Intermittent battery drain issue

[JGood]

I have a battery that keeps draining in my track car. It just started one day out of the blue, I didn't do any work on the car. Checked amps on the battery (between neg terminal and neg cable, got 36 miliamps which disappeared when I pulled fuse 21, which seems normal to me. So I replaced the battery, and it was fine for a few days. Now it drains again.

Any ideas? The car is gutted, but still retains most wires. I checked all connections I could find, with the multimeter hooked up, and it never exceeded .36 mA.

What are common things to check with e30's? I'm pretty sure it's being charged properly, as I can jump it, let it run for a few minute,s and it will keep starting right back up again, no problem. It's only if it sits for a few hours or more that it won't start.

[jlevie]

This is either an intermittent drain (above 60ma), a bad battery that won't accept/hold a charge, or a weak alternator that isn't fully charging the battery.

The first diagnostic I'd do would be to check system voltage at idle and 2500rpm (should be 13.5v and 14v or more, respectively). I'd also disconnect the battery, charge it overnight, and see if it holds 12.7 volts over the next several days.

[JGood]

Thanks jlevie.

It was the trunk light. I forgot that I removed all of the trunk trim, including the long flat plastic piece that covers the top of the rear of the trunk, where the lid closes down on. This is where the light switch is located, and it was no longer being depressed far enough. I just removed it altogether.

Oh, and my 36mA draw was actually 360mA. I was using an old multimeter that had some confusing displays. I found a high-end automotive meter that does the trick nicely.

One thing though, I was getting 13.7v at idle, but it never increased. I could peg it at 5k and it would still be at 13.7v. Is my alternator going bad?

[jlevie]

That sounds like it might be worn brushes in the voltage regulator. You should see an increase in system voltage as the engine approaches 2500rpm. I like to see 14-14.5v at higher rpm.

[JGood]

That sounds like it might be worn brushes in the voltage regulator. You should see an increase in system voltage as the engine approaches 2500rpm. I like to see 14-14.5v at higher rpm.

I'll keep that in mind if I have charging issues in the future. Or do you think this warrants swapping the voltage regulator now to prevent related problems (decreased battery life)? It's a track car that rarely gets driven on the street.

Thanks for you help.

[jlevie]

To avoid the possibility of a lost weekend, I'd pull the V-Reg and replace the brushes.

[JGood]

Can you replace just the brushes, or do you have to do the whole regulator?