Re: [CAD_CAM_EDM_DRO] Re: Power Supply

In a message dated 31-Jul-02 22:25:23 Central Daylight Time,
elson@... writes:

> As for wire gauge, you need to use somewhat heavier wire than you'd
> use in conduit, for instance, because the heat can't escape as easily, and
> there is also some eddy current loss in the windings. Usual practice is
> to use the heaviest wire that will fit in the 'window', or through hole,
> of the transformer. This may not apply to big toroid cores, however.
> In smaller transformers, the core is selected by figuring out how many
> turns will be needed, and then finding a core that has just enough window
> to fit that area.
>
>

Use 750 circular-mils per amp, if your workmanship is good, and winding is
tight and properly Formvar-insulated, etc. If you want to be
ultra-conservative, use 1000 cm per amp. The 750 is "industry-standard".
Cheapo transformers that might warm up more than some of us would like may go
as low as 500 CM/amp. NOT good!

The "core window" for the coil is generally industry-standard, expecting
professional "layer-wound" work. There may be a couple of choices of "window
size" for a given core-width (the width of the "middle leg" of the "E"), for
SOME sizes, but unless you are salvaging old used E-I punchings from an old
transformer (po' folks with TIME on their hands might do this), it is often
difficult to "choose" window-ratio to core-width!

Jan Rowland


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