Parasitic current drain at Fuse 21

Post Mon May 27, 2013 8:34 pm

Hoping for some expert help, please! The battery on my 1989 320 Auto Convertible drops below cranking voltage if the car stands for a week. I installed a new battery but the problem remains. Testing for parasitic current drain shows a 0.07A drain. Pulling fuse 21 drops this to a 0.01A drain and pulling fuse 27 as well drops it to zero. Is 0.07A more than normal?

When I disconnect each of the components listed on fuse 21 in turn, the current draw remains at 0.07A. That's the interior light, boot/trunk light, glovebox light, torch/flashlight, radio CD and the OBC. Is there anything else I have overlooked on this circuit that could be causing the drain? When I remove fuse 21, I can't find anything obvious which is not working apart from these items. The car is standard apart from an aftermarket Cobra immobiliser but this is still functioning with fuse 21 removed. I don't have any extra ICE equipment...

Thank you in anticipation.

Mike

Post Mon May 27, 2013 8:50 pm

0.07A is higher than average, but not massively so, and a half decent battery should have no problem dealing with it for a week.
Are you sure you have your decimal point in the right place? 0.07A is 70mA; 0.7A is 700mA, and that would kill the battery in a week.

Post Mon May 27, 2013 9:00 pm

Mike316 wrote: The car is standard apart from an aftermarket Cobra immobiliser but this is still functioning with fuse 21 removed.

I could be wrong, but whenever I read something like that, that's the first thing I'd bet is causing a problem. Aftermarket alarms and immobilizers are nothing but trouble.

Post Mon May 27, 2013 11:27 pm

Thanks for the three replies to date. Just double-checked, Brian, and the reading is definitely 0.07 when the DC current scale is set at 10A on the multimeter.

Aftermarket alarms and immobilizers are nothing but trouble.

I also had the same thought but I haven't a clue how the immobiliser is wired in and it still works with fuse 21 out...you could well be right but I don't know how to begin to test that!

Aftermarket or standard ICE?

Just a CD/radio which I installed as a straight replacement for the radio/cassette - no fancy amplifiers or speakers or anything...and unplugging it has no impact on the current drain![/quote]

Just puzzled where the current is going...

Post Mon May 27, 2013 11:35 pm

Brianmoooore wrote:0.07A is higher than average, but not massively so, and a half decent battery should have no problem dealing with it for a week.

Post Tue May 28, 2013 11:27 am

Thank you for the advice. I wasn't sure how much drain was 'normal', so this helps. New battery, then...

Mike

Post Tue May 28, 2013 1:27 pm

I consider around 40mA to be 'normal' for an E30, so if this was my car, I'd still be investigating a little further to find out exactly where the power is going, but 70mA shouldn't kill a battery in a week.
I take it you are measuring the current by connecting your meter in series with the battery negative lead, and so are measuring all of the drain.

Post Tue May 28, 2013 2:07 pm

I take it you are measuring the current by connecting your meter in series with the battery negative lead, and so are measuring all of the drain.

Yes, that's how I'm doing it. I'm not sure what else to try to investigate further. None of the items on fuse 21 alters the drain when I unplug each one or remove bulbs etc. Only pulling the fuse reduces it by 60mA. That seems odd - the OBC and the radio memory should surely use some current - yet there's no change when I disconnect them.