Thread: battery drain
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  #23  
Old 01-17-2013, 01:14 AM
Billwill Billwill is offline
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Location: South Africa
 
Join Date: Oct 2009
Posts: 511
Mein Auto: BMW E30 318i 1991
A reading of 0.03 Amps is OK.

You get a "surging" of a current reading from the capacitance that you find in any large electrical circuit such as the E30 has....the radio has noise suppression capacitors inside it, same for ECU, cluster etc.

When you disconnect your battery to put your meter in series with it, the various capacitors discharge themselves back to ground.
When you now put your meter in series with the battery....all the capacitors "charge" themselves up....initially at a high current which then tapers off to a low current. This is standard capacitor behaviour....if you have a large capacitor handy....try connect your Ohm-meter over it. The internal meter battery will charge up the capacitor until it is fully charged at which stage it will show virtually open circuit on the Ohm-meter.

If there is a fused diode in the alternator it will allow current to flow back to ground. The diodes act as one-way valves normally so that positive current can flow into the battery from the alternator to charge the battery up.
Disconnecting the alternator temporarily to check for current drain will expose a fused diode but with a drain of only 0.03 Amps (30 milli amps) there is no problem with draining in this case.

A common problem for draining current is if there is no light bulb fitted in the glove box socket. The socket acts as the switch as well and having no bulb fitted at all...even a blown one...can cause a short to ground but this tends to be a rather large current drain which is not the case here.

Last edited by Billwill; 01-17-2013 at 01:15 AM.
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