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Phase Speed Control?


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#1 Dan123

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Posted 31 March 2009 - 09:17 PM

Hi i have a Viceroy Woodturnig lathe that i need to change the motor on. I would like to use a 2 or 3hp motor, to be able to turn large objects at a low speed with lots of torque..

Does anyone know, if i use a single phase motor if i can use a varible speed control on it? or if 3 phase is better for this application with an inverter?

And wether a ac or dc motor is best ?

I am baffled by the options available plaese help??

Thanks
Dan

#2 jraef

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Posted 03 April 2009 - 04:47 AM

QUOTE (Dan123 @ Mar 31 2009, 02:17 PM) <{POST_SNAPBACK}>
Hi i have a Viceroy Woodturnig lathe that i need to change the motor on. I would like to use a 2 or 3hp motor, to be able to turn large objects at a low speed with lots of torque..

Does anyone know, if i use a single phase motor if i can use a varible speed control on it? or if 3 phase is better for this application with an inverter?

And wether a ac or dc motor is best ?

I am baffled by the options available plaese help??

Thanks
Dan

Hi Dan,
Most single phase motors, especially the one's you would use for a tool such as a lathe, CANNOT be controlled by a VFD. The only way to do it with a single phase motor is to use a variable sheave (a.k.a. Reeves drive or mechanical Variable Speed Drive).

Most small VFDs (up to 3HP) can now accept 1 phase input power and will provide 3 phase out to a 3 phase motor without doing anything special.

When you turn down the speed with a VFD, the torque remains constant but the HP is dropping with speed. However when you use a mechanical VS drive to turn down speed, the HP remains constant and you are INCREASING torque by the same ratio as the decrease in speed. So if you are used to that, replacing a mechanical VSD with a VFD often leaves people disappointed. But for a lathe, it's usually OK because the work you would want to do at low speeds is usually not HP dependent, it just needs constant torque. That's why VFDs are the method of choice for lathe applications.

DC is fine and sometimes less expensive at 2HP and under, but DC motors need brushes and that means maintenance. Lathes are notoriously dirty, so you would have to be extra vigilant about blowing out the dust and shavings every time you finish working. You can get "brushless" DC (BLDC) motors, but they use rare-earth magnets and are more expensive as a result. AC VFDs and motors are usually less expensive BLDC motors and drives.
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#3 Dan123

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Posted 05 April 2009 - 07:58 PM

Thanks jraef, that is a big help, i think that i will get a 3 phase 3hp motor with VFD/ inverter so that i have speed control and the constant torque...

Do you know of any decent manufacters and websites for moters, VFD and inverters?
I have seen some on ebay but not sure which is best..

Dan






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