[Swede]

After my wail for VFD help, and some excellent advice, I went out to PolySpede (www.driveswarehouse.com) here in Dallas to pick up a shiny new VFD for my vertical mill.

The current mill installation consists of a 4/8 pole (0.75/1.50 HP) 3p motor, 240V, fed with a "Phase-A-Matic" rotary phase converter. The rotary converter has served me well for many years, and being rotary, it produces a true, high-quality waveform. The 2 drawbacks are the noise it creates (even in the attic rafters; it's a nasty hum), and the mill itself, being step pulley, can be a bit irritating to change speeds.

Before I went out and bought this VFD, I did some experiments with a much smaller Hitachi VFD, a 4A job. Since the motor is 2-speed, I was able to attach the small 4amp VFD to the 4-pole motor inputs and proved to myself that the concept was sound and that the motor would respond well without overheating. It generated nice torque even at slow speeds. There was some PWM carrier noise which improved when I jacked the carrier freq. up to the max of 16 KHz. Upping the PWM carrier forces one to derate the VFD 20%, but the behavior of the VFD improves.

Here is the original 2-speed switch which I have dismounted.