Karl Townsend wrote:

My Supermax has landed. This knee mill has both horizontal and vertical
spindle motors. They are 5 hp. The vertical spindle will start with my 3
phase converter system, but repeated start/stop/start/stop will trip the
breaker. The horizontal spindle trips the breaker unless the drive belts are
removed. And then it "just" starts. Running load is just a few amps and I
know I'll never go to full horsepower cutting.

I have a 30 amp breaker on #10 wire going to a homemade "Fitch" RPC. Then
#12 wire throughout the shop. I can't read the nameplate on the RPC motor -
I think its a 3 hp.

I'm looking for suggestions to be able to start this mill without a complete
re-wire job. Some kind of soft start?? larger RPC pony motor?? I'll
consider a VFD only as a last resort.

Otherwise, this is one serious mill. I can now look down my nose with
disdain for those folks using a Bridgeport.

Karl

Larger idler motor on the phase convertor would probably do it, as would
starting the vertical spindle before trying to start the horizontal so
the vertical motor acts as an additional idler. The VFD is certainly the
best way to go, and you could with appropriate safety interlocks
multitask a single VFD to run either motor (one at a time).