I'm trying to test whether I have a battery drain. I don't have an amp clamp, so I'm using a multimeter.

I'm struggling to perform an inline amperage test - here's what I'm doing after ensuring the car is fully asleep, bonnet switch disconnected, interior lights off, red P light off on gear indicator etc.:

1) disconnect the negative cable from the battery
2) touch the negative cable with the red multimeter lead
3) touch the negative battery terminal with the black multimeter lead.

When I do this I can hear things start to 'wake up' and buzz in the engine bay and the reading on my multi-meter goes to 3A to 6A to 9A then 10A+. I break the connection because I'm worried I will fry my multimeter!

I understand that by connect my meter in this way I am essentially reconnecting the battery circuit which is going to mean systems wake up, but I wasn't expecting the reading to be so high.

I've read another method which is to connect the multimeter between the negative terminal on the battery and a good earth point but leave the main earth cable connected, then (once car is fully shut down) remove the battery earth cable from the body while leaving the meter in place, to give a drain reading without waking the car again. Where is the battery earth cable? How do I remove it from the body?

Advice much appreciated. I'm thinking an amp clamp would be so much easier!?

Btw, I'm using a Ultrics multimeter. Red lead in the 10ADC socket and set to 10A.

Click image to enlarge

Quote:

I'm thinking an amp clamp would be so much easier!?

It is

Guessing the age of your car from your dash image in your other topic, try disconnecting the SatNav DVD in the boot.

Take it out and dismantle it to check the PCB, clean with contact cleaner / isopropyl and a toothbrush .
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You could try one of these, the advantage being you can check for current drain on individual fused circuits. EBay item number eBay Item No. 400433639239.
If you do decide to use one mount it so that you can read it through the passenger side window with the doors closed. The car will fully go to sleep then and the reading will be accurate.
I used one when l had a problem and found the fault without any issues.

Joe90 wrote:

Quote:

I'm thinking an amp clamp would be so much easier!?

It is

Guessing the age of your car from your dash image in your other topic, try disconnecting the SatNav DVD in the boot.

Take it out and dismantle it to check the PCB, clean with contact cleaner / isopropyl and a toothbrush

nicedayforit wrote:

If you do decide to use one mount it so that you can read it through the passenger side window with the doors closed. The car will fully go to sleep then and the reading will be accurate.

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Last edited by Phoenix on 23rd Dec 2023 10:51pm. Edited 2 times in total

camcc wrote:

nicedayforit wrote:

If you do decide to use one mount it so that you can read it through the passenger side window with the doors closed. The car will fully go to sleep then and the reading will be accurate.

Thanks for the suggestion. You mean mount the amp clamp so I can read it from inside the car?

Outside the car.

Phoenix wrote:

Amp clasmps are not ideal for mA measurements unless you want to spend serious money. The best thing to do is use a multimeter.
With the battery connected, connect the red lead to the battery clamp, connect the black lead to a good body ground point, lock the car, let everything shutdown >30 mins, then disconnect the end of the battery ground lead from the body. Doing it this way you have already established a parallel ground connection through your meter, when you disconnect the body connection to the battery negative, all the current will flow through the meter without disrupting or disconnecting the vehicle ground connection.

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Last edited by Phoenix on 23rd Dec 2023 10:52pm. Edited 1 time in total

better solution - use clamp amp meter.

Clamp meters are notoriously inaccurate (unless you're spending a few hundred on one) for any measurements over a few minutes as the DC current will cause eddy currents in the metal clamp, in turn creating a small permanent magnet, which causes an increasing 'drift' in the reading, which is why it is specified to use an in-line ammeter in dealer diagnostic routines for measuring quiescent current draw.

In situations where you need to accurately measure <50mA, a few minutes setting up for accurate measurement will prevent you chasing 'ghost' clamp ammeter readings.

Phoenix wrote:

Yes, you need to disconnect the brown cable from the body after you have set up the multimeter as a parallel ground path and obviously after the vehicle has shut down for >30 mins. I would also suggest pushing the door, bonnet & tailgate latches to their closed position (but with the doors open) so that you have full access to the inside of the vehicle without activating any of the door latches which will, of course, wake up vehicle systems.

nicedayforit wrote:

You could try one of these, the advantage being you can check for current drain on individual fused circuits. EBay item number eBay Item No. 400433639239.
If you do decide to use one mount it so that you can read it through the passenger side window with the doors closed. The car will fully go to sleep then and the reading will be accurate.
I used one when l had a problem and found the fault without any issues.

I do like your approach, but it seems you can only test up 20 amp fuses with those devices, so I suppose the sensible thing to do is not to use them on 30A fuse holders

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Last edited by Phoenix on 23rd Dec 2023 10:52pm. Edited 1 time in total

True enough Phoenix - thx