Alternator rebuild Q

[tequilaiam]

Why would there be no voltage and the "GEN 1" warning light be dimmy lit?

I rebuilt my alternator using all new parts I ordered from CUCV Electric a while back. I didn't both testing the old stuff, I just changed everything.

Yes, I removed the little grenade pin from the brusholder after it was all together.

To test I reinstalled in truck, connected only the pig-tail for the exciter and was getting nothing out.
the warning light in the cab was "half on" I guess. Not full brightness but it was there.

I pulled it back out, tested continuity of the rotor windings and it seemed fine. My only guess is that maybe the new brushes aren't worn into the curve of the rotor contact point.


I dunno.... I just said screw it and ordered a new one from the parts-store but wouldn't mind having this one around as a backup or to make a PTO welder or something out of.

 

[Skinny]

It should charge right out of the gate, the brushes may need to "break in" for full output but it shouldn't create any real issues.

I think to help you out, we will need a full report of voltages at the charge wire in various engine speed and electrical load configurations.

 

[Barrman]

The power lead that bolts on needs to be connected as well for the alternator to start charging. Just the pigtail won't do it.

 

[tequilaiam]

The pig-tails should excite the rotor and create an output voltage when spinning right?
I tested the power leads with a volt meter, engine running and pigtails connected, to see if it was generating anything before I connected it in with the rest of the truck just to be safe.

I guess I should have also mentioned that the dimly lit GEN1 light was dim with the ignition on and engine stopped as well as when the engine was running.

Would the regulator just shut off the exciter with no load and hence I get no open-circuit voltage on the output?

Kind of a moot point now as I just picked up a rebuilt delco from a chain store but I'm just curious what I messed up in the rebuild.

 

[Keith_J]

The regulator has two terminals plus a negative. Number 1 terminal is used by the regulator to measure battery charge state (voltage), Number 2 is used to turn the regulator on and is the idiot light.

Now, if the regulator cannot determine battery charge state because the output is disconnected, the regulator does not know if the alternator is putting out any voltage so you get the idiot light to illuminate.

Furthermore, the Delco handbook 1G-266 specifically warns against running the alt without the output connected.

 

[nyoffroad]

I just rebuilt one of mine and I don't remember (from years ago) haveing to let the brushes 'break in'. But with that being said thats exactly what happened! IIRC the alt light was on and I thought I screwed something up inside the alternator, I had to move the truck and "gassed" it a little and lo and behold the light went out and it's been fine for a over a month now.

 

[cpf240]

...IIRC the alt light was on and I thought I screwed something up inside the alternator, I had to move the truck and "gassed" it a little and lo and behold the light went out and it's been fine for a over a month now.

Having to bump the throttle to get the GEN lights to go out is mentioned in the TMs.

 

[the skull]

^^^^And that's kind of a universal Delco thing at least where I come from.
We put lots of 1 wire Delco 12V alternators on old tractors, trucks, etc
and you gotta pump the gas once to make em charge. All the old Farmers
accept that fact, especially since they start so well