Thread: 3phase on single phase plus a capacitor ?

... and on ce you do, Simon, you can buy a 415V VFD to get 415V 3-phase....

Thanks Joe & Ray.

Joe, welcome back (are you back yet) The beauty of a RPC over a VFD is you can chop in and out whatever motor you want. In fact I assume you can run the output to a couple of 3 phase power points rather than just specific to one machine/motor. Of course the features of VFD's do have certain advantages which you can't get with a RPC.

I'm just thinking…..

Cheers

Simon

Originally Posted by simonl

In fact I assume you can run the output to a couple of 3 phase power points rather than just specific to one machine/motor.

Yes that is correct. You can in fact run multiple machines at once from an RPC as long as you keep within it's HP limit.

I'm not too familiar with using VFD's, but how do you handle a machine (like a milling machine for example) which has multiple motors on it ... do you need a VFD for every motor?

VFDs CAN run multiple motors, but it is not recommended to switch ALL of them off at once. I've run two mtors at once but not tried switchin one of them on and off downstream of the VFD. Should be OK if at least one was kept running I think.
A friend has a surface grinder with dust extraction which we will try running on a single VFD - both motors always on. I guess a surface grinder with hydraulics and cooling would also be a good candidate for a single VFD... as long as combined kW matched the VFD capacity.
Feel free to have a different opinion with rationale.

Originally Posted by jhovel

VFDs CAN run multiple motors, but it is not recommended to switch ALL of them off at once. I've run two mtors at once but not tried switchin one of them on and off downstream of the VFD. Should be OK if at least one was kept running I think.
A friend has a surface grinder with dust extraction which we will try running on a single VFD - both motors always on. I guess a surface grinder with hydraulics and cooling would also be a good candidate for a single VFD... as long as combined kW matched the VFD capacity.
Feel free to have a different opinion with rationale.

Hi Joe,

I run hydraulics and coolant from one vfd, it's not a problem, in fact I'll go one step further and say that most of the time you could get away with switching loads downstream of the VFD, provided we are talking about a "dumb" V/F drive and not some fancy sensorless vector drive. The VFD is generally more than capable of looking after itself.

One of these days I'll setup a 415V VFD running on a 240v to 415 v single phase step up transformer, and try starting and stopping motors on the downstream side and see what happens. I have a couple of spare 11kw PDL drives and I'm thinking I'd I'd only be switching a few kw on the downstream side.

Ray

PS On the surface grinder, I'd keep the spindle on a separate vfd, just so you can set speeds and acceleration independently.

Originally Posted by RayG

PS On the surface grinder, I'd keep the spindle on a separate vfd, just so you can set speeds and acceleration independently.

That's one aspect I hadn't really thought about with multiple motors on a single VFD i.e. depending on the application you might not be able to make use of the variable speed feature of a VFD.

If you are planning on using the VFD for variable speed then obviously every motor attached will be along for the ride. I will be running 3 motors from a VFD for the surface grinder and I can't see the frequency deviate too much from the 50 - 60Hz region and so the hydraulic pump motor and coolant will not be any worse off. They will be switched on/off independently with the only contraint being that I will have to start with the spindle always first so that it enjoys the slow ramp up time. Once it's up and running, then switching on the other two motors is not an issue. The only other real constraint is you must choose a coasting stop so that once you stop the VFD it no longer needs to be connected to a motor.

Cheers,

Simon