View Full Version : Speed control

07-28-2001, 11:16 AM
Is there an electrical method of providing variable speed to a belt drive machine with a 2 hp 220v 1 phase motor?

Darn belts are over 7' up on the mill-drill and a pain.

I use a VFD on my lathe to supply 3 phase 208v form a 1 phase source and get variable speed from 0 to machine max on my SB lathe without having to change the belt or use the backgear.

I've become so spoilt by the lathe that the mill is almost intolerable!

Robert Jones
07-28-2001, 03:19 PM
Ken you can't vary the speed of a 1phase motor. You already have a vfd, so look around for a motor, e-bay or a commercial building demoliton site for example, and connect it to your vfd. Run one machine at the time and everything will be alright as long as the two motors draw the same amperage. If they are different, then you would either have to set the parameters for each one as you use it or go to a seperate vfd for each one. There is a chance you will still have to adjust the belts for the proper amount of torque on some jobs, but it wouldn't be every time.Just think, a couple hundred dollars more and no more continually changing of the belts. Pure pleasure! Bobby

07-28-2001, 05:31 PM

Another motor. Shouldn't be too hard to find.....maybe. Meantime I'll try to settle on a speed for all purposes, or keep climbing the dumb little shakey ladder.

Thanks Bobby!

07-29-2001, 02:58 AM
I'm an electrician and yes a vfd unit will cause a single phase motor to vary in speed just like the three phase motor. Now comes the but... when the single phase motor reduces in speed the start winding kicks back in and energizes a set of windings that are only meant to start the motor. They are not continuous duty windings so they will burn out if they are allowed to run too long. There is no simple way to remedy this problem. Possibly a type of motor called a "capacitor-start capacitor-run" motor which has a pair of windings that are rated to run continuously. Also when you run a single phase motor at some rpm that is less than what it is rated for there is not enough air flow through the windings to cool the motor and it will burn up. The fix is to mount a small muffen fan to blow through the motor independently for cooling especially if you want to run a single phase or a three phase motor at reduced speeds for some length of time.


07-29-2001, 09:18 AM
Used three-phase motors can be found for cheap money. That's probably your best bet. Look in the phone book for "motor repair" or some such. They'll probably have a pile of used motors sitting around they would love to get rid of.

I've got a VFD on my mill and nearly always leave the belt on one set of pulleys. It's really handy.