Re: [CAD_CAM_EDM_DRO] SERIES BUCKING was Re: SeriesII Gecko210 voltage people use

Hi Paul,

A VARIAC is a tapped auto transformer, meaning a single winding
transformer, with a variable tap. The tap provides the "variable
voltage", but NO ISOLATION.

A "bucking" transformer is an additional step down transformer, that is
connected such that it's secondary (12V) is connected in series with the
main transformer's primary. This additional transformer can either be
connected in series aiding, or series opposing (bucking). We connect it
in "bucking" to SUBTRACT it's voltage (12V in this example) from the
available MAINS voltage. So a 120V mains would effectively look like
108 to the main transformer. The main transformer does it's job, and
the secondary voltage is lowered by the appropriate amount. so what was
88V out before, may now be 79V. The "bucking" transformer's secondary
current rating should be equal or greater then the primary current it
needs to buck.

HTH

Alan KM6VV


paul_norton2001 wrote:

>
> Hi Alan
> Have use Variacs many times and understand what you mean but what do
> you do with the primary of the "bucking" transformer to control the
> output of the main transformer?
>
> Many thanks, Paul
>
> -- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...> wrote:
> > Hi Lee,
> >
> > Yes, 88V is a little high. What you can do is find a 12V (or as
> > desired) filament transformer with a secondary current the same or
> > greater then the PRIMARY current needed by your transformer.
> Connect it
> > in SERIES BUCKING, and you can drop the resultant secondary voltage
> as
> > required. This sounds similar to what your "control transformers"
> might
> > have been doing! But simpler, smaller!
> >
> > Kinda like a "fixed" VARIAC!
> >
> > HTH
> >
> > Alan KM6VV
> >
> >
> > studleylee wrote:
> > >
> > > Hi Alan,
> > > My DC supplies are 88vdc or so, which is alittle high for the
> G210's
> > > They are the original seriesII supplies (x3)run from 110vac vs the
> > > 220vac. Basically just a big transformer, bridge rect. and cap.
> > > This yields a healthy 88vdc output ( down from the original
> unipolar
> > > bi-level drive of 160vdc/12vdc ).
> > >
> > > I removed the original primary-side 'control' transformers which
> > > controlled the primary drive to the output transformer. These
> control
> > > transformers acted as a 'variac'-like element to drop the voltage
> > > after the stepper coils slewed up to 10amps or so. Then the
> voltage
> > > was dropped to a holding level about 12vdc. This was the circa
> 1978
> > > way of increasing speed. Its funny how convoluted the original
> > > controls look at 1st, then after dissection, how simple
> > > it really was.
> > >
> > > Right now the variac is to bring the primary side down to 100vac
> or so
> > > to get the output side to a more usable voltage.
> > > -Lee
> > >
> > > --- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...>
> wrote:
> > > > Hi Lee,
> > > >
> > > > You don't need to regulate the motor voltage, just rectify and
> > > filter
> > > > it! And please use ISOLATION (a transformer)!
> > > >
> > > > Alan KM6VV
> > > >
> > > > studleylee wrote:
> > > > >
> > > > > Thanks Tim and Peter.
> > > > > I'm working on a big regulator to use on my supplies
> > > > > vs. the variac I'm currently using to bring the mains down so
> > > that my
> > > > > vdc out doesnt exceed 70vdc.
> > > > > -Lee
> > >
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