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Re: transformer cores

Hi Mike, all,


> Original Poster: Mike Nolley <mnolley-at-mail.slc.edu> 
> 
> 
> 
> > 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.

Coilers - you do NOT have to worry about LOAD currents saturating 
a transformer core. It will not happen - period!  As I've explained 
before, LOAD currents may be treated as a separate entity from 
MAGNETIZING currents.  I(mag) is dependent on Lp, Vapplied, the 
amount of iron in the core and the amount of coupling to that core 
and is inversely proportional to applied frequency.
       The worst you can do if you load a transformer too heavily is 
overheat the windings and blow fuses. The end result might be the 
same but I(mag) does not affect heating in the secondary windings 
and sucking too much load current will not damage a core 
susceptible to overmagnetizing (such as some ferrites)..

Regards,
Malcolm

>     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.
> 
>