Drum swith between VFD and Motor

[saabman]

I am reading conflicting info regarding placing a drum swith (reversing switch) between a VFD and the motor. I think CNC turnkey mills repurpose the original drum switch and add an E-Stop button. Some suggest that the VFD will create a voltage surge if the load is removed suddenly.

What is the collective wisdom? (I know that the VFD can reverse under PC control). My desire is to have a means of reversing when using a MPG.

Chris

[mactec54]

saabman

You can not have any Switching between the VFD & the Motor, the drum switch you are talking about is/has to be before the VFD, & is only used for a Power on / off switch

All your foward/ reverse is done with the VFD in manual or auto mode, Read up your manual you will see how to do what you want to do

[Al_The_Man]

I think CNC turnkey mills repurpose the original drum switch and add an E-Stop button. Some suggest that the VFD will create a voltage surge if the load is removed suddenly.

What is the collective wisdom? (I know that the VFD can reverse under PC control). My desire is to have a means of reversing when using a MPG.

Chris

It is not so much the load removal as if you inadvertently reverse the motor with the VFD in a run condition, which not only should not be done it is not necessary, you use the low level logic inputs for all control.
A contactor should be used on the incoming feed for E-Stop purposes. A Contactor N.O. auxiliary contact can be used to interlock with the VFD stop input.
Al.

[saabman]

In an IH control cabinet, the input to the VFD is taken right from the main power switch in the cabinet. So while not impossible it is impractical to put a contractor in the cabinet. However, I think that under mach control the speed controller relays can be used to turn off the VFD. So an E-Stop or limit trip will kill the VFD.

Can an IH turnkey user with VFD confirm wiring from the IH cabinet to the motor.

Chris

[SCzEngrgGroup]

Any decent VFD should be capable for reversing the motor electronically. If you put the drum switch between the VFD and motor, you MUST NEVER change the switch while the motor is turning, or you WILL blow up the VFD. I have the original drum switch for selecting High/Low motor speeds between the VFD and motor on my BP clone. It's been working fine for years, but, as I said, never, never, ever change the switch when the VFD is actually driving the motor.

Regards,
Ray L,

[tyler774]

Good info guys, thanks!

This is contrary to what I was told when I bought my turn key mill. Was told I could tap by using the quill and switching direction with the switch, ( OK to do as long as in Low 1 ).

That said, I did have to replace the VFD last winter, it stopped responding to signals from the computer, continued to work fine in manual mode though. Lucky enough to receive a replacement VFD free of charge.

Tyler