Erratic behavior from VFD

M

mikegt4

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I have a TECO VFD on my Millrite that has exhibited erratic behavior for the 15 years that I have owned this machine. It isn't a big problem, just annoying.

I use the original F-OFF-R drum switch to control the TECO (EV series 201-H1). Sometimes when I switch from OFF to FWD the spindle shutters and slowly moves about 30* in the proper direction then reverses and slowly runs backwards. The Millrite motor (GE 1hp 3ph 220V) doesn't sound very happy when that happens. If I immediately move the switch to OFF then back to FWD the motor will usually operate normally, sometimes it takes 2 or 3 tries. Once I switch the motor off/on several times during the course of milling a part the problem seems to go away.

Being electrically challenged I am clueless but I have tried different "acceleration time" settings in the TECO with no change in the problem. Reverse rotation always works as it is suppose to. I also have a TECO EV series vfd on my Weiler Matador lathe, it works flawlessly. Could it be the contacts in the drum switch? Any suggestions?
 
It should be east to check out the contacts on the drum switch, a bit of sanding / filing should take care of any problem there, otherwise, electronics are as much a mystery to me as you.
 
Is the switch wired to the low voltage inputs on the VFD?

You might try removing that switch and using the panel on the VFD if there is one.

I had some odd behavior on a Bridgeport motor that was fixed by changing a parameter labeled "Rated motor frequency". The default was 400Hz. Dropping it to 60hz helped significantly. It's not the speed frequency, I think it has something to do with the internal switching frequency. My newer grinder motor didn't need it adjusted.
 
I'd check the drum switch. They're meant to carry high voltage and current, probably not making good contact and the low voltage control signal isn't going to arc the contacts closed. Have a similar problem with the on/off push buttons on my radial arm drill.

Greg
 
Agree with Greg, could be contact resistance or contact bounce causing your problems- If the wires to the drum switch are long and unshielded that may also be a factor
I guess the simplest test would be to substitute a small electronic-type toggle switch for the drum switch and try it out for a while, see if the problem goes away.
-Mark
 
by the symptoms described, i would infer that the contacts in the drum switch have degraded or otherwise not engaging properly

a quick fix would be to run the switch opposite and swap 2 of the motor wires to reverse the direction of the motor
it would involve retraining yourself to switch the drum in the opposite direction for forward operation
but you'd only have the problem in the reverse direction now
or you could buy a new drum switch after reconnaissance deemed necessary
 
Thanks for the suggestions. The mill is 25 miles away so the next time I am there I will look at the drum switch.
 
What you are describing is what happens if you use the wrong motor voltage or speed settings in the VFD. What speed is your motor? I believe mine has the 900 rpm motor, I think they supplied a 1200 rpm motor as well on some models. Make sure in the motor data section that the entries there match your motor data plate. Also, if it is a dual voltage motor, you need to make sure you are wired for the correct voltage at the motor. The proper ratio of voltage to speed is important to the motor and if it is too far off, will give erratic performance.

Are you using the drum switch on the output of the VFD to the motor, or as control inputs into the VFD to control the direction and the VFD is wired directly to the motor? If the contacts are dirty as already mentioned, the VFD might not be getting a consistent run signal from the switch, but if you have the drum switch on the output of the VFD and you are trying to control forward and reverse that way, that needs to be changed immediately, the VFD cannot be operated that way and you could have damaged it.
 
I run one of my Bridgeport mills with the VFD output connected to the drum switch. I do not change the drum switch while the VFD is energized.
 
If you switch when it is deenergized, then you should be fine. How are you stopping and starting it?
 
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