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# Re: transformer cores

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> Original Poster: "bob golding" <yubba-at-clara-dot-net>
>
> hi all,
>         I have found a couple of transformers. I think they are HV filament
> transformers of some sort. With the present windings I reckon they will
> handle about 150 Watts. Is there an easy way to find out at what current
> the core will saturate? They are two section c type cores with a cross
> sectional area of about 1" The whole core is about 4 1/2". Of course if
> anyone wants to buy them as filament transformers I will restrain from
> killing them just yet. If anyone is interested let me know off list.
>
> cheers
>
> bob golding

I would also be interested in any formulas out there that can be used to
predict saturation in transformers.  I have a couple of Mots that I will be
using in a power supply, whose primary turns are minimal.  I'm afraid that
despite the huge core area they may saturate if short circuit current is drawn
from them.  I don't want to try them out in a Jacob's ladder because I can't
replace them easily.

In the archives I found these equations--who posted them I can't remember.

(N/Vw) = 58183/(Ac x Bmax)

where the N/Vw is the turns per volt, Ac is the core area in square
inches, and N is the number of turns. Bmax is the maximum flux density
allowable to
avoid excessive core loss (core loss gets very large before saturation
is reached). For typical modern transformer steels Bmax is of the order
of 12,000 gauss.

With this equation you can tell which transformers are overdesigned and
which ones aren't, but it's hard for me (with my limited math background) to
translate this into a function of the primary current.

```