Other 70 Problem: Battery Draining whilst car unused

[Snowdon]

I have problem find the battery volts drops below 12v if the vehicle is not used for 1wk or so.

Charging and electrolyte/water levels are okay, but the current drain of 3.75A (ammeter in series with battery –ve to disconnected black lead) seems high, before investigating further does anyone have the typical current drain.

[jimathan]

I haven’t checked but given that mine will start after three weeks, I recon the drain must be no more than 100ma. Any interior lights staying on? Boot, glove box, foot wells etc
Jim

[Snowdon]

Thanks,
Interesting I was expecting drain of around 100-250ma too.
Sorry should have said, I removed all interior bulbs prior to testing.

[jimathan]

What about faulty diode in alternator? You can check for this by measuring the AC voltage across the battery while it is charging on the car. There shouldn’t be any!!!!!!!

[jonnyjohnson]

Just a simple and easy test.

Connect an inline 21w or 5w bulb between battery earth pole and earth lead.

With ignition off, pull and refit fuses whilst looking at bulb.

Depending on brightness of bulb, when bulb goes out fault would appear to be on that circuit.

[Snowdon]

Thanks for replies, very useful tests will try later.

Just stopped and thought, with a 3.75A drain measured the maths don't compute, only guide I have for battery is 800A & 170minute --- no idea what actual AH rating is, so if 80 - 90AH would be flat in 21-24hrs, which isn’t happening, so will retest with another meter and do you think some circuit(s) switched on and need to time out for the true current drain and I didn’t leave the meter connected long enough.

[jimathan]

I know the ECU stays awake for a while, not sure how long though. Maybe only ten mins or so.
Jim

[Clan]

the systems take about 3 or 4 mins to shut down , to speed it up set the alarm , the 40 watt drain will then reduce to about 20 ma which is normal ..
A 40 watt drain is going to generate some heat somewhere !

[Snowdon]

Carried out full tests today, and importantly apologies, after rechecking I did miss some interior lights and it appears that when connecting the ammeter into the disconnected circuit it causes them to trip on?

The 3.75A drain lasts 34 seconds then falls to 135 milliamps, after a further 10mins drops finally to 14 milliamps.

Charging system,
Analogue Multimeter DC volts 14.4v - AC volts 5.5v (30v range) & 8.5v (10v range)
Digital Multimeter DC volts 14.4v - AC volts 0.034v.

After the above does look like the battery needs some attention, cycling or replacement.

[jimathan]

Yes I think your battery is the problem. analogue meters are not much cop on low level ac, but the digi one sounds rite. Your alternator sounds fine.
Jim