Mystery current draw

[CJH]

I'm looking for inspiration here - trying to trace a significant mystery current draw from my starter battery.

I had a flat battery the other day, and after charging it up off the vehicle I put it back in this evening, connected up the terminals, and proceeded to monitor the battery voltage for a couple of hours. It's been dropping steadily, so I simply assumed the battery was on its way out. I disconnected it in order to bring it back indoors to monitor it with nothing connected, but before I disconnected the live terminal I put a multimeter between the battery negative terminal and the disconnected earth strap and measured a not insignificant 2.4A.

I've now also disconnected the leisure battery, and everything on the starter battery except the original fat factory positive cable, so everything apart from the basic vehicle electrics should now be disconnected - no ZIG, no fridge, no LVD, no Smart relay, no nothing. I've also disconnected the radio, and disabled the courtesy lights, and made sure the vehicle lights aren't on. And I'm still measuring 2.4A. So that explains why my starter battery died overnight.

But what's causing this drain? Had it been there all the time I'd have had a flat battery every time I left it 24 hours. So it's something new. The only thing I did over the weekend was fit a few new seals to the engine, including the distributor seal, and then reset the timing. To get power for my timing light I connected up to the terminal on the back of the alternator, and did momentarily cause a short. Could I perhaps have damaged something in the alternator to cause it to draw 2.4A continuously?

With everything connected up the van starts and runs fine, and the alternator appears to be charging the battery. It's too dark and cold now to be doing any more diagnostics this evening, but I'm rather stumped anyway - I don't know what to check next. If the alternator short is a red herring, is there something else in the engine bay that I could have disturbed to cause this? I also disturbed the coil low tension circuit to get a tachometer pulse so that I could get the revs right for the timing measurement.

I've left everything disconnected for now, a) because I don't want to flatten the battery again, and b) because 2.4A through a mystery component is obviously a fire risk.

Any bright ideas anyone?

[kevtherev]

I'm looking for inspiration here - trying to trace a significant mystery current draw from my starter battery.

I had a flat battery the other day, and after charging it up off the vehicle I put it back in this evening, connected up the terminals, and proceeded to monitor the battery voltage for a couple of hours. It's been dropping steadily, so I simply assumed the battery was on its way out. I disconnected it in order to bring it back indoors to monitor it with nothing connected, but before I disconnected the live terminal I put a multimeter between the battery negative terminal and the disconnected earth strap and measured a not insignificant 2.4A.

I've now also disconnected the leisure battery, and everything on the starter battery except the original fat factory positive cable, so everything apart from the basic vehicle electrics should now be disconnected - no ZIG, no fridge, no LVD, no Smart relay, no nothing. I've also disconnected the radio, and disabled the courtesy lights, and made sure the vehicle lights aren't on. And I'm still measuring 2.4A. So that explains why my starter battery died overnight.

But what's causing this drain? Had it been there all the time I'd have had a flat battery every time I left it 24 hours. So it's something new. The only thing I did over the weekend was fit a few new seals to the engine, including the distributor seal, and then reset the timing. To get power for my timing light I connected up to the terminal on the back of the alternator, and did momentarily cause a short. Could I perhaps have damaged something in the alternator to cause it to draw 2.4A continuously?

With everything connected up the van starts and runs fine, and the alternator appears to be charging the battery. It's too dark and cold now to be doing any more diagnostics this evening, but I'm rather stumped anyway - I don't know what to check next. If the alternator short is a red herring, is there something else in the engine bay that I could have disturbed to cause this? I also disturbed the coil low tension circuit to get a tachometer pulse so that I could get the revs right for the timing measurement.

I've left everything disconnected for now, a) because I don't want to flatten the battery again, and b) because 2.4A through a mystery component is obviously a fire risk.

Any bright ideas anyone?

disconnect the alternator, there's a diode in there that can be damaged with shorting.
also the brush pack/regulator can cause a drain...this one happened to me
just remove the brush pack and check again

[CJH]

disconnect the alternator, there's a diode in there that can be damaged with shorting.
also the brush pack/regulator can cause a drain...this one happened to me
just remove the brush pack and check again

Thanks Kev - I knew someone would have a suggestion. If it's the diode, will a new regulator fix it, or is the alternator stuffed?

[nicq]

After that take the fuses out one at a time with the meter connected to find out which circuit is drawing the current.

[kevtherev]

disconnect the alternator, there's a diode in there that can be damaged with shorting.
also the brush pack/regulator can cause a drain...this one happened to me
just remove the brush pack and check again

Thanks Kev - I knew someone would have a suggestion. If it's the diode, will a new regulator fix it, or is the alternator stuffed?

separate things mate.
try different regulator/brushes first... it's the cheapest fix and the easiest

the diode is a long shot

[CJH]

Thanks guys. A few things to go at there tomorrow. I suppose if its the regulator it'll be a relatively cheap fix. It's a shame I only replaced it a couple of months ago. Pretty sure I chucked the old one out too.

[kevtherev]

Now that's weird
I too bought a new one and it happened soon after like you

at least you'll have a spare if it proves not to be the problem
but just removing it will stop the draw if it is the problem

[smavan]

I am having the same problem with mine. came out one morning and it was flat, charged it up and it was ok for a week.
then, flat again! I am now connecting it when I drive it and disconnecting it when not.
I will keep my eye on this thread to see if you find a solution to our problem.

[CJH]

...but just removing it will stop the draw if it is the problem

That was it. I removed the regulator/brushes this morning, and the current draw has gone. So it looks like it'll be a cheap fix after all. Still won't have a spare though.

[Marmalade67]

Just wondering if this is similar to a problem I am having. The battery is good and fully charged. I cleaned every earth front to back in the summer. However this is intermitant but happens in winter months mostly. If i dont start first turn it is like the battery is flat. It will then jump start no problem. I have taken the battery out straight away at times and put on charge but it is maintaining in a few seconds so not flat.

[kevtherev]

Just wondering if this is similar to a problem I am having. The battery is good and fully charged. I cleaned every earth front to back in the summer. However this is intermitant but happens in winter months mostly. If i dont start first turn it is like the battery is flat. It will then jump start no problem. I have taken the battery out straight away at times and put on charge but it is maintaining in a few seconds so not flat.

No it's not similar.. you have a connection issue with the starter..
check your connections with the solenoid and the braid that runs from the solenoid to the starter motor

or you have a worn out dog bush in the bell housing. (likely)

[CJH]

Well the good news is I may now have a spare regulator after all, because (and here's the bad news) I fitted the new one and the mystery current draw is still there. Disconnecting the alternator stops it, so I figure it's either the alternator itself or some component further downstream from that point in the circuit. Any bright ideas about how to trace it, bearing in mind I don't have another alternator to hand? Is there a description of what each of the wires in the alternator multiplug does? I guess an abnormal voltage drop across a crucial pair of terminals will tell me whether it's the alternator that's actually at fault, and if everything is normal then it must be something else that connects to that multiplug.

[CJH]

A bit more progress: if I isolate the alternator from the engine, electrically, by resting it on a sheet of polystyrene (it was off its mountings anyway, to swap the regulator over), then the current draw stops. If I then put my multimeter between the chassis earth and the alternator body I get the same current value. So something inside the alternator is shorting to earth. Looks like I need a new alternator after all.

My existing alternator is the 45A version, so maybe the sliver lining in this case is that I can now fit a bigger one. But they're not cheap. Does the advice in the wiki, about the BMW alternator from a scrapyard, still apply to my early-1.9DG-with-a-45A-alternator?

[colinthefox]

If you're thinking of fitting a larger alternator, it might be wise to think about the thick red wires going from the alternator to the black box or the starter solenoid. These take the full output of the alternator and are pretty skinny for the smaller alternator, let alone a bigger one. Often these wires show signs of long term overheating, and will need upgrading for a bigger output. The existing ones are 2.5mm2, and could be upgraded to 4mm2 or just doubled up.

[CJH]

Thanks Colin - yes, the wiring does seem to be 2.5mm2. I knew it couldn't be that simple. To save some expense I'm now thinking I might just get this alternator repaired/refurbished, rather than buy a new one. Does anyone know if that's likely to be any cheaper, or should I just look for an exchange unit?