Re: How many kva for a control transformer...?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "washcomp" <jeff@w...> wrote:

>
> Lance,
>
> I think you may be mixing metaphors.
>
> I can see seperating 60 hz A.C. from D.C. I can see isolating
> noisemakers (like vfd's) from things that can be affected. It is
> vital that proper attention be shown to shielding, transient
> suppression and proper grounding techniques. The is no reason that

I

> can think of to isolate single phase AC from 3 phase AC. Assuming
> your 3 phase feed comes from the same panel as your single phase,

I see your point. It's not so much separating 1ph from 3ph like I
said. It's more trying to isolate the VFD from the low voltage
control devices. What it boils down to is that I'm not an
electrician, and I've got little experience with electronics.
However, this application, and applications in the future will be put
to use in a real industrial environment. I'm trying to to learn to
do it the right way, the first time. Maybe after a few projects, I
will have learned enough to be able to build a solid, secure and
reliable control system that will be at home in an industrial
environment, or maybe not, but that is my goal. Fundamentals like
shielding, transient suppresion and proper grounding techniques are
exactly where I'm lacking. Because I don't know better, I guess I
feel like I need to separate/isolate everything.

Jon

> is right, why not use a 110v circuit from the same panel (can be
> pulled in same conduit as three phase) instead of adding the
> complexity, heat losses, expense and "real estate" of an additional
> transformer?

Another good point, as I've got 2x 36 x 24 enclosures, I've got
plenty of room. However, 2x 1 kva transformers are huge, and heavy,
and eat up alot of space.

>
> I would put a DECENT surge suppressor/EMI filter on where the 110
> feed comes in (I use Corcom filters, then a Tripplite Isobar on
> mine). This also helps cut down on "backfed" crap from the VFD
> (loads of filtering and transient suppression on that as well).
>
> Just because you CAN put a transformer in, doesn't mean you have to
> <G>
>
> Jeff
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lance Hopper"
> <snaggletto@c...> wrote:
> >
> > Hey,
> > Yes I know, but this machine will actually be in an industrial
> > environment. My goal is to have only the 220 3ph coming into the
> > machine as power. Therefore, all lower voltages will be derived
> from
> > the 220 3ph input power.
> >
> >
> > I've got 2x 1 kva transformers with 120 secondaries, and then
> I've
> > got a single 2 kva with 120 secondary.
> >
> > I've got 2 separate NEMA 3R enclosures. My plan is to mount

all

> > the 3ph in one and 1ph in the other. These will be physically
> > separated on the machine, about a 5 ft separation.
> >
> > 1)... Being that the VFD is the big noise maker, should I mount
> the
> > control transformer(s) in the 3ph box with the VFD and run the

120

> > 1ph across to the 1ph enclosure?. Or should I run the 3ph across
> to
> > the 1ph enclosure and mount the control transformer(s) in the 1ph
> box?
> >
> >
> > Also note, there will be 120 back to the 3ph box for the

contactor

> > coils.
> >
> > 2)... Then there is the Digispeed, PWM to analog converter, which
> is
> > used to control the VFD. Somehow these low voltage control wires
> > will have to cross the ~5ft span to the 3ph box. Which would be
> more
> > noise tolerant, the PWM side or the analog output side? (IE

should

> > the Digispeed be mounted in the 1ph box with the breakout boards

or

> > in the 3ph box with the VFD it will control?)
> >
> >
> > Thanks for any info.
> >
> > > 36 V 10 A is only 360 VA. You can get 1700 VA out of a 15 A

120 V

> > > outlet.
> > >
> > > > Wouldn't it be beneficial, electrical isolation-wise, to

have

> > > >separate transformers supplying the servo drives and for the

PC

> > and
> > > >control components? Or, should I just go with one big
> transformer
> > to
> > > >power all the 120VAC components?
> > > >
> > > >
> > > >
> > > Possibly, but most computers, etc. are pretty tolerant of noisy
> > power.
> > > Actually, the VFD is the real culprit, the servo drives are

going

> > to be
> > > much more benign.
> > >
> > > Jon