Re: [CAD_CAM_EDM_DRO] transformer question

Not only that, but driving 110v into a 220v primary is going to be less
efficient than if it is run at the rated voltage. The windings and the core
are designed to be near saturation at 220/460v. You will get less power
transfer at a lower primary voltage. Without detailed performance graphs it
would be impossible to calculate the reduction.
--
Phil Mattison
http://www.ohmikron.com/

----- Original Message -----
From: Peter Reilley <micrio@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, May 07, 2006 6:46 AM
Subject: Re: [CAD_CAM_EDM_DRO] transformer question


> I don't think that this is the best way of doing this.
> More below.
>
> ----- Original Message -----
> From: "Jon Elson" <elson@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Saturday, May 06, 2006 8:55 PM
> Subject: Re: [CAD_CAM_EDM_DRO] transformer question
>
>
> > turbulatordude wrote:
> >
> >>Hi,
> >>
> >>I have a transformer with a lable of 220/460 primariy and 110/220
> >>secondary.
> >>
> >>1kva.
> >>
> >>Would I be able to connect it 110 to get 55 volt ?
> >>
> > Yup, that's right, you'll get 55 VAC from each secondary winding.
> > Note than 55 V AC into a rectifier will give 78 V on the capacitor.
> >
> >> and if so, any idea
> >>what current I could pull out of it ?
> >>
> >>
> > Best is to put the secondary in series and use a pair of big diodes (or
> > half of a bridge rectifier) with the center tap of the windings
> > connected to the
> > - of the capacitor. OK, starting with the KVA rating at the design
> > voltage of
> > 110 V, the current would be I = (KVA * 1000)/V. So, a 1 KVA transformer
> > would provide 1000/110 = 9 A. This may be a little optimistic for
> > continuous
> > duty at full load, but will certainly be fine for most CNC applications.
> >
> > Jon
>
> Using the transformer in this way will work but it will have double
> the heating. The rated current for the output of this 1KVA transformer
is
> 8.33 amps when wired for 120 volts. Therefore each secondary winding
> is rated for 4.17 amps.
>
> When wired as center tap full wave rectifier you are doubling the rated
> current in each winding for half the time. Thus you are drawing 8.33
> amps from the 4.17 amp rated winding but for only half the time. This
> will work but you are doubling the IR loss. Just for argument,
> lets say that you drop 1 volt in the winding at 8.33 amps. That is 8.33
> watts loss. Each winding's loss will be 4.17 watts but there are two
> of them so the total is 8.33 watts.
>
> The alternative connection is to parallel the windings and use a full wave
> bridge rectifier. Your voltage drop would be .5 volts and at 8.33 amps
> your loss would be 4.17 watts in this example.
>
> That type of center tapped rectifier was used back when rectifiers were
> expensive and transformers were cheap. Now a full wave bridge rectifier
> capable of this power load is common and cheap.
>
> Pete.
>
>
>
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