Battery drain not resolved.

[derdle]

The ammeter needs to be connected in series but I gues the best thing is to connect it to the offending expected source of the drain rather than to the car battery (as this will read all sources of drain e.g. car alarm, blue tooth etc etc).

Good luck and keep the extinguisher to hand just in case the ammeter can't take the current!

[peterb]

Yes, connect in series. Logically, it doesn't matter which side, but it's safer to play around with the -ve (in case you inadvertently short to the chassis).

[Mo_S3]

Dont really fancy ripping my car to bits again to access each and every seperate item. How to the ADT guys do it or the dealers? Vag com or something else more specific?
thanks

[derdle]

If you just put the ammeter onto the battery it may pick up a drain that should be there (perhaps the audi car alarm??) I think the only sure fire way is to check the suspect item as well. if there is a drain of say 500mA at the battery you may find that 100mA should be there and then yoiu need to find the other 400mA ... so you'll need to test the suspect items. until you can account for all the drain. That's the way I'd tackle it, but I'm an accountant so possibly not the right thing to do?

Paul

[peterb]

I guess it might be worthwhile pulling each fuse in turn and measuring the current at each one. Beware though, that there might be some circuits which are separately fused (or even unfused? )

Also, note that some units shut down in stages - Radio/SatNav, for instance, can be set to receive and store traffic announcements for some time after you turn the car off. RNS-E units go into a lower power mode when you lock the car (and wake up again when you unlock the car).

[Mo_S3]

cheers guys i will give it another go, but since replacing the battery and sorting the other unit out its seems to be fine at the moment

[clived]

If you just put the ammeter onto the battery it may pick up a drain that should be there (perhaps the audi car alarm??) I think the only sure fire way is to check the suspect item as well. if there is a drain of say 500mA at the battery you may find that 100mA should be there and then yoiu need to find the other 400mA ... so you'll need to test the suspect items. until you can account for all the drain. That's the way I'd tackle it, but I'm an accountant so possibly not the right thing to do?

Paul

Just connect the ammeter to the battery and pull each fuse till the drain goes away. Watch the current drop progressively first though as the various car systems shut themselves down - then start pulling fuses.

[toasty]

worth noting also, if you don't have an ammeter that will handle a large number of amps, you can get a similar (indicative result) by connecting a sensitive voltmeter across the earthstrap of the battery (connect one probe to the negative terminal and the other to the connection to the bodywork)

The larger the voltage shown, the larger the current draw.

[shineydave]

Won't that just show a reading which reflects the resistance in the earth strap? when you measure voltage you're measuring the difference in potential and since there's no consumers between the battery terminal and the earth bolt you should get a 0v reading unless the earth strap has a very high resistance.

[toasty]

Not quite Dave.

Remember that the earth strap has a small (but nevertheless important) resistance, therefore as ohm law states if a current is passed though it, there will be a voltage drop across it of some description - clearly as the current increases, so will the votage drop, so measuring the voltage across it will give an indication of the current flowing.

Of course if you have an ammeter capable of a few amps or more I'd use that, but the earth strap method works, especially if you have a sensitive meter - which most digi meters are.

Just an example, but assuming it has a resistance of 1/100 of an ohm then a 1 amp drain will cause a voltage drop of 1/100 of a volt or 10 milivolts, most multimeters can easily resolve that.

Anyway, hope this helps.