# speed control for a single phase motor.



## Motorwinder (Dec 30, 2010)

Farm Duty said:


> Does anyone know if anyone makes a speed contoller to slow down or speed up a single phase motor up to 5 hp? Something like a vfd but not as complicated. I have seen one with like a speed pot on it before but don't remember the brand.


AC motor speed is determined by the frequency and the number of poles.

A 4 pole motor running on 60hz will run at 1800 rpm. Therefore to change the speed on an AC motor, you have to change the frequency, or the number of poles.

VFD. 

You might have seen a DC controller.


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## Netree (Sep 3, 2011)

You can do this with a "variac". Think also that slow motor is not cooled as well as fan make slower turns.


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## micromind (Aug 11, 2007)

Generally, single phase capacitor-start motors cannot be speed controlled. It'd be ok, but only for a narrow range of speeds. Once the speed reached the start winding switchover, speed control would be impossible. 

Speed control based on reducing voltage would cause enough of a current increase to burn up the motor fairly quickly.


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## joethemechanic (Sep 21, 2011)

Usually better to use a vfd with a single phase input and a 3 phase output. 3 phase motors are cheaper anyway


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## Netree (Sep 3, 2011)

micromind said:


> Speed control based on reducing voltage would cause enough of a current increase to burn up the motor fairly quickly.


Never a motor gone bad on the variac. I must be full of luck!


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## Farm Duty (Dec 30, 2011)

joethemechanic said:


> Usually better to use a vfd with a single phase input and a 3 phase output. 3 phase motors are cheaper anyway


Thanks guys for the quick feedback! I wasn't sure because I have never been asked to slow a single phase motor down. What I have is a farmer with an auger feeding corn into a roller mill and its feeding it faster than the mill can grind it causing him to have to turn the auger on and off several times per batch which is wearing the starter out. Both are run by 5hp single phase motors and have the same rpm. I need to slow the auger down enough to feed continuous. Maybe change to a smaller pulley?


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## nolabama (Oct 3, 2007)

Farm Duty said:


> Thanks guys for the quick feedback! I wasn't sure because I have never been asked to slow a single phase motor down. What I have is a farmer with an auger feeding corn into a roller mill and its feeding it faster than the mill can grind it causing him to have to turn the auger on and off several times per batch which is wearing the starter out. Both are run by 5hp single phase motors and have the same rpm. I need to slow the auger down enough to feed continuous. Maybe change to a smaller pulley?


Smaller pulley without question is the smart money.


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## Netree (Sep 3, 2011)

nolabama said:


> Smaller pulley without question is the smart money.



And less money. :thumbsup:


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## joethemechanic (Sep 21, 2011)

nolabama said:


> Smaller pulley without question is the smart money.



Yeah, if a single speed works for him, that would be the cheapest and best way out


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## John Valdes (May 17, 2007)

Farm Duty said:


> Thanks guys for the quick feedback! I wasn't sure because I have never been asked to slow a single phase motor down. What I have is a farmer with an auger feeding corn into a roller mill and its feeding it faster than the mill can grind it causing him to have to turn the auger on and off several times per batch which is wearing the starter out. Both are run by 5hp single phase motors and have the same rpm. I need to slow the auger down enough to feed continuous. Maybe change to a smaller pulley?


You could slow this down mechanically as stated by the others. 



nolabama said:


> Smaller pulley without question is the smart money.


If it is direct drive, the introduction of a gear box could be beneficial. This will be much appreciated by the motor.
There is most likely a gear box in place already. This type of load would be bit much for a motor alone and might be way to fast. (exceptions do exist). I have seen it done. But a geared output is the norm.


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## Farm Duty (Dec 30, 2011)

John Valdes said:


> You could slow this down mechanically as stated by the others.
> 
> If it is direct drive, the introduction of a gear box could be beneficial. This will be much appreciated by the motor.
> There is most likely a gear box in place already. This type of load would be bit much for a motor alone and might be way to fast. (exceptions do exist). I have seen it done. But a geared output is the norm.


Thanks for all the help guys! I think we have the solution!


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## manoc (Mar 10, 2021)

Farm Duty said:


> Thanks for all the help guys! I think we have the solution!


hey i'm thinking of doing the same thing on my farm. Was the roller mill on an electric motor or no?


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## Kevin (Feb 14, 2017)

manoc said:


> hey i'm thinking of doing the same thing on my farm. Was the roller mill on an electric motor or no?


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## manoc (Mar 10, 2021)

Kevin said:


> Are you an electrician?
> 
> Please see the link below. A profile is required here at Electrician Talk. Please make sure to include occupation and general location.
> 
> ...


Yes I’m a jman


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## Kevin (Feb 14, 2017)

manoc said:


> Yes I’m a jman


thank you.


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