drainage

[adil325i]

hello all,

just came back from my bank holiday weekend break to find my 325s battery dead again! i usually leave one terminal detached if i know im not going to drive it for a while - in that i mean a week. but until recently, the battery dies over a much shorter time span - now about 3 days! ive changed the battery 3 times now, and the alternator seems fine.

i dont know if it makes a difference, but the indicators and wipers stay on even without the key in the car... anyone had these symptoms with their cars?

your help is much appreciated,

adil

[Andy_magic]

The first things I would check are that things like the boot light isn't staying on etc.

Then get the battery charged up and make sure the car starts well etc and then switch it off and pull the connectors off the back of the alternator.

The alternator has a diode pack inside that lets charge out of the alt and into the battery, but not from the battery back to the alternator. (Think one way valve)

If the diode pack dies it can let power flow from the battery to the alternator, the coils inside the alternator soak up the power from the battery trying to turn the alternator and flatten the battery. Leave your car overnight and see if it starts in the morning. If it does, then you've found the problem.

Good luck with it!

[Borderbmw]

Charge your battery up and put a digital meter on the terminals and watch for a current draw......just another idea mate

[Andy_magic]

Make sure your meter can handle high currents though, most of them can only handle 10amps. You might be lucky and have an inductive current loop adaptor, but these cost about Ԛ£300.

If you put the meter accross the terminals you will only measure voltage, you have to put the meter in as part of the circuit to measure current draw.

[adil325i]

hi guys,

thanks for the advice - andy, ive had a look at all the interior lights and they seem fine. ill run the test youve described on the alternator too just to be sure. the only thing is, i think its got something to do with the electrics staying on - a short somewhere maybe? i dunno.

ill definately check the alternator, just to be sure.

cheers,

adil

[Brianmoooore]

You don't need a meter with a particularly high current range. If the leakage is of the order of whole amps, then the fault should give itself away by the fact that it will be getting hot. (Like the time one of my electric windows jammed on overnight - didn't need a meter to find that).
Clamp the black lead of your meter to the car bodywork, loosen the neg terminal on the battery, and push the pointed end of the red meter probe vertically down into the centre of the battery post, with the meter set to the highest mA range.
Carefully lift up the battery terminal, and your meter will now read the leakage current, without causing any surges or losing radio memory or suchlike.
Turn the meter range down untill you get a reading that uses all the meter's digits. Push the battery terminal back on again.
A meter reading of up to about 90mA is OK, 50mA better.
Anything higher than this needs investigating.