Speed Control of Motor

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laketime

laketime

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We are looking for a solution for speed control of a 240v single phase motor. These motors control big exhaust fans at a painting company and they want to be able to slow them down. The nameplates are almost non existant due to residue and age. Our supplier gave use some 10amp solid state motor speed control switches. We installed and seemed to work ok but the motors got super hot and burned up the overload switch on one of them. I am not really good with motor control design but can someone tell me what is happening and options to be able to acheive speed control.
 
You cannot just try to lower the voltage (assuming that's what the device was) without risking burning up the motor. But the problem is that this is a single phase motor, so there are very few possibilities available to you and if you can use anything at all, you have to know exactly WHICH type of single phase motor you have, there are several.

IF it is a Permanent Split Capacitor (PSC) type, then you can use what's called a Variable Frequency Drive that alters the voltage and frequency together, which avoids stressing the motor out. Tis is the only viable option open to you. If that can work, you need to use a VFD that is SPECIFICALLY designed to operate a SINGLEPHASE MOTOR. There are many many available to operate a 3 phase motor, and many that can operate a 3 phase motor from a single phase source, btu only a small number (2 or 3) that can operates a single phase MOTOR. Be careful about what you read.

If the motor is a Capacitor Start / Induction Run (CSIR) or Capacitor Start / Capacitor Run (CSCR) , or a Split Phase type, you cannot use speed control of any type without ruining the motor. Sorry. (I am assuming this is too big to have a Shaded Pole type single phase motor)

How to tell the difference? It's difficult without full motor details from the nameplate and/or manufacturer of the motor. Split Phase type will not have a capacitor "bump" in the side of the motor case, CSCR will have two bumps on the side. But there is no outside visible difference between a PSC and a CSIR type motor.
 
How big is big? 10 amp speed controls would indicate these are not very big.

Paint makes me think they may be in a classified area.

If not, then replacing the burnt up single phase with three phase motors and putting a properly sized VFD ahead of them would be an easy route.
 
Jraef said:
You cannot just try to lower the voltage (assuming that's what the device was) without risking burning up the motor. But the problem is that this is a single phase motor, so there are very few possibilities available to you and if you can use anything at all, you have to know exactly WHICH type of single phase motor you have, there are several.

IF it is a Permanent Split Capacitor (PSC) type, then you can use what's called a Variable Frequency Drive that alters the voltage and frequency together, which avoids stressing the motor out. Tis is the only viable option open to you. If that can work, you need to use a VFD that is SPECIFICALLY designed to operate a SINGLEPHASE MOTOR. There are many many available to operate a 3 phase motor, and many that can operate a 3 phase motor from a single phase source, btu only a small number (2 or 3) that can operates a single phase MOTOR. Be careful about what you read.

If the motor is a Capacitor Start / Induction Run (CSIR) or Capacitor Start / Capacitor Run (CSCR) , or a Split Phase type, you cannot use speed control of any type without ruining the motor. Sorry. (I am assuming this is too big to have a Shaded Pole type single phase motor)

How to tell the difference? It's difficult without full motor details from the nameplate and/or manufacturer of the motor. Split Phase type will not have a capacitor "bump" in the side of the motor case, CSCR will have two bumps on the side. But there is no outside visible difference between a PSC and a CSIR type motor.
Click to expand...

Thank you very much. I will check into it more
 
ptonsparky said:
How big is big? 10 amp speed controls would indicate these are not very big.

Paint makes me think they may be in a classified area.

If not, then replacing the burnt up single phase with three phase motors and putting a properly sized VFD ahead of them would be an easy route.
Click to expand...
For sure, if the motor is already toast, replace it with a similar 3 phase version and use a low cost VFD that accepts single phase input power. That may be a solution no matter what. The few VFDs that can be used on PSC motors are not cheap, so you may be able to buy a 3 phase motor and VFD for only slightly more than just the single phase VFD alone.
 
Just to toss out ideas.

You could look into inlet vane dampers to throttle air flow.

No matter what you do you would seem to need "something" on the "controls" side to decide what CFM/Hertz to control to.

Single phase motors are just a bad choice. Perhaps acceptable at home but otherwise they need to go IMHO. At least on anything above fractional horsepower.
 
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