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Speed control for 220 single phase

Butch Lambert

Titanium
Joined
Oct 30, 2002
Location
Poetry Texas USA
All of my machines are 3 phase and I have rotary phase converters and VFDs, but I'm adding a 220 single phase machine with a 2hp motor. How do I address a speed controller?
 

jim rozen

Diamond
Joined
Feb 26, 2004
Location
peekskill, NY
All of my machines are 3 phase and I have rotary phase converters and VFDs, but I'm adding a 220 single phase machine with a 2hp motor. How do I address a speed controller?

Nobody else, so:

1) inspect data plate on the single phase motor, read the speed there. That's how you address it.

2) replace the motor with either a 3 phase one, and use a VFD, or replace with a dc motor and use an appropriate controller for that.
 

Butch Lambert

Titanium
Joined
Oct 30, 2002
Location
Poetry Texas USA
A simple circuit that you can make. The torque in the speed range won't be like that for a VFD. Maybe you can check that.

triac speed control circuit - Google Search

Thanks, I'm not an electrical person. My brother said I called the Comanche Peak Nuclear Power Plant to shut down while I changed batteries in my flashlight. I did forward your link to a couple long time friends that I'm sure can help. One is a retired EE from Rockwell-Collins Radio and the other is a retired Motorola EE.
Thanks for the leg work.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
There ARE VFDs for single phase. But with typical single phase motors (anything with a centrifugal switch for starting), there is basically no point, because the switch will cut in on anything but a very modest speed reduction.

Mostly those VFDs are only good with "PSC" motors, and shaded-pole motors. Your 2 HP won't be either of those.
 
Last edited:

Butch Lambert

Titanium
Joined
Oct 30, 2002
Location
Poetry Texas USA
From one of my Buds.

"Single phase speed control will not work with typical single phase motors that use capacitors and a starter switch, if you did slow the motor down the start switch would activate and burn up the start capacitor. Triac speed control is mostly applicable to low (not constant) torque motors like those used in fans. There are single phase motor VFD’s that you essentially connect the run coil and start coil directly to the VFD, they are expensive and a poor substitute for a 3 phase motor. No other way to get speed control and retain any reasonable performance of the motor below and above its base speed."
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
Yes.

In addition, the PFC and shaded pole motors DO work with a triac type control. BUT....... They are still an induction motor.

What that means is that speed control is by adjusting "slip", so that even when set for a slower speed, if you remove the load, they will speed right up to their normal speed. The basic motor is set up to run at a speed according to the number of poles. A 2 pole 60 Hz motor; very close to 3600rpm at no load. A 4 pole very close to 1800 rpm at no load, etc. That no-load speed is not affected much by voltage changes.

The same thing is true of changing the load. That will speed or slow the motor, depending on whether the new load is less than or more than the previous load.

The speed controls work the best with loads which vary greatly with speed. Fans and pumps are good examples. Then at any setting, the motor can find a load (and speed) where the power input is just balanced by the load.

Most any machine tool would be quite unstable in speed if one of those types of motor were used with a triac type control, or any voltage-varying type of controller. Every small change in chip loading would result in a speed change. In some cases that may be acceptable, but...........

Use with a frequency varying control might be acceptable, but both PSC and shaded pole motors are generally low power. They also are somewhat unstable in speed even at constant voltage and frequency.
 
Last edited:

rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
Thanks, I'm not an electrical person. My brother said I called the Comanche Peak Nuclear Power Plant to shut down while I changed batteries in my flashlight. I did forward your link to a couple long time friends that I'm sure can help. One is a retired EE from Rockwell-Collins Radio and the other is a retired Motorola EE.
Thanks for the leg work.

With wave chopping the speed range is limited. If you can get below 1/3 motor nameplate rpm then don't.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
PSC is a motor type (Permanent Split Capacitor).

PFC = Power Factor Correction, something totally different, not a motor type.

Indeed it is! I seem to have had something else on my mind when I was typing

I fixed them to avoid confusion.
 








 
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