Re: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?

The problem is that with a variac you could potentially have a hot case
with out the fuse blowing. Just to keep your power supply isolated run the
output of the variac through a 1;1 transformer that is rated for the power
you need. This will give you the isolation you need with the the ability
to adjust the variac. Or rebuild the power supply to take all of the
design factors into consideration and not use a variac in you power supply.


Dan in Auburn

On Fri, Jan 13, 2012 at 8:29 PM, Phil@Yahoo <yahoo@...> wrote:

> **
>
>
> The potential danger in using a variac is that one side of the output is
> connected directly to the power source and, if you turn it all the way up,
> both sides are. So it becomes as dangerous as, say, a wire plugged into
> the
> wall socket. 110v residential power is typically one leg of a three-phase
> line from a Y-connected three-phase transformer. Generally the common leg
> of
> the three-phase line is in fact connected to earth ground, so one side of
> your 110v line is at ground potential. This is where we get the
> hot-wire/ground-wire terminology. So if you connect the common side of
> your
> variac to the ground side of the 110v line, and use the variac to reduce
> the
> line voltage, and bear these facts in mind, it is in fact no more
> dangerous
> than an isolated transformer. On the other hand if you don't know what
> you're doing it probably is more dangerous than an isolated transformer.
> But
> in that case, working with high voltage is dangerous no matter what you
> do.
> I suspect that the argument arises from the tendency for people who don't
> know what they're doing to assume everyone doesn't know what they're
> doing,
> and that to be safe we all should live with the same restrictions as the
> least competent. Another name for that reasoning is socialism, but that
> would be OT (wink wink nudge nudge.)
>
> So the moral of the story is, if you know what you're doing, you can be as
> safe as you choose to be.
>
> --Phil M.
>
>
> ----- Original Message -----
> From: "Andy Wander" <awander@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Friday, January 13, 2012 7:24 PM
> Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?
>
> > Hi Mike:
> >
> > I had a big argument/discussion about this very subject on one of these
> > message boards a few years back. It was basically me against everyone
> > else(who cared to comment).
> >
> > The gist of the explanation that I got was, "There's no galvanic
> > isolation", and "If you can't see that it's dangerous, I'm not going to
> > bother telling you why". People got very upset and angry at me, but
> nobody
> > seemed to be able to explain the danger.
> >
> > I have since looked at it a lot more, and I believe that the danger
> exists
> > because even a big transformer, if it has isolated windings, will tend
> to
> > limit the current that can flow through it, and so the case where there
> is
> > a direct connection to the power line "could" be more dangerous. But I
> > have still not seen a good, easily understood explanation.
> >
> >
> >
> > Andy Wander
> >
> > -----Original Message-----
> > From: CAD_CAM_EDM_DRO@yahoogroups.com
> > [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of mikep_95133
> > Sent: Friday, January 13, 2012 9:02 PM
> > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > Subject: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?
> >
> > Understood. So why do I need the power supply isolated? Everything in
> the
> > shop is grounded. The floor is concrete.
> >
> > When I first set this variac up, I took a voltmeter and probed from the
> > mill to everything within 6 feet and there was no voltage delta.
> >
> > Mike
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "picengraver" <picengrave@...>
> > wrote:
> >>
> >> Mike,
> >> A Variac's output is NOT isolated from it's input as standard
> >> transformers are. The risk of electrocution is high if one comes into
> >> contact with the output voltage and earth ground (floor, water piping,
> >> machine frame, etc.) Why risk someone's life?
> >>
> >> Regards,
> >> John Champlain
> >> www.picengrave.com
> >>
> >> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "mikep_95133" <mikep_95133@>
> >> wrote:
> >> >
> >> > Really? How so? It's only been a part of the system for years now.
> >> >
> >> > Mike
> >> >
> >> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dan Mauch" <dmauch@> wrote:
> >> > >
> >> > > Using a variac isn't safe. You really shouldn't use one with your
> >> > > servo
> >> > > system.
> >> > >
> >> > >
> >> > >
> >> > >
> >> > >
> >> > >
> >> > >
> >> > > Dan Mauch
> >> > >
> >> > > www.camtronics-cnc.com
> >> > >
> >> > > dmauch@
> >> > >
> >> > > Stepper and servo motors
> >> > >
> >> > > Kits, assembled and custom CNC using Gecko products.
> >> > >
> >> > >
> >> > >
> >> > >
> >> > >
> >> > > [Non-text portions of this message have been removed]
> >> > >
> >> >
> >>
> >
> >
> >
> >
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> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
> > aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach
> it
> > if you have trouble.
> > http://www.metalworking.com/news_servers.html
> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
> > sister site to the CCED group, as many of the same members are there,
> for
> > OT subjects, that are not allowed on the CCED list.
> >
> > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
> > DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> > bill
> > List Mom
> > List Owner
> >
> > Yahoo! Groups Links
> >
> >
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>
>


[Non-text portions of this message have been removed]