01-23-2018, 09:31 PM
(01-23-2018, 06:00 PM)f350ca Wrote: Coming into this discussion late but I'll add some more confusion. Why would you retain the lathes original contactor to turn the VFD on and off. From what I was led to believe switching the power to the VFD off when its under load is really hard on them.
I'd wire a disconnect ahead of the VFD then turn the motor on and off using the VFD.
Greg, in my case I'm using my lathe's original contactor AS that disconnect ahead of my VFD. My lathe and mill are both wired on the same 240V circuit in my breaker panel. When I'm not working in the shop the breaker is turned off, killing all power to both machines. When I turn the breaker ON there is still no power to either machine with one exception. A single phase indicator on the lathe to let me know the breaker is turned on. It's a reminder for me to turn off the breaker before I leave the shop.
Pushing the start button on the lathe only latches the contactor to apply power into the VFD. It also lights up to let me know the VFD is now "hot". Starting and stopping the lathe motor itself is done with low voltage controls via the VFD control panel itself or the original lathe control lever, which was rewired for low voltage inputs to the VFD. The emergency stop button is only used when the lathe motor is NOT running - except in case of an emergency of course. That way if I am done using the lathe the stop switch simply turns off the power to the VFD. My disconnect. That also allows me to run my mill without having the lathe VFD running the whole time I'm using the mill, since they are both on the same 240V line power. Likewise I also have a manual disconnect going into my RPC that powers the mill.
As far as powering off the VFD while it's under load... if I'm getting caught up and wrapped around a lathe spindle, what happens to the VFD will be the LAST thing on my mind. Plus the stop button kills all power to the VFD to protect whoever has to come and rescue me or clean up the mess afterward.
Willie