Battery Draines Overnight - BMW Forum

dand65 · 07-07-2005, 09:43 AM

I have a 1987 L6, and recently I thought the battery was bad and purchased a new one. Installed new battery and the car started right up. But the next morning the battery was totally drained. removed the alternator and had it checked, it was in good condition. Tried everything like bare wires or loose connections. Last resort was I removed all the fuses while the car was running, except one that would kill the engine. Checked voltage the next day and it was at 12.5 and the car started. Does someone no how to fine the short through the fuses links that is causing the draining if the battery.. Thanks

Bear · 07-07-2005, 11:30 AM

Take negative cable off of battery and hook multi meter between negative cable and battery negative post. With key off, amp draw should be in the 100ma or less range, if not, take fuses out one at at time until the amps drop into correct range mand you have isolated your culprit.

Dirty_Tool · 07-11-2005, 01:24 AM

Bear is right on the money except that 100mA would be too high. Make sure you are under 50mA, that is the spec for e32.

DT

dand65 · 08-01-2005, 03:01 PM

Quote:

Originally posted by Bear@Jul 7 2005, 08:30 AM
Take negative cable off of battery and hook multi meter between negative cable and battery negative post. With key off, amp draw should be in the 100ma or less range, if not, take fuses out one at at time until the amps drop into correct range mand you have isolated your culprit.

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Bear, I did what you suggested and I did find the fuse which was reading 158 ma, The fuse line was for the interior lights, radio etc fuse# 21 7.5 amp. I removed that one fuse and the Ma reading dropped to 100 Ma. I connected the battery and read the voltage and it was steady at 12.40V. The next day I went and try to start the car, but it was dead. Please give me your input what could have caused this. Thanks.

dand65 · 08-01-2005, 03:09 PM

Quote:

Originally posted by Dirty_Tool@Jul 10 2005, 10:24 PM
Bear is right on the money except that 100mA would be too high. Make sure you are under 50mA, that is the spec for e32.

DT

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Dirty, The time when this all happened was when I removed the antena and try to replace it with another type. not a BMW part. I coul not use the antena, because the connector going to the radio was not the same type. So I cut the cable and connected them together , but the reception was still bad, I decided to just do with out the radio. Could this be the reason of draining the battery

Dirty_Tool · 08-01-2005, 03:16 PM

Could be..... the thing to do is after you removed the fuse that dropped the battery draw down to 100mA keep going with removing fuses until you get the draw down below 50mA. Once you have the draw down to an acceptable level then take note of the fuses. Using a wiring diagram see what exactly these fuses drive and then disconnect components 1 by 1 until you find the individual component that is causing the draw. Repair or replace this component. You may have more than 1 component causing the problem. Since you know this all started after replacing the antenna start by disconnecting the antenna 1st and then maybe the radio and see if the draw goes down to an acceptable level. Remember 100mA is NOT an acceptable level.

DT

dand65 · 08-12-2005, 01:57 PM

Quote:

Originally posted by Dirty_Tool@Aug 1 2005, 12:16 PM
Could be..... the thing to do is after you removed the fuse that dropped the battery draw down to 100mA keep going with removing fuses until you get the draw down below 50mA. Once you have the draw down to an acceptable level then take note of the fuses. Using a wiring diagram see what exactly these fuses drive and then disconnect components 1 by 1 until you find the individual component that is causing the draw. Repair or replace this component. You may have more than 1 component causing the problem. Since you know this all started after replacing the antenna start by disconnecting the antenna 1st and then maybe the radio and see if the draw goes down to an acceptable level. Remember 100mA is NOT an acceptable level.

DT

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DT, It seems what is causing the draw is the passenger power seat adjustment switch, can a bad a bad switch drain this much voltage. Thanks ofr all the INFO.

Dirty_Tool · 08-12-2005, 02:38 PM

dand65,

What is most likely happening is the switch is jamming in to the on position and running the seat motor in whichever direction until it reached the end of its travel and then continuing to send current through the motor after it has reached the end of its travel. This would be a HUGE load and would drain the battery extremely fast. i have seen this happen several times before. The switch may be internally faulty or it may just be catching on the plastic seat trim panel and hanging up. I gather that you must have disconnected the switch and now the draw has gone away and the battery stays charged? If this is the case repair or replace the switch and you should be ok.

DT