Wiring A Vfd To A Momentary Pushbutton Switch (update)

[Eddyde]

I just installed a Teco L510 VFD to run my mill. I wanted to use a momentary pushbutton "Forward", "Reverse" and "Stop" switch, However, the VFD requires the switch status to be constant, so I designed a simple circuit using two latching DPDT relays to achieve the correct interface. I also made it so the latched relay will shunt the other relay, thus preventing the switch status from being in "run forward" and "run reverse" simultaneously. The VFD does have protection against that condition, but I figured it easy enough to do and it allows me to possibly attach other things to the circuit such as indicator lights etc.
I will be adding other features in the near future. One I am considering is a switch on the Hi/Lo Shift lever that would swap the forward and reverse relays so the directional pushbuttons will always be correct.
I attached photos/video of the schematic (please excuse the sloppy drawing) breadboard testing, final build and installation.

 

[kd4gij]

nice job

 

[derf]

What is the advantage of a momentary switch?

 

[Eddyde]

What is the advantage of a momentary switch?

Well for me the main advantage is circumstantial, I had a couple of those NOS switches on hand. I also had all the other components so I didn't have to buy, and wait (the worse part) for, any additional items. I also feel the flush pushbuttons are less prone to accidental actuation or breakage (In fact, the original switch on the machine was broken). The other is I guess personal preference, I like the action and retro industrial look.

 

[gr8legs]

Actually, at least with the Teco drive I have, you can set the parameters to use momentary switches by appropriately setting the VFD system parameters.

I have a TECO MA7200 drive, so other Teco drives may vary but I'd think the control circuitry is the same.

To implement drive control with momentary contact switches get into program mode and click to System Parameter S-25. The factory default of 01 sets terminals 1 and 2 as 'sustained contact forward-reverse'.

Changing the S-25 parameter to 00 makes it momentary contact. Your 'Stop' pushbutton (N.O. contacts) then connects from 24VG (the same 'source' as for the 'forward' and 'reverse' ) to Terminal 5 which is designated a "Multi Function Contact Input". The supplied documentation is rather poor. You can implement any of the functions on any of the multi-function inputs by selecting the appropriate S- register 25 through 28.

Standard industrial 3-button switches use an N.C. switch for the 'Stop" button so that has to be reversed. There is a way to keep the same NC switch configuration but I don't want to unnecessarily confuse the issue.

 

[Eddyde]

Thanks gr8legs, for the suggestion.
However I don't think it will work on this model, I went through the entire manual,several times, searching for a way to change the switch parameters to momentary, because I thought "there must be a way". The only thing I found was a way to change the switch status from NO to NC... It only gives three choices; "Run Forward-Stop, Run Reverse-Stop" 2 switches. (this is the one I used)
"Run-Stop, Forward-Reverse" 2 switches.
and "Run, Stop, Forward-Reverse" 3 switches.
I cannot find reference to the parameter you mentioned in the manual either, Perhaps I'm still missing something? I would like to do away with the relay circuit, even though it was fun to build. I still have to wire my drill press to a VFD...

 

[gr8legs]

Yeah, your control is way different from mine and reading through the manual online I can't see a way to do it either. Sorry for the bum steer!

But at least it got me to looking at my Teco VFD control and figuring out how to make it work with 3 buttons. I like that a lot better.

Stu

 

[KMoffett]

I'm in the process of adding an auxiliary water-cooled, high-speed, VFD spindle to my mill. I wanted a box remote from the VFD to control the spindle. The box will have push-buttons for Power-ON, E-Stop, RUN, STOP, and a pot for the Speed.
Power-ON is separate from the mill's.
E-Stop is linked to both the VFD and the mill's E-Stop.
RUN is forward only, because I can never see using the spindle in reverse.
So, this is what I've come up with so far (attached). I'm looking for switches for Power-ON, RUN, and STOP that I like.

Ken

 

[JimDawson]

Looks good!

 

[Eddyde]

Ken, It looks like a nice solid setup!
Thanks, Your schematic reminded to point out that I omitted the diodes across the relay coils in my circuit. I figured they weren't necessary for such small low power relays, it's all analog, no logic signals in out of the VFD and the circuit is only temporary till I do the CNC conversion. But anyone using larger DC relays or building for keeps should add them.