static vs rotary converter questions / suggestions

[dustin wassner]

I have a grizzly static phase converter rated for 3-7.5 hp. I will be running a 3hp jointer and 5hp bandsaw with it. After doing more research, it appears that these static units are rough on motors and decrease power by 1/3.

I have not had issues with the decrease in power so at this point the power loss doesn't bother me.

Being in a small one-man shop, I don't see it being worth while to get a rotary converter as everything else I own is 220 single phase. I could replace the motors in these two units for less than the cost of the rotary converter.

I don't think either are vector motors, but if I use a vfd and don't manipulate frequency, will this create full, clean power?

My question: what would you do in my position? I could sell the converter/ 3hp leeson motor / 5hp motor while they still work great and use the money for single phase motors. I could also just run them till I have an issue, if ever. Maybe someone here has an even better idea? Not trying to overthink this, but just trying to be proactive.

thanks.

[dustin wassner]

how long can i expect the motor to last if I use the static converter?

[Kevin Jenness]

I have been running my slot mortiser on a static phase converter for 25 years with no problem. It has a 3hp motor and is not used that heavily, so perhaps that is not comparable to a machine that needs the full rated power and is more of a shop workhorse.

A rotary converter has the advantage of being able to start and run several motors up to its capacity at their full power and gives access to the used industrial machine market if that interests you. I have a couple machines running off an rpc and a couple more with vfd's, but only because I wanted speed control on them (edge sander and exhaust fan).

I would have been better off had I bought an rpc when I started out. Swapping out your three phase motors for single phase would not be my choice, as it is hard to get back the value of the used motors, single phase motors have the additional complications of capacitors and centrifugal switches, plus you have the labor of changing them out.

[Bruce Wrenn]

Building a RPC is a piece of cake. You need a three phase motor and some way to spin it up to speed. Go over to "Practical Machinest" and you can see close to a hundred different ones.

[Mike Henderson]

I'd get a VFD for each machine, or replace the motors with single phase motors. A VFD should not cause any problems for your motors, and they should last a very long time operating on a VFD, especially since you'll probably run them at 60Hz (you won't use the VFD to slow the motors down).

Mike