Can I use my old rpc for new application

I started my shop as a side business about nine years ago with a 5hp RPC and a few manual machines. Along the way I have since sold my manual machines and have purchased a couple of used CNC's and a new air compressor and I have begun to experience some problems.

My air compressor is a 5 hp and it bogs down the whole works when it cycles on and off. My CNC lathe is a 7 1/2 hp machine (I was told that the motor I have on my RPC is actually equivalent to a 7 1/2 hp by today's standards). From everything I have read, the air compressor and the CNC machines should have an RPC that is about double their motor size. I don't want to ruin anything and I can hear the motor on the air compressor is not what it used to be. It has grown more sluggish than it used to be.

My question (I guess) is whether or not I can use my existing panel and get a bigger motor? I really don't know what questions to be asking so maybe you all can ask me and help me sort out what need. I really don't have another two or three thousand dollars for a new phase converter but I can't afford to ruin my equipment either.

My current RPC has a 5hp motor that I have been told is at least fifty years old and it is hooked up to a panel that has a bunch of wires and some capacitors. Is my solution as simple as disconnecting the 5hp motor and replacing it with a 15hp motor to my existing panel? Oh yeah, I have a 100amp service panel and my current RPC is connected to a double 30 amp breaker (does that make it a 60 amp breaker?). Off that same panel I also run my lights and PC and window ac unit.

Any help would be much appreciated. If anyone has a larger RPC for sale I guess I would be interested in that too.

Thanks,

Joe

Joe,

As you know, you are seriously overloading your RPC and I bet your voltages get quite low when the Air Comp starts.

Possible solutions: You are limited to no more than a 15 hp RPC and you do not really have enough power available to handle a 15 hp load. I think you should limit the total 3 phase load to 10 hp at any given time.

1. My best solution would be to use a 15 hp idler on a 60 or 70 amp circuit. This will only deliver about 12 hp total as the circuit is not large enough to put out a full 15 hp. The oversize idler will give you much better motor starting capability and give you much better voltage stability. The main concern here is the inrush current when starting the RPC. A good solution is to use a belted pony motor start which uses a 1 hp (maybe less) single phase motor to spin up the 15 hp idler to 1800 rpm then power is turned on to the idler.
Your present control panel can not be used with a larger idler. All the components will be too small for the larger circuit.

2. somewhat cheaper but not as clean a solution is to keep your present RPC and connect another 10 hp RPC in parallel with it. This will give you the 15 hp idler when both are running. You can run either of them one at at time if you do not need both. I think you could probably operate the new 10 hp on a 60 amp circuit. Starting these one at a time helps with the inrush current problems.

Now you have something to think about.

Bruce Norton
Kingsport, Tn