# Question about controls with a VFD...



## jduncan (Oct 11, 2012)

I have a VFD on the way for my SB lathe.  The lathe currently has Start, Reverse and Stop on a box mounted to the top of the lathe.  This box is wired to a box on the rear of the lathe which has the relays and whatnot to do those things.  The power is supplied to a pigtail with a 220 twist lock connector on it.  My plan was to mount a similar pigtail to the output of the VFD and then just plug in the lathe when I want to run it.  I also bought a mill which uses an identical plug, so when I get it running I will plug it into the output of the VFD using the same pigtail.

I figure I will not be using both machines at once so why hardwire everything.

The concern I have it that I read somewhere that you must use the VFD controls for off and on, etc., and that switching off the power between the VFD and the lathe will kill the VFD.  Does this apply to my situation?  If so, I might as well take the controls off of the lathe and just make a remote from the VFD.

Am I thinking this out correctly?  I don't want to fry my VFD....


----------



## joe_m (Oct 11, 2012)

The VFD will do all the work that the big box of electronic stuff behind the lathe is doing now, you bypass it with the VFD. Yes, interrupting the flow between the VFD and the motor can hurt the VFD. I made that mistake on mine and it turned itself off before it killed itself. 

You could, if you want to use the VFD for both pieces of equipment, make a pair of plugs like you describe, but the wire would go from the plug straight to the 3-phase motor so that as soon as you turn on the VFD you have power to the motor. You'll still need to use the VFD for the controls though and there should be instructions, hopefully english, in the manual that would tell you how to run a remote on/off switch.


----------



## Pacer (Oct 11, 2012)

Only switch to turn the VFD on/off 

I would think something like coming out of the VFDs 3ph power terminals to a receptacle box and have a plug for the lathe and one for the mill - unplug one and replace with the other.

Yes, this should be doable but think it over carefully because the motor need its signals determined only with the low voltage terminals.


----------



## jduncan (Oct 11, 2012)

Reading some of the threads around here, I think I can use the existing on, off and reverse switch by wiring them up to the VFD.  I could then either use the control on the VFD for speed control or wire up a separate pot in a box.

I see references to relays but am am not sure why those are necessary.

As far as using it with both machines, that might be troublesome as I would have to hook up the various switches to the same contacts on the VFD.  As long as either one or the other is not powered I guess it would not matter.


----------



## refinery Mike (Nov 8, 2012)

My VFD manufacturers do not recommend any disconnect between the VFD and the load. I guess you could get away with several different loads but remember to never unplug the feed without turning the VFD off before you unplug. And do remember that a VFD can store a lot of energy. Never touch any power connections until you have let it bleed off for a while, and then tested it for power. DC and AC. Another safety reminder, just because you stopped the VFD, does not mean that there is no juice on the wires to the motor. They will still light you up. Dont ask how i know. Certainly do not put any sort of a switch or disconnect between the VFD and the Motor to switch between two machines. I also would not disconnect the input of the VFD and then slam it right back on. I have blown two VFDs that way. The engeneers say that it is impossible. I have seen it. (I work with VFDs on a daily basis) And i still have trouble programing them. LOL


----------



## jus1975 (Nov 10, 2012)

same thing I want to try.


----------



## 8ntsane (Nov 10, 2012)

jduncan said:


> I have a VFD on the way for my SB lathe.  The lathe currently has Start, Reverse and Stop on a box mounted to the top of the lathe.  This box is wired to a box on the rear of the lathe which has the relays and whatnot to do those things.  The power is supplied to a pigtail with a 220 twist lock connector on it.  My plan was to mount a similar pigtail to the output of the VFD and then just plug in the lathe when I want to run it.  I also bought a mill which uses an identical plug, so when I get it running I will plug it into the output of the VFD using the same pigtail.
> 
> I figure I will not be using both machines at once so why hardwire everything.
> 
> ...



Though you could run two different machines on the same VFD, it may, or may not be worth all the trouble. I understand you will only use one at a time, but you would need to wire it up so you would have all the motor hookup, and controls separated.
Then you would need to go into the settings, and ajust for the motor settings, amps, voltage and so on. Unless the motors are identical in name plate specs, then you could get away with it.

The VFD will hook up direct to the motor. No switches, relays inbetween. So from one machine to the other, you should be able to have a simple plug to go from one to the other. The remote controls could be where it gets tricky. You will need a forward/reverse, start/ stop, and the pot for the Vari speed. Your looking at a fair bit of wiring with all this stuff.

Most of the guys do wire the VFD up for remote switches. Reason being they want the VFD out of the path of chips, but still need the controls at a easy to reach spot.  The other thing is wearing out the key pad is another reason. At minimum, the F/R, and E-stop would be wanted at each machine. So if your planning to use the same VFD on one machine, its going to take some plannig on your part.

Not that what your thinking can,t be done, it can, and allready has been by some. But you should think it over very carefully, before committing to such a deal. If you where to use only the VFDs key pad for controls, then it would be easy, but certainly not ideal. The input wiring would be simple, but the wiring the output from VFD to motor/motors and all remote controls would make for alot of work.

I myself comtemplated this same thing way back when. I decided against it, and after getting it all wired up for the one machine, I realized it was best to just pickup a seperate VFD for the other machine.

Im sure you can pull it off, with carefull planning.
You know the deal, if there is a will, there is a way.

Good Luck


----------



## mitsue (Nov 11, 2012)

Put the motor output on a plug to switch between motors and make a remote/portable control box with the control switches in it. You could also wire it with a multi pin plug and put each machine control switches on matching plugs. Motor parameters/voltages might be an issue but lots of problems can be avoided by using the largest motor settings and longer excell/decell times. 
Be carefull with the power. Always give the drive time to discharge before messing with power plugs.


----------



## refinery Mike (Nov 15, 2012)

If you wanted to use both machines how about building a box with the stop start (Momentary contact) switches and the pot for the speed control in it. then use a couple of big magnets (or some other clamp) to hold the box on either machine. then locate the vfd near the center and swing the box on a pendant wire to which ever machine you are working on. The programing of the vfd would not be a problem so long as both motors are similar in size. PS also remember that you should have fuses in the line where the power goes into the VFD. About twice the full load current of the motor. If you motor shorts out a breaker will take way to long to cut the vfd out, it will be toast before the breaker gets around to tripping. Fuses act way faster in a short. AT 600 percent overload a fuse is about 1000 times faster than a breaker. 1/20th of a second. faster if you buy the really expensive fuses.


----------

