Three motors, one VFD

silver_pilate

silver_pilate

Joined
Oct 30, 2002
Messages
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After going through the trouble and expense of setting up my VFD in a clean box and running the remote controls for it for my KMG, I just didn't want the headache or bill from doing the same thing two more times. However, after adding a disc grinder set up on a 3/4 hp 3phase motor and another 2x72" grinder with a 2 hp 3phase motor, I needed an option to control the extra grinders.

I had the idea of using change over (rotary cam) switches. These types of switches are designed for use when changing over 3phase power from shore to a generator on big boats, but the switches are pricey. Pretty much all of the rotary cam selector switches that can handle the load were just too pricey to pull the trigger. So instead, I opted for plain on toggle switches. After some searching, I found these 3 pole, 2 position, screw post toggles rated at 30 Amps @ 250V. I ordered two of them and set up the switch box tonight.

It has the capcity to add another switch if I add a horizontal grinder in the future.

The input comes in from the VFD via 14/4 stranded wire and on to the first switch. When the switch is in one position, power goes to my 2hp KMG. When it is switched to the second position, power is sent to then input on the second switch. The second switch can be thrown to either control the disc grinder or my EERF 2x72" grinder. All the grounds are tied in to each other seperate of the switches.

My VFD is 2hp, and you can control anything at or under 2hp with it. I use the same remote controls and VFD to control all three of my grinders!

switchbox.jpg


Just thought I'd share. Thanks for looking!

--nathan
 
Nathan,
There is nothing wrong with a setup like that with the following caveat:
NEVER throw any of the switches with the VFD turned on.
A safety cover to prevent accidental knocking of the switches would be a good idea. Throwing the switch while powered could destroy the VFD.


Also, 14/4 is a bit light for running a 2HP motor, I would use 12/4. The rating for 14 gauge is about 6Amps, while 12 gauge is 9 Amps. Your 2HP motor draws about 6 amps /leg.
The lighter wire is fine going to the smaller motors, but you should change the input wire from the VFD and the power line to the 2HP to 12/4.

Stacy
 
Your box is pretty sweet! I use 600v 10/3 and 10/4 for everything even my smaller stuff. I did not even know that TPST switches existed! Where did you get em if you do not mind me asking. I think I really wanna make one of those.
 
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it is my understanding that 14ga. is rated for 15 amps and 12ga. is good for 20 amps. At least that was the cities code rating for all the buildings I have helped wire .
 
Thanks, Stacy. I forgot to add that part in. I always wait until the motors are completely powered down to throw the switches. The saftey cover is a good idea.

I'll check into the wire ratings for sure. I recall the wire I'm using being rated at 15 amps, and I was thinking with the short distances I would be good. Running the KMG for the last year + has never caused any overheating of the wire. Even after hours of grinding, the wire has never even been warm. Thanks for the info, though. Better safe than sorry.

--nathan
 
When it comes to amperage, distance doesn't matter, you can get a voltage drop with distance, but it's the current you're worried about. For a simple analogy, you can think of wires like pipes and your current like water. You can only fit so much water through a pipe of a certain size. In the case of water if you force more through it you raise the pressure, in a wire, you raise the temperature. Too small of a wire and you create a fire hazard.
 
For anyone that does this struggling to find TPDT switches you can use a DPDT switch and just have a common leg for all the motors that is unswitched.

I really like the way you have the switches wired, seems kind of weird I'd probably opt for 3 switches, but the way you have it wired it's completely impossible to have 2 motors switched on, very good to protect the VFD and wiring.
 
And when switches are running $30 a pop, it's not only prevents multiple motors from trying to draw power from the VFD, but it also is cheaper :).

--nathan
 
Hi guy's
what I have done in the past is use ice cube relays and spst switches to turn on the relay
for the motor that you want to run. in this way you can add to the system as you go.
Dan
 
Nathan,
My mistake. I don't know what I was thinking. 14 ga. is rated at 15amp, and 12 ga. is 20 amp.
Stacy
 
No problem, Stacy. I'm just glad you're looking out for me and that I wasn't completely loosing my mind ;).

--nathan
 
Nathan, could you get an inside pic of your switch setup when you have some free time for the "denser" folks like me?
 
Nathan, You mentioned you set up your VFD in a clean box. Could you show us how you did that? Does the VFD need a cooling fan? Love the switch setup as I have two 3ph motors I need to put into service. Jesse
 
Cool, Nathan. I blew my first VFD out, luckily when I set it back to Factorymation they covered it under warranty. Since then, I mounted it high on the wall under a shelf outside the grinding room, (much less dust) and ran the wires back through the wall into the grinding room.

I made a remote controller box for the grinder(s) that I mounted on the wall of the grinding room. I ran the 220V from the breaker into the box to the main power switch. From that switch I ran the power through the wall to the VFD. The controller box also has fwd/rev, run/stop, and a 10K potentiometer for speed control. These controls all run through the wall to the VFD. From the VFD I ran the power out back into the grinding room and terminated it in a plug. (I had one, and didn't want to shell out the $ for a wall mount receptacle). The plug hangs on the wall, basically acting as a 3ph. 220 volt variable Hz. power supply controlled by the remote box. Any machine 3 hp. or less with a 3ph. motor gets a male plug wired directly to the motor, and can then be plugged into the female power supply plug for power and speed control.

I thought about using switches, but I didn't have them and while it would be nifty not to have to plug-and-play my machines, at least I absolutely can't brain fart and ruin my VFD this way.

I like your system Nathan, just thought I'd mention another option for wiring this way.
 
Pat, I'll see what I can do when I get back in town. And Jesse, check out the shop tour on my website for a few picks. I didn't use a fan for mine, and it's mounted to the metal toolbox which acts as a heat sink. It's worked fine for me so far for hobby use. I picked the idea up and pretty much copied it from another member who used to post here a while back.

--Nathan
 
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