Alternator hums and drains battery with ignition off
 

OK - this one goes into the hall of fame for weird:

My battery has been draining on me if I leave my car without driving for two days or more. After pulling every single fuse and relay 1 by 1 to try and track down the 300 mA current draw, I noticed a *faint* hum coming from the engine. I have finally tracked it down to the alternator, which was warm to the touch (engine not run recently).

Anyone have any idea what this is? The alternator charging is perfect when driving, so it is not affecting its performance. It just drains the battery and hums with the engine off.

Thanks!

Re: Alternator hums and drains battery with ignition off
 

sounds like a short and your battery power is being transformed into heat <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

Re: Alternator hums and drains battery with ignition off
 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by DriveATransAm:
<strong>sounds like a short and your battery power is being transformed into heat <img border="0" title="" alt="[Sad]" src="gr_sad.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">That's what I thought, but I can't figure out why that would hum <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> AC current would make sense, but not DC.

Re: Alternator hums and drains battery with ignition off
 

It's going back thru rectifier bridge to the short. That what makes this noise internally on bad alternators & not just gm pieces.

Re: Alternator hums and drains battery with ignition off
 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by wrencher:
<strong>It's going back thru rectifier bridge to the short. That what makes this noise internally on bad alternators & not just gm pieces.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Thanks - I wondered if it was something like that. Already have another alternator ordered through Autozone.

In the meanwhile - do you think this could be a fire hazard? The alternator is warm, but not too warm.

Unfortunately, my car would still be under warranty if it were stock <img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" /> Don't think I have much of a chance here - the alternator, power steering pump, and radiator are about the only things under the hood that are still stock.

Re: Alternator hums and drains battery with ignition off
 

No current should flow back through the
rectifiers, short or no. If it does,
there is one (or more) bad rectifier in
the diode pack.

Single-wire alternators (ones without a
separate field terminal / remote sense)
power their regulator from the output
terminal. Ones with a field lead power
it from field. Not that it makes much
difference, but you could have the excess
back-current running there and not in the
diode pack. The regulator, if messed up,
might be unstable and commence to squeal.

In any case, bad is bad.