Repeat Alternator failure?

Question

I have a 1990 toyota corolla that has a failing alternator. Seven months ago I replaced the alternator and it also failed within a month. What is happening? Could it be a faulty electrical circuit? The car runs pretty good and I would rather not scrap it but this situation isnt good. Please help. thanks.

Answer 1

It depends on if you are using new or rebuilt.  If new you ptobably have a bad circuit.  If used you could be getting lousy rebuilds.  Either way it should be under a warranty.  Get a replacement and see how that goes.  If it fails again then the real fun comes.

Answer 2

Alternators hardly ever go bad prematurely without any external cause. More often, they just don't work in the first place. That's not to say it's impossible you got 2 bad ones in a row that failed after working for a while. But if you do the math, the the odds are very, very low.

The first thing I would do is check the Voltage differential between the Alternator output tap and the Battery Positive terminal. With the engine running, connect a digital voltmeter, positive lead to the Alternator output tap, and negative lead to the Battery Positive terminal. Then I would connect my Battery load tester to work the Alternator hard. The Voltmeter shouldn't read more than a couple tenths of a Volt maximum. If higher, there's a bad connection, or the wire itself is faulty.

This would cause the Battery to be constantly low on Voltage, and the Voltage Regulator would sense this. That would make the Alternator constantly try to charge the Battery up to a level that is difficult to reach, overworking the Alternator, especially when lights and heater and such are being used. Of course, all of this applies to the ground side too, so some Voltage drop tests there would be a good idea too.

Considering that the Alternator that lasted the shortest amount of time was in the winter, when most people are using their lights and heater the most, it wouldn't surprise me if this were the problem.