My 318i battery drains overnight.
I fitted a new battery and still happens. I can now guess that it's the alternator or a short / drain somewhere sucking it dry. I have a multimeter to run a few tests to see whether the alternator is putting anything out and also to see for shorts and start pulling fuses to narrow the culprit circuit.
1) To test the current from the alternator, where do I put the multimeter and on what settings?
2) To test the current draw whilst the car is off (OBC and Immobiliser present) where do I put the multimeter and on what settings?
Any and all help appreciated.
Measuring current / volts...
Moderator: martauto
To measure the output of the alternator set the meter to DC voltage and put the red positive probe on the + terminal of the battery and the neg. probe on the neg. battery terminal. With as many consumers switched off, start the engine and you should get a minimum of 13.2V at idle and up to 14.2 at 2000 rpm. Switch on headlights, fan blower and RWD and check to see how the alternator reacts. It should be at a minimum of about 13.8v with these consumers on.
The volage regulator could also be responsible for an incorrect charging rate too and it would be worthwhile checking the length of the carbon brushes of the regulator if you don't obtain these basic figures.
To measure the current draw, switch the meter to DC amperes and select the 10A slot.
Then loosen the terminal attached to the negative battery post but don't detach it.
Connect the neg. probe to a good earth point, like the suspension turret and place the red probe on the top of the neg. battery post. If you then raise the neg. terminal upwards, maintaining contact with the + probe on the battery post, you can read off the current draw, which should be in the region of 25 mA-40 mA and shouldn't exceed 80 mA.
You can then switch the multimeter connector from the 10A to the 200mA slot to get a more specific readout but don't do this if the 10A reading exceeds the mA setting, as you will damage the meter.
Quite often the boot light, glovebox light and/or dubious after market alarms are responsible for substantial drains.
The volage regulator could also be responsible for an incorrect charging rate too and it would be worthwhile checking the length of the carbon brushes of the regulator if you don't obtain these basic figures.
To measure the current draw, switch the meter to DC amperes and select the 10A slot.
Then loosen the terminal attached to the negative battery post but don't detach it.
Connect the neg. probe to a good earth point, like the suspension turret and place the red probe on the top of the neg. battery post. If you then raise the neg. terminal upwards, maintaining contact with the + probe on the battery post, you can read off the current draw, which should be in the region of 25 mA-40 mA and shouldn't exceed 80 mA.
You can then switch the multimeter connector from the 10A to the 200mA slot to get a more specific readout but don't do this if the 10A reading exceeds the mA setting, as you will damage the meter.
Quite often the boot light, glovebox light and/or dubious after market alarms are responsible for substantial drains.
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FlappySocks
- E30 Zone Regular
- Posts: 860
- Joined: Sun Jan 22, 2006 11:00 pm
- Location: Fareham, Hampshire
- Contact:
The boot light is a common one. Check to see if it's warm when you open the lid, or pull the bulb, and wait till morning.
Motronic to Megasquirt Plug and Play Guide-
Turbo_Bozo
- E30 Zone Newbie
- Posts: 25
- Joined: Sun May 11, 2008 11:00 pm
Cheers much guys - will check it out.