Re: ballast core

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

On 2 Apr 01, at 9:38, Tesla list wrote:

> Original poster: "harvey norris by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <harvich-at-yahoo-dot-com>
> 
> 
> --- Tesla list <tesla-at-pupman-dot-com> wrote:
> > Original poster: "Malcolm Watts by way of Terry
> > Fritz <twftesla-at-uswest-dot-net>"
> > <m.j.watts-at-massey.ac.nz>
> > 
> > On 1 Apr 01, at 14:54, Tesla list wrote:
> > 
> > > Original poster: "by way of Terry Fritz
> > <twftesla-at-uswest-dot-net>"
> > > <CTCDW-at-aol-dot-com>
> > > 
> > > No, I would not have the E from this core. I just
> > have a large (4.5 x
> > > 4.5 x 14") straight core. My understanding is that
> > open ended cores do
> > > not saturate easily. 
> The increase of inductance or impedance may also be
> much lower than close looped transformer analogies.
> 
> I know of ballast inductors
> > made of 300 turns of
> > > wire around a form stuffed with 'I's from old NSTs
> > I don't think I
> > > would have to make this a multi-layer winding..
> > I'm pretty sure I have
> > > enough length to do it in one shot, but I haven't
> > actually checked it
> > > yet. I'm still in the "can I do this without
> > wasting money" stage :)
> > > 
> > > Chris W
> > 
> > Why 300 turns? My approach would be to build an
> > air-cored inductor to 
> > meet the minimum inductance requirements of my
> > system in such a way 
> > as to allow the core to be slid in to boost
> > inductance when required. 
> > 
> > Malcolm
> > 
> I have recently compared the air core 57 henries
> inductance from 80 lb.essex 23 gauge coils, to that
> with insertion of strontium ferrite,(unmagnetised
> ceramic 8)in the majority of the core area. This only
> increased the inductance to 73.5 Henry. The greater
> inductances suspected by insertion of a ferromagnetic
> core do not seeem great with a single core area of a
> single coil interior volume. This still leaves quite a
> bit of leakage for the magnetic loops that must still
> take an air path around the coil.

Ah - but the core could be an E-core slid in to mate with an I 
sitting at the end or, if not so much of a variation is required, an 
I end section moved towards the poles of an E sitting permanently in 
the solenoid. A minimum air gap must be maintained when the core is 
"fully" mated of course. Your measurements are an excellent example 
of how to elongate the B-H curve and why it is very hard to saturate 
a gapped core.

Regards,
Malcolm