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Old 02-27-2010, 06:04 PM   #1
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Default Cars resistance

Has anybody ever checked their cars resistance (with a ohm meter/fluke)? My battery has this nasty habit of draining so I checked my charging system and I am getting a steady 14v. Then I checked the resistance through the positive and negative leads (with battery disconnected) and my resistance was only at 56.5K, which seems low in the first place. Then after the initial reading it stared to trickle down until it got to 11.5K and it stayed pretty steady at that point (took about 5 minutes to get there). After seeing that I then pulled each fuse 1 at a time looking for something to change the readings but was unsuccessful. I don't think this is normal and was wondering if anybody could confirm my suspicion. Also looking for recommendations, I really don't like having to keep my battery on a trickle charger :/
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Old 02-27-2010, 08:36 PM   #2
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My battery drains over a week time as well. It's been about a year and haven't been able to find it.
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Old 02-27-2010, 08:39 PM   #3
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A week would be fine with me, mine eats it overnite :(
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Old 02-27-2010, 08:40 PM   #4
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To find dark currents, you use an ammeter (not a voltmeter) and measure the current through the battery while pulling fuses.
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Old 02-27-2010, 08:42 PM   #5
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you should have really low resistance like .04 or better....
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Old 02-27-2010, 09:39 PM   #6
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car alarm? i leave my car for weeks at a time and it always starts right up...even in 20 degree weather.
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Old 02-27-2010, 10:06 PM   #7
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I'm with Joe. Use an ammeter.

You should use one with a high amp capability (50A analog) at first. I clamp one side to the positive cable, then stab the positive terminal on top while lifting the cable off its post. Once you prove that the current won't be lethal to your DMM, switch to that.

Then as Joe stated, check what the current reading is, and pull fuses 'till it goes away. That'll be the offending circuit. Then pull the prints and go through that circuit.
--Alex
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Old 02-27-2010, 10:12 PM   #8
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you can also disconnect the ground cable from the battery, attach a test light inbetween them, and see how bright it is. pull fuses one by one till its really dim, after you figure out the fused circuit its on, start disconnecting each item on the circuit till it goes dim again.... does it have a aftermarket radio,factory amp, any sorta alarm, or has anyone gotten into the wiring ?
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Old 02-27-2010, 11:12 PM   #9
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Those are all great recommendations, I had been talking with a friend about doing the very same thing...but I wasn't convinced it would do much seeing how neither of us had used that particular technique. Now I have something to occupy my mind on Sunday! Thanks for all the help. I'll have to get a new fuse for the ol' analog...I'll post updates as soon as I find the source. Also the car has an alarm system that hasn't been armed since the start of the dying battery, seeing how it's locked in the garage and all.
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Old 02-27-2010, 11:36 PM   #10
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All recommendations are good for checking the car, but I find that most of the time it is an older and failing battery. Take the leads off and see if the battery drains itself over the week. Should have a shop do a load test on your battery.
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Old 02-28-2010, 09:20 AM   #11
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I will be doing that today also, it is an optoma red top (about 2 years old) so from what I was reading all bets are off. Thanks again guys!
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