How do you measure the amount of amps the alternaor is putting out. And how do you know when the alternator is going bad? I hooked up my multimeter and got a reading of about 13.5 volts with the car running? Does that sound right? With well over 150k miles on my alternator, I think my alternator is going bad.

 

i thought it was 12 volts when car is off and 14.4 when car is on then again im not quite sure

 

In order to measure the charging current out of the alternator you need a current clamp. It is a type of hall effect sensor that connects up to a DMM. I think the other guy was right, the voltage should go up to around 14V but not at idle. It might not hit that until the engine is revved up over 3K or so.

 

These are correct, but still only approximations. The current should be somewhere in that range.

Not very many will still reach 14.4 exactly. Like Maxima Dan had said this is definately NOT at idle though.

If your alternator IS going bad, then it would most likely be in the amperage not the current.


--Don

BTW if you dont have the neccesary tool to check amperage, go to Sears, tell them you may want a new alternator. They will actually check it for free. Then buy one (if needed) anywhere you choose.

 

12 to 14.4 is the Voltage output of the rectifier/regulator which is driven by the alternator.

Secondly Current is measured in Amps.

You are right on about taking it somewhere to get tested. Way cheaper than buying a current clamp.

 

Thanks for all your help guys! I'm going to autozone to get it tested.