Thread: Two GMFs and one VFD

Over the weekend I got a really good deal I could not refuse on another GMF 1HP 3P grinder and am now looking at putting my small multitool Linisher onto that grinder as well as making it variable speed.

One thing I did not want to do was fork out for yet another VFD
but
its proposed next door neighbor will be this identical grinder


So I thought, why not use the same VFD with a suitable cross over 3P switch between the two grinders.
Now because of the some individuals who occasionally use my workshop I won't feel comfortable unless there is some sort of lock that prevents switching the cross over while the VFD is running a grinder.

I have in the past proposed using a manual cross over switch placed inside a box, the inside of which is only accessible when the output of the VFD is off.
I was thinking of using a simple 12V door door latching solenoid to lock the door, and the lock is activated by a DPDT switch with the other side activating the VFD.
VFD ON - door locked

Maybe there is some sort of 3P switch that does this already but I expect that it will be pretty ex..

Any other suggestions welcomed.

Originally Posted by BobL

I have in the past proposed using a manual cross over switch placed inside a box, the inside of which is only accessible when the output of the VFD is off.
I was thinking of using a simple 12V door door latching solenoid to lock the door, and the lock is activated by a DPDT switch with the other side activating the VFD.
VFD ON - door locked

Maybe there is some sort of 3P switch that does this already but I expect that it will be pretty ex..

Any other suggestions welcomed.

If you have the changeover switch in a box you could put a micro switch on the door so when it is opened the drive is tripped.
That way the drive output power will be off before the motor connections are changed over.

Close door. Restart drive.

Hi Bob,

Do you coasting stop or braking?


Stuart

Originally Posted by GuzziJohn

If you have the changeover switch in a box you could put a micro switch on the door so when it is opened the drive is tripped.
That way the drive output power will be off before the motor connections are changed over.

Close door. Restart drive.

I like it!

Yes I use coasting stop, decelerated stop undoes the wheels.

Originally Posted by BobL

I like it!

Whats the vsd going to do if you just lift the latch and let it drop agian? I've not tried it on a huanyang.

What are your plans re start switch/switches?

Stuart

Originally Posted by Stustoys

Whats the vsd going to do if you just lift the latch and let it drop agian? I've not tried it on a huanyang.

Same as flicking a remote on/off switch, I do that quite often on my DP.

What are your plans re start switch/switches?
Stuart

Just one of these - probably with the same REE magnet on the back so I can move the switch to the front of each grinder as required.

Originally Posted by BobL

Same a flicking a remote on/off switch, I do that quite often on my DP.

Well thats good, if I recall correctly the Teco doesn't take to well to that sort of thing.

Originally Posted by BobL

Just one of these - probably with the same REE magnet on the back so I can move the switch to the front of each grinder as required.

Then you wont need my ummmm rather complicated setup then

Stuart

Originally Posted by Stustoys

Well thats good, if I recall correctly the Teco doesn't take to well to that sort of thing.

With the HYs on my DP and WW lathe I used light weight small switches and with the reverse on the same switch
Because the switches are light weight I sometimes flipped the switch to off and through into reverse!
Doing this the VFD/motor goes though its normal deceleration stage and then starts the reverse acc stage.
Then I realise, hey its going in reverse so I go to turn it off and I end up pushing it into few again - no problem.
Eventually I realised I had to be a bit more careful when switching these machines.
That's why I have now gone for more positive acting switches but I'm now used to the lightweight switches and although it still happens occasionally it doesn't appear to have harmed them

Then you wont need my ummmm rather complicated setup then
Stuart

Still wouldn't mind hearing it - could be useful somewhere else?

Originally Posted by BobL

Doing this the VFD/motor goes though its normal deceleration stage and then starts the reverse acc stage.

Yes, but doesn't sound like you're using coasting stop.

Originally Posted by BobL

Still wouldn't mind hear it - could be useful somewhere else?

Knock yourself out
There isn't as much detail in the thread as I thought.
To be honest I've forgotten exactly how its wired. The switch uses a 4th pole to switch control of the VSD from one machine to the other.
I think there is something thing in the wiring to stop the machines controls latching on(or maybe they wont turn on at all) unless the controls are plugged into the vsd enclosure.
http://www.woodworkforums.com/showth...ight=enclosure

Originally Posted by Stustoys

Yes, but doesn't sound like you're using coasting stop.

Ah - you mean am I toggling back and forth on a machine with a coasting stop.
I haven't tried that - the machines with a coasting stop are 2 grinders and the BS.
I will try it out and report back.

Knock yourself out
There isn't as much detail in the thread as I thought.
To be honest I've forgotten exactly how its wired. The switch uses a 4th pole to switch control of the VSD from one machine to the other.
I think there is something thing in the wiring to stop the machines controls latching on(or maybe they wont turn on at all) unless the controls are plugged into the vsd enclosure.
http://www.woodworkforums.com/showth...ight=enclosure

It's way past my bedtime and I have the flu so I will look through that thread tomorrow.

If you want a positive interlock, you can get 3phase motor contactors that have mechanical interlocks, when one is energized the other is locked out.

Then you can wire the on/off switch at each grinder to pull in the appropriate contactor, no other changes required.

Originally Posted by Stustoys

Knock yourself out
There isn't as much detail in the thread as I thought.
To be honest I've forgotten exactly how its wired. The switch uses a 4th pole to switch control of the VSD from one machine to the other.
I think there is something thing in the wiring to stop the machines controls latching on(or maybe they wont turn on at all) unless the controls are plugged into the vsd enclosure.
http://www.woodworkforums.com/showth...ight=enclosure

Ah yes I remember that thread. My requirements are almost trivial compared to yours because the two machines are identical so only one set of controls are needed.

Originally Posted by RayG

If you want a positive interlock, you can get 3phase motor contactors that have mechanical interlocks, when one is energized the other is locked out.

Then you can wire the on/off switch at each grinder to pull in the appropriate contactor, no other changes required.

Cannot Electrical interlocks do same?...ie isnt mechanical just a sureity to electrical

Originally Posted by BobL

Ah - you mean am I toggling back and forth on a machine with a coasting stop.
I haven't tried that - the machines with a coasting stop are 2 grinders and the BS.
I will try it out and report back.

I did that - no problems, it resumes its acceleration from whatever RPM it happens to be doing.

Hi Bob,
If you connect the VFD output to the line side of a contactor on each grinder (connected in parallel) and then electrically interlock the contactors so only one can operate at a time, you are all sorted, no need for a changeover switch.
When grinder one is running, grinder two cannot be started and vice visa.
If you don't have contactors with the required spare contacts, you could probably add relays to achieve the desired result.
When I do things like that I tend to use whatever I've got about the place, so sometimes it can end up a bit unnecessarily complicated.