BMW M5 Forum and M6 Forums banner
1 - 5 of 5 Posts

·
Registered
Joined
·
389 Posts
Discussion Starter · #1 ·
Hi Guys!
Just wondering what the usual current drain should be when the car is not running as i find using my M5 at weekends isn't often enough to stop the battery discharging. I measured the current with car unlocked and alarm off and it was 180mA which i think is a little high, but once the car was locked it rose to 220mA so no wonder the battery is getting flat if that's the current all the time. This extra current must be the alarm sensors that had activated. Does this sound too high to you lot?

I've got the little battery in the boot but that seems isolated from the main battery with testing, and only seems to power the CD changer. I've also got an 'auto saver' rust prevention system fitted which uses about 40-50 mA so ignoring that then when the car is locked the current drain is 170mA- still seems high to me??

I also bought a solar panel recently that should trickle charge the battery (15w) but even this doesn't seem sufficient.
 

·
Registered
Joined
·
178 Posts
Hi madm5,

That sounds high to me. I haven't measured my discharge rate but the car starts just fine after sitting one week. Do you have the factory alarm fitted?

Battery discharging seems to be a fairly common problem on E34's. It has happened twice on the family's regular E34 that the wiring to the trunklid has been worn against the body (cables move with the trunklid) causing short-circuits that increase the discharge for example by keeping the trunk lights on when the trunk is closed. The wiring runs in the left 'support arm' to the trunklid. Check the moving cable which you see inside the top of the trunk.

Hope this helps.
Patrik
 

·
Registered
Joined
·
189 Posts
For most BMWs the max it should be is 50ma. Most cars I've checked are closer to 20 or 30 ma. You definitely have an excessive draw. The E34 may not have to, but newer BMWs have to enter sleep mode before the draw drops all the way down. This takes approx 16 min.
 

·
Registered
Joined
·
183 Posts
Yes - 250mA is too much - mine was drawing that and flattening the battery - turned out to ba a faulty relay for the wiper tensioning mechanism. Once fixed, draw was down to 20-30mA with alarm on. I suggest you pull fuses until you see the current drop - if it doesn't try pulling the wires on the alternator in case a diode has gone in that.
 

·
Registered
Joined
·
389 Posts
Discussion Starter · #5 ·
day said:
Yes - 250mA is too much - mine was drawing that and flattening the battery - turned out to ba a faulty relay for the wiper tensioning mechanism. Once fixed, draw was down to 20-30mA with alarm on. I suggest you pull fuses until you see the current drop - if it doesn't try pulling the wires on the alternator in case a diode has gone in that.
Sorted thanks for all the advice- removed all fuses one by one and measured the current across every circuit- couldn't locate anything that was drawing too much, then removed every relay. After replacing all fuses and relays current was reduced. I then reconnected the ammeter across the battery, and strangely enough, anything open on the car - door - boot or bonnet was draining current. However the bulb has blown in the boot and i switched off all internal lights so I guess it must have been the VDO sensing something was open. Anyway, closed all doors, boot and bonnet and got current drain down to 60mA which seems fine to me, thanks for all the advice.
 
1 - 5 of 5 Posts
Top