Can you get variable speed from a single phase motor?

LARRYZ10

LARRYZ10

Joined
Feb 6, 2010
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Can you buy and hook up a vfd that gives variable speed from a single phase motor? Also can one do this with 115 volt current? If you can are there drawbacks versus 230 volt wiring? I am trying to figure out if I can run a direct drive c mount 2 hp motor in single phase on 115 volt and have varible speed. Im thinking of using the GIB grinder. Am I deluded? Thanks for any advice, Larry Lehman
 
I've never heard of anyone doing this, but on my understanding of electricity and motors it would work, but with some big caveats.

Long answer:

A single phase AC induction motor can be sped up or slowed down within a narrow range. For example, most motors can be run at 50 Hz or 60 Hz no problem. The start winding would only work properly near the design frequency. When running, slowing the motor might result in the normal phase slippage to reach a point where things would overheat, perhaps at about 75% normal run speed would be as slow as you could go with a load without burning something up. You could probably speed up a four pole motor to speeds of a two pole motor before mechanical issues with balance would limit you.

So, long answer, yes. With problems and in a fairly narrow range. Short answer, like Stacy said, no.
 
I think it may work with a dc motor and a speed controller but if you already have an AC motor it sounds like you would have problems.
 
110volt single phase motor,variable speed = step pulley's
Stan
 
Nope, won't work all you will do is blow fuses if your lucky or a fire.

I bought a wilton single speed 2X72, and a year later bought the DC motor and variable speed control for it and am glad for every dollar I spent on it, that was back in the late 1980's. It runs cooler than the regular single phase motor that came with it, motor brushes are still in good shape even though the whole unit shows alot of wear from over the years.
 
I sure do thank you all for giving me a straight no nonsense answer. I want a reliable grinder that works well just you all do but I didn't know a thing about electrical motors.. Verone tells me so far that the best thing would be to have a 220 volt outlet put in my garage and use a 3 phase 2 hp motor with a VFD and pony up the money to do it right the first time. I've decided not to try the cheap route. It would be a lot more fun to make knives with good equiptment and less worry. Thanks, Larry in Bakersfield
 
Gee, guys. I don't know much about electricity, but what exactly do I have on my 110 volt, 1.5 hp Leeson variable speed AC motor on my KMG. It sure looks like a VFD and it takes my grinder from dead slow to full speed.:rolleyes:;)
 
jdm61 said:
Gee, guys. I don't know much about electricity, but what exactly do I have on my 110 volt, 1.5 hp Leeson variable speed AC motor on my KMG. It sure looks like a VFD and it takes my grinder from dead slow to full speed.:rolleyes:;)
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You would have a 230V 1.5HP 3PH Leeson AC motor, with a 115V 1PH input VFD.

Now if you do try to find a 2HP 115V VFD you will be drawing about 20-25A on the input.

I would personally go with a 230V 2HP 1PH VFD with a 230V 2HP 3PH motor.

That will let you go from about 10%-150% RPM (mind you running at 150% is hard on everything.)

Running under 20% you start loosing torque pretty quickly. Keeping it between 50-100% is your best range.
 
jdm61 said:
Gee, guys. I don't know much about electricity, but what exactly do I have on my 110 volt, 1.5 hp Leeson variable speed AC motor on my KMG. It sure looks like a VFD and it takes my grinder from dead slow to full speed.:rolleyes:;)
Click to expand...

You have a 110 volt 3 phase motor.Not single phase.
Stan
 
SBuzek said:
You have a 110 volt 3 phase motor.Not single phase.
Stan
Click to expand...

AFAIK there are no 110V 3PH motors currently made. Certainly never heard of 110V 3PH power, you would have to have 3 transformer cores at 2:1 to get 110V from 230V.
 
My Bad,It's a 220v 3 phase and the controller converts the 110 to 220 3phase.
Stan
 
There is a way to get variable speed out some 110 and 220 single phase motors, but they have to be the "old style" motor with carbon brushes and a commutator. Then you need a variable transformer, aka Variac, to step the power up and down. I've got such a setup for a blower running a solid fuel forge. I don't know if you can get something like this setup with lots of torque and umph though.
 
Phil Dwyer said:
There is a way to get variable speed out some 110 and 220 single phase motors, but they have to be the "old style" motor with carbon brushes and a commutator. Then you need a variable transformer, aka Variac, to step the power up and down. I've got such a setup for a blower running a solid fuel forge. I don't know if you can get something like this setup with lots of torque and umph though.
Click to expand...

Those are called universal motors, they have a field winding and a wound armature like a DC motor. They run of either AC or DC and only spin in one direction. They can be speed controlled but the torque drops off quickly. They are great for blowers but would bog down and stall on a grinder.

The two variable speed options are DC motor with controller or 3PH AC motor with VFD.

There is always step pulleys and jack shafts though.
 
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