MTFCA Forum

Recently, I have been working on a few Model T generators. When setting them up, I had some trouble with setting the brushes to the neutral plane. The general procedure I’ve been using is
1. Raise the 3rd brush
2. Loose the four screws that hold the brush rigging
3. Apply 6 volts to the output terminal
4. If the armature shaft turns, rotate the brush rigging until the shaft stops rotating.
Seems easy enough, but sometimes the armature shaft will not rotate at any position of the brush rigging. Then I remembered how we used to set the brushes on DC machines at the power plant. AC current was passed through the field and AC voltage was measured at the output terminals. If the output voltage was more than 1/2 volt, the brushes had to be adjusted. I thought I'd try a variant of this on the Model T generator. Since this is basically transformer action, the source AC could be applied on the armature and the results measured at the field. Since the Model T armature can withstand more than 10 amperes, I used a 500 watt lamp to limit the current from the 120 volt wall outlet. Then with the 3rd brush raised, I measured the AC voltage at the field. Rotating the brush rigging, I could get 4 or 5 volts at the field and by rotating the brush rigging the resultant field voltage could be reduced to about 0.25 volts. I deemed this a success and will use this method in the future. Here is the circuit for my setup.
Mike

500 Watt lamp. Did you have to wear sunglasses?

Anything for science. You know my eye sight is not as good as it once was.

I have also had problems setting the null point via the service manual.
Thank goodness for Ron Patterson. I use his method.

Set the 3rd brush to its minimum. Thats turned the furthest from the engine.
Run the motor/test stand.
Adjust the output for 2 amps by rotating the whole brush assembly. (loosen the 4 screws to adjust)
Tighten the 4 screws.
Move the 3rd brush toward the engine to the desired output. About 6 amps depending on your power needs.

Mike

Your testing method and your results would probably make for a good seminar/video.

Speedy, this morning I tried your (Ron's) method of setting the brushes at the neutral plane. Setting the brushes using my method I measured 0.145 volts at the armature. Then I set the brushes using your method and measured the voltage (had to use my setup to measure) and got 0.865 volts. This is really close, maybe one of two segments different. This is probably me just being a little sloppy. I like my method in that as you push the brush rigging to reduce the voltage, should you go too far the voltage starts to rise again, giving a definite spot to secure the brushes down. I don't think that the difference would amount to much. The whole idea of setting the brushes this way is to reduce brush sparking and save some wear on the commutator. Thanks for sharing, Mike