Regulating the Speed of a Single-Phase Motor

Mine is equipped with startup capacitors. It appears then that I must find a way of substituting a 220 VAC 3 phase motor for the existing Single phase 2 HP unit.

Fortunately, the manufacturer of the Grizzly 17" Band saw, has a 3 phase motor for that machine that swaps without modifications.

I will check to see if they are amenable to exchanging the single phase unit for a three phase.

Thanks for responding. Your efforts on my behalf have saved me a great deal of time.

I appreciate that a great deal.

L.J.

An equivalent 3 phase motor would be the better solution. When used with an inverter drive (1 phase input - variable 3 phase output), you will get full speed control with optimum torque and horsepower performance. The 1-phase motor conversion will never perform as well. A direct motor swap (1 to 3 phase) from the manufacturer would be ideal. If that option isn't available, you can sometimes find bargain 3 phase motors and drives on eBay. I got a 2 HP, 3 phase motor and inverter drive combo for under $75. If you can find the same the NEMA frame and shaft size, mounting is usually easy. Even if it's not a drop-in replacement, I've been able to mechanically modify the mounting hardware to make the new motor fit.

Good Luck!

Close.

Cap start, split phase and cap start cap run (two different capacitors fitted) are as stated but cap run has the cap permanently connected.

Most designs that are not refrigeration based use a centrifugal switch, but a current relay can also be used as in refrigeration compressors which eliminates much of the speed problem.

A cap run motor will speed reduce, but the 3 phase option is best if you can arrange it. Just be sure you can delta connect it to the required lower voltage available using a single phase to 3 phase VSD. For instance when only 240 vac single phase is available connect in 220v delta, leaving it in star (wye) 415v just won't do.

Not a good way but it works is to use a European 220V light dimmer. in your case a 2kW dimmer will suffice. For three phase you can try and hook 3 of them mechanically in parallel. never tried this but it might work? Wangito.

Good way to smoke a motor...

Agreed! This is a very bad idea. Using a dimmer or rheostat would reduce the voltage causing the motor to strain to maintain the speed dictated by the HZ (cycles per second). The HZ is the main determining factor that regulates the speed of a single phase motor. If the motor is not keeping up with the HZ then it is under too much load regardless of the actual work done. Thus, the amperage would go up and either burn up the motor or, more likely, trip the safety (breaker or overload switch) device. The way to control motor speed, unless it is a brush type or DC motor is to control the frequency, which is normally done with motor controllers. This applies to 3 phase motors primarily. However, I have seen some single phase motors that are designed for 2 speeds, forward and reverse. This is not a variable speed application though, just a selectable speed application. The one that stands out to me is one that I mounted on a lathe, some years ago, to provide a wider range of speeds for turning different types and sizes of stock. The speeds and direction were selected by a multi-pole switch and this switch not only swapped motor windings but also how the capacitors were connected in the circuit. I would agree though that your best solution would be a 3 phase motor with a motor controller.

Regards,

Mr. Jimmy