How to vary the speed of a single phase 1HP motor?

[chknifemaker]

I have a very nice single phase 1 HP motor that runs at 1725 RPM and I wanted to know if there was a way to make it variable speed? seeing as it is not 3 phase.

Thanks

 

[ev13wt]

Pulleys or possibly a really fat variac?

 

[SBuzek]

Step pulleys.

Stan

 

[timgunn1962]

Realistically, no.

There are ways of varying the speed, but the loss in torque as the speed is reduced is extremely severe. It limits single-phase variable speed to things like fans, where the loss of torque is not a problem (the power drawn by a fan varies as the cube of its speed; at haf-speed, it uses one-eighth power).

Most non-fan applications effectively need a constant-torque characteristic.

 

[Nathan the Machinist]

There are ways of varying the speed, but the loss in torque as the speed is reduced is extremely severe. It limits single-phase variable speed to things like fans, where the loss of torque is not a problem (the power drawn by a fan varies as the cube of its speed; at haf-speed, it uses one-eighth power).

You probably already know this and were just being succinct, but I think most AC motors are locked to the line frequency (minus a tad of "slippage") whereas fan motors are designed a little differently and can be varied with voltage.

For example a regular AC motor connected to a dimmer switch will stay pretty close to it's nominal RPM as the voltage is clipped, but an AC motor such as a router behaves differently.

just FYI

 

[LAHST Handmade knives]

Realistically, no.

There are ways of varying the speed, but the loss in torque as the speed is reduced is extremely severe. It limits single-phase variable speed to things like fans, where the loss of torque is not a problem (the power drawn by a fan varies as the cube of its speed; at haf-speed, it uses one-eighth power).

Most non-fan applications effectively need a constant-torque characteristic.

Isn't it the other way around the slower your belt goes( with the motor at full speed using step pulleys)the more torque you have, like a bicycle switching gears.

 

[Nathan the Machinist]

Isn't it the other way around the slower your belt goes( with the motor at full speed using step pulleys)the more torque you have, like a bicycle switching gears.

He's talking about slowing the motor, not gearing it down.

 

[LAHST Handmade knives]

Got it

 

[timgunn1962]

Nathan, I was actually trying to cover all the bases on the remote off-chance there'd be someoneone out there as pedantic as me

There are actually single-phase-output VFDs available http://www.emainc.net/downloads/optidrive.pdf

I'm also fairly sure I've run fans with "normal-looking" industrial single-phase AC motors on speed control (standard motor casing and a capacitor mounted on the side; definitely not universal motors). I've never needed to pull one apart and see how it is wired though.

The real point though is that they are not very useful for the sort of stuff we might want to do with a variable speed motor.