Measuring battery drain

emoose · May 30, 2012

Trying to track down battery drain, have the latest RF receiver and the alternator is kicking out plenty of power (and after a decent run the battery is nicely charged up again).

1) How can I measure the drain with an ordinary multimeter(draper 6079)?
Tried connecting it in serial between the negative cable and neg terminal but I get no power to the car(nothing works)...10 fuse in the meters DC circuit is not blown so not sure what I've got wrong.

2) Can anyone recommend a decent cheap priced DC clamp meter? (lots of cheapo ones seem to be AC only)

3) How can I stop the rover complaining about the bonnet being open, I want it too go to sleep but would need the bonnet open to read a clamp meter. Tried taking off the bonnet catch(offside where the micro-switch is) from the bonnet and just pushing it in. Somehow it still knew the bonnet was open.

Note to self, next time stick something heavy over the bare catch...it fly's quite a long way when you pull the bonnet release otherwise!

dogsbody · May 30, 2012

Removing the battery earth lead and connecting the meter in series should give you a reading. Did you have the multimeter lead in the correct socket in the meter?

Datatek · May 30, 2012

CPC sell a Temko clamp meter for about £20 works well.

emoose · May 30, 2012

dogsbody said:
Removing the battery earth lead and connecting the meter in series should give you a reading. Did you have the multimeter lead in the correct socket in the meter?

Had it connected to common and the 10amp DC socket. Funny thing was the rover had no power with the multimeter connected.

eightinavee · May 30, 2012

Not sure I'd trust a cheap clamp meter to read accurately down to the 20-30mA drain you are looking for.And dont worry about the bonnet being open,the BECM will happily go to sleep with it open.
This is what I use; Testoon / instruments de mesure - Chauvin-Arnoux K1 - AC/DC ammeter probe for very low current 4.5A DC, 3A RMS, 4.5A peak - Probes with banana or socket output

TCubed · May 30, 2012

One way of finding the drain is to remove each fuse in turn and put the metre across the gap. When you find the culprit the handbook has all the fuses.
Do you have anything aftermaket in your P38? They can often be a source of drain.

Datatek · May 31, 2012

eightinavee said:
Not sure I'd trust a cheap clamp meter to read accurately down to the 20-30mA drain you are looking for.And dont worry about the bonnet being open,the BECM will happily go to sleep with it open.
This is what I use; Testoon / instruments de mesure - Chauvin-Arnoux K1 - AC/DC ammeter probe for very low current 4.5A DC, 3A RMS, 4.5A peak - Probes with banana or socket output

It's accurate enough, I checked it against my Fluke DVM. Like all clamp meters the position of the clamp round the wire is important.

Saint.V8 · May 31, 2012

emoose said:
Trying to track down battery drain, have the latest RF receiver and the alternator is kicking out plenty of power (and after a decent run the battery is nicely charged up again).

1) How can I measure the drain with an ordinary multimeter(draper 6079)?
Tried connecting it in serial between the negative cable and neg terminal but I get no power to the car(nothing works)...10 fuse in the meters DC circuit is not blown so not sure what I've got wrong.

2) Can anyone recommend a decent cheap priced DC clamp meter? (lots of cheapo ones seem to be AC only)

3) How can I stop the rover complaining about the bonnet being open, I want it too go to sleep but would need the bonnet open to read a clamp meter. Tried taking off the bonnet catch(offside where the micro-switch is) from the bonnet and just pushing it in. Somehow it still knew the bonnet was open.

Note to self, next time stick something heavy over the bare catch...it fly's quite a long way when you pull the bonnet release otherwise!

I wouldn't turn the ignition on with a Multimeter attached, the poor thing will melt surely....

The various systems even in boot up mode could take a lot more than 10A and blow the multimeter fuse.....

Or am I again over-thinking and being to much of a H&S Slave??

emoose · May 31, 2012

eightinavee said:
Not sure I'd trust a cheap clamp meter to read accurately down to the 20-30mA drain you are looking for.And dont worry about the bonnet being open,the BECM will happily go to sleep with it open.
This is what I use; Testoon / instruments de mesure - Chauvin-Arnoux K1 - AC/DC ammeter probe for very low current 4.5A DC, 3A RMS, 4.5A peak - Probes with banana or socket output

If I don't need to worry about the bonnet being open that makes things simpler.

I'll try again tonight with the meter in series and take a photo of what I'm doing, must be something stoopid!

emoose · May 31, 2012

Saint.V8 said:
I wouldn't turn the ignition on with a Multimeter attached, the poor thing will melt surely....

The various systems even in boot up mode could take a lot more than 10A and blow the multimeter fuse.....

Or am I again over-thinking and being to much of a H&S Slave??

No I didn't power up the ignition, but I couldn't lock the doors either, the car didn't seem to be getting any power . Had to EKA it afterwards.

emoose · May 31, 2012

Datatek said:
CPC sell a Temko clamp meter for about £20 works well.

Must be going blind but I can't see anything made my Temko on CPC | CPC - Over 100, 000 products from one of the worlds leading distributors of electronic and related products. can you post a direct link?

d.

wammers · May 31, 2012

emoose said:
Must be going blind but I can't see anything made my Temko on CPC | CPC - Over 100, 000 products from one of the worlds leading distributors of electronic and related products. can you post a direct link?

d.

You need a meter that can be set to amps. Usually there is a seperate input on the tester for this. Then connect between disconnected neg lead and battery. I get about 0.76 amp with BECM awake and 0.15 amp when it goes to sleep.

StuckAgainSteve · May 31, 2012

72-7224 - TENMA - CLAMP METER, WITH FREQUENCY | CPC

wammers · May 31, 2012

Or go to your local Machine Mart and get a Clarke "Engine analyzer" CA500 £23.98. It does everything you want.

emoose · May 31, 2012

StuckAgainSteve said:
72-7224 - TENMA - CLAMP METER, WITH FREQUENCY | CPC

wammers said:
Or go to your local Machine Mart and get a Clarke "Engine analyzer" CA500 £23.98. It does everything you want.

Thanks and thanks!

I'll give the serial connection another go tonight before I splash out, must have been doing something wrong.

Saint.V8 · May 31, 2012

If you are doing it on the Negative Terminal....don't forget to have the Red Multimeter Lead connected to the Battery Strap and the Black Multimeter Lead connected to the Battery Terminal......

Not teaching you to suck eggs if you knew that already, but just incase....

emoose · May 31, 2012

Saint.V8 said:
If you are doing it on the Negative Terminal....don't forget to have the Red Multimeter Lead connected to the Battery Strap and the Black Multimeter Lead connected to the Battery Terminal......

Not teaching you to suck eggs if you knew that already, but just incase....

I'm pretty sure I did this, but then again it didn't work so maybe it was as simple as this!

emoose · May 31, 2012

Had another going reading it with the meter in series.
Still no joy it really. It started reading around 0.5 amps...but it just kept going up, by about a hundredth of an amp each second or so.

Also the car had no power, couldn't lock it to put the BECM to sleep or anything, so not really sure what the meter was reading.

Here's how I had it connected

eightinavee · May 31, 2012

You dont need to lock it nor close the windows or bonnet to get the BECM to sleep,just key out of the ignition and it should nod off in about 2 mins 15secs if all is well.Factory sleep current is 20-30mA.

emoose · May 31, 2012

eightinavee said:
You dont need to lock it nor close the windows or bonnet to get the BECM to sleep,just key out of the ignition and it should nod off in about 2 mins 15secs if all is well.Factory sleep current is 20-30mA.

Right that's useful to know.but the fact that the locks etc had no power seems to me very odd. And the reading just kept going up, didn't seem related to the cart at all...beginning to think my meter is acting up.

Measuring battery drain

Member

Very senior member

Well-Known Member

Member

Well-Known Member

Active Member

Well-Known Member

Dyed-in-the-wool 100% RR Junkie

Member

Member

Member

No longer with us, RIP

Well-Known Member

No longer with us, RIP

Member

Dyed-in-the-wool 100% RR Junkie

Member

Member

Well-Known Member

Member

Similar threads