Re: Calculating the VA rating of transformers?

>
>
> Excelent post. I've been waiting for something like this for years.
>
> I do have a question.
>
> Most of my transformers have the center section as a rectangle that
> is roughly 2:1 height by width, and then the thickness is dependant
> on how many laminations have been stacked.
>
> The measurements have been square area, not cubic so I am wondering
> which measuremetns to use ? Thickness of laminations and one face
> side ? both face sides and not the thickness ? Lam thickness and
> average of face ?
>
> Dave

Imagine you are looking down on top of the center core section and
slice off the top of the transformer. Just the area you can see in
the *top plane* of the center leg is the cross sectional area. The
depth (length of the center leg) is not part of the equation. The
lamination thickness has more to do with things like airgap (each
lamination has a finite air gap) and helps to control the saturation.
The more air gap a core has the harder it is to drive it into
saturation. Saturation in a magnetic core is in essence a
magnetic "short" and is normally a bad thing. Audio transformers
tend to have thinner laminations while power transformers that
operate in a very narrow range of frequencies have thicker
laminations. Powdered core magnetics like those used in toroids have
built in air gaps to tune the saturation characteristics. Toroids
get better usage of the core and are typically smaller per watt than
traditional EI cores but they are harder to wind (no bobbin and the
wire has to be wound directly on the core). They concentrate the
magnetic field in the cinter of the 'donut'so product less EMF. On
the minus side they are more expensive to make and typically have
higher in-rush characteristics.

There are a lot of subtle things in designing transfromers but the
basic physics are not overly complex.