Electrical Gremlin

[poolnoodle]

Hi, Can someone confirm this as the best way to isolate a slow battery drain:
1. Connect a multimeter in series between earth strap and neg battery terminal and note voltage
2. Remove each fuse in turn and observe for change in reading

Also notice that when the battery is almost dead and I turn (well try) the car over I lose the occasional SI light? More anoying than anything but any suggestion appreciated.
TIA

[Brianmoooore]

Open a window.
Set meter to a current (amps) range - at least 2A, if your meter isn't auto ranging.
Clip the black meter lead to a good earth.
Loosen battery neg. clamp, but don't remove.
Push the pointed probe of the red meter lead vertically down onto the centre of the battery neg. pole.
Lift the battery clamp off of the pole, around the meter probe.
Adjust the meter range to the lowest one that doesn't overload the meter, and note the reading.
Replace the battery clamp.
Remove and replace each smaller wire connected to the battery + terminal in turn, repeating the above procedure to measure the current while each wire is off.
The smaller wires are the feed to the fusebox and ignition switch, the feed to the engine loom, and, on some models, the ABS. The thick wire is the connection to the starter motor and alternator.
Identify which wire is related to the excessive drain, and if it's the fusebox feed, start pulling and replacing fuses one by one, testing for current drain as above, while each one is out.
The fuses that are live while the car is parked are 21 to 28 inclusive.

If disconnecting the battery affects the SI board LEDs, then the SI batteries are shot.

[poolnoodle]

Hi Brian, Started tackling this one today and after following your steps seem to have traced the drain to Fuse 21.
Forgive my lack of electrical knowledge, could you confirm I am on the right track.
Removing each fuse in turn gave a reading of -0.271A but 21 gave -0.312A.
Does this seem right?
I started testing each item on that fuse and removing the glove box torch gave a similar result as removing the fuse itself. Could this be the problem? If so, is there a solution other than ditching the torch?
TIA

[Brianmoooore]

Not sure I quite follow the above.
What is the total battery drain with all fuses in place, but the torch removed?
Are you sure your decimal point is in the right place?
There is a current limiting resistor inside the torch, between the battery and the power plug. I don't have the value of this resistor written in my notes, or have a disassembled torch to hand to check, but, IIRC, its value is in the low hundred(s) of ohms, limiting the current to less than 10mA.
Torches have certainly never featured in "battery drain" threads before.

[poolnoodle]

OK, bit of an electrical dunce so please bear with. Had another crack at it and does this sound make more sense:
Total Battery Drain fully from fuse box = 18A (mA?)
Removed each one individually and got
with torch out = 10
with OBC out = 10
with Stereo out = 15

[Brianmoooore]

10 + 10 + 15 = 35. Where does the 18 come from??
If these figures are mA, then they are normal.

[poolnoodle]

The Multimeter reading changes from 18 to 10 when I remove the torch, does this mean it is drawing 8mA. Similarly 8mA for the OBC and 3mA for the stereo.

[AussieM20]

If you have the original Hirshmann aerial, this could be the cause. Unplug the 2 pin connector at the aerial and see if the draw drops.

Regards
Greg

[poolnoodle]

Is the aerial powered separately from the stereo (all wiring is original)?
If none of these drains are excessive, could it possibly be that the car is not charging the battery properly?
How is this tested?

[m_jermyn]

Run the car with a volt meter across battery terminals?

[Brianmoooore]

If these figures are mA, then THEY ARE NORMAL - they are NOT the cause of your battery drain.
Either the drain is intermittent, and hasn't put in an appearance, there is a problem with the charging system, or the battery itself is dud.
As per your last post, what's the voltage across the battery with the engine running?

[poolnoodle]

The battery shows 12.5V when the engine is off and 13.9V when running.

As a little further background, the car has had this same issue since I bought it in 1995!
It was never a hassle as the car used to get driven more regularly but now with a company car and my 2002 in the driveway it lets me down after about 8-10 days of sitting.

[Speedtouch]

There is a current limiting resistor inside the torch, between the battery and the power plug. I don't have the value of this resistor written in my notes, or have a disassembled torch to hand to check, but, IIRC, its value is in the low hundred(s) of ohms, limiting the current to less than 10mA.

The value is 2k2 (red, red, red, verified by a DMM), in a couple of dismantled glovebox torches that I have.

So, if the torch battery were to go short circuit, it would still only drain 5.5mA at a nominal 12V.

[poolnoodle]

Took the car for a longish drive this afternoon and found the following:
Battery before:12.59V
Battery after: 12.82V
Charging... do these numbers look OK?
The battery is about 5 years old.

[psychochild187]

battery age ?
and does the car have an alarm that could be causing this?

[Speedtouch]

The battery is about 5 years old.

Irregular use like this isn't kind to batteries, so it's highly likely that the battery is sulphated and not holding sufficient charge.

One recent tip I heard on a motorbike forum is to drop the battery from a height of approx. 1 foot onto a solid floor; this supposedly shakes off the sulphate from the lead plates and revitalises it.

[poolnoodle]

and does the car have an alarm that could be causing this?

No alarm fitted

One recent tip I heard on a motorbike forum is to drop the battery from a height of approx. 1 foot onto a solid floor; this supposedly shakes off the sulphate from the lead plates and revitalises it

Not sure about this one but worth a try

If the battery is good, what sort of charge should it have when fully topped up by a trickle charger?

[Brianmoooore]

The readings from all your tests look about right, but none of them tests the capacity of the battery.
The only way you can approximate a test for this is to fully charge the battery, turn the ignition, full beam headlamps, heater fan, all fog lights and wipers full on, and see how long the battery can maintain this lot.

[poolnoodle]

I am pretty sure the battery is OK. The problem was apparent even when the (heavy duty) battery was new. I might monitor the drain on the battery over the next few days and see what happens.
BMW dealer service was perplexed by the problem when I got them to check it a few years back. Their advice was it might take a lot of time and dollars to locate and wasn't worth the cost unless it started discharging more quickly. Maybe they were right, it is a little thing but frustrating at times.

[Brianmoooore]

The most common intermittent drain an an E30 saloon is the boot light not always switching off.
Same applies to the glovebox light on pre '89 models.

[poolnoodle]

I checked these early on in the piece and they seemed OK but obviously can be difficult to track if intermittant.
Typically, how long should a battery hold enough charge to start the car with the 18A drain I am experiencing?
Should I remove the bulbs from the boot and glove box for a bit and see what happens?
If nothing else, I am getting a better understanding of BMW auto electrics!! Could be handy as I am about to start restoring my 2002

[Speedtouch]

An 18A drain is quite substantial, equating to 216 Watts, or ten 21W flasher bulbs permanently left on!

Are you sure you don't mean 18mA, which is probably normal, and a thousandth of the first figure.

[poolnoodle]

Sorry 18mA is correct

[poolnoodle]

Aaarrrggghhh.
Still have this battery drain problem. Have been monitoring the battery and find it drops a little each day (that I don't drive the car) until it reaches about 12.2 at which point it won't start.
Where should I look next? I have removed the torch but it made little difference.
I am almost certain it isn't the battery as it has always done this - even when the battery was new. That said - how can I check the battery. When fully charged (on trickle charger at mo) what should it read?
HELP

[Brianmoooore]

You can check the battery by charging it, then leaving it disconnected until you want to use the car. If it has still gone flat, then bin it.

[poolnoodle]

Thanks Brian, will check this again. I had the battery out of the car last year for about 3 months whilst I was replacing interior / dash etc and when I hooked it back up - started first time. Will do this test again.
How many volts should it show at full charge?

[poolnoodle]

OK, next step and I might have solved the problem in a rather embarrassing manner
Fully charged the battery and it tested at 13.8V as soon as I removed the charger. Within a few hours is had dropped to 12.8V.
What does this indicate?
....so checked when I had bought the battery and it turns out it was 2005. How times flies, again .
In that time the car has only covered about 4000kms.
Does this suggest my problem is a simple as needing a new battery?

[Brianmoooore]

Open circuit voltage of a fully charged lead acid battery should be 12.65 volts at normal temperatures.

[poolnoodle]

Just got back from a 15 minute drive and it is sitting at 12.7V.
I have monitored it and it seems to drop by small amounts per day until it won't start after about week without driving

[Brianmoooore]

That's fully charged, but it doesn't mean it's accepted all the charge that it should, or that it isn't self discharging.
Disconnect the battery earth lead now, and see if it will start the car in several days time.