RPC or VFD sizing question probably a millionth time

JST said:

The simple way is RPC.

5 HP should drive the snot out of it. You really only need an RPC rated to drive a max single motor of 2 HP, because when it is on, it will act to some extent as a "helper" for the others. No more than 3 HP should be needed. But 5 is OK.

The VFD would need to be capable of a total current, continuous, equal to at least the sum of all the motor currents. VFDs start slow and speed the motor up, so they are not rated for start current on their HP rating. You could not just throw a switch and start/stop the machine , the way you can with RPC.

With a VFD "it's complicated".... dont go there.

A phase perfect would run it, and anything else you want, but the RPC is simple and pretty much trouble-free.

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CarbideBob said:

A VFD will drive it fine but question number two is a killer.
If you slow speed grind at 750 RPM your Hyd pump and even the coolant system will be unhappy.
If you want to play with grind wheel speeds you would use two VFDs.

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dcsipo said:

I have a B&S 618 micromaster. It has 3 motors. total power is 3.5 HP or slightly less. the main spindle is 2 HP, the hydraulic is 1 HP, and the coolant is less than half HP, can't read the face plate properly it is either. 0.5 or 0.3.

So question number one. will a VFD drive this? or do i need an RPC. Question 2: what size? How much over size do i need? Will 5 HP do?

I know an RPC does not care as much about the load as the VFD. That is all i really know which is not much. I like the idea of the VFD but is it a good idea to run the hydraulic pump at different speeds?


dee
;-D

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