Running two grinders off one VFD

B

Bob Duguay

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Aug 28, 2017
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Ok so I am going to take my old grinder and set up with my SGA. Will add a second grinder for everything else. Who is running another tool off one VFD ? What do I need to know and what additional parts do I need? Thanks
 
I am running a disc grinder and 2x72 off the same VFD. You basically just need a switch to choose which machine the output of VFD goes to. I think some will wire up a female plug to the outlet of VFD then put male plugs on each machine. I'm very unqualified when it comes to electrical so I'd look up the tutorial from someone knowledgeable. I followed the one on Ed Caffrey's site as I recall.
 
You can also just add male plugs to each grinder and a female plug to the out putt of your VFD, then switch as needed.
 
Salem is the king of multiple machines off one VFD. I swear his entire shop is connected to one VFD. He has a wired pendent he takes with him to each machine. And a quick flip of a switch and a speed knob twiddle and he is off and running on that machine. Me I use a plug and just plug in machines as I need them.
 
You just need a rotary cam switch with the correct amount of poles and positions.
Here's when I split one of my VFDs between honing wheel and disc grinder.
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I then added another disc grinder using another identical switch. They are like $10. There are single cam switches that have enough positions for three motors but the ones I found were bulky, so I went with two smaller ones instead.
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You just need a three pole, double throw, center off switch. You really don't need the center off, but it is a good feature.
 
I went with the male/female plugs as mentioned, but after 3 months of use I believe the switch as mentioned above will be easier, and faster.
 
The switch you want is usually sold as a "3-pole Disconnect Switch". It is often used to switch from the main power to a backup generator. They come from 30 amps to a couple hundred amps, but that does not matter with a grinder (about 6 amps per leg). Ebay and other sites have lots of them from a cool looking Frankenstein switch with a big handle for $16 to the standard rotary switch for less than $30.

You connect the VFD to the center terminals and the two grinders to the outer terminals. Switching from one grinder to the other is done by changing the switch position. ALWAYS turn the VFD off before switching.
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Now, lets talk about remote control.

Say, your VFD is on the main grinder. You have a second grinder or a disc grinder you want to run off that VFD. Install the switch in the line as above. But, you will have to run back and forth to turn the second grinder on/off and adjust speed. The answer to that is making a remote control box on a long enough cord to reach the other grinder. This is called a "pendant". The pendant needs a potentiometer to set the speed and a forward/stop/reverse switch. A power on/off switch is also good. These three devices are readily available from KBAC and ebay for about $50 total.
You plug these controls in your VFD where the on-board controls were plugged. Some units have pins for remote control already on the board. Put them in a plastic outlet box (Home Depot and you are in business.

HINT:
Placing a magnet on the back of the pendant allows it to be stuck almost anywhere.
 
Thanks guys for the suggestion. The company I want to buy my grinder from says they will not have any VFD for a couple of months. Three other places I called same the same.
 
A thread that might help here. Has a good wiring diagram. https://www.bladeforums.com/threads/vfd-setup-for-controlling-multiple-machines.1457370/

There are VFD's on Ebay and amazon, and I am sure on line. I bought a second hand vfd for about $100 (can't remember exact price) that wasn't Nema 4. Got a metal enclosure that I doctored up with furnace filter material to house it in and made my own remote box. Thread is here for the remote box. https://www.bladeforums.com/threads/vfd-external-control-pot-build.1595572/
Basically you can set your less expensive chinese non nema 4 vfd up away from the metal dust then and use the remote pot to control the machine. Don't quote me, but I think this is what Salem does....uses the chinese vfd.
 
Just curious, can multiple machines connected to a single VFD run at the same time?
 
Hengelo_77 said:
Just curious, can multiple machines connected to a single VFD run at the same time?
Click to expand...

Probably yes, if the combined amps for the two are lower than the rating of the vfd.

But it's probably also not a good idea. There could be some weird feedback loops I'm not aware of that will break your VFD.
 
I wouldn't do it. The VFD circuitry is sensitive and may read the two motors as an error signal and will shut down. Besides, how hard is it to flip a switch.
 
I think I remember Salem saying something about making sure that the motor comes to a complete stop before reversing it or you could wreck your vfd. Do you have to make sure one machine is stopped before switching to the other?
 
The VDF needs to be turned to STOP first, and then you can throw the switch to change machines. NEVER throw the switch while the VFD is running one of the motors.
 
Thanks guys. For those that are using the individual plug ins can you post a picture of that set up? Thanks
 
That is really simple:
A NEMA 15-15R socket on the VFD cord and NEMA 15-15P plugs on the grinders. You can also use twist-lock plugs/socket - NEMA L14-20 R or P.
 
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