Alternator - Low current

My Alternator is charging - at least the battery tester I have says it is charging at circa 14volts, but doesn't seen to be supplying much current, If I run the car during daylight - no lights, no air con etc the in-car voltmeter shows charging - any load and the voltmeter drops. As stated, If I check with a voltmeter across the battery, without engine running then I get about 12volts and with it running about 14volts with engine running.

Is this a "fixeable" problem - ie is it an output pack failing, or is it likely to be a winding or similar. I don't wish to purchase a new alternator if its an easy fix, but don't want to throw good money after bad if it really needs replacing.

If your voltage under light load exceeds 14V but drops with a moderate load, it's probably a bad diode in the alternator. If you use an external regulator, you can test the system with a jumper on the regulator plug.

Also check the grounds on the alternator and the voltage regulator.

Bob Putnam said:

If your voltage under light load exceeds 14V but drops with a moderate load, it's probably a bad diode in the alternator. If you use an external regulator, you can test the system with a jumper on the regulator plug.

Also check the grounds on the alternator and the voltage regulator.

Click to expand...

I agree here...

I've had a case where one of the three diodes in the rectifier bridge shorted out and was dumping AC current to the battery and electrical system. Luckily this was a very simple system with no computers or sensors on board. The AC current caused the battery acid to boil - even though it never read more than 14v charge. So in the end it cost a battery and a new alternator as the old one was not feasible for servicing.