Thread: Two GMFs and one VFD

Originally Posted by Michael G

With my "take no prisoners" attitude to electrons. I would have done it like this -

Attachment 351107

A No Volt Switch could be added but the VFDs that I have can do that anyway I think. The door switch will just be a power interuption.

Michael

You've "lost one prisoner" with that circuit, and maybe it's not all that VFD or user friendly for my situation.

The "prisoner" is the zero XO switch position. - with your circuit someone could accidentally set the XO to zero - i.e. no grinder connected, close the door and start the VFD. The simplest way around that is to put Connection 4 on the XO in series with the door. I have thought of all these methods but have not gone that way because of the following - possibly splitting hairs a bit on some of these things but that's just me.

From the way I use the existing grinders there will be a fair bit of switching between the two. I don't like repeatedly powering VFDs up and down unnecessarily and as they take time to power up and down, the more I do it the longer they seem to take. Usually I turn the VFDs on as I need them and only turn them off if there is little likelihood of me using that machine again that session. The others on oft used machines like grinders, drill press etc stay on and get turned off at the end of the session.

In this specific instance the VFD is going to be on a steel post behind and above the two grinders, so no reaching over the grinders to control the VFD. This means it need a remote control anyway so an external on/off switch and speed control. I figured putting the door switch into that circuit saves the power cycling of the VFD and the extra NVS in the control circuit is my attempt at B&B.

Any large (preferably mushroom type) push button switch has to be a better emergency switch than relying on the little off switches used on most VFDs. Two of the machines in my shed that have no remote switches are the Hercus lathe and the linisher. I don't know how many times I have thought I have pushed the off switches on those and have not managed to turn the VFDs off. On Cheap VFDs I reckon the little pads, or at least the plastic on top of the switches are eventually gonna wear through.

I did a bit more work on the shared VFD across 2 grinders over the last few days and got it to the point where I could start assembling things this morning.

I decided to install the grinders on my tri-grinder stand, so step one was to add a swivel base for the VFD in the centre and on top of the existing stand
The white washer is teflon


Then a length of 40 x 40 x 2.5 SHS slides over the top and is held in position with the screw knob.
This setup allows the stand to be rotated to be in front of the required grinder if required.


VFD, cross over switch and other controls bolted onto a piece of ally plate which is bolted onto the central post.


Here is close up of the controls.
XO is where the Xover switch is supposed to be
S1 is the main power switch - also acts as a safety switch
S2 is in series with the door switch in the XO switch box, the zero position in the XO switch, and a relay under S2.
When all 4 of these are closed S3 becomes available to start/stop the VFD
S4 is just the speed pot.


The X0 switch was an absolute bear to wire up because the plastic boxes I used to house the switch in were a tad too small to hold 3 x 3 phase cables plus a control cable for the door switch so everything had to be squeezed in rather too tight for my liking.

Before I turned everything on I checked the continuity of everything and it was at this point I noticed the contact resistance of the XO switch was all over the place.
Cleaned with contact cleaner several tines - no change.

Then I made the fatal mistake of opening up the switch and when I finally had it apart I realised the permutations of reassembly was going to be very tricky AND the springs (there are around 20 of them) were going to be bastards to refit.


My level of embarrassment eased when I checked out the contacts and found that they are pretty corroded/pitted anyway so I will ditch this switch and look for a replacement.

What an out and out PITA - I reconnected one of the grinders up to the VFD to least have that one available.

Now the VFD wouldn't work at all in remote mode. After lots of futzing, changing parameters etc, I remembered that the jumper that switches between the VFD pot and the external pot had been a bear to remove - when I looked closely at it I could see what looked like some (hot) glue residue on it and also on the pins on the VFD - I reckon it had been glued in place. So I scraped the glue of the pins and used a new jumper and all was then working.

This has been a lot of trouble and I wonder if it has really been worth it.
I guess I have made some progress because the rest of the controls are now fully tested and they work well.

I was thinking of getting a 3 way cross over so all 3 of the grinders on the trigrinder stand could eventually be run off the single VFD.

Originally Posted by BobL

This has been a lot of trouble and I wonder if it has really been worth it.

It was a challenge, and if you are anything like me you can't let a challenge go unbeaten.

Originally Posted by BobL

I was thinking of getting a 3 way cross over so all 3 of the grinders on the trigrinder stand could eventually be run off the single VFD.

Hell Bob you're a terror for punishment

Wow Bob, wish you lived around the corner from me. Id really enjoy oicking your brain

Dave TTC
Turning Wood Into Art

Originally Posted by DaveTTC

Wow Bob, wish you lived around the corner from me. Id really enjoy oicking your brain

Dave TTC
Turning Wood Into Art

You will have to do it remotely Dave.

Ok a few questions. And yes much of this (now that i have read the entire thread) goes way over my head.

1) does your lazy Susan have a lock so which ever grinder you are using does not move while in use

2) can your vfd be left 'switched on' while not connected to or powering anything?

3) if yes to the above can you switch it to a grinder without having to turn it off first?

4) can you just disconect your grinder from the vfd (while running) withiut any issue.

I have some thoughts as to various solutions pending the answers above. You may have answered some of these already but i have faiked to understand the issues.

Also what is a bs? You referred to a bs in one of your posts.

Dave TTC
Turning Wood Into Art

Originally Posted by DaveTTC

Ok a few questions. And yes much of this (now that i have read the entire thread) goes way over my head.

1) does your lazy Susan have a lock so which ever grinder you are using does not move while in use

Yes it does - look here http://www.woodworkforums.com/showth...16#post1484716

2) can your vfd be left 'switched on' while not connected to or powering anything?

The sequence is turn on mains switch to VFD and wait about ~3 seconds for it to boot up.
This wait time is small but quite irritating so I tend to e.g. turn the VFD on when I need to use each machine and then leave the VFD on for the rest of the day as they consume very little power.
Each machine motor is then started via the switches on the VFD, or remote wired switches.
Like computers, power the VFDs constantly up and down is not good for them,
Most VFDs have rows of little terminals that allow for wired remote switches t turn the motor on/off./fwd/backward/jog and connections for multiple speeds etc

3) if yes to the above can you switch it to a grinder without having to turn it off first?

Yes - I could (except my cross over switch is buggered and I've ordered a new one)

4) can you just disconect your grinder from the vfd (while running) withiut any issue.

Yes provided the motor is not running.otherwise this will damage the VFD.

I have some thoughts as to various solutions pending the answers above. You may have answered some of these already but i have faiked to understand the

You're thinking one VFD and connect it up to multiple machines.
Sorry - no good.

Some of your motors will be 1440 and others will be 2850 rpm and some might be something else. Some will draw high currents others will draw low currents, some machines can do high speed others cannot.
Each VFD needs to be programmed with all this info so when you switch between different machines/motors all this info needed to be entered again.
On fancier VFDs you can pre-program a number of setups and recall these specific programs later - sounds good, real good, BUT it is VERY EASY TO STUFF IT UP because the VFD cannot check that it really is connected to the motor for that program.
Believe me you do not want to be flipping between programs and waiting for the parameters to reset etc when all you want to do is touch up a drill bit.
You just want to turn it on and go.

That is why dedicated VFDs are a lot more user friendly. Like I said in my previous post, the two identical grinders I'm running off the one VFD should be a dead simple operation but setting up all the interlocks and switches makes it an out and out PITA even for someone like me where I enjoy farting around with these things just to see if I can get it working.

Also what is a bs? You referred to a bs in one of your posts.

Bands saw - this onehttp://www.woodworkforums.com/showthread.php?t=195900

Ok this is an idea for your set up. Ill try dot points. Let me know if it is viable or I'm on the right track.

You have vfd contacts near the arm of your grinder support, posibbly brushes.

The grinders have corresponding contacts that only contact when in the locked and user position.

The grinder is switched by its own switch off and on when locked in position.

There could be some kind of magnetic lock pin so that while under power or rotating the grinder can not be swung around.

Contacts on grinders could be a disk which make contact with brushes like in a motor. A continuous segemted disk all the way round your centre column which is only conductive in the range of the device in the locked position.

If your centre column wad like a goose neck it would bring the controls within range of use without need for remotes. Other option would be to have it under thenarms but set forward so in reachable spot.

Im not an electrician so dont know how viable these ideas are but thiught id put it out there

Dave TTC
Turning Wood Into Art

Originally Posted by DaveTTC

Ok this is an idea for your set up. Ill try dot points. Let me know if it is viable or I'm on the right track.
You have vfd contacts near the arm of your grinder support, posibbly brushes.
The grinders have corresponding contacts that only contact when in the locked and user position.
The grinder is switched by its own switch off and on when locked in position.
There could be some kind of magnetic lock pin so that while under power or rotating the grinder can not be swung around.
Contacts on grinders could be a disk which make contact with brushes like in a motor. A continuous segemted disk all the way round your centre column which is only conductive in the range of the device in the locked position..

It would take too long to go into specifics about all the problems with these suggestions but here are a couple of points.

The assumption that there is a specific "user" position that requires each grinder to be moved to that position is not the case . Moving the turntable is a bit of a pain and having to move the turntable to make electrical contact would be an extra nuisance. Mostly the turntable stays in one place with the two grinders I'm most likely to use facing outwards. The two most commonly used are the one with the CBN wheel and the grinder with the finisher on it. The grinder with the wire wheel and the coarse grit wheel usually sit at the back up against the wall. I move the turn table maybe only or twice a day. I also have a floor standing 10" pedestal grinder that runs off its own VFD

The other problem is the use of wipers or brushes. In VFD manuals they usually state there should be no contacts/wipers or switches between the VFD and the motor - there's just too much of a chance that one of those connections doesn't connect so well or at slightly different times and that could be the end of the VFD. I'm using one simple crossover switch protected by two interlocks and that is about as far as I'm prepared to go.

With regards location of switches at grinder level or below the grinder, these very dirty places, lots of grit and metal dust - the best place for switches and the VFD is definitely above the grinder.

Thankyou for the education. It has been interesting. I have much to learn

Dave TTC
Turning Wood Into Art

Originally Posted by DaveTTC

Thankyou for the education. It has been interesting.

No worries

I have much to learn

I think we all have much to learn

Originally Posted by BobL

I I'm using one simple crossover switch protected by two interlocks and that is about as far as I'm prepared to go.

Don't worry to much Bob, I've run a few of my VSD's with nothing corrected to the output. Vsd's didnt seem to care(or even notice), and no smoke was released.

How long and how often you can get away with this sort of behavior I have no idea

Stuart

Originally Posted by Stustoys

Don't worry to much Bob, I've run a few of my VSD's with nothing corrected to the output. Vsd's didnt seem to care(or even notice), and no smoke was released.

How long and how often you can get away with this sort of behavior I have no idea

Stuart

Yeah I've tried to start one a couple of times without the VFD being connected and it wouldn't start. Another time I started one where one of the phase connections on the motor wasn't tight and it got part way into the acceleration cycle and then shut down. I've never disconnected one while it was under load though.

Originally Posted by BobL

I've never disconnected one while it was under load though.

Oh yes, I have no plans to try that. I haven't even been game to try switching the coolant pump on/off with the main motor running, even thought the guy at Drives Direct says it will be fine.

Stuart

The new cross over switch arrived and has been installed.

Nothing much new to see really.
Here are the two GMFs running alternately off the one VFD with cross-over switch above.
I need to tidy up the cables a bit with some cable ties but there has to be some slack in the cables as the grinders can be moved back and forth and rotated on the tri-grinder arms.



The new switch is smaller than the old one and I had to chop the switch box around to fit the the old one so there is a bit of a gap around the new one)
The contact resistance of the new switch is all less than 0.2Ω, the old one was anywhere between 0.2 and 20 Ω.


How does it work - well read on.

All the interlocks work to turn the VFD ON-OFF switch as designed

BUT (near in mind the VFD is set to a coasting stop)

While testing, with the VFD running a grinder I opened the door to the X-over switch and yes the VFD did switch off and the grinder started to coast to a stop but I then immediately flipped the X-over switch door (now the VFD is connected to the other grinder and it started turning? I didn't wait to see what happened because I immediately cut the power to the VFD. So it's like there is some residual Potential/current in the VFD? Remember the VFD on-off switch had been switched into the OFF position.

I'm not that worried about it because I will wait unit the running grinder has stopped before switching but other folks who want to power more than one machine might run into some problems with this so this is why I thought it was worth posting.

[EDIT] It turns out I did not have the VFD programmed for a coasting stop, I had it on a 20s deceleration, so with a coasting stop it does not start the other grinder. However, the situation still applies if you have a decelerating stop.