Hey guys, I’m having a hell of a time with a Otis 63 Ga generator fresh from a motor shop (well actually 2 generators)

Back story: we had a GAL relay logic controller with an Otis generator and machine start losing compounding and would shoot 3” above the upper floors in the up direction. Unit would stall in when trying to level down after overshooting. Fount that the commutator was very out of round causing brushed to move 3/16” when rotating generator by hand. We purchased a refurbished Otis 63 GA generator that a motor shop had on the shelf to replace it. After wiring unit up and running it on inspection we found it to be working normally. Armature was putting out 10-30vdc depending on direction. When we went to run the unit on high speed, the generator loads up and armature voltage drops to zero. The unit runs normally on the leveling field alone, but when the shunt is introduced in the circuit, the above condition happens. Tried swapping the Shunt and the generator loads up and startup with no direction. Also tried swapping the series field. Called motor shop and they advised swapping the armature leads, shunt, and leaving at the same time. Same exact issue. Motor shop said send us the original unit and we will just turn and undercut the commutator and not touch anything else. We send original generator out and get it back. Find that the AC side had been rewound and we have new leads coming from the fields as well as the commutator being turned and undercut. Start up generator and have the exact same issue. Call motor shop and they say they did not rewind DC fields, but had to take everything apart and reassemble. Now I’ve got this issue on 2 generators from this shop, and had a working unit with a commutataor problem originally. I’ve verified North South on the fields with a compass , my controller to generator wiring, swapped everything I could at the generator connections and have moved electrical center with no luck. At this point I’m thinking there is an internal generator wiring mistake but I can’t prove it. Let me know if you have any thoughts or ideas. Sorry about the long post. Thanks in advance!

It sounds as if you are over-compounded. Have you looked at the series field shunts? On an Otis controller, the series field is shunted with that coil spring-looking thing in the back of the controller. In your situation, you probably are using some german silver shunts in the series field. Also with the Gennie at idle with no demand, you should not have much more than 5 to 7vdc, measured at the brushes. If it is much higher than that you are prob out of neutral.

Need to make sure its not wired up differential compounded

Should be cumulative compounded

Where are you located? Generator loading up with no direction is a problem in the suicide circuit or series field reversed or miswired. Do you have a generator print? I need to look in my records to see if I have one