trying to trace parasitic current draw

ballcock · 29 Jul 2017

Check to see if the windows are powered with key out of the ignition .. they should work doors open but the feed should be cut off when doors are closed.

A993LAD · 14 Aug 2017

Hi all,

A quick update on this just in case it helps others in future, as the problem has been solved.

IT WAS THE BLOODY BATTERY!!! Which had failed.

So having checked, double checked, triple checked the current drain and replaced the earth strap, it turns out it was the battery that had failed all along, and it could not hold a charge for any period of time.

The reason I thought this was unlikely is because I bought the battery only one year ago and it was a high spec, high cost (certainly in terms of Halfords stock at the time) Yuasa 75 Ah Lifetime guarantee model.

If I started the car on a mains booster you could then drive it around all day and it always had enough charge to start again without any problem for the rest of the day. But you only had to leave the car overnight and the voltage would drop to 12.2 V and it didn't have enough power to start the car again. If left for three days the voltage drop to 11.5 V.

Annoyingly I started the car with the booster and drove it to Halfords and explained my problem seeking a replacement under the lifetime guarantee. But they came out to the car, put their official Yuasa test meter on the battery, and pronounced it was fine. I tried to explain that that was because my very efficient alternator had been charging it up for the last 10 miles, but it was highly unlikely it would start the car the following morning if I drove it home. They refused to accept that the battery had a problem if their "£2,000 testmeter" said it was okay. I foolishly spent 10 minutes trying to reason with them on what possible benefit I could get by changing one good battery for another good battery and therefore why would I waste my Sunday afternoon pursuing such a course of action. But they refused to be convinced and I had to return home with the faulty battery.

I just left the battery on the car for a week, by which time it was down to 11 V. I put another battery on the car temporarily and took the faulty one back and carried it into the shop where they replaced it without quibble.

The new battery is now on the car and I just got back from a week's holiday and the car started perfectly having sat idle whilst I was away.

So it turns out I didn't have an exceptional parasitic current draw at all and as suggested here 60mA draw is fine if your battery is in good condition.

Many thanks to all those that made suggestions

trying to trace parasitic current draw

ballcock

Paul Ricard

A993LAD

Hockenheim

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