Re: VFD question

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Brian Botton <bbotton@a...>
wrote:

>
> > > VFDs *MUST* be permanently wired to a motor. If you turn one
> > > on without a motor you will probably damage something.
> >
> > Not true. Most if not all drives will do just fine if you run
> > them with no motor connected.
>
> Well, my manuls very explicity state never turn it on, much less
> press the run button, without a motor wired in. If your manual
> explicitly says this is okay, then I stand corrected. The 3 or 4
> different vendor's manuals I've looked at say always keep a motor
> connected.

If your manual says don't do it, then don't do it. I suspect
they are covering themselves - they want to be very sure you
don't switch a motor in or out while running.

> My lathe has a 5hp motor, which means a big, expensive VFD.

"Big" is relative. I design VFDs in the 200-1000HP range.
Medium is 50-100HP, anything less than 20HP is small <grin>.

> I spent close to $700 for one with the needed capacity. I want
> that thing to last forever and I'm not going to risk damaging it.

Can't blame you there.

I have run VFDs without motors many times. In fact I if I'm
suspicious about things and want to be sure it doesn't blow up
I run it with the motor disconnected first. But I didn't design
your VFD, and I agree that you should only do what the manual
tells you to do.

John Kasunich