1 VFD, 2 mill - switching outputs and controls between

I have 2 milling machines. A Rockwell witha 3/4hp motor and a Bridgeport clone (enco) with a 1.5hp. I have a Hitachi L100 VFD rated for 1.5hp.

Money is very tight for projects like this. And, I am an electronics guy with lots of switches, relays, boxes, shielded wire, etc.

The 2 machines are withing 5' of each other.

So, here is what I'm thinking. I could build a box with relays that would switch between the 2 machines. It would switch both the 3 phase power as well as control lines for remote fwd/rev/stop buttons and speed pots.

My concern is the potential risk of damage to the VFD if it got switched while power was on to one of the machines. I suspect it would not be good for the VFD to have its load suddenly taken away, and then another load reapplied.

I could have big pilot lamps on the switchbox that would be powered by one of the legs, and a warning not to switch while the lights are on.

Or have some logic that watches the monitor signals on the vfd and will not throw the relay unless the time is right.

Boy this is getting complicated- maybe I better just look for another vfd for the 3/4hp motor...it may be a false economy to try to use one vfd for both- I dunno.

I have my mill and surface grinder powered by an SJ-200.

You can switch between the machines using a simple drum switch (3 pole double throw). My SJ-200 has the ability to support 2 motor profiles, I dunno if your L-100 does or not. If so, I'd HIGHLY suggest setting a profile for each machine with a selector switch for it. THis is the way I have my VFD setup. I also have a magnetic mount control box that I move from machine to machine. Makes life a little easier. If you MUST have separate controls on each machine, you can do it with relays. If you do it that way, MAKE SURE you locate the selector where it won't accidentally gets thrown. You can smoke your VFD if you switch the output while it's driving a motor.

As JJ said... yes you CAN switch the VFD between two machines, and yes you CAN blow up your VFD.

Use latching relays to control the connections between the VFD and the two machines. These will retain their last state when power is removed.

A control system which supplies voltage to the latching relay selector switch ONLY when power has been removed from the VFD is the safe way to go. There are many different ways to accomplish this, depending on how your source the AC power to the VFD. If you provide info on that I could make some specific recommendations.

Perhaps the best option, and certainly the safest, is just get another VFD for the 3/4 hp machine.

- Leigh