Heiss5

Sorry I keep putting up these long posts, but I could really use some help on this one.

I bought a DC to AC inverter so I can obviously plug in various electronics while in my car. The problem is, when I turn on the inverter I get an initial buzzing noise that then stops after about 2-3 seconds, I think it's just because the unit is gradually turning on. Well, then everything sounds fine unless I turn my stereo up past about 2/3 or 3/4 of it's volume, at which point I get static/buzzing. Now, if I unplug the DC to AC inverter without adjusting the volume at all, the static/buzzing goes away. What can I do to eliminate the static/buzzing while still having the thing plugged in and my stereo up?

The inverter I have is a dual AC output with 300 Watts RMS and 600 Watts Peak. I also tried my dad's smaller 100 Watt inverter which only has one AC output and plugs into your cigarette lighter but I still get static/buzzing.

Heiss5

Anyone have any ideas?

Tommy

You may be getting voer the limit of the power supply of your power socket - putting up the volume does swallow quite some energy and your inverter may complain about lack of energy or maybe complains about the change in supply of energy - I know that a transformer from AC to DC buzzes as well when the demand is not balanced to the capacity of the transformer.

TexaZ3

You getting static cause your converter is not grounded. I have no idea how to ground it though.

Heiss5

So would adding a capacitor help out?

Heiss5

You think if I just ran a wire from the inverter housing to the car it would ground it?

dlevi67

Adding a capacitor in parallel to the socket should help - possibly two caps in parallel (one electrolytic say 10,000 uF // 0.1 uF mylar or other high Q material to filter high frequency noise above 10kHz - electrolytics tend to "fail" that test, or at least they did 20 years ago when I last studied these things ). This would mean that actually the noise is always there; it simply does not get amplified enough until you pump up the volume.

I'm also wondering if perhaps using one of the other sockets would prove to be less noisy - especially the one in the boot. This because a) it's closer to the battery, and b) it's further away from the audio source (probable site of injection).

The other possibility is that rather than being the converter that is injecting noise, it's alternator noise that comes to the fore because the battery is being drained quite severely. If your inverter is absorbing 25+ A (assuming full 300 VA load) and the stereo is getting another 10 A (120 W), plus all the other ancillary equipment, CPUs, fans and motors, you may be getting in that situation.

Quick diagnostic test: try leaving the volume at the loudest setting at which you can't hear the noise, then switch on a high-power ancillary (e.g. "defrost" the rear windscreen for a few seconds, or turn on the seat heaters) and see if the noise comes up. If so, it's probably an alternator-generated noise, and there is not too much you can do, except reduce the load.

HTH.

Good luck!

Pre-posting edit: I was assuming that the buzzing comes out of the speakers - not the inverter! But re-reading your posts I am not so sure. If it's the inverter that is buzzing, then I don't think there is too much you can do, except revving up the engine and getting the alternator to full power (1500/2000 rpm should do it). I don't think grounding has anything to do with it - the casing should be doubly insulated, and there is no reason why grounding this to the car body would decrease noise levels - I think.

Heiss5

Thanks dlevi67. Sorry if the original post wasn't that clear, the buzzing is coming from the speakers. I tried plugging the inverter into the socket in the trunk and I also tried connecting it directly to the battery, still had the buzzing. I'm going to try playing with the load on the battery and alternator to see if that changes anything. The inverter shouldn't be drawing that much though because I only had a 15 watt load on it, but who knows, 15 watts on top of everything else could be the problem.

dlevi67

Mmm - curiouser and curiouser. I don't think the load is the problem, if a 15 W load does that - heck, the cigarette lighter will draw a lot more than that, and I'd bet you aren't getting a noise then.

I'd like to attach a 'scope to your power plug and see what's going on there...

Heiss5

I know that a large portion of it is due to my aftermarket stereo. However everything is fine until I turn on the inverter so I'm at a loss for ideas.