bad ground loop when charging the axim in car and listening to music

saint-francis · 03-05-08, 09:50 AM

I have a power inverter which plugs into the cigarette lighter of my car and my car stereo has an 1/8 inch jack for an input. If I plug the axim into both at the same time I get a terrible buzzing which is far louder than the sounds coming from the axim. I'm assuming that this is a common ground issue. The question now is, how do I eliminate this? It's pure hell. It happens when I try it with my lap top also. I have thought about grounding the cigarette lighter directly to the negative battery pole (on the car battery that is) and I have also thought about doing the same for the stereo. Needless to say this would involve some labor which I'm not interested is spending if it's not going to work. I would need to find a body plug in the firewall and then dig out the negative leads on the stereo and the lighter which could take several hours. Has anyone else had such a problem ir does anyone have any input on this?

Bill_Todd · 03-05-08, 11:18 AM

Changing the supply ground is unlikely to work .

The simplest solution is a couple of isolating transformers . They're available from most in-car stereo suppliers (search ebay etc.)

mirskym · 03-05-08, 12:25 PM

Originally Posted by Bill_Todd

Changing the supply ground is unlikely to work .

The simplest solution is a couple of isolating transformers . They're available from most in-car stereo suppliers (search ebay etc.)

The buzzing is coming from the inverter. The inverter doesn't actually create a pure sinusoidal AC voltage, but usually a triangular shape or similar. This is loaded with harmonics and it's getting into the output of the Axim. You need a filter in the supply to the Axim which should be available from the same source mentioned above. I have heard of similar problems coming from the the alternator if the filter on that isn't working (the alternator makes AC which is rectified by a diode bridge to DC to charge the battery. The DC often still has a ripple in it that needs to be filtered).

JakeRich · 03-05-08, 12:33 PM

What car? The Toyota RAV4 has a Technical Service Bulletin out about this that provides for it to be repaired by Toyota under warranty. You might check to see if your car also has some coverage.

mirskym · 03-05-08, 02:29 PM

Another solution might be to forget the inverter and buy one of those USB/cig lighter Axim chargers.

saint-francis · 03-05-08, 02:32 PM

The car is a 95 Honda Civic. As far as I can tell there is no public information on this for that car.

What kind of "filter in the supply to the Axim" do I need and how would I go about getting and installing it? I'm no EE but I do know about how cars work and I know how to handle a soldering iron.

What are "isolating transformers" and how would they be installed? Same as above.

Thanks everyone.

saint-francis · 03-05-08, 02:34 PM

Originally Posted by mirskym

Another solution might be to forget the inverter and buy one of those USB/cig lighter Axim chargers.

I have thought long and hard about doing that but I'm afraid that I would run into the same problem there. Would I?
And that still wouldn't solve the problem of the noise coming from the lap top too. I don't use it in the car anywhere near as much as I do the Axim, but some times I do use it on long trips.

mirskym · 03-06-08, 12:29 PM

Originally Posted by saint-francis

I have thought long and hard about doing that but I'm afraid that I would run into the same problem there. Would I?
And that still wouldn't solve the problem of the noise coming from the lap top too. I don't use it in the car anywhere near as much as I do the Axim, but some times I do use it on long trips.

It's hard to say. After I read your post yesterday I Googled around and did find some articles that claimed a bad ground can cause this. But I also found some sites selling filters for ~$20. But if the buzzing is because of the inverter, the USB solution will work.

I have used my Axim with the USB charger in my car and fed the output to one of those dummy cassette tapes that you put into your cassette recorder in your car (yeah, my van is that old!)

I had no problems with a buzz.

saint-francis · 03-06-08, 03:58 PM

For the record when I use the inverter and plug the Axim into a stereo with one of those cassette adapters I don't get the noise.

What are these filters you speak of? Could you post a link?

mirskym · 03-06-08, 05:12 PM

This site talks about alternator noise and has this link to some filters.

Also this and this talk about fixes for inverter noise.

Hope this gets you going on the road to a solution.

eyesineyes · 03-10-08, 10:47 PM

I think you may want to try one of these
SONY Car Cassette Adapter for CD/MP3 Player, etc
New SONY CPA-9C Car Cassette Adapter For CD/iPod/MP3/MD - eBay (item 170200170906 end time Mar-11-08 12:17:40 PDT)

Bulkin FM transmitter
Belkin F8V367 TuneCast Mobile FM Transmitter NEW - eBay (item 190205745924 end time Mar-15-08 17:32:01 PDT)

Tell the the truth, I have both of them, and I like the Sony cassette. My car is very old , '94 Nissan Altima, and it works very well. The quality of sound is very good. If you don't have cassette play in your car. You may use the bulkin FM stransmitter as well. It turns your MP3/CD, you name it, into a FM station.