Assistance finding a 3PDT rotary switch - Yup... 2 Grinders, 1 VFD

Erin Burke

Erin Burke

KnifeMaker...ish
Joined
May 19, 2003
Messages
1,330
Hi Guys,
As I mentioned in another thread, I'm in the process of adding a dedicated 9" disc grinder to my shop. I currently run my 2hp KMG off a KBAC-27D VFD. I bought another 2hp motor for my disc grinder and would like to install an ON-OFF-ON switch on the output of the VFD to toggle between the two motors.

In an old thread, I found where Salem used a 3PDT ON-ON toggle from McMaster-Carr (part #8001K41) to switch between machines... this looks like it would work, but I'd prefer to have an OFF position in the middle.

McMaster-Carr also lists a couple 3PDT ON-OFF-ON (part #8001K15 [set screws] or #8001K42 [quick disconnects]) which looks like it should work. The quick disconnect switch is much cheaper than the set screw version... but I want to make sure that it'll handle the motor load at 240V. I'll also need to buy a sealed switch box -- and probably a switch boot -- to protect it from grinding dust.

Has anyone else done this? What switch did you use? Where did you buy it?

Thanks in advance.

Erin
 
I personally use #7343K862

I don't want a dead position in the middle though.
I want the power to go somewhere.
Not sure if it's good or bad to have power out of a VFD running to nowhere, but I can't see a good reason to do it, so I don't.
 
My motors have a full load rating less than 7 amps. I could probably get away with a 15amp rated switch.

Fellhoelter said:
I personally use #7343K862

I don't want a dead position in the middle though.
I want the power to go somewhere.
Not sure if it's good or bad to have power out of a VFD running to nowhere, but I can't see a good reason to do it, so I don't.
Click to expand...

Brian... I hadn't thought of that. I can't imagine the VFD would have too much problem being disconnected from the load... but I could be wrong. My main concern was for accidentally hitting the switch while the VFD was running and momentarily paralleling the loads during the switching transition. I figured the OFF position in the middle would ensure that one load would clear before the other was connected.
Mind you, I would never intentionally flip the switch while the VFD was powered on… but I've been known to do stupid things when I'm not paying attention.
 
I've never even wondered if this was an issue but you guys talking about it brought this to mind-

I use my Teco FM50 VFD to power my surface grinder and do experience the VFD in the "ON" position with power going nowhere. This happens because the surface grinder has it's own on/off switch so I plug it in to the VFD and crank the VFD to 60 hrtz then flip the VFD on but the surface grinders switch remains in the off position until ready for use. This allows me to use the switch on the surface grinder with no need to fool with the VFD's controls.

The VFD's reaction to this situation when the SG is plugged in but in the off position- The digital readout on the VFD will "cycle" from zero to 60 and back continuously until the SG is switched on at which time it functions like normal. I haven't noticed any ill effects of this situation and I've used it quite a bit.

I can't say with certainty that it's not harmful to the VFD in any way but I haven't had any problems thus far.

Take care fellas- Josh
 
I used some 3PDT switches from Mouser rated at 30 amps and mounted them in a junction box. They're solid and work well. I tried to find rotary switches, but couldn't find anything I could afford. This one has gone up a bit since I ordered it.

--nathan
 
Thanks guys... good info. Sound's like I was basically on the right track.
Erin
 
A 2hp 9" disc sander?!? Dang Erin, that's going to be a beast! Me likey :)

I have a couple new 3ph motors, I guess I should have thought about this switch possibility rather than just being sad that I haven't bought any new VFD's yet eh? lol

Aren't you an electrical Engineer? You can do stuff like this behind your back with your eyes closed. ;) :D
 
Josh Dabney said:
I've never even wondered if this was an issue but you guys talking about it brought this to mind-

I use my Teco FM50 VFD to power my surface grinder and do experience the VFD in the "ON" position with power going nowhere. This happens because the surface grinder has it's own on/off switch so I plug it in to the VFD and crank the VFD to 60 hrtz then flip the VFD on but the surface grinders switch remains in the off position until ready for use. This allows me to use the switch on the surface grinder with no need to fool with the VFD's controls.

The VFD's reaction to this situation when the SG is plugged in but in the off position- The digital readout on the VFD will "cycle" from zero to 60 and back continuously until the SG is switched on at which time it functions like normal. I haven't noticed any ill effects of this situation and I've used it quite a bit.

I can't say with certainty that it's not harmful to the VFD in any way but I haven't had any problems thus far.

Take care fellas- Josh
Click to expand...
Good point, I actually do the same, with the same VFD.

Haven't even turned it off in months.

Mine does not do the cycling you speak of though.
 
NickWheeler said:
A 2hp 9" disc sander?!? Dang Erin, that's going to be a beast! Me likey :)

I have a couple new 3ph motors, I guess I should have thought about this switch possibility rather than just being sad that I haven't bought any new VFD's yet eh? lol

Aren't you an electrical Engineer? You can do stuff like this behind your back with your eyes closed. ;) :D
Click to expand...

There's a big difference between an electrical engineer and an electrician. ;) I know just enough to think that I know enough... :eek:

Yeah, my VFD is set up for 2hp output... it was cheaper to buy a 2hp motor (and not have to buy another VFD) than it was to buy a smaller motor w/ VFD. Nothing wrong with a big di$#. :p
 
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