View Full Version : Using a single controler for 2 motors

Diamond G Knives
05-15-2010, 01:40 PM
Hello Rob

Im in the process of moving my shop and have had a thought.

I have been using my 9"Disc Grinder for just over 6 months (And LOVE IT!!!) but until I got this had never experianced variable speed controlers. What a God Send!

I need a new motor for my KMG and was wondering if it would be possible to use the controler off of the Disc Grinder to control both the Disc and the KMG?

If so, since the Disc has a 1HP motor, could I use a 1.5 or 2 HP motor on the KMG as long it is the same RPM?

Any input you have on this would be greatly appreciated.

And a Heart felt Thank You for making such a well built and engineered line of equipment for us knifemakers!

God Bless

05-17-2010, 07:42 AM
Hi Mike,

Yes and no....the controller on the disk is rated up to 1 hp. It will run the KMG....but with an output of only 1 hp regardless of the motor size used. If you use a 2hp motor, the controller will run it up to an output of only 1 hp. This is way too small and you will constantly be tripping it with an over load fault.

Ideally, you need the 2 hp controller for the KMG.....this controller will run motors upto 2 hp...meaning that it can also run your 1hp disk...no problem.

But your disk already has a 1 hp controller, so there is nothing to be gained.

I think the bottom line is that you just need to buy a new motor and drive for the KMG. This is something that you don't want to comprimise on....because you'll end up buying it again if you cut corners.

Sorry for the bad news...

These are just my thoughts and I hope I've been able to answer your question. Let me know.

Thank you for the kind words!


05-18-2010, 07:42 AM
Mike, just for future reference, here's how I wired up my controller. It's a 2 hp rated VFD, and it's currently running 3 grinders (my 2hp KMG, another 2 hp 2x72" grinder, and a 3/4 hp disc grinder). As Rob said, if your controller was rated for 2 hp, it would be no problem, but as you're limited to 1 hp motors on your existing controller, your KMG won't be all that it could be.

If you do decide in the future to pick up another, larger hp rated VFD, here's how I set mine up to switch between machines (because we could always use more grinders :D).

I put together a box with special, high voltage/amp toggle switches that I picked up from an electronics supplier. They are rated beyond the amperage and voltage for my motors. When you set it up, you want to make sure that there is no way that two motors could possibly be drawing power at the same time (mmmm....smells like burnt VFD ;) ). That why on the first switch, power either goes to my VFD or to the second switch. The second switch can then toggle between the disc and the EERF. At no time can two machines draw power together.


I wanted to do a setup with change-over switches / cams, but it was way too cost prohibitve, so this will do for now. I set it up so I can add a third switch to add one more grinder in the future (a horizontal perhaps....:) ). The only bad thing with this setup is that all grinders share a common remote mounted control which is mounted on my KMG stand. I have all my grinders together, so it's not much of an issue for me.

By the way, just for grins, here's my grinder stable:



Diamond G Knives
05-18-2010, 10:40 PM
Thanks guys!

Hey Rob whats the trade in value for a "Slightly Used" 1HP VFD ?????:rolleyes:

And Nathan, what you have done is what I have in mind. Im currently constructing my new shop from 20' container boxes. 2 - 20' boxes sitting 24' apart, then with a roof built over them using the boxes as the outside walls.
My plan is to have all of my buffing and grinding done in one container box (the dirty room) an 24' x20 open forge and bulk shop, and a "clean room" for fit up and precision work and an office.

Nathan, if you dont mind me asking, where did you get your set up and what was the cost? Is it wired for 110, or 220 from the wall?

Thanks again guys!

God Bless

05-19-2010, 07:41 AM
Mike, I got the switches (3 pole hi-volt/amp toggle) from Mouser Electronics for just under $40 a pop. That's a good chunk of change, but much cheaper than the alternative cam switches. I also picked up a bunch of standed 4 core line from the local hardware store to connect everything together (can't remember the gauge...enough to cover the load).

My VFD is a 2hp TECO FM50 I picked up from FactoryMation for $145. It's not wash-down or dust resistant, so you have to spend a few extra bucks and build a clean box for it (the red tool box on the wall). There are NEMA4 enclosed units as well, but they start getting as pricey as the drives Rob sells. If I had the extra change, I'd jump for Rob's drive, but this is the route I had to take to save a few $$ in trade for some extra of my time. The VFD is powerd off of 220V single phase from the shop. It also has remote mounted controls. The swtiching box only comes into play on the output of the drive (three phase to the motors) and switches the output between the three grinders.

If you were eventually wanting to run two grinders off of a new, higher HP VFD, you just need one 3-pole switch. The input goes into the middle pole, and the toggle switches it between two sources connected to the other two poles.

Here's my clean box/VFD:


Hope that helps some. If it were me, I'd keep Rob's drive for the disc, as it's a perfect match, and then get a second VFD for the KMG.


Diamond G Knives
05-19-2010, 10:37 PM
Thats my plan. I could not bring myself to mess with the 9" disc! Its just to good to monkey around with!

I appreciate you showing me this though. I have a few options, but it seems I will run out of shop money before I run out of shop!!! It is going to be a work in progress though.

Again thanks for your input and advise.

God Bless

05-21-2010, 01:28 AM
1hp VFD sell quickly at the right price :):cool: