Re: VFD question

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Marv Frankel"
><Dcdziner@p...> wrote:
> 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
>

That's OK Marv,
It's just that I know some people seem to think the output from a VFD
is juat like from a convertor and can be switched at will.

I did post another reply after my last one but it disappeared in the
Yahoo fog or the mist's of censorship.
I think I'll carry this subject over to the DIY-CNC list as it's
really getting OT for this list.

message timed at 13.07 GMT

John S.

> --- 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