measuring alternator current; rebuild
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Cargo Master
Joined: Aug 2004
Posts: 2,899
Likes: 2
From: Lynnwood, WA
measuring alternator current; rebuild
I think my alternator isn't working very well because if I have my headlights and rear defroster ON while the engine is at idle, I can see a noticable voltage drop; furthermore, last night I checked my battery and it was showing only 12.2V, and I was charging it for over 15 minutes in a 10A setting until it was showing a more reasonable 12.5V.
So, questions:
a) what is the best way to measure the amount of current my alternator is capable of supplying?
b) what's normally going bad? the brushes?
c) how difficult is to rebuild an alternator?
Car is a '95 Bronco, BTW.
So, questions:
a) what is the best way to measure the amount of current my alternator is capable of supplying?
b) what's normally going bad? the brushes?
c) how difficult is to rebuild an alternator?
Car is a '95 Bronco, BTW.
Postmaster
Joined: Jan 2003
Posts: 4,417
Likes: 3
From: Durham, NC
The way most alternator testers work, a load current is applied across the battery until a drop in voltage is seen, and this is the output current of the alternator. Make sure the battery is fully charged when this is done.
Senior User
Joined: Feb 2004
Posts: 112
Likes: 0
Check the voltage at the battery with a meter. When it's not running, 12+ volts is OK. Check again when you start it up and it should read 14+ volts. If it's much lower or higher than that check the alternator and regulator.
Moderator
Joined: Jan 2001
Posts: 56,980
Likes: 2,735
From: Virginia
I would get a voltmeter and check the battery voltage with the truck running, but no current draw, and then turn on your headlights and defroster, and measure the voltage again. With the current draw, also rev the engine a little bit and see if the voltage rises. The measurements can give clues to how bad the situation is. You could also take it to a car parts store that has a testing machine.
