Re: Toroid ballast design

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hi Steve, Gerry,

On 11/15/05, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: Steve Conner <steve@xxxxxxxxxxxx>
>
>
> >I dont know where these cores saturate and if 24600 gauss is no
> >problem, the fewer number of turns will mean less winding loss.
>
> I've heard that 17000 gauss is about where transformer iron starts to
> saturate. Commercial transformer designs seem to aim for about this
> 17kG peak figure. 24600 seems a bit "Out there" :-o

Ah, good to know about the 17kGauss figure, i had wondered what most
transformer cores were good for :-).

>
> One handy rule of thumb I heard when designing gapped ballasts is
> that gapping the core doesn't change the volt-second capability. (To
> a first order at least.)

I dont think it changes at all, assuming the equations ive been usind
are not approximations.  What does change is that you can put more
current through it because the L is lower.

 So the number of turns you need to avoid
> saturation is the same as for an ungapped transformer. Hence a good
> starting point with a gapped variac core would be "The same number of
> turns as the variac had".
>
> I guess with two stacked cores, you only need half the number of
> turns, or is it 1/sqrt(2)?

Its half.

>From memory,

B = (L*I*10^4)/(A*N)

So you can see, as A doubles, N can be cut in half with no change
(assuming you went for the same L*I in either case, which is what you
are after anyway).  B is in Tesla's, L in henries, I in amps, A in
cm^2, and N is number of turns.

Steve Ward

>
> Steve Conner
> http://www.scopeboy.com/
>
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