20hp Rotary Phase Conveter balance questions

Heavymetal70 · Feb 25, 2018

I built an RPC using a 20hp or 25hp( have to check ) 1750rpm electric motor and capacitor bank. The problem I have is that I run several machines off of this unit that vary greatly in hp and load. If I run it balanced for say a 1 1/2hp drill press, it's not balanced for the 15hp planer. My question is, can I use relays to bring in more caps based on the machine I need. If I balance it for the planer, and then let it idle, the CEMF makes the motor hum loudly and my idle current is way too high.

Bob-J-H · Feb 25, 2018

You can put the run caps on the load side of the large machines, so they will only be in the circuit when the machine is operated. Bob

R_Audano · Feb 25, 2018

if you enjoy a science project go for it. Otherwise just keep any high legs off the control side

rons · Feb 25, 2018

You can do that but the extra hardware will require logic (either human or smart control) to switch the correct capacitors in/out. By the time you add the additional hardware you would have enough stuff to build another RPC for the lower HP machines.

hitandmiss · Feb 25, 2018

My question is, can I use relays to bring in more caps based on the machine I need?

Short answer is yes.

You must do the switching when the RPC is off.

Also, be sure to use discharge resistors on the caps that are unhooked.

Bill

hitandmiss · Feb 25, 2018

Bob-J-H said:
You can put the run caps on the load side of the large machines, so they will only be in the circuit when the machine is operated. Bob

Connect them to the correct phases on the load side of the motor starter of the planer.
Then they are connected to the motor for discharge and no other switching is required.

Bill

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20hp Rotary Phase Conveter balance questions

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