View Full Version : VFD

Gary Helmick
08-19-2005, 10:28 AM
I will be getting a new milling machine this weekend (well new to me). It is a Bridgeport with three phase motor.

I also want to get a used (new to me)lathe that will probably have a three phase motor. My question is can I use just one VFD to run both of them?

Not at the same time. I was thinking about maybe using a receptacle for the VFD and a plug for each the lathe and mill.

The VFD is a Sumitomo AF-3000 2hp.

This VFD thing is something I have never worked with before so any help would be great.

Gary Helmick

08-19-2005, 10:36 AM
As long as power to the VFD is off when you do the swap, I don't see any problem.

[This message has been edited by SGW (edited 08-19-2005).]

08-19-2005, 11:54 AM
It is not as straight forward as it seems because the VFD MUST be connected directly to the motor it controls. Unfortunately each of your machines will have on/off/reverse switches (mill/lathe) or contactors (lathe)
between the power cord and the motor. Connecting the VFD to a 220vac outlet and swapping the machine power cords or paralleling two outlets and running one machine at a time mean you will be putting switches/contactors between the VFD and the motor. This is the best and easiest way to kill a VFD. They are robust but not that robust. What you have to do is isolate both machines motors from the machine controls, and then breakout the machine control wires so that the on/off/reverse functions on the machine can be equivalent to a spst switch for each function (ON, OFF, Reverse). Most VFD will allow either separate switching for each function or combination switching- read the VFD manual. The on, off, reverse and for the lathe maybe a jog and E stop, can all be set up with the remote (low voltage) terminal board on the VFD. You will need to run the machine control switches to a breakout box that switches from lathe to mill and outputs to the VFD remote controls, and the VFD 3ph 220vac output can then be switched from lathe motor to mill motor. Motor switching MUST be done with the VFD completely disconnected from 220vac 1 ph power. Note that the VFD takes about 20-30sec to completely shut down when turned off. All of this rewiring of machine motors and controlls can be done with some study and is tedious but the risks of blowing the VFD if you do otherwise are significant. It would be best to have one VFD per machine. A rotary converter would not have these problems. Steve

[This message has been edited by sch (edited 08-19-2005).]

08-19-2005, 11:58 AM

Here is a reference to a post (particularly the one by Forest Addy) suggesting an approach to the single VFD problem.

Here is a nice article on rotary converters:

[This message has been edited by sch (edited 08-19-2005).]

08-19-2005, 11:59 AM
message dup

Forrest Addy
08-19-2005, 12:48 PM
Yup, no problem so long as you run a cord directly from the motor to the VFD plug. You cannot switch the power between the VFD and the motor (but it does work. DAMHIKT). You cannot use the machine's controls unless you wire them to the VFD's control terminal strip.

For several years I had a portable control station with Fwd/Stop/Rev pushbuttons and the speed control pot connected to the VFD with a 15 ft cord. I had a strong disk magnet on the bottom. When I needed the lathe I plugged the motor cord into the VFD moved the portable control station to the headstock and went to town.

When I needed to mill I plugged in the mill motor cord and moved the control station etc.

Works great. Just remember to size the VFD to suit your largest motor.

Mike Burdick
08-19-2005, 01:45 PM
...also you’ll have to change some of the function parameters as to amperage for each motor depending on which one is in use. This is because the VFD is now providing the overload protection for your motor. Doesn’t take too long to do this but it’s just a couple of more things you’ll have to remember to do...which is often forgotten because your mind is on the project at hand rather than the machine electrical switching.