Alternator Rebuild Frustration
 

I replaced the alternator last week and it looks like the rebuilt unit isn't working. This happened once before about 5 years ago. Anyone else have the same run of bad luck with rebuilt alternators?

weird. Battery's not roasted from the other alternator? My rebuilt one worked great.

What's also strange is the alternator light doesn't go on when I turn the key to the first position. I jumped started the engine and then disconnected the battery which caused the engine to die immediately. If the alternator was good I thought the engine would continue to run.

You need a partially charged battery to excite the field in your alternator. Put a trickly charger on the battery overnight and try again. If the battery is totally dead, the alternator won't function.

You meant that you disconnected the jumper battery with the engine on, right? Don't ever disconnect the car's battery with the engine running. The battery plays an important part in clamping the voltage from the alternator. If you disconnect it with the engine running, you'll do some serious damage.

If you disconnected the battery (should never do while the engine is running) or if it was bad you may have fried the diodes in the rebuilt alternator when you disconnected the jumper cables or the battery cable (which ever you did). Battery should be charged separately; it is bad practice to expect the alternator to charge a dead battery. Jim

I've never figured out why alternators needed electricity in order to make electricity...but it seems that is the case...

"Seed" magnetic field has to come from somewhere: either an electromagnet (field coils) powered by an external voltage source (like a battery) or from a permanent magnet. Jim

There are 50 threads in the archives that describe exactly this situation in detail.