What Size Idler motor?

[split63]

I have a 2HP Bridgeport CNC. What size RPC motor do I actually need. I've seen recommendations such as 1.5x your Motor size which would call for a 3HP. But in practice would a 2HP do the job. I'm trying to keep the power down and a 2HP RPC draws less power than a 3HP.

Thanks,

[Al_The_Man]

There is one general rule used in RPC, that if all the loads are 3 phase motors, then the RPC can be 1/3rd to 1/2 of the size of the total motors, as long as the RPC is equal to the largest motor, this is because as soon as you start a motor with a RPC, this motor now also acts as a third phase generator, just like the RPC itself, and aids the main RPC.
Al.

[split63]

Originally Posted by Al_The_Man There is one general rule used in RPC, that if all the loads are 3 phase motors, then the RPC can be 1/3rd to 1/2 of the size of the total motors, Al.

So this would say that I could have a 0.66 to 1HP RPC for my 2HP 3PH spindle motor....when its running, and at least a 2HP to start it. So if I have read you correctly, a 2HP is the right choice. Note that the RPC only runs the CNC Mill, I don't have any other three phase machines.

Thanks

[Al_The_Man]

No,the RPC has to be equal to at least to the largest motor, so in your case it would be 2hp.
Al.

[split63]

Originally Posted by Al_The_Man No,the RPC has to be equal to at least to the largest motor, so in your case it would be 2hp. Al.

Al, I don't think you read my two line respone completely.