Six 1 minute lessons in AC motor speed control:
1) You cannot control the speed of an AC squirrel cage motor (as this is) by voltage alone, you must vary the voltage and frequency together. The electronic device that does this is called a Variable Frequency Drive, VFD for short. Your foot pedal would serve just as an interface device for the VFD, the VFD would power the motor.
2) VFDs are generally for 3 phase motors, yours is a single phase motor. There are a small number of suppliers of VFDs for single phase motors. The choices are limited because single phase motors are not well suited for VFD operation and the motors must be either Shaded Pole, or Permanent Split Capacitor (PSC), as yours is. So at least you are in luck there.
3) PSC motors generally are not well suited for high torque or low speed applications, which means they generally are used in things like pumps and fans, which lend themselves to VFD application. However in your case it is attached to a gear reducer which tends to compensate for those deficiencies. But it is still going to depend on how slow you want the final output shaft to turn. That motor already has a 10:1 gear ratio (173RPM), so if you don't want it to turn slower than about 80RPM at the work shaft, you should be OK from that standpoint. If you were thinking of going slower, it isn't going to work very well.
4) That motor unfortunately has a brake built-in. Electric motor brakes typically work from springs that are held open by the motor power when energized. When you reduce the voltage with the VFD, the brake probably will not release and even if it does, will likely smoke in short order.
5) You will need to either disassemble the motor and figure out how to separately power the brake whenever the VFD is running, or abandon the idea. This is not something for the novice.
6) You will probably pay as much or more for the single phase OUTPUT VFD as you did for the motor. Your desire for speed control had better be great.
PS: I stressed the word OUTPUT in #6 because invariably, someone will post a link to a cheap VFD that takes 1 phase input power, but fail to notice that it only works for 3 phase motors. Happens every time.
5 cents worth of advice:
Before spending more money on this project just to discover more problems, consider using a DC motor and speed controller, or get a 3 phase gear motor, one without a brake or at least a separately controlled brake.
Free bonus advice: Better yet, hire someone to engineer this for you who knows what they are doing.
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376
