[mwp]

After searching for some time, I have finally settled on and purchased a kasuga cnc knee mill(8' tall 6200lb beast). This mill has the Bandit 3 control (working) as well as a "factory" vfd interfaced with the control driving the 4hp 3phase spindle motor. As with most here, my house does not have 3phase power installed and I am going to need to figure out how to run this thing off of 240 single phase. The previous owner used a 10 hp rotary convertor to power the machine on single phase and has offered to sell it to me for $400. The spindle motor is 4hp so the 10hp is serious overkill in my opinion...Which means big wires breakers, etc needed to the convertor.. I think. What I am wondering is can I simply run the vfd off of the single phase 240 and rewire the machine's distribution panel as appropriate? I am concerned with the VFD having insufficient capacity to run off of the single phase since it was originally sized for 3p. Am I going to burn something up trying this or just have less power? Also, any future 3phase machines will be run off of properly sized VFDs(for single phase) so the rotary convertor will not be of much help there.

Anyone have any ideas on how to proceed?

Mitchell

[Al_The_Man]

If the VFD is capable of running off of 1ph then you should be OK, you may not be able to get the maximum power from the motor, as usually there is some de-rating, there are makes out there that claim no de-rating on 1ph, the deciding limitation in a VFD is maximum current, and you can usually limit that by parameter.
If the DC Buss voltage is not sustained as much as on 3phase then the derating applies.
Al.

[mwp]

Al, Thanks for the reply.

I'm not sure if the vfd is able to run off of single phase as it is at least 10 years old and has no documentation or markings that I remember--far from the newer units I have seen. But the principle is the same on all of them, right? Rectify mains into dc & chop with some sort of solid state bridge into three phases with frequency as needed. Is it possible that the VFD would not be able to take the single phase for some other reason? From what I understand, I should be able to get at least 1/2 times the rated output at three phase (if it is limited by the rectifier stage).

I guess I could just build a rotary converter from a 5 hp three phase motor and play it safe. Seems like a waste if I really don't need it though.

Mitchell

[Al_The_Man]

Some very early ones had a three phase transformer for the low voltage supply and also had phase loss detection, but if you do use 1ph then generally you input on the first two designated phases i.e. R&S of R-S-T or L1 and L2.
Al.