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Variable speed controller

squerly

Supported Ben Carson
GOLD Site Supporter
If I were to put a variable speed control on a fan, would it hurt the motor? I don't really understand how a VSC works but it seems to me like it would send less electricity to the motor and that might be a problem if the motor was designed to run on a certain amount of power. But maybe not, anyone know?
 

Snowtrac Nome

member formerly known as dds
GOLD Site Supporter
with I believe that you will run in to issues with the motor over heating if you run low voltage to it they do make variable speed motors.
 

AAUTOFAB1

Bronze Member
SUPER Site Supporter
or use a DC motor with appropriate controller and have infinite control and reverse.
 

squerly

Supported Ben Carson
GOLD Site Supporter
Thanks guys. I really don't want to change to a DC motor as this motor has the power I need and runs on very little electricity. Just has a little too much power for some apps and I was hoping to calm it down a little.
 

waybomb

Well-known member
GOLD Site Supporter
Not cheap, but you could buy a small Allen Bradley powerflex drive. You should be able to run the fan down to about 30% no problem. But it would be way cheaper to simply buy a fan with multiple speeds
 

tiredretired

The Old Salt
SUPER Site Supporter
Use a VFD. Variable Frequency Drive. You cannot adjust the voltage on an AC motor and have in run right. You will burn it up. It is the frequency that is adjusted. Slang terminology is freak drive. They work slick and you sizing them is easy. Just know your motor HP and the supply house will take it from there. Oh, single phase or three phase? Most likely single. You will need to tell them that too along with voltage.
 

squerly

Supported Ben Carson
GOLD Site Supporter
Use a VFD. Variable Frequency Drive. You cannot adjust the voltage on an AC motor and have in run right. You will burn it up. It is the frequency that is adjusted. Slang terminology is freak drive. They work slick and you sizing them is easy. Just know your motor HP and the supply house will take it from there. Oh, single phase or three phase? Most likely single. You will need to tell them that too along with voltage.
Thank you TR, and thank you Bobcat who PM'ed me almost the exact same explanation!
 

waybomb

Well-known member
GOLD Site Supporter
AB Powerflex is a VFD. You can probably find a good surplus one on PLCCenter.com.
 

squerly

Supported Ben Carson
GOLD Site Supporter
Use a VFD. Variable Frequency Drive. You cannot adjust the voltage on an AC motor and have in run right. You will burn it up. It is the frequency that is adjusted. Slang terminology is freak drive. They work slick and you sizing them is easy. Just know your motor HP and the supply house will take it from there. Oh, single phase or three phase? Most likely single. You will need to tell them that too along with voltage.
Is this what I need?
 

FrancSevin

Proudly Deplorable
GOLD Site Supporter
Is this what I need?

Yes. A freak drive controller is what you need. Take the motor or the motor specs to your electrical supply house. Even Grainger can help you with it.

HP, Voltage, Amp draw and phase.


I'm not sure that all AC motors can take a freak drive. But most modern ones can. It is fairly simple to alter and install if you have the right controller. Pretty much the same wiring setup as DC.
 

indago

New member
If I were to put a variable speed control on a fan, would it hurt the motor? I don't really understand how a VSC works but it seems to me like it would send less electricity to the motor and that might be a problem if the motor was designed to run on a certain amount of power. But maybe not, anyone know?

Triac-dimming-waveform.jpg


The triac pulsing process works as shown in the illustration. With a full waveform, the fan will run full speed. With the adjustment turned down, the pulse will be later in the waveform and will reduce the amount of power to the motor. The link shown has a controller that will handle 15 Amps. I don't know what kind of fan you have, or what kind of motor is driving it, but if it has brushes, the linked controller will probably handle it.

Buy it and try it. If it doesn't work, we can always say we thought it was gonna...
 

squerly

Supported Ben Carson
GOLD Site Supporter
Thanks All! At the price, it's worth giving it a try. Not the end of the world if it doesn't work and certainly cheap enough if it does.
 
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