primary and 8 ohm secondary.

you can try this for isolation but the volume level/signal strength will be reduced. You might try connecting the speaker side of the transformer to a speaker, then the higher resistance side of the transformer to the sequencer

edit to add:
post the data sheet(it is not avail online) so we can add to the confused suggestions


I'll definitely try this out, I'm not worried about volume level too much. I'll keep you guys posted. Quickly, since I've never used a transformer, let alone, an audio transformer, does it support left and right, or is it per speaker, or is mono better than stereo?
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Re: Inverter Interference

Postby BBadger » Thu Jan 24, 2013 2:57 am

So how does the amp perform if you have the audio source connected directly to the amp and then you run the EL-wire separately? If that's not a problem, maybe you can do something like leave the audio source close to the amp, and then string out the connect to the EL-wire, or even use some balanced interconnects with transceiver circuitry.

Also, what hardware are you using (model, brand, etc.)?
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Re: Inverter Interference

Postby EspressoDude » Thu Jan 24, 2013 3:49 am

the transformer is mono. it would normally be used to match a speaker load (8 ohm) to the driving circuitry like output transistors or tubes(gasp!) The impedance ratio is the square of the turns ratio. i.e. 10:1 turns ratio is 100:1 impedance ratio. Your rs transformer 1000/8 impedance ratio or (square root) about 11:1 turns ratio. 11 volts on the primary side is 1 volt on the secondary side. depending on your system connect the primary to a speaker and secondary to your controller input. 11 volts to a speaker(loud) should give 1 volt to the el controller.

all you really need is isolation, not the stepdown or( reversed )step up of the signal level

edit to add:

looking at the rs website the photo show 3 wires on one side, 2 on the other.
the two (red and white) on one side are likely speaker side
3 on other side are likely (blue and green) ends of the primary winding, with black being the center tap of the primary

try red and white to a speaker, then blue and green to the el controller.

the transformer will provide galvanic(direct path) ground and signal isolation, and some high freq filtering(choke as described above)
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Re: Inverter Interference

Postby Token » Thu Jan 24, 2013 5:05 pm

El wire is not a very good antenna. It is a real long cylinder capacitor. I'd venture a guess that the reduced noise with shorter length was due to lower load on the sequencer. Antenna effects are sensitive to length; multiples of wavelength and all that jazz.

If this is a case of antenna to cable transmission then your cables are crap and you should get shielded cables.

Based on the drawring, it looks like you are using a simple splitter to feed both circuits. That would be your electrical path for all that noise.

As others said, an isolation transform could minimize this.

Capacitors will not help since el wire is driven with AC signal in the audio spectrum (1-8 KHz).

An easy test:

From splitter, feed amp on one branch, leave other unconnected.
Use microphone to drive your sequencer audio input.
Put microphone near speakers.

That will do line isolation so that there is no electrical path to the audio amp circuit from the el wire gear other than the power lines.
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Re: Inverter Interference

Postby Gonzo Frothwood » Wed Feb 06, 2013 2:24 pm

when I hook up one of my big bass rigs to an inverter i have to move the inverter some distance away and run longer cords. might work and easy to test.
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Re: Inverter Interference

Postby arcen1k » Fri Feb 08, 2013 8:38 pm

Gonzo Frothwood wrote:when I hook up one of my big bass rigs to an inverter i have to move the inverter some distance away and run longer cords. might work and easy to test.


Hadn't thought of that. I will definitely test that out, however for the final build it needs to fit in the size of a backpack.
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