RPC output vs. input

I recently bought a Tree J325 CNC knee mill, which has a motor capable of 5HP for short periods, and 3HP continuous. Part of the deal was a 10HP RPC. My current power setup has a 3HP RPC, put together from a Phase-a-Matic 1-3HP heavy-duty static converter and a 3HP idler motor. It has been working fine, for 2HP lathe, and a couple of BPorts, occasionally with 2 machines running at once.

The 10HP RPC has a mfr's label that states "10 HP 50 amps", and little else in the way of specification. It was built by Anderson Converter in Arizona, who I think may be out of business. My question is regarding the input to the converter, and what the resultant output is in terms of current. I had planned to provide a 30A circuit for the "new" RPC, with 30A 2-pole breaker on my single phase 220 sub-panel, and appropriate wire sizing for 30A. The Tree mill says it wants a 30A 3-phase circuit.

So, is it realistic that a 30A single-phase 220 supply to the 10HP RPC results in having 50A available as output into the 3-phase distribution circuit?

I seriously doubt that I will ever be requiring the full output of the RPC capability, but I want to make sure I have breaker and wiring set up correctly. It does involve some re-wiring in my existing power arrangement, so I hope to get it done right the first time, and not end up with frequent breaker trips, or (worse) over-heated wiring.

A 10 hp idler will produce about 27 amps. The FLA rating is what it will produce. If more machines are running under light or no load, they will add to the idler output.3
The 50 amp rating is the single phase circuit size the rpc was built for.
I consider 50 amps to be the minimum for a 10 hp idler. If you divide 50 by 1.73, you will have the maximum 3 phase amps this rpc can produce.
30 amps is too small for the single phase circuit. I would use a 50 amp circuit.
Bruce

If your mill requires 30A 3Φ you will need to supply the RPC it's full 50A 1Φ input requirement.

Here's a comparable unit from a builder near you.



Maximum output capacity is 28A 3Φ with a 50A 1Φ input. So 30A 1Φ input is a little light for your needs.

Downlad Manuals - phoenixphaseconverters.com

SAF Ω

Thanks, guys -- that makes a whole lot more sense to me.

Hold on there.......

What does the RPC supply vs the mill wanting?

The RPC ONLY supplies ONE phase to the mill. The rest comes directly to the mill motor. So the RPC supplies 1/3 the total power. The rating of the RPC may include ONLY what it draws when providing the 3rd phase at full power, since that is what it controls.

So, the output of the phase converter will be only between 1 HP long term, and about 1.6 HP short term. The draw of the phase converter will therefore be roughly its idle current, plus that power, plus small added losses. The rest of the draw will be the mill.

Now, an RPC does not "MAKE" power, it converts power. If your system is supposed to produce up to 5 HP, then you will draw up to 5 HP plus losses Between 4500VA and 5000VA. That's around 21A. A bit more including the RPC losses.

A 3HP motor will draw about 10A FLA. 5HP 15A.

The big draw would be the 10HP idler, which could draw 15 to 20A at a horrible power factor, with no load. You can correct the input power factor with capacitors on the input to the RPC, and decrease that significantly. You start with a PF possibly of 0.15, and if the PF were improved to only 0.5, your current draw would be cut significantly, and probably would allow the 30A to carry your machine fine.