Re: VFD question

John,
I should have explained further that I do not start, stop, or
reverse the mill, with the original switch. The VFD is always shut
down first, which doesn't present a big problem, Because of the built-
in braking of the VFD, the machine stops pretty quickly.

Marv Frankel
Los Angeles


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "stevenson_engineers"
<john@s...> wrote:

> >--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Marv Frankel"
> ><Dcdziner@p...> wrote:
> > Guys,
> > The VFD I have feeding power to my Enco mill, is wired

directly

> > into the original switch, which has 2-speeds forward, and 2-

speeds

> >in
> > reverse. I hardly ever touch the speed controller on the VFD, and
> > this setup has been running like that for about 1 1/2 years.
> >
> > Marv Frankel
> > Los Angeles
> >
>
>
> This is a definte NO NO.
> The power to the motor MUST NOT be removed whilst the invertor is
> running. If you need to switch speed outside the invertor then you
> must stop it first then restart.
> It's like running a stereo without speakers and load resistors ,

the

> power has to go somewhere.
> All the makers books tell you this and they are right. I supply and
> fit around 20 new invertors every month to mixing machines.
> The failure rate is very very low, they either don't work out the

box

> or they fail because of motor / wiring problems.
>
> Reversing on a FVD is quite simply you feed a signal to the

terminal

> marked REV instead of the one marked FWD. Far less trouble than a
> three pole change over switch and a damn sight safer as the signal
> voltage is around 10 to 24v and 20 or so milliamps depending on

make

> of invertor.
> You can place a pendant style control anywhere you need it with
> start, stop, reverse, jog and speed control running off a simple
> length of multicore signal wire with no hazard problems.
>
> John S.
>
> John S.
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...>
> wrote:
> > >
> > >
> > > metlmunchr wrote:
> > >
> > > >Obviously if you're feeding in single phase power, the

reversing

> > > >starter would have to be on the leaving side of the VFD.

Where

> > > >should it be if you're feeding the VFD with 3 phase power?
> > > >
> > > >
> > > No, you don't need any reversing starter, and the VFD makers
> > strongly
> > > discourage using one. Any VFD can generate the 3-phases in
> forward
> > > or reverse sequence, thereby reversing the motor electronically.
> > >
> > > Most modern VFD's under 100 Hp don't care about the phase

sequence

> > > of the input power. They just turn it to DC, and then create

the

> 3-
> > phase
> > > output from that.
> > >
> > > Jon