View Full Version : wiring up a VFD

06-25-2009, 01:18 AM
Hi everyone,

In anticipation of my new Bridgeport being delivered next week I'm trying to sort out my plans for wiring everything up. I decided to go the VFD route and purchased a 2hp Teco EV-series VFD. My plan is to mount the VFD on the wall where it will be away from any flying chips or coolant and then run some external controls to the mill itself. I am undecided about exactly what I want to do for the external controls and am looking for some ideas of what other people have done. My first thought was to wire up the existing drum switch to provide the forward, stop, and reverse signals to the VFD but I'm not sure it this is the best way to do it.

Any advice would be appreciated.


Jim Shaper
06-25-2009, 01:31 AM
I just got a pendant that houses the master on/off (which latches a relay to control all power to the machine's outlets and the vfd) and run/reverse/stop momentary buttons. Eventually I'll add the speed control pot as well.

http://i6.photobucket.com/albums/y242/FishyJim/th_DSC00899.jpg (http://s6.photobucket.com/albums/y242/FishyJim/?action=view&current=DSC00899.jpg)

06-25-2009, 10:30 AM
On one lathe I used the existing drum switch, plus a pot for the speed control. Works great.

On another lathe, the drum switch was broken, so I used household switches for on/off and forward/reverse, and a pot for the speed control. It works, but I intuitively reach for the broken drum switch. One of these days I'll replace the drum switch like I should have done to begin with.

BTW, the EV has a pot built into the control panel, so if you can mount the EV within reach of the mill, that'll take care of your speed control. Otherwise, it's no big deal to run a remote pot.

The EV "enclosure" is not very shop-friendly. You'll definitely want to shield it from coolant and flying chips, and provide some support for the wiring -- yet you can't block the air flow to the VFD.

06-25-2009, 10:47 AM
WHEN you add in a remote speed pot.. well... every vfd I have worked on in the last fifteen years requires it to be programmed into the "keypad"...

Some vfd's the keypad is optional.. Most is standard.
You need to go through and enter in the horsepower/amps of the motor.. and the "start time" and decel time.. it seems like a good idea to "plug" the motor to a stop fast like.. but actually is rough on the vfd.. it applied a reverse rotation to stop the motor building a lot of heat..

Let is coast down.. make the decel two or more seconds.

Accell is the same way..

As with anything else that is in "CHINGLISH" speak you must decipher the manual into a understandable format.. go through sitting in a comfortable chair and make notes on setup.. external controls, max hz, accel, decel, and amps.
THE amps is the most important.. it protects your motor if it starts being worked too hard.. you will probably bypass the original heater styled overloads on the machine.

There was one inverter, it could not accept a external foot switch.. In all my years.. I got aggravated and had to walk off.. later as I suspected it was a software problem he had to have a new board sent from the factory.. someone never using anything but the keypad on the face of the inverter would have never known. It sure made my 30+years as a electrician seem to "them" like I was a fool.. I could not fix it on the spot..

06-25-2009, 11:00 AM
I have retained the drum switch on both my lathes and added one to my mill - all with the VFD external switching option. I just feel more comfortable with them. And, they are fairly easy to wire up.

I guess it comes down to personal preferences.

Good luck.


06-25-2009, 12:46 PM
i just stuck the vfd on the side of the mill head,(laziness, needed to get up and running) no problems so far.

if you are going to use the aux. control strip, you can put sart stop switches all over the place,
i did a drill press a while back with a vfd, i put a start stop at eye level, and a large stop switch were i could get it with my foot.

my small boxford lathe , has a vfd, i used the existing controls, it also has a
foot operated stop, i am going to get the mill set up this way one day.

06-25-2009, 01:16 PM
The EV "enclosure" is not very shop-friendly. You'll definitely want to shield it from coolant and flying chips, and provide some support for the wiring -- yet you can't block the air flow to the VFD.

I figured as much, which is why I intend to mount it on the wall a few feet away from the mill. I think I will try wiring up the drum swith as one of my external controls as every mill I've ever used has had one and it is pretty instinctive to reach for it.

@ David: I agree that setting a fast decel time will be unnecessarily rough on the VFD and I don't plan to use that feature. I pretty much always instinctively whack the brake lever on the mill after I've switched off the motor anyways.

06-25-2009, 01:16 PM
VFD installs: I'm big into chip-proof and robust installs. I've posted these pics before so here's just the links:

My Bridgeport : http://s238.photobucket.com/albums/ff150/lakeside53/BP%20VFD/

My Lathe : http://s238.photobucket.com/albums/ff150/lakeside53/V10%20VFD%20project/

And now... my Brown and Sharpe Surface grinder (twin VFD's) - work in progress. Original 1957 electrical box (cleaned up and painted). The transformer in the upper right (115v for contactor control voltage and fan) is also original. You need a fan (upper center on right) to remove the heat from the box. I put the exit (top) and inlet (bottom) on the rear with hoods to deflect any coolant etc. For service (and initial assembly), the entire internal assy is on a separate mount plate and can be removed. The front panel detaches with all switches via the molex connector and has a "gasket" to prevent water/coolant leaks.




06-25-2009, 01:32 PM
@ David: I agree that setting a fast decel time will be unnecessarily rough on the VFD and I don't plan to use that feature. I pretty much always instinctively whack the brake lever on the mill after I've switched off the motor anyways.

If you're going to use the brake lever, you'll need to program the VFD to "free wheel" down, not decelerate, or you'll trip it. Decelerate means applying power with decreasing frequency over time. If you brake during that time, the vfd/motor current will rise rapidly and the VFD will trip. Also hard on the brake. Freewheel or coast or whatever your VFD calls it is just 'kill the driver power".

Also, braking isn't tough on the VFD at all. There is very little you can do (other than incorrect wiring) to mess up a modern vfd - it has everything required to protect itself. DC injection (if enabled) into the motor can cause a temperature rise, and although it's something you need to be aware of, rarely causes issues on a mill. Worried? Put a thermistor in the motor and connect it to the VFD. if you're going to run the motor at low speeds, ditch the motor fan and install a 5 inch computer fan on top.

I set mine (on the mill) to 1.5 second accelerate, and 1 second braking - I have a braking resistor installed - without it you would not be able to brake fast from speed anyhow. I never use the manual brake unless I'm changing a tool. Braking via the vfd is something you'll get to like, a lot;)

Tyro 001
06-25-2009, 10:59 PM
Where are you installing the drum switches? When I bought my Teco, the people at Factorymation didn't think I should wire in any switch downstream from the VFD as it could cut the power to the motor and fry the VFD.

Jim Shaper
06-25-2009, 11:02 PM
You wire the control circuit with the drum switch. The motor is wired directly to the VFD. This is what I did with my lathe so the handle still controls the on/off and direction.

06-26-2009, 09:31 AM
My mill's VFD has no braking resistor, and I set the decel time to 5 secs to avoid tripping. I use the spindle brake only for changing collets. The unit itself is housed in a NEMA enclosure on the wall, and I use the remote control panel to control the mill. I removed the OEM switch and wired the VFD directly to the motor.

06-26-2009, 12:16 PM
i dont think you should wire controls to the 3 phase output from vfd,
instead you use the low voltage out put from the aux. strip on the vfd to connect your existing controls, should be spelled out in the manual