Re: Would this work? (air gap in ballast core)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gerald  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Aaron,

I too think saturation will be a problem.  The flux thru the core will be 
concentrated where the holes are.  If my understanding is correct, this 
portion of the core will now saturate sooner and once this happens, no more 
flux can be created and the ballast inductance will precipitiously drop in 
an uncontrolled way.  An air gap doesn't directly affect saturation.  It 
allows magnetic poles to form at the gap to greatly increase the H field in 
the gap (and air gaps don't saturate).  The gap will allow you to get a 
lower inductance without having to reduce the number of turns (hence the 
flux density stays the same in the core).  If you do drill the holes, I 
think you should be prepared to throw away the core (or figure out how to 
turn the holes into an air gap).

Gerry R

> Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>
>
> Well, we'll find out!  I've booked the shop time, so
> I'll try it and let you know if you're right! :D
>
> The transformer these came from was dated 1963.  Not
> sure when steel cores became the norm, but this stuff
> is *extremely* soft.  Might be iron...?  Anyway, I'm
> hoping high speed drilling will prevent any/much mess.
>  The idea is that all layers will have holes in them,
> but all layers will also have some uninterrupted areas
> (between holes).