MTFCA Forum

TO set the third brush position on a generator, we usually connect the genny to as battery and 'motor' it. (edit) After lifting the third brush so it does not contact the armature, moving the third brush holder back and forth to set the position. Rotating one way motors the genny 'forwards' and rotating the other starts it motoring 'backwards'. The spot for setting the genny is right between the two, so it is neither motoring either way.
This method works well.

Until this week.

We have hit 2 genny's that motor forward but not backwards. We set them at the point just where motoring stops, so all is OK and they charge well.

The question is: Not that it matters but, does anyone have any idea why they only motor one way instead of both? (fields intact and wires to brushes are all good - gennys put out good charge when tested - yes we do fine tune the position of the third brush on our test stand to about 5 amps).

You need to lift the 3rd brush to set the null point. Then drop it down and set the output.

Thanks Mark - yes we did lift the third brush to find the null point as described (apologies my explanation missed that out).

I am running into the same issue with the last couple of generators I worked on. They work but only am estimating the null point. Can't get them to rotate in the reverse direction but will motor fine clockwise but seem to be fighting going that direction so just adjusted till they seem to motor somewhat smoothly. I checked for shorts and checked the armature on a growler but could not find anything to be of issue. While the insulators are maybe suspect, could not find any shorts there.

I have had the same problem occasionally. The Ron Patterson method has been my go to.
Set the 3rd brush just off its minimum position. Rotate the brush ring for minimum output. (amps)
Lock the ring. Adjust the 3rd brush for desired output. I normally set @ 4 amps.

Thank you John, I will have to try that.

Thanks Mark - yes it seems we have the same experience, must be a 'quirk' of the genny design or build.