tachogenerator

[rbond]

Hello All
I have picked up a G E tachogenerator hoping to use it as a spindle drive motor for my mill.
It is a pm rated at 100 volts per 1000 rpm.It is apprx . 7 inches in dia. and 10 inches long,has
four brushes 180 degree spacing. When I apply 100 volts it rotates ,but with a 2 inch pulley
on the shaft I can stop it by hand a turn it in the opposite direction.
So my question is , is there something I can easily do to this motor to increase its torque?
I also notice the magnets for being quite large , do not seem very strong.

Thanks Rick

[Al_The_Man]

A DC motor of that size should have a considerable torque, If you have it connected correctly then the field magnets may have become de-magnetized.
Is that a pair of brushes each at 180°? or 2 for the motor and 2 for the tach?
But even so, if you stall it at 100v applied, the current should go through the roof.
Al.

[rbond]

Hello Al

This unit is the tach, it has two brushes in line about 1.5" apart for one connection, and 180 degrees 2 more.I want to know if there is something I
can change in order to get some torque.
I do know that it was only designed to produce voltage though, so maybe
nothing can be done.

Thanks Rick

[Al_The_Man]

At 7"dia and 10" length, that is quite the size for a tach, which normally only provides voltage relative to rpm only, no appreciable power is required to be supplied.
Are you sure the rear two brushes are not the tach and the other two the armature of the motor?
Measure the resistance across the brushes you are supplying power to.
Also check continuity between all four brushes, detect if separate pairs.
Al.

[rbond]

I will check tonight.

Rick

[rbond]

I double checked tonight and two sets of brushes running parrallel with the
shaft , all on one commutator. Two on one side are wired together and 180
degrees apart two more.
I put the ohm meter on the 200 scale and get a reading of 0.02. I checked
a couple of treadmill motors I have here and get readings of 0.002 and 0.003.
Quite a difference ,so maybe not a good dc motor.

Thanks Rick

[Al_The_Man]

Think about it, if the reading is that low and it is possible because you are reading the armature winding and brush resistance, if you apply 100v across this resistance and stall the armature, this means there is no back emf to apply against the 100v as there would be if the armature was rotating.
The resultant current would be E/R !!
The huge current would obviously flatten out or blow the 100v supply.
There is obviously something missing here.
Al.