Optima battery life
12-21-2004, 10:17 AM
#22
Registered User
Originally Posted by Koz
To check the battery connections; To check the positive terminal, set your voltmeter to DC Volts. With the car off, place the positive (red) lead of the voltmeter on the positive + battery post, and the negative (black) lead on the cable terminal that clamps around the positive post. If your voltmeter is not an autoranging type, set it to about a 2 volt range. Turn on the headlights, if the connection is good, the voltage will be zero, or a few millivolts (1 mV = 0.001 Volt). If you read in the tens or hundreds of millivolts (100 mV= 0.1 volt), you may want to clean the connection. You can repeat this test for the negative terminal, except reverse the leads from the voltmeter. Side mount terminals will be a bit trickier, but if you can get access to the bolt and the terminal on the cable, the same process should work.
Koz is explaining how to measure "voltage drop", which (in this case) is the difference in voltage from one meter lead (the battery) to the other (the battery cable). If there's a difference in voltage (shown by a non-zero reading on the meter) then it would mean that the battery terminal or cable clamp is causing a resistance in the circuit - which is robbing you of voltage/current.
But, using a meter like this can give you false "good" readings. When you use the pointed end of a meter probe, you might pierce through any corrosion that's on the terminal or clamp and actually get a good connection for the purposes of the test. But this connection won't be good enough to support the normal current loads of the vehicle.
So... if you do get a good reading (i.e., 0.00v) then test a few times holding the probes on other places on the terminal and clamp. If any of them show a non-zero reading, then you can figure that there are connection issues.
WARNING! Do NOT try to turn over the engine while doing this. A standard multi-meter can NOT handle the current required to run a starter motor, and you'll pop a fuse in the meter. Or, the result may actually be a LOT more spectacular.
12-21-2004, 10:48 AM
#23
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Originally Posted by midiwall
WARNING! Do NOT try to turn over the engine while doing this. A standard multi-meter can NOT handle the current required to run a starter motor, and you'll pop a fuse in the meter. Or, the result may actually be a LOT more spectacular.
i was giving the battery a jump, went to crank it, and it blew up in my friend's face!! luckily he had glasses on and wasn't hurt, but got acid all over his shirt.
yeah, that was fun
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