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Old 12-30-2011, 04:32 PM   #1
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Default speed control for a single phase motor.

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.

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Old 12-30-2011, 04:53 PM   #2
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Quote:
Originally Posted by Farm Duty View Post
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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Old 12-30-2011, 09:07 PM   #3
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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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Old 12-30-2011, 09:33 PM   #4
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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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Old 12-30-2011, 09:47 PM   #5
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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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Old 12-30-2011, 09:55 PM   #6
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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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Old 12-30-2011, 09:57 PM   #7
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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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Old 12-30-2011, 10:35 PM   #8
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Quote:
Originally Posted by Farm Duty

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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Old 12-30-2011, 11:20 PM   #9
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Smaller pulley without question is the smart money.

And less money.
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Old 12-30-2011, 11:23 PM   #10
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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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Old 12-31-2011, 12:13 PM   #11
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Originally Posted by Farm Duty View Post
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.

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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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Old 12-31-2011, 03:12 PM   #12
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Quote:
Originally Posted by John Valdes

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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