What current/power from alternator to battery?

Fri Nov 30, 2007 8:30 am

The car is a 92 318 M40 Convertible

The car hasn't been used much in the past 4 years and in that time i have fitted 2 batteries. Fair enough!

Now the car will be used and i have fitted a new battery, The thing is it was sat for 3 weeks and when i tried to start it the battery was flat?

No alarm the only thing running is the clock.

i was wondering if its the alternator OR could it be something else?

Fri Nov 30, 2007 9:00 am

Could be the alternator, or could be many other things. Get the test meter out and check the current drawn from the battery when parked up. The procedure has been detailed many times before, several times by me, so use the forum search function.
'Normal' current drain will be around 30 - 50mA, in some cases up to about 90mA. Anything more needs checking out.
Boot light will be your main suspect, BTW.

Fri Nov 30, 2007 9:01 am

Get the car running then check the charge to the battery, should be in the 14 volt region. Let the car charge for a while if you are getting that sort of current, then switch the car off and check the charge on the battery (without the car running ) every half hour. You might see that there is a drain on the battery by just holding the multimeter on it for a short time. If there is, check interior lights etc.

Fri Nov 30, 2007 9:04 am

I doubt the clock alone will make a battery go flat after 3 weeks. You should maybe look for another cause.
If you know the car won't be used for 2 or 3 weeks then disconnect the battery.

The alternator provides power to the car and recharges the battery when the engine is running. To check your alternator you will have to put a voltmeter across the pos and neg terminals of the battery when the engine is running. A healthy alternator will put out 13.5 to 14 volts.

G

Fri Nov 30, 2007 10:23 am

And you might read through this, it was how I solved the problem with help from the zoners.

http://www.e30zone.net/modules.php?name ... highlight=

Fri Nov 30, 2007 4:37 pm

Thanks all,

I will get on the case........bit of a long distance repair.

If your interested. Click below

http://www.e30tech.com/forum/showthread.php?t=45747

Sat May 17, 2008 9:05 pm

GDBN wrote:To check your alternator you will have to put a voltmeter across the pos and neg terminals of the battery when the engine is running. A healthy alternator will put out 13.5 to 14 volts.

G

What should the meter be set to?

Sat May 17, 2008 9:12 pm

Volts

Sat May 17, 2008 9:19 pm

DC or AC?

Milliamps?

Sorry to bore but theone I'm using has a billion options to switch to.

Sun May 18, 2008 6:03 am

Never be afraid of asking questions it is important

DC volts, red lead to the positive, black to the negative with the battery in place in the car and both leads connected

check battery voltage with the car off should be about 12V (Volts) then repeat with the car running should be about 14V.

second set the multimeter to read Amps (A) or even better milliamps ( mA) . remove the battery negative lead and connect the multimeter red lead to the battery negative and the black lead to the car body (or the loose end of the negative lead)

now you should get a current reading of as Brian suggests about 50mA (milliAmps or 0.050 Amps)

note your battery needs to be charged to do this, and dont try to chargong the battery by the car as it really does not work so well, charge the thing overnight with a mains powered battery charger on slow or trickle charge

do this and let us know, and welcome to the zone

mrlee

Sun May 18, 2008 8:12 am

does adding a grounding cable to the alternator straight from the battery -ve terminal helps?

A friend of mine was suggesting to add 2 grounding cable. One to the battery +ve and another to the battery -ve terminal. It was said to assist the alternator to charge. Don't know how true is this.

Had anybody tries this?

Sun May 18, 2008 9:41 am

stormhunt3r wrote:does adding a grounding cable to the alternator straight from the battery -ve terminal helps?

A friend of mine was suggesting to add 2 grounding cable. One to the battery +ve and another to the battery -ve terminal. It was said to assist the alternator to charge. Don't know how true is this.

Had anybody tries this?

BMW know how to design electrical systems! If another 'grounding' cable was required, it would have been factory fitted.

Sun May 18, 2008 3:27 pm

A friend of mine was suggesting to add 2 grounding cable. One to the battery +ve and another to the battery -ve terminal.

attaching a ground to the battery positive will result in some nice sparks when you connect it and assuming you do sucessfully connect the lead - plenty of heat and probably an engine fire.