Running multiple machines with 1 vfd

A.W.Stovall

A.W.Stovall

Well-Known Member
anyone have a part number for a switch to do this I am about to do a disc grinder and would like to use the same vfd.
Thanks Anthony
 
I have gotten some good info about this issue reciently from a customer who wants to do this. I don't have any personal experience but I think that it may be a good way to go.
I have tried getting on/off/on switches but found them to be expensive. I have suggested using 4 prongs plugs from the motors and a 4 prong outlet from the VFD then you just plug in the motor that you want to use. Here is the info that was forwarded to me from BladeForums: s

"seems like they run about $15-20 each. They are DPDT 9 pole switches, and install right into the VFD front panel. The switches these guys used are ‘on-on’, but I think I would get ‘on-Off-on’ versions:

http://www.bladeforums.com/forums/s...e-2-disc-grinders-to-a-KBAC-24D?highlight=vfd (see post #3)
http://www.bladeforums.com/forums/showthread.php/857177-What-is-a-good-way-to-design-multiple-grinders-on-1-VFD? (see post #9)

I don’t know what kind of switches were used by this fellow, but you can see what I assume are the same type installed and in action here:

http://www.bladeforums.com/forums/showthread.php/977970-3-grinders-1-VFD!!?p=11130494#post11130494

Check all this out and then get back with me and see what seems to work. Keep in mind that you are working with 3 phase power so need more contact points, and you need to have the same speed motor and hp motor on each machine."

Maybe we can figure out a way to help save some money.
 
I use 4-prong plugs on the machines and a matching socket on the VFD. I have a local control box on a long trailing lead that I can move to the machine I'm using at the time. It has start and stop buttons, a speed control potentiometer and a keyed reversing switch (so I can take the key out to disable reverse when I'm running anything that should not be reversed).

Most of the VFDs I've used in the last few years are pretty insistent that the wiring to the motor is direct: no fuses, contactors, etc, to break the output circuit. It was not always this way and the very first VFDs I used industially had contactors in the output circuits. When these VFDs eventually failed and were replaced by then-current VFDs, we got drive failures very quickly on the new drives, until we rewired them without the contactors on the output side. We are talking plant built in 1995, with VFDs replaced in the early 2000s, so things may have moved on since, but I don't want to risk killing a VFD if I can help it.

I feel the plugged arrangement makes it less likely that the circuit will be broken under power than a switch does.
 
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