Re: inductor/transformer concepts

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Finn Hammer by way of Terry Fritz <twftesla-at-qwest-dot-net>" <f-h-at-c.dk>

> Finn made his own big transformer:
> http://home5.inet.tele.dk/f-hammer/tesla/museum/pig/porkchop.htm

And I have just yesterday received the core for a 3-phase, 16 kVA
continous, transformer, which I am (perhaps) going to wind for 12 pulse
rectification. Wether or not depends.....

But having actually wound a couple of transformers myself, I would like
to point out, that you don`t need a lot of fancy magnetic theoty to do
so.

What you _do_ need to know, is how many turns/volt the coil needs to
have, so that the core does not saturate, when it is unloaded.

Too __few_ turns, and the inductance gets too low-> the current gets too
high, and the core saturates.

Too many turns, and the wire will have to be too thinn, in order to cram
it into the window,  and you get too much heat in the copper.

Luckily, you can determine the voltage per turn pretty easily: assemble
the core around a winding of known turns, then apply voltage across the
coil with a variac, measuring the current draw. Increasing the voltage,
at a certain point, the current starts to increase rapidly.
Back off the voltage a bit, and there you have your voltage across the
coil. Divide with the amount of turns in the coil, and you get
turns/volt.

This is all you need to know, in order to determine the turns needed to:
1 handle the voltage across the primary on the unloaded transformer
2 Calculate the turns needed on the secondary, to get the high voltage
that you need.

Now set up a spreadsheet to calculate the space occupied in the window,
with different wire thicknesses, and interleavings.

It is not that hard from a theoretical point of view, but it is labour
intensive.

Cheers, Finn Hammer