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Draw testing an idle battery
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Lonsmrydr
New User
Jun 16, 2005, 8:31 PM
Post #1 of 3
(2434 views)
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Draw testing an idle battery
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Is there a way to check and see how much amperage draw is on a battery, with a multimeter, while the key is in the off position? I've heard people tell me that you can put the meter between the battery and the negative cable to see how much draw there is. Someone please point me in the right direction.  I just lost a battery from 12 volts to 9 volts in a 5-6 hour period, and wanna make sure something isn't sucking the battery while idle. Any information would be greatly appreciated.
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DanD
Veteran
/ Moderator
Jun 17, 2005, 12:57 AM
Post #2 of 3
(2431 views)
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Re: Draw testing an idle battery
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You can connect your multi meter between either the positive or negative cable and the battery as long as all the current flow has to go through the meter. If you’re using the positive for your connections, connect the meter red lead to the battery, if you’re using the negative connect the red lead to the cable. It really doesn’t matter it’s just to have the polarity of the meter showing correctly
Be careful a lot of hand held meters can only handle 10 to 15 amps of current flow so don’t be trying to turn to many things on while the meter is connected or you’ll either blow out its fuse or the meter itself. Even just turning the ignition switch on can blow out the meter, due to things like, wakening up the computers, fuel pump cycling can draw up to 30 or more amps.
Speaking of wakening up computers, the same thing can happen when you reconnect the battery or connect the meter in series with the battery and cable.
What I do is connect a jumper wire first and then the meter, wait until the computers, door chimes and possibly interior lights all go to sleep and then disconnect the jumper wire. Could save your meter.
Now you’re ready to start the tests, what I do is open a door or turn on the interior lights and see if they come on. That’s just to verify that there is a connection through the meter, you may see 4 to 6amps while the lights are on.
One more thing about the computers going to sleep it could take up to 45 minutes for all of them to completely shut down, so don’t rush around looking for a draw take your time. Also remember that every time you activate something you are likely going to wake somebody up and will have to wait again until whatever shuts down.
You will never see zero draw on the system because of computer memories, digital clocks or whatever, the rule of thumb is no more them 50mili-amps max, that’s .005 amp. (I think I put the dismal in the right place)
If you have more then this you’ll have to start looking to who or what is not turning off, glove box and trunk light are famous for killing batteries. They’re kind of like the fridge light in your house is it really off when the doors closed? LOL
As for finding the source of the draw there is no easy way other then disconnecting or unplugging things until you find the culprit. The fuse panels are a good place to start, you may get lucky and narrow down what circuit the problem is on.
Good luck and I hope I didn’t loose you with this gibberish.
Dan.
Canadian "EH"
(This post was edited by DanD on Jun 17, 2005, 2:47 AM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 17, 2005, 10:14 AM
Post #3 of 3
(2414 views)
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Re: Draw testing an idle battery
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Simple - just put a volt meter on battery's disconnected neg and battery with everything off. It should be dang near zero. Unplug hood light if that was on.
The battery itself can short within it. If it's over three years old it's OLD. They flake and short from the bottom and can be intermittent or a disaster. If old get a quality new one and keep on testing for a drain if a new one doesn't stop the problem. If this battery can go dead by itself get rid of it soon. Don't park the veh in a garage if a short within battery is suspect. Start a new post if you have a drain on it, from the vehicle, good luck,
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