HELP. Battery question

[dnick]

update? you get a chance to install the alt?

[jdvorwe]

I meant wouldn't that eliminate the draw on it though? So any other reason that it would drop in voltage?

[jlevie]

I just thought of something, I have actually been disconnecting the battery when not using the car or testing it. Would that make any difference?

It shouldn't unless the battery is disconnected for a long time (like months).

[jdvorwe]

I just thought of something, I have actually been disconnecting the battery when not using the car or testing it. Would that make any difference?

[jlevie]

The current drawn from the battery when the car is off is referred to as the parasitic load. It will normally be in the range of 30-60ma. Improperly installed aftermarket electronics are the most common cause of excessive parasitic draw, but faults in the few circuits that are powered when the car is off is possible.

To check for excessive parasitic draw one disconnects the battery ground cable, uses a jumper cable from the ground cable to the battery to power up the car, connects the meter set for current measurement between the ground post and ground cable, and then removes the jumper for the current measurement. The jumper cable prevents the meter from seeing the starting surge as the car powers up. With all doors and the trunk closed if the current draw is more than it should be, remove one fuse at a time to find the offending circuit. Then trouble shoot that circuit. In most cases you will find the fault that way, but there are a few things that aren't fused, like the alternator.

A fuse that is blowing indicates that the circuit powered by that fuse is drawing too much current.

When chasing electrical problems the wiring diagrams for the car are a big help. See http://wedophones.com/BMWManualsLead.htm

[jdvorwe]

Excessive current draw when the car is off, or a bad battery.

Ah, I had a fuse blow and when I replaced it the fuse immediately blew. I originally thought it may be bad voltage regulator (and linked to this), I read that sometimes a bad voltage regulator can cause fuses to blow. But, my problem could also be, if I am understanding correctly, that an item connected to this fuse isn't grounded correctly and could be causing a current draw/draining my battery?

[jlevie]

Any reason that would make the battery drop from 12.5 to 12.2 in two days? I'll take the battery back to auto parts store and see what they say.

Excessive current draw when the car is off, or a bad battery.

[dnick]

damn man, i didnt know you were having these problems! In the mean time, I can get you that alternator.

[jdvorwe]

Any reason that would make the battery drop from 12.5 to 12.2 in two days? I'll take the battery back to auto parts store and see what they say.

[jlevie]

If the system voltage doesn't rise with an increase in engine speed with a fully or nearly fully charged battery, the alternator is suspect. But if the battery is only reading 12.2 volts with the engine off, the battery is only at 50% charge or is bad. Charge the battery overnight and check 30 minutes after disconnectin the charger (should be 12.7v). Then turn on the head lights on high beam to see that the voltages is at least 12.6v. If battery voltage falls below that, replace the battery. Then repeat the alternator system tests.

[browntown]

My eta had an odd little water catch gizmo in line with the breather hose that collected red water like that. My i just has the breather hose straight out the bottom grommet. Next battery will be sealed gel I thinks.

[jdvorwe]

I had my girlfriend press the gas, she didn't really get the concept of "rev it". haha. Anyway, before I could explain it to her it started raining and then she had to go to work.

She lightly pressed the gas and held it and the readings on the multimeter stayed the same. They were varying from 13.3-13.6. Isn't that a little low? My battery was reading a little more drained though, 12.2 (with the engine off).

[jlevie]

The alternator is probably good. Prove that by checking the system voltage at 2500rpm with and without a load from the high beams and HVAC blower set to max.

[jdvorwe]

Alright. Just went and tested again.

Engine off: 12.5ish
Idle: 13.6ish
Didn't get to test it reving because I was by myself.

So with these results, that means my alternator is good?

[jlevie]

Smoke from the meter probably means it was configured for current measurement, not voltage.