'05 3.0 not charging but no charge light?

[franklin2]

Confirmed its the brushes. I mounted the VRM with washers under it to try to space it back onto a better spot on the slip rings. It charged for about 20 seconds then cut out. I figured it would wear through pretty quickly on a corner like that but it's a proof of concept. Now to figure out if it's fixable.

That's strange because if you have a brush/slip ring problem, it would not have passed the full field test.

The field is the rotor turning in the middle. So when you full field a alternator, you are putting a full 12v through one of the brushes, through the slip ring, through the windings in the rotor, back out the other slip ring to the other brush.

Think of the rotor as just a big magnet turning inside the windings on the outside of the alternator case(those are called the stator). They vary the voltage on this spinning field, which varies the amount of magnetism, and that varies the output of the alternator.

The outside stator windings(think of the word "stationary" to remember) are configured into groups of 3 coils. So the alternator actually generates 3 phase A/C power from the windings on the outside as the rotor spins in the middle. They take this 3 phase power and send it to a pack of 6 diodes. These diodes are arranged to take the 3 phase A/C and convert it to single phase DC, which is then sent out on the output lug of the alternator.

When you are rebuilding your alternator, check these diodes. You can have one bad, and the alternator will charge but not as good. And sometimes one of these diodes will short across. This causes the famous "drain" and will run your battery down as the power from the battery runs backwards through one of the stator coils.

 

[pentode]

That's strange because if you have a brush/slip ring problem, it would not have passed the full field test.

The field is the rotor turning in the middle. So when you full field a alternator, you are putting a full 12v through one of the brushes, through the slip ring, through the windings in the rotor, back out the other slip ring to the other brush.

Think of the rotor as just a big magnet turning inside the windings on the outside of the alternator case(those are called the stator). They vary the voltage on this spinning field, which varies the amount of magnetism, and that varies the output of the alternator.

The outside stator windings(think of the word "stationary" to remember) are configured into groups of 3 coils. So the alternator actually generates 3 phase A/C power from the windings on the outside as the rotor spins in the middle. They take this 3 phase power and send it to a pack of 6 diodes. These diodes are arranged to take the 3 phase A/C and convert it to single phase DC, which is then sent out on the output lug of the alternator.

When you are rebuilding your alternator, check these diodes. You can have one bad, and the alternator will charge but not as good. And sometimes one of these diodes will short across. This causes the famous "drain" and will run your battery down as the power from the battery runs backwards through one of the stator coils.

Yes, you're completely right, I knew I was being "dyslexic" for lack of a better word, I realized my logic was backwards once I de - stressed enough to think clearly.

So it was easy enough to test for brush contact without tearing anything down.

However, the brushes were totally shot and the slip rings are really bad. What I can't explain is why i was able to get it charging again for 30 seconds by moving where the brushes were landing. I did change the brushes, and it still doesn't charge. So now, having thought it through a bit more, I'm back to thinking it's the VRM... Which is unavailable locally and $130 shipped from Rock Auto. So I guess I'll be making a trip to the u pull tomorrow.

I appreciate the logical feedback. I know how this stuff works but under stress, the mind tends to fixate on the answer it wants. I knew I was missing something.

Edit: oh, I'm sort of afraid I'm missing something obvious again. Any chance this could be a PCM problem? My wife did say every light came on on the cluster a couple times... I'm wondering if something failed in there