Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: benha on March 23, 2016, 10:50:50 AM

Title: VFD Enable Question
Post by: benha on March 23, 2016, 10:50:50 AM

Apologies if this should be obvious.  I've tried searching but couldn't find what I was looking for.

I have a Fuji Frenic Mini VFD that I use to drive a spindle on my CNC router.  During normal operation, I control the speed of the spindle using the PWM circuit on a Gecko G540.  This includes "stopping" the spindle by running it all the way down to zero.  This has all worked fine.

By default, when the VFD is powered up it's in "Stop" mode and I need to hit the green "Run" button on the front of the VFD to enable it to accept input from the PWM circuit system.  In this case, "Run" means it's ready to accept PWM input, not necessarily that the spindle is spinning.  The display on the VFD blinks steadily in Stop mode and is solid in Run.  So my workflow is generally:  Turn on the machine controller; Turn on Mach; Energize the VFD; Hit "Run" on the VFD; Start making parts.  Sometimes, however, I forget to hit "Run" on the VFD and end up damaging work or breaking bits because the spindle doesn't start spinning before the tool hits the work.  It's annoying.  

The VFD has digital inputs for "FWD" and "REV" which, when a logic signal is applied, appear to be equivalent to pressing "Run" on the panel.  I'd like to set things up so that the when the charge pump is active to the G540, the FWD terminal on the VFD goes high.  Theoretically the VFD will then always be ready to accept input from a properly functioning Mach3.

First off:  Is this a bad idea?  It's entirely possible that I'm missing something and that I'd be shooting myself in the foot by doing this, or if there's a better / more industry standard way of accomplishing my goal.  Please do tell.

Second: I'm not sure how to set up Mach so that a G540 pin is always high when the charge pump is functioning properly.  Assuming the answer to the above is not "you're nuts", how do I do this?

Finally:  Assuming it makes sense to use an output pin to activate the FWD pin on the VFD, is there any reason I would need to run that through a relay, or can I just connect the output from the G540 directly to the logic input on the VFD?


Title: Re: VFD Enable Question
Post by: Davek0974 on March 23, 2016, 11:26:00 AM
I can't answer the G540 stuff as i have never used one, but stopping a VFD by reducing speed is not a good or safe option for me.

You are correct in that Mach3 should command a Start signal regardless of the speed setting, this is how my mini-mill works. The VFD is triggered by a little relay on the break-out board which in turn is operated by a pin on the outputs from Mach3. This is controlled by the M03 / M05 commands in my G-Code.

The VFD should start then ramp up to the set speed, at switch off it can either ramp-down, coast  to a stop or forcibly slow down using DC-braking.

Does the G540 not have any floating relay outputs?
Title: Re: VFD Enable Question
Post by: benha on March 23, 2016, 12:13:30 PM
Ah. Okay. Epiphany.

So the spindle relay signal could be mapped to one of the output pins, and then that could just go directly into the VFD's FWD digital input, couldn't it?  Presumably that relay control would then go high when Mach wanted the spindle to start, and go low at the end of a job / on an eStop / etc?

Given these are all logic connections I wouldn't actually need that signal to go through a relay I would think, right?

Title: Re: VFD Enable Question
Post by: Davek0974 on March 23, 2016, 03:27:50 PM
Yes spot on.

The relay is mapped to an output, that output is mapped in Mach3 ports&pins as the spindle, also in spindle setup i think, the relay normally-open contacts then go to the VFD.

It is possible to direct-connect but i would not, the relay provides excellent isolation between the VFD and in your case the Gecko, there is no drawback to having a relay in this position. To direct connect both signal levels must match or damage will occur.

Usually the VFD has inputs marked FOR, REV & a COM or maybe just numbers - you will need the manual, plus if you are currently using the front panel buttons you may have to alter the VFD parameters to accept remote start/stop - this should all be in the manual is usually easy to do.
Title: Re: VFD Enable Question
Post by: benha on March 23, 2016, 07:27:35 PM
Got it.  Yes.  On further inspection I do need a relay.  Actually, if I want to get fancy and support forward and reverse I guess I need two relays.  The VFD has its own logic voltage source that you route through a relay.  Easy peasy.