Pat
Actually, I should have clarified this in my original post, but I am not adverse having multiple ranges as long as they have overlap. As VFD's are new to me I am trying to understand the practical limits. I realize that a motor designed for 400 Hz operation uses different magnetics than one designed for 60 hz. but what is the practical top limit of a 60 hz motor with derating. The vfd's I have looked at specifically the Hitachi X200 series show an output frequency range 0.5 to 400Hz. How much of that is usable. Just spotted a torque characteristic curve base on a Hitachi standard 4 pole motor that shows a continuous duty range of 45% rated torque from 6-120 hz. and a short time down to 1 hz. It also shows the peak continuous performance of 95%. So this looks like a reasonable 20 to one range for 45% torque and 4 to 1 range for 80% torque. With this in mind I could probably go to a dual range mode of 10-1000 assuming 10-50 are short periods. and 50 to 5000 assuming 50-250 are short periods. A 4 pole motor would require a step up ratio of 5000/3600 and a step down of 1000/3600. Does this make sense to others. Maybe a third mid range would be useful as well of 36 to 3600 or 3600/3600 with 600-2400 high torque range that would be good for steel. This would give low range for Drilling and Tapping, Mid Range for cutting Steel, High range for cutting Aluminum and with My Proxon with 5000 to 20000 spindle a super range for engraving.
To me this looks feasible. Does anybody have some recommended motors?
Hubert  |