Flat battery after a couple of days fuse 21

[e30-wheels]

Trying to fix a friends 325 Cab, the battery goes flat after a few days, done all the normal checks and the problem is with fuse 21
I was getting a drain of 0.09 amps. Disconnected everything associated with fuse 21 the last item being the blue plug on the instrument cluster when disconnected the reading reduced to zero. The instrument cluster appears to work correctly, i have reconnected everything except the instruments and the drain is 00.000 and the battery is fully up after being left for a week Does any one know what the current draw should be for the instrument cluster with the ignition turned off as it seems this is the likely problem unless there is something i have missed. Any help will be much appreciated.

[Brianmoooore]

If the drain is zero with the blue instrument cluster plug disconnected, then it looks like the car has an OBC instead of an analogue clock. The OBC draws its power from the instrument cluster via the yellow cluster plug, so repeat the test with the blue plug connected and the yellow one disconnected.
I don't know what the cluster should be drawing, but it's nothing like 90mA, and is probably different for the two types of SI board.
The normal total drain for an E30 is around 30mA - 50mA, and a good, charged battery should be able to sustain this, or even 90mA, for weeks. Are you sure this is the total battery drain?

[e30-wheels]

Thanks Brian. The car does not have an OBC or yellow plug just a blue and a white one, if i dont connect the cluster and plug the clock back in my meter reads zero the same with the radio, the clock and the radio work ok. I will try another test meter and re check the readings, The battery does not go dead flat but does not have enough power to start the engine, it a a new Bosch S4 battery and as its ok with my zero readings i am presuming its good but i will test it, I have the old type drop tester which certainly sorts the good from the bad.

[e30-wheels]

Results of further testing The car battery tested good. tested battery drain with another meter and im getting 10 mA drain with no instrument cluster connected just the clock, swapped the instrument cluster for a known good one one (borrowed from my 325 e30), disconnected the clock and connected the cluster only, the battery drain was zero reconnect the clock and got a reading of 10mA all test with ignition off, It appears the answer to my question as to the battery drain of the instrument cluster with ignition off is Zero. Looks like i need to get a new instrument cluster, i note there are refurbished SI boards on ebay in the States, has any one tried one?

[Brianmoooore]

You didn't say that you'd left the clock disconnected......
Chances are that the NiCd batteries on your SI board have gone short circuit, and the current drain is via the overloaded charging circuit. Open the cluster up and check the batteries. If they haven't leaked and corroded the board, a couple of new batteries is a much cheaper option than an exchange board.

[e30-wheels]

On reading what you have said i tested the battery's and they are good, the owner of the car is an electronics engineer and modified the cluster by moving the rechargeable battery's into a battery clip outside the casing about a year ago and has no problems until now also the instrument cluster was working ok. I think you are correct in what you say but not the battery's but something connected to that part of the si board possibly caused buy soldering on the circuit board board but only just gone faulty If the battery's were at full capacity when the fault developed it would explain why the instrument cluster worked ok and given time the cluster would stop working.

[e30-wheels]

Decided to look at the modified SI board, no problem with the printed circuit board, the wiring for the external battery holders had been soldered to the old battery's, took the covers of the external battery pack and found the chap had use 3 volt non rechargeable battery that were leaking, strangely they were reading 3 volt and 2.99 i replaced these with rechargeable ones tested the cluster in the car and it works fine with zero battery drain every thing else associated with fuse 21 was disconnected, The car owner said he ordered the battery's as rechargeable but did not look at them. Cant work out why they didn't give a problem soon after they were originally fitted.

[Brianmoooore]

The 3 volt lithium batteries used in one version of the SI board ARE non rechargeable, and this board has no charging circuit fitted. The NiCd batteries fitted to the other sort of board are rechargeable, and are 1.2 volt.
Are you sure this guy's an electronics engineer?

[e30-wheels]

The original battery's are sanyo 3v lithium laser, im amazed that they are non rechargeable how do they manage to last for years and years. i have only ever seen the 1.5 volt ones and as such thought they were all rechargeable, anyway Im totally confused now, having put new battery's in the cluster which seems to have dealt with the batter drain problem leaves me with the question, if they are not rechargeable and if they were u/s with no charging capabilities it would not have cause the drain of 90mA i was getting, i can only think I disturbed something when i removed the coding plug and SI board . Hate it when you sort of fix a problem without knowing what the actual fault was. Many thanks for you help on this Brian

[Brianmoooore]

No current is drawn from the batteries on the lithium version of the board while the cluster is connected to the main car battery.
The batteries are there to maintain the board's memory (design pre-dates NV memory) if and when the car battery is disconnected, and current is only drawn from them then. I measured the current that was drawn from them a few years ago, and worked out that they should be good for around seven years in total (IIRC) before they need to be replaced.
Some E30s were fitted with lithium boards from the battery, and these differ slightly from boards that were supplied as spares. The replacement boards have a large orange arrow sticker on one of the larger ICs, pointing towards a row of three terminal pins, with a jumper link fitted to two of them, and the writing on the sticker instructs you to move the jumper to the other pin before fitting. This jumper link then connects the batteries to the circuitry, and from that point onwards the batteries are running down until the board is installed in a car with a charged and connected main battery.

[e30-wheels]

Very interesting, my cluster has the big orange sticker, i have always wondered if the jumper was i the correct place it has i small white mark which lines up with the arrow sticker point, do you know if this is correct , what stops the lithium battery's discharging when the board is connected to the main battery.