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American Rotary ADX10 can it run a 7.5hp design B motor?

Cap comment makes little sense to me either.... unless you are talking about a "static converter", which is ONLY capacitors and a relay.

Yeah, if the capacitors on your RPC can cut in again, maybe.

It is not "about" the size of motor so much as it is "about" the load on that motor when it starts. Can be an inertial load, or something that is doing cutting, etc.

Torque in a motor is related directly to current. The RPC has to provide enough generated leg current to get the load turning, since that is what provides the torque via the "internal rotating field" of the motor. Without the generated leg, there is no rotating field.

A 15HP nominal RPC may start a 15 HP load motor, or even a 20 HP load motor, if it is basically just starting the motor, and not a lot of rotating mass with it. Lathes with clutches are an example. Depending on where the clutch is in the drive, there may not be much turning when the clutch is "out".

Yes, you can add another motor with no load, and that will add idler capacity. Many have done it and it works.
Jst where in the circuit would you add an additional idler motor?

Here is a pic of my current 3-phase power center.


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Thank you Johansen.

I will keep this in mind as I move forward with the build. I may need some additional assistance on the electronic modifications you laid out above.

Please let me know if your willing to guide a bit at that time.

I can just mail you one. I pull them out of the dumpster regularly, most of the time there is enough material on the contacts to be filed down, they dont last forever but once the contacts are polished up, they are reliable again.
Jst where in the circuit would you add an additional idler motor?

Here is a pic of my current 3-phase power center.
Anywhere. You need a 3 phase disconnect or contactor solenoid and overload. Connect it to all 3 phases from your main RPC, add extra run caps directly at the extra motor(s)

You can get creative and use the on off switch of the rotary to turn off the second motor, but not turn it on.
Thank you Johansen,
That would be very kind of you, not sire how to private message. I'll have to figure that out.

I do have 2 - 2hp and two 5hp motors that could be used as an additional idler.

Does the additional idler hp add cumulatively to the existing system or is some other proportion?

10hp current + 5hp additional = 15Hp of RPC capacity?