Another battery/ABS/alternator 850 question..

By the way,

what is the definitive method for determining whether you have a bad battery or alternator? Or both?

Thanks in advance.

Reply to
Robert
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I'm going to qualify this by saying I don't know if this is good advice, but here's what I was told a long time ago. Take a voltage reading of the battery with all accessories off (and the ignition off). It should be very close to 12 volts (11.6 - 12.4). If you don't, the battery is in poor condition.

Now with the engine on, accessories off, and alternator at about 1500 rpm take another reading. You should get about 14 volts (13.8 - 14.2). If you don't, the alternator may be in poor condition.

Beverly

Reply to
Bev A. Kupf

First charge the battery. There are 2 load tests, one using high current for a short period (to see if it's going to work the starter motor), and the other a much lower current for a longer period (to see if it will run the car properly if the alternator fails). Usually batteries fail the first test while still passing the second, but not always. (There's a third test involving no current, and nothing but time, some batteries have internal current leaks that cause them to discharge over a 2-3 day period, but are otherwise fine if used every day.)

The alternator test involves measuring voltage under load - start the car, run at 2000 rpm, turn on the lights, heater fan, rear defogger, and measure voltage at the battery. If it's at or above 14 then your entire charging system (including alternator wiring) is probably OK.

Reply to
Mike F

Reply to
Ryan

I would not do that! In older cars, without computers, that is ok to do. Not with any car with a computer. It could cause damage to some component that costs a lot more than an alternator, and could be difficult to track down.

You should be able to pull it off and get it bench tested. You could also try to take a reading off the connectors from the alternator itself.

Reply to
Jeff Lesperance

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