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Discussion Starter #1
I recently picked up a NOS MTC 4001 forklift motor. I see from the specs that it’s reversible but I noticed the brushes are angled for CCW rotation but I need to run CW. Seems to me it’s a bad idea to turn the comm against the brushes for extended periods of time, so one option is to remount the brush holders at the correct angle. If I do this I need to make sure I locate precisely and get the timing correct.
any ideas or advice from anyone?
 

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Hi jehan,
The angle of brush centerline to commutator radius is irrelevant to direction of rotation. It's primary purpose is to reduce chirping or bouncing. That 22.5° angle is used for decades on all Prestolite motors which rotate both ways.
Of more concern is the factory brush advance of 4.5° favoring its 'as shipped' rotation. That can be changed by redrilling the holes in the aluminum comm end head casting. The relief pockets for the 4 screw heads are wide enough to accommodate the additional hole. After doing that, the motor will work perfectly fine.
major
 

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Discussion Starter #3
Hi jehan,
The angle of brush centerline to commutator radius is irrelevant to direction of rotation. It's primary purpose is to reduce chirping or bouncing. That 22.5° angle is used for decades on all Prestolite motors which rotate both ways.
Of more concern is the factory brush advance of 4.5° favoring its 'as shipped' rotation. That can be changed by redrilling the holes in the aluminum comm end head casting. The relief pockets for the 4 screw heads are wide enough to accommodate the additional hole. After doing that, the motor will work perfectly fine.
major
Thanks for the reply. That leads to my next question, the nameplate says 96 volt but I’m planning to run 144 or 160. So I’m wondering how much more advance I will need.
Thanks
Jehan (John)
 

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Really none. It's doubtful that you'll see much over 100V at the motor even with higher V battery. RPM would be excessive. If commutation is too sparky, look into split wafer brush.
major
 

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Discussion Starter #6
Really none. It's doubtful that you'll see much over 100V at the motor even with higher V battery. RPM would be excessive. If commutation is too sparky, look into split wafer brush.
major
FYI this is where the hole would be if I go 10 deg from the current position which equals 5.5 deg advance. I have enough room to go to 6.5 . So I could stick with 4.5 as you suggested or just go with an even 5. Just not sure how much effect that would have. My other option would be to slot the holes so it’s adjustable.
 

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I don't think it's terribly critical to +/-1/2° . You seem concerned so I see nothing wrong about doing 5 or 6°. Watch for interference with connectors when twisting the casting. I just don't see need to drill and tap new holes in steel frame. Slots? Some motors are designed with that type of adjustments. I feel it's unnecessary and even problematic. We're talking a few degrees which are within tolerance of brush seating so can change as brushes wear.
major
 

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Discussion Starter #8
120092

I don't think it's terribly critical to +/-1/2° . You seem concerned so I see nothing wrong about doing 5 or 6°. Watch for interference with connectors when twisting the casting. I just don't see need to drill and tap new holes in steel frame. Slots? Some motors are designed with that type of adjustments. I feel it's unnecessary and even problematic. We're talking a few degrees which are within tolerance of brush seating so can change as brushes wear.
major
Thanks for the response. That’s just what I needed.
 

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Really none. It's doubtful that you'll see much over 100V at the motor even with higher V battery. RPM would be excessive. If commutation is too sparky, look into split wafer brush.
major
Does this also depend on how many amps he's dumping in? I would have thought BEMF could continue to climb with enough incentive.

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