The motor needs to be inverter duty to handle the full range of a VFD. Many will go to 200Hz or higher and that can breakdown the insulation in older motors. You can always limit your frequency to 60Hz then any good quality motor will work. The torque speed curve depends on the number of poles in your motor and the current capacity of the VFD. For something like a lathe, you don't need a lot of bells and whistles. A programmable ramp up and ramp down will lower the current you need to start, and be gentle on the equipment. You probably don't want any breaking as that can unscrew a threaded lathe chuck, like an old SB. Ebay is a great resource for things like that. I have bought several lightly used or NOS name brand VFDs for pennies on the dollar. But there are also a flood of new low cost Chinese VFDs that might be another option. You might want to go with a VFD that is rated to a little more HP than what you plan to use, if you go that route. You should make a list of what options you would like to have. Some have displays that can be programmed to display RPM even taking a reduction system into account, while others just display the frequency or a 0-100% count. If you can power the VFD with 240 single phase, your input amperage will be much less than what it will take running on 120. Also be aware that some VFDs that are 3 phase input can also run on single phase but with a lower HP rating. Do you have a flat belt or a V belt spindle?
Last edited by Rambozo; 01-03-2014 at 12:35 AM.
Long arc, short arc, heliarc and in-the-dark!
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