variable speed control for 1ph motor

lesmar96

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Join Date
May 2017
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PA
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I have a customer that came to us, looking for a variable speed control for a 115V motor

He bought a 115V vibrator. The motor is a cap start. According to my understanding, it is not trustworthy, or maybe not even possible, to vary the speed of a single phase motor.

I read this thread
http://www.plctalk.net/qanda/showthread.php?t=117583&highlight=1ph+vfd

and it has strengthened my understanding.

Am I correct? Is there any new controls any one has heard of to do this or is it even electrically possible?

Any advice would be helpful. Thanks.
 
No, there is nothing new and it's mainly because if you vary the speed of a capacitor start motor, the capacitor re-engages and can damage the VFD, the capacitor or both (it becomes a race to destruction, the winner making you a loser no matter what).


See if you can replace the motor with a 230V 3 phase version and then get a VFD that takes in 115V single phase and puts out 230V 3 phase. There are dozens of them on the market.
 
How much draw does the motor have? I'm going to hate myself for suggesting this, but you could try using the capacitor or leading edge type fan controllers that are used on ceiling/workshop fans. All the stuff we get here is good for up to 240V/10A - Yep, hate myself already.


Also, am I the only one who laughed? Giggity.
He bought a 115V vibrator.
 
No, there is nothing new and it's mainly because if you vary the speed of a capacitor start motor, the capacitor re-engages and can damage the VFD, the capacitor or both (it becomes a race to destruction, the winner making you a loser no matter what).


See if you can replace the motor with a 230V 3 phase version and then get a VFD that takes in 115V single phase and puts out 230V 3 phase. There are dozens of them on the market.

This makes sense with what I was thinking as well, I am just young without a lot of experience and wanted some verification. It seems you could start it at full speed to get the start windings to disengage, then you should be able to slow it back down as long as the centrifugal or electronic switch doesn’t kick back in. But that only seems to be asking for trouble as you have mentioned.

The manufacturer of the unit told my customer that they can sell a variable speed control for this unit but it is very expensive. He bought the unit figuring he could buy a control elsewhere.

It make me curious what the OEMs plan for varying speed is, but I don’t think I can recommend anything.
 
I'm looking at a Home Depot ad, an 8 amp 115 volt vari-speed motor control.

But I'm with Jraef - the capacitor would probably fry it.

Can the motor be replaced with one of similar power which does not have
a starting capacitor?

The Home Depot says Model # AVS-8 115. $78.75.

Poet.
 

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