Generator Question

I have a PDF excerpt of a "Standard Auto-Electrician's Manual" that shows Volts and Amps for various RPM's.  During one of my nightly sleepless times this morning, it dawned on me the chart must be for engine RPM's, not generator RPM's.  So I calculated the equivalent generator RPM's from the pulley ratio.  I tested the low and high end RPM's on my drill press. Voltage is about where it should be.  I played around with moving the third brush and at the upper end of the speed in my chart,  I'm getting about 15 amps when I have two 12-Volt bulbs across the battery.  I'll leave it where it is for now and wait until I have the car restored to make the final adjustment with everything wired up.

Note, the voltage comes up much faster now.

Bedding down the brushes is making them fit the copper communicator perfectly. You wrap a piece of 300 grit sand paper around the copper. Then hand spin the armature a few times. It wont take much. clean it and thats all it takes.


Gary Parsons

What does "bed down the three brushes to the copper commutator" mean? Is a good analogy like lapping a valve to a valve seat? Anyway, I suspect I need to adjust the third brush. I just checked it again. At 540, 600 and 700 RPM on my drill press, I'm getting less than 1 volt. At 770 and 900 RPM, I'm getting 6.3 to 6.5V.

Its admiral you got into this three brush generator that deep. Did you bed down the three brushes to the copper commutator? Have you tried moving the third brush to see if that allows a "faster charging start"...


Gary Parsons

Is it normal for a Delco 6-Volt generator to take 15 seconds or so to come up to 6 Volts?

Background:  I rebuilt my Delco Remy 955H 6-volt positive ground generator.  I had the armature rewound and I replaced the field coils & brushes.  Cleaned everything up and repainted the case & put on a new ID tag.  Originally it was a 3-brush system with only one wire coming out from the armature brush and on the other side it had a resistor in parallel with a thermostat coming off the field coil going to internal ground.  I kept the three brushes, but added a wire from the field coil to exit through the case.  I replaced the resistor, thermostat and external relay with a saddle mount voltage regulator from Brillman.

I chucked up the shaft in my drill press set to 770 RPM.  I polarized the generator, temporarily shorting the Gen & Bat terminals on the regulator, following a service manual from Delco Remy.  I had a 6-Volt lamp connected to the Gen terminal on the regulator.  After temporarily shorting the two terminals with shaft turning, the lamp lit up and I measured 6.3 to 6.5 Volts with a multimeter.  But whenever I turn off the drill press and restart it a few minutes later, I find it takes about 15 seconds for the voltage to slowly build up.  Seems like a long time,  but the good news is it seems to hold pretty level at 6.3 to 6.5 Volts.