Universal Motor

Hi,

I have a 110v 5amp universal drill motor. I wish to design a motor
controller which will allow speed and direction control, and interface at
TTL to a PIC uC. I can run the motors in AC or DC. The motor is a series
or universal type which requires the polarity to be switched at the coils in
order to change direction. There are 4 wires going to the motor, 2 for the
stator and 2 for the rotor coils. Shorting either side of the coils will
change the motor's direction.

I have looked at crydom.com solid state relays to switch coil
polarities, but it would required 6 relays for each motor. ( running on DC
and PWM the relay ) I also have looked at using igbt/mosfet combo, but I
would still need to find a way to change polarity at the coils...

Can anyone point me to any designs/schematics/appnotes available
somwhere on the web to accomplish this?

Cheers,
Steve

 

Really you've chosen a hard motor for the task. Getting your hands on a
permanent magnet DC motor would make your life easier.

Failing that you might consider supplying a fixed current to the field
winding (stator), and varying the voltage to the armature (rotor). This
would mean some sort of a high-current low-voltage power supply for the
stator, but it would be at a fixed voltage. Then you could just control
the armature voltage like a normal motor.

 

Shorting? I dont follow. The way to change direction is to swap the
connections over for either the armature or field winding.

Why 6 relays? I see a need for one mechanical relay, to change
direction, and one fet/tr to control the PWM output. I think you could
do with explaining your plans in rather more detail.

I see your point, and the desire to keep field current steady. Whether
thats actually necessary is going to depend on the application. I'm
doubting this is to control an old drill, since new ones are so cheap.
The OP said drill motor rather than drill....

I think we need far more info from the OP, both on the intended app,
the reason for building own controller, reason for picking a universal
motor, and an explanation for his/her controller design ideas, which I
suspect will reveal something.


Regards, NT