Standing current of VW Golf R

[Smolley]

Further to a post a few weeks ago, about the battery being flat in my car after standing idle for a few weeks. I subsequently charged the battery in the house using a laptop power supply and a couple of headlight bulbs in series to deliver a charging current of ~2 amps over several days. I eventually put the battery back in the car and fitted a knife switch isolator. Yesterday I went out in the car and returned after about 10 miles. This morning after the engine fan had stopped I measured the standing current across the open knife switch and was surprised to see the meter was reading 3.26 amps. No wonder the battery flat!

[newshound]

That sounds like a wiring problem. A mate of mine had a similar problem in the 70's with a 60's car, that turned out to be a failed on/off switch on the radio (this had no lights to indicate it was on, and didn't make a sound tuned between stations). IIRC it was drawing an amp or so.

Slightly different, but the reason my ATV battery was going flat even when used regularly was that the glow plug timer relay had failed, so these were drawing 20 amps or so, well over the charging current on idle.

[T i m]

<snip>

How long did you leave it measuring for? When you connect the ammeter you are effectively re making the circuit and it will then go though any diagnostics etc until it goes into sleep mode.

Cheers, T i m

[Caecilius]

The current will start high, but will settle down after a few minutes as things go to sleep. You need to wait for a while before measuring the quiescent current draw.

[Smolley]

The meter was connected across the knife switch before the circuit was opened, so it shouldn't have seen any break in supply.

[Dave Plowman (News)]

You need to make sure everything is allowed to go to sleep mode before measuring the quiescent current.

3.6 amps would run the battery flat in less than one day.

A normal figure would be more like 0.03 amps (30mA)

[Dave Plowman (News)]

You need to leave it for say 20 minutes or so, and check again.

[Jim GM4DHJ ...]

[Martin Brown]

The standing current once it has finished all its power on self tests and become quiescent is likely to be in the range of about 30-100 mA. It varies a bit with the car, model and how many LEDs it decides to flash.

[T i m]

Fairy muff (and good idea), so how long did you observe it for after opening the switch?

Cheers, T i m

[Jim GM4DHJ ...]

valves ?...

[Harry Bloomfield, Esq.]

Dave Plowman (News) presented the following explanation :

I agree, some electronics wake up, even with just a slight change in voltage across them.

My car, loaded with electronics, sleeps at <20mA, with an odd higher short pulse, which I assume is for the alarm system.

[Brian Gaff (Sofa)]

What on earth is it doing? Brian

[Brian Gaff (Sofa)]

Really? I'm sure somebody told me that audis only fiddle about for a minute or so after everything has stopped and the car locked etc, mind you I guess there could be some issue if you have the battery in view and are still close enough for it to know you are there if its one of them there intelligent cars. Brian

[Dave Plowman (News)]

You'd have heard the vibrator...

[Dave Plowman (News)]

That's good. I've got quite a bit of extra junk on the old Rover, much of it home designed/installed. And couldn't get it down under 30mA. The original central locking took about 10mA. Got that down to under 1mA.

[Smolley]

About 100,000 counts

[mm0fmf]

VAG cars share most components. The user interface maybe Volkswagen or Audi or Skoda or SEAT specific but the underlying components and low level software are the same.

[mm0fmf]

Powering the hundreds of CPUs that modern cars use.