3HP Rotary Phase Converter

Ulma Doctor

Infinitely Curious
H-M Supporter Gold Member
Feb 2, 2013
I had a request from a good friend,
to build a Rotary Phase Converter for his brother's, new (to him) Hardinge lathe.
the requirements were straightforward,
run a 3 phase machine on 240v single phase supply.

the lathe has a 1hp main drive motor , runs a small coolant pump and a 1/4hp variable speed motor at the same time, switched on/off when necessary.

for longevity, i started with a spare 3hp 184T 3 phase motor for use as the idler motor,
then created the control box from my design from long ago..

3HP RPC.jpg

also for longevity, i used a contactor rated for 10HP@200v- (way overkill)
12 Gauge SOW wire cords
there is 200Uf of starting capacitance for instant idler starting
the RPC design will not restart unless the start is actuated, in case of power outage.
the input power requirements for this RPC is 10A single phase @200v.
we selected L14-20 twist lock plugs and connectors for the 3 phase output
the RPC can easily handle continuous loads up to 3hp.

i hope the unit will serve him well for many years to come. :)
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