20hp idler with 15hp control box

Any thoughts on a 20hp idler with a 15hp control box ? Motor is 1200 rpm. Thinking I'll use a pony motor to spin it up to speed before hitting rpc start button.

Once started, any problem starting a 15 hp machine ? I dont plan on working the 15hp machine to full horse power though.

not a good idea, internal contactors are sized to current draw of a 15hp and not a 20hp.

The idler on my RPC is 20hp. It starts my 15hp #11 Blanchard within 3 sec. According to the ammeter, I push it pretty hard sometimes.....35-40amps on the grinder and the idler is barely warm after an hour. I don’t know if motors are made differently or not but according to the idler motor tag, mine is made specifically for a RPC. My control is made for 20hp. I bought it from a PM member that owns Phase-Craft.

I currently use a 7.5hp rpc, both motor and control box are 7.5. Idling, no load, I have 8.7 amps per leg on my two single phase legs that power the rpc.

I found a post from 2006 where a fella with a 20hp rpc said he figures 12 amps idling, no load, on the single phase inputs. If in that vicinity, that's not as terrible as I guessed:
How many amps to start a 20hp rpc

I'd really like 15hp max, and down grade the motor size in two machines, 15hp & 10hp, to 7.5hp. Simply to save on the electric bill . But I won't run the larger rpc all day anyway. . . My 7.5hp rpc motor is 1200 rpm and nice and quiet. I just won a local auction on a 20hp motor, also 1200 rpm, and need to upgrade for two larger machines I have. The cost of the 20hp motor and no shipping was attractive, plus I won't have to change motors in those two machines.

My thinking was, if I get the 20hp motor spinning to 1000 to 1200 rpm before hitting start on a 15hp control box, that my amp draw will be minimal. And once started, I should have no issue starting machines with 15hp and 10 hp motors. Looking at 15 and 20hp control boxes, seems like not too much difference in capacitors, and I won't start motor from a dead stop.

15hp:



20hp:

Hobby Shop said:

The idler on my RPC is 20hp. It starts my 15hp #11 Blanchard within 3 sec. According to the ammeter, I push it pretty hard sometimes.....35-40amps on the grinder and the idler is barely warm after an hour. I don’t know if motors are made differently or not but according to the idler motor tag, mine is made specifically for a RPC. My control is made for 20hp. I bought it from a PM member that owns Phase-Craft.

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Electrically it is still a wire wound motor. Mechanically the difference is probably a rotor that was from another design and they made it lighter in weight.
It will spin up a little easier. Phase-A-Matic does that.

Add a bunch of run caps as pf correction and it will reduce the amps at no load a bit. May have enough margine to start it without tripping overloads.