can I add a 5hp motor to my 15hp motor to achieve 20 hp with my current phase convert

I am currently running a 15hp phase converter set-up. I recently purchased a Cincinnati VMC that's 7.5 hp. I would like to increase my capacity somewhat to allow for start up inrush. Will adding a 5hp motor to my system give me 20hp? And if so, how do I "link" the two motors together?

I will save all the balancing questions for another thread. So my first thoughts are whether or not this is possible or advisable.

You can parallel two motor to get added capacity, its the same as paralleling two transformers. The problem is balancing as you suspected.

Before going to the trouble of two motors, try starting the VMC from what you have. In the event that the existing RPC won't start the VMC, then try paralleling. One common trick is to start other machines in the shop connected to the RPC. Each one becomes a contributor to the network.

In the event that you want to permanently parallel a second RPC, connect it to the existing motor with a magnetic contactor. Start the main motor, then close the contactor to start the second motor. You will most like have to balance out the second motor with capacitors, just the same as the main motor. The magnetic contactor is so that in the event of a power failure, it drops out so that on restart its not part of starting circuit. If all you need the second motor for is starting, it can be dropped out after starting VMC.

Electrically connect the second motor just as you would a machine. T1 to L1, T2 to L2 and T3 to L3. T - RPC main motor, L - line connection to slave motor.

Tom

"So my first thoughts are whether or not this is possible or advisable."

You may parallel as many idlers as you wish.

The aggregate capacity is the algebraic sum of the rated powers of all the idlers.

Also, a machine which is powered-on, but has no load applied to it its spindle, is also acting as idler, up to its power rating minus an allowance for parasitic loads (belts, unloaded spindle, etcetera).

tdegenhart and peterh - you guys are awesome! Thanks for the help. Ok, I will try hooking up to what I have and see if I can get it to fire up. It looks to me like I am going to be very close on the amperage draw based on what the manual is saying. I have my phase converter running off a 60 amp breaker. The manual says at 230 volts the draw is 62.

A little more info - when I started this business 15 years ago, it was just a side business. Since that time two of my sons have come to work for me full time so we often have more that one machine running at a time. Even with more than one or two machines running at a time we never trip the breaker and barely runs warmer than room temp. But i though that I would give more info in case that matters.

So how might that impact the amperage draw?

I would start one idler at a time.

The conventional wisdom is to start the largest first, and then add additional, smaller, idlers as needed.

However, if your smallest idler is 5 HP or less, then it makes sense to start that 5 HP idler (assuming it is self-starting), and then add additional, larger, idlers thereafter.

Not all idlers need to have starting circuits, but at least the first idler must have a starting circuit.