How to test what current is being drawn from the battery?

[Gmac]

Evening all!

I'm looking to get to the bottom of a battery drain issue, and I would like to know how you go about seeing what current is being drawn from the battery when the car is sat engine off and locked.

Here's what I think.... I undo the positive lead from the battery, and then connect up a multimeter, with it set on amps, and the leads plugged in to common and 10A.  I then use the multimeter with one if its leads on the battery positive and the other on the lead that has been detached from the battery.

What sort of current should I see? Less than 1amp, perhaps 3-400mA????
I'm hoping to get to the bottom of whether or not it's a parrot handsfree kit that I've recently installed (separate thread ongoing!).  I've disconnected the handsfree kit for the moment.

I'm also wondering, if the correct technique is correct, how do I go about getting round the alarm siren blasting its head off when I undo the positive lead from the battery?  Background to that is.... I went to test for a current, (wasn't using the multimeter correctly, so no reading obtained) and with the car locked and undoing the lead from the battery, this made the alarm go off!

Any help would be great, cheers

[baka]

Hi ya, this article on Popular Mechanics seems to cover everything really well:

http://www.popularmechanics.com/cars/how-to/a5859/how-to-stop-car-battery-drains/

[pudding]

What sort of current should I see? Less than 1amp, perhaps 3-400mA????

Way less!  1 amp draw will drain a 72AH battery in 3 days.

0.01 to 0.05 amps is about right.

Have you got an RNS510?  Older ones are known to chew batteries on <2008 cars.

[Gmac]

What sort of current should I see? Less than 1amp, perhaps 3-400mA????

Way less!  1 amp draw will drain a 72AH battery in 3 days.

0.01 to 0.05 amps is about right.

Have you got an RNS510?  Older ones are known to chew batteries on <2008 cars.

I've got the rns MFD2 (black buttons), and it looks as if it's the original one. Cars 2005.

[Gmac]

Hmm, interesting results...

Just been out and with the doors closed, bonnet open, I'm getting approx 1.5amps!  I then pull the radio fuse (F19 15amp, in the engine fuse box) and it drops to about 0.75 amps.  This is on the 10amp reading setting on the multimeter.  So, it seems there is something draining the battery.  However, even if I find this, the radio is still drawing 800ma...

I've made sure the interior lights are not on, and glovebox is closed.

Any thoughts?

[Eddie-NL]

use this method to check where the problem could be

http://pics.tdiclub.com/data/500/TSB_27_08_04_Matrix.pdf

Also if you have vcds get a scan as faulty ignition switches or broken can wiring in the doors can cause problems

[chrism3]

I read somewhere that the stock headunit drains power. It is a common fault apparently. Remove the fuse for it and see if it still happens.

[Gmac]

Thanks Eddie, I'm sure that will come in handy! 

I've vcds, and scanned the car the other day and the only fault code that was coming up was for the navigation cd not reading, which was weird as the navigation seems to be working fine.

[Gmac]

I read somewhere that the stock headunit drains power. It is a common fault apparently. Remove the fuse for it and see if it still happens.

Read above..

[Gmac]

I've been testing the rs4 this evening and I've got that reading 50mA/0.05A.  This is with the car locked, bonnet open, and have waited 10 mins, then keeping the multimeter on the battery terminal and the lead, whilst disconnecting the lead from the battery, so as not to 'wake up' anything.

I'm going to try tomorrow with a similar technique on the golf and see what readings I get. I've read that the cangate can take a good while to properly go to sleep, ie up to 45mins!

So yeh, thanks for the help so far...

[chrism3]

I read somewhere that the stock headunit drains power. It is a common fault apparently. Remove the fuse for it and see if it still happens.

Read above..

Ahh missed that. Are you sure that's not the issue tho?

[Gmac]

I read somewhere that the stock headunit drains power. It is a common fault apparently. Remove the fuse for it and see if it still happens.

Read above..

Ahh missed that. Are you sure that's not the issue tho?

That's what I'm trying to figure out!! Haha.  So by getting a reading and base line to work from, and then working back to see what is drawing more power than it should be, I can find out what the issue is.  I wasn't having any battery drain problems prior to trying to fit a handsfree kit though.  Also, from what I have read, it seams to be aftermarket head units that cause drain problems as they are correctly working with whatever model of canbus the car has.

I've bought and fitted a new battery today, so I can rule out a bad battery giving false indications.

[Gmac]

Been testing again with the new battery fitted, and stil getting weird results.  It's a bit of a pain testing it because as soon as something doesn't go right, and say my testing lead from the multimeter slips of either the battery terminal or the battery lead, it'll wake some system up and I'll have to wait again until say the highline clocks go out again.

So results are a bit weird, getting say 0.5A then sometimes it'll be 0.28 then, as the radio fuse is right there in the engine fuse box, (F19 15amp), I'll pull that and take another reading and there is no difference!  So, yeh, pretty frustrating. I'm still trying to get a baseline reading which seems consistent.  Wondering what else could be drawing significant power?

Any thoughts/tips welcome.

[Gmac]

Right well update...



Since fitting the new battery, 71Ah one, I've tested the draw when the car is locked without the handsfree and with it.  This time I was waiting a good 30 - 45 mins before testing to make sure that things were 'sleeping' and both tests came out with the same result.. ie on the 10A setting on the multimeter I was getting a reading between 0.01 and 0.00, it would flick from one to the other.  A bit weirdly when i went to 200mA setting, I wasn't getting any reading, when i was expecting to see the 0.10 or something like that ( can't remember how it displays the decimal scale) but nothing.



Here is a video of the set up on 10A scale. Let me know if it doesn't work.



It should be noted that i haven't suffered any battery drain with  the handsfree kit fitted again.  I left the car for a good day and a half, and it started no probs, without hesitancy... so perhaps the battery change has done the trick!

[Flyingscotsman]

On the 200mA scale it should read 10mA, which sounds OK for a drain, would take 300 days to drain a 72Ah battery!
You need to change the red lead on the meter to the right hand plug for the 200mA scale to work.