DIY Battery drain measurement ?

jlspost · 12-08-2008, 01:01 PM

I am UN-installing a "boomerang" security gps device tommorrow … and it would be nice to measure the current right after removal somehow ...

Bmw had it Friday and says I have battery parasite draw which is constantly draining the battery of 100ma to 200ma … which they suspect is an aftermarket device by BOOMERANG.

QUESTION : do you know of a way to measure how many amps my battery is supplying when the car is off ? Ie. with a volt/amp meter ??

Could I just put the meter on the battery terminals and read the current being drawn from the battery?

Thanks a ton guys,

bsamoul · 12-08-2008, 02:48 PM

you can put an ammeter on the battery to see how much charge it has and let it sit for awhile to see if it goes down a lot..

SoCalTech · 12-08-2008, 03:26 PM

You can do it with a multimeter, but it's tricky because of the way that BMW's electronics are. You need to connect the multimeter in series between the battery and the negative cable. But you don't want more than 10 amps going through the meter, so you need to have a jumper bypassing the meter until the car goes to sleep about an hour later. After that, you would turn on the meter (set to amps), remove the bypass, and see how much amperage it is drawing.
Kind of confusing to explain...

Saintor · 12-08-2008, 05:02 PM

The good old fashion way is to remove the fuse one at a time until the mA goes down. I suggest that you have the Boomerang just disconnected.

If you play with amperemeter, you ghave to know exactly what you are doing. Not a good idea for novice.

As alredy discussed and relating to my case, there are quite a few cases of current drains related to the central locking system. I would print them out and bring the pile to BMW Laval.

12-08-2008, 01:01 PM	#1
jlspost New Member 1 Rep 13 Posts Drives: 330i Join Date: Nov 2008 Location: ottawa iTrader: (0)	DIY Battery drain measurement ? I am UN-installing a "boomerang" security gps device tommorrow … and it would be nice to measure the current right after removal somehow ... Bmw had it Friday and says I have battery parasite draw which is constantly draining the battery of 100ma to 200ma … which they suspect is an aftermarket device by BOOMERANG. QUESTION : do you know of a way to measure how many amps my battery is supplying when the car is off ? Ie. with a volt/amp meter ?? Could I just put the meter on the battery terminals and read the current being drawn from the battery? Thanks a ton guys,
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12-08-2008, 02:48 PM	#2
bsamoul Major General 167 Rep 7,433 Posts Drives: E90 325i Join Date: Feb 2007 Location: Walnut Creek, California iTrader: (2)	you can put an ammeter on the battery to see how much charge it has and let it sit for awhile to see if it goes down a lot.. __________________ -Brian 2X 2006 BMW 325i [Electric Red & Mystic Blue] \| ZPP \| V1 \| Rear Fogs \| M3 Lip Spoiler \| EAS RemoteKey \| BMS Powerbox \| Projector90 Headlights w/ LED AE \| LED plate lights \| OEM Blacklines http://www.tech-shine.com
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12-08-2008, 03:26 PM	#3
SoCalTech Captain 24 Rep 648 Posts Drives: Not a BMW yet... Join Date: Oct 2008 Location: Redondo Beach, Ca iTrader: (0)	You can do it with a multimeter, but it's tricky because of the way that BMW's electronics are. You need to connect the multimeter in series between the battery and the negative cable. But you don't want more than 10 amps going through the meter, so you need to have a jumper bypassing the meter until the car goes to sleep about an hour later. After that, you would turn on the meter (set to amps), remove the bypass, and see how much amperage it is drawing. Kind of confusing to explain...
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12-08-2008, 05:02 PM	#4
Saintor Banned 82 Rep 2,446 Posts Drives: E90 Join Date: Sep 2005 Location: MTL, Canada iTrader: (1)	The good old fashion way is to remove the fuse one at a time until the mA goes down. I suggest that you have the Boomerang just disconnected. If you play with amperemeter, you ghave to know exactly what you are doing. Not a good idea for novice. As alredy discussed and relating to my case, there are quite a few cases of current drains related to the central locking system. I would print them out and bring the pile to BMW Laval.
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