On Tue, Nov 3, 2015, at 09:41 AM, Todd Zuercher wrote: > I recently purchased an inexpensive router spindle off of ebay. It is rated > at 6kw and 380v 3ph. The old spindle I'm replacing was dual voltage and could > be wired Y or delta, for 200-240 or 380-460 (7HP). Stupid me I didn't think > to check the old VFD and it is only capible of low voltage (running 208 3ph). > > So my question, what are the repercussions of feeding this motor with only > 208 3ph? > > If the only problem is a loss of a percentage of power, but not more than > half, I can live with that. (It cost less than 1/3 the price of the > original.) >
If you keep the same voltage-to-frequency ratio and maximum current the motor will be happy. But of course the speed will be lower. For example, if it is designed for 380V, 240Hz, 14,400RPM, the volts-per-hertz ratio is 380/244 = 1.5833. If the VFD can only deliver 208V, then you will be limited to 208/1.5833 = 131Hz, and the top speed will be 7860 RPM. It will still deliver rated torque at rated current, but since the speed is lower the kW will be lower - only about 3.8kW. You can run it at a lower voltage-to-frequency ratio, but you won't get the same torque. For example you could run it at 208V and 240Hz. You would get a no-load speed of 14,400RPM, but the torque- per-amp will be lower - you'll still only get 3.8kW. -- John Kasunich jmkasun...@fastmail.fm ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
