PMDC motor, what makes one none reversable?

[LUCKY13]

Basically I have a treadmill motor that is only rated to turn one dirrection. What is the difference in this one & one that could rotate C/W-CCW?


The motor will reverse even thought its not rated to do so. IS this because of brush angle, or some other reason?


If it is brush angle could I machine a new end housing and relocate the brushes? I am sure this would not be as easy as it sounds because of possible phasing or something I dont even know about?


If it is possible I would like to do so. It would make a good project for this mill to cut. The only real reason for needing to reverse is ridged tapping and lefthand twist drill bits for cutting out broken bolts. I guess there may be some reverse twist end mills but we dont have any.

The end cap has some cracks in it so we need to make a new one anyway ( or it would be best to).


WEll I just noticed I put this in the wrong section. If a mod could move it to General Electronics, or where ever it should go. If its OK here thats fine also. Thank You.


Jess

[RomanLini]

The "rating" that says CW or CCW on the label is basically a guide, so that if you connect +ve to RED and -ve to BLACK the motor will turn in the direction as specified.

If it is a permanent magnet stator it should run in reverse with no problems, as the brushes are typically mounted 90 degrees radially to the commutator. Brush wear can make them feel a little different when turning in each direction by hand, but generally the motor should be reversible.

[john_100]

most motors the brush position is a compromise that works equally well in both directions
it doesn't matter if they are permanent magnet dc motors or universal ac/dc

on some motors the brush assembly can be rotated
so that for a given direction the sparking can be reduced .
this position is where there is the minimum voltage between adjacent commutator segments

so depending on the motor being run in one or both directions
the brushes can be in one of three positions

John

[Al_The_Man]

If it is built as a unidirectional motor with offset brushes, you should be able to bring the brushes up to the 90° with a new end plate and make it bi-directional.
Al.

[LUCKY13]

Thanks for all the replies. Yes the brushes are offset, and maybe even at a angle ( I will have to look again).


Al, thats what I was hoping. The bidirrectional motors I seen I believe had the brushes at 90*. The offset brushes must be a compromize to try and help the brushes run with less sparks, or last longer. When I run this motor the other way thats what happenes, it puts out more sparks and makes more brush noise. With it turning against the angle of the brush that would make sense.


Well this is good because this motor is perfect size for my little mill. Plus I believe it turns more RPM and thats what this small mill needs. With a belt drive I should be able to reach 6000, if not a little more RPM. Considering I dont have the funds for a new motor this will help alot. The owner before already installed new bearings in the spindle so it should handle it alright. If not I can change them again, but for now it runs very smooth. Infact as long as its cutting within its limits it cuts better than the big mill. May just be the smaller tooling and the fact it turns more RPM anyway than the big mill, plus aluminum being what we work with mostly.




Jess