Re: toroid transformer - back to basics

The original specifications for the transformer were:

115/230 Volt, 50/60Hz Output: 20 VAC @ 10 AAC 118 VAC @ 13 AAC

Let's let W1 represent the primary, W2 the 118V secondary, and W3 the
20V secondary. An aspect to note about transformers is that any
winding or combination of windings can be used as the primary. Here
we have three separate windings, one known to be center tapped.

Going back to basic transformer theory, the voltage ratio is
equivalent to the turns ratio of the transformer.

W1 : W2 : W3 = 230 : 118 : 20

If we put windings one and three in series, using it as the 'primary'
our turns ratio becomes:

(230 + 20) : 118

= 250:118

Pumping 115 VAC into this 'primary' yields an output at W2 of

118 * 115VAC / 250 = 54.28 VAC

Multiply by 1.4 to get the DC equivalent

=76 V

Subtract diode losses

yields approximately 75 VDC


Now lets check the current.

Primary power - losses = secondary power

Assuming zero losses, and substituting with original values

V1 * I1 = (V2 * I2) + (V3 * I3)
I1 = ((118 * 13) + (20 * 10)) / 230
I1 = 7.54A

We'll use this as the maximum current for our joined winding primary
as it is the lesser of the two current ratings and compute our
secondary current.

I2 = (V1 * I1) / V2
I2 = 115 * 7.54 / 54.28
I2 = 15.97

We note that this is more than the rating of our secondary, meaning
that we can safely draw the rated 13 amps from this configuration,
and recompute our primary current.

I1 = (V2 * I2) / V1
I1 = (54.28 * 13) /115
I1 = 6.14 Amps

The conclusion is that by connecting the full primary, and the 20 V
secondary in series we can use this transformer to build a DC power
supply with an output rating about 75V 13A.

Tony










--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<davemucha@j...> wrote:

>
> > >
> > > Interesting idea.
> > >
> > > does running them out of phase effect the current of the
> output ?
> > > would it be the same as the the higher voltage rating or

changed

> > by
> > > the lower one ?
> > >
> > > Also, is the input current effected by this ?
> > >
> > > Dave
> >
> >
> > Dave,
> >
> > I'm not sure how this will affect the input current. My guess

would

> > be it doesnt but i'm not sure. I mean there is no current flowing
> > due to them being out of phase.
> >
> > The current would be limited by whatever tap has the lower rating.
> >
> >
> > Thomas,
> >
> > I'm not sure what voltage your looking for but if you plan on
> > running geckos then 220 will not be an option. 110 is be redily
> > available so its no big deal. The DC voltage obtained is roughly
> > 1.41 (root 2) times the AC voltage.
> >
> > Mark
>
> too far removed.....
>
> If one puts 110 on the 220 line, that drops the 118 to 59vac.
> Therfore, 59 less 1.4 for the rectifier drop = 57.6 VAC, with the
> filer cap, 57.6 VAC x 1.414 you jump to 81.4 VDC not too bad.
>
> A couple of diodes and it's under 80V, use the second secondary to
> drop the first secondary ? not sure exactly how that works, but if
> it does, then great.
>
> Dave