Re: help - mill project - Bridgeport Series I CNC

Scott, sounds like you have a static phase converter. This is pretty
much a bunch of caps that provide some phase shift for the 3rd leg in
a 3 phase system. You can make a rotary converter by adding a large
old 3 phase idler motor. The static converter gets the idler motor
started, then the idler acts as a generator to provide the 3rd leg.
Lower RPM 4 pole motors are easier to start than higher RPM 2 pole
motors. You can improve the phase and voltage balance by adding some
oil filled run capacitors between the generated leg and the other two
legs from the utility. This kind of setup should generate pretty
clean power.

A rotary converter has the advantage over a VFD in being able to run
multiple motors/machines. The VFD is dedicated to one motor/machine
(unless you have one of those spendy models with multiple parameter
sets and do some serious re-wiring). Of course the VFD has many
advantages over a rotary: speed control, motor protection, dynamic
braking, etc.

~petev

--- In CAD_CAM_EDM_DRO@y..., "Carey L. Culpepper" <culpeppe@b...>
wrote:

> Scott: What type of phase converter? Rotary or static?
> I used a static phase converter for a while on my bridgeport and

most of

> the time it wouldn't start the motor. It was also used to run my

surface

> grinder. It would start the grinder. What I had to do was start the
> surface grinder and let it run while I was using the Bridgeport.I
> eventually got a rotary phase converter and that has worked great

for

> years.Even quick reverses are no problem. With the static

converter, I

> had to make sure the spindle was stopped before reversing. I have a

new

> VFD sitting here that I need to hook up and give a try. That may be

a

> good way to go.Actually, for $350 that would have been the best way

to

> go. Carey