Hi Jim,
Magnetic circuits can be a bit confusing. Especially the part where
most of the energy is stored in the air gap! You can think of the air
gap in an inductor as being loosely analogous with the gap in an air
capacitor. In either case, most of the electrical energy stored in the
system is concentrated within the magnetic or electrical field of the
gap between magnetic or electrical "conductors". A readable
explanation of how the total energy in an inductor is split between
the core and the gap can be found in the following passage from one of
professor Heinz Schmidt-Walter's books:
http://schmidt-walter.eit.h-da.de/snt/snt_eng/snteng6a.pdf
Iron-core inductors that are designed to store significant energy will
always have an air gap somewhere in the magnetic circuit. With
laminated cores, the gap is usually obvious. With sintered ferrite or
iron powder cores, the manufacturer often distributes the air gap
throughout the entire core by adding non-magnetic materials and
binders into the mix before pressing or firing, thereby reducing the
overall permeability of the core. The air gap reduces the overall flux
density within the magnetic circuit, allowing more DC current to pass
before the core becomes saturated.
The charging inductor in a resonant charging system will temporarily
store, and then transfer, 25% of the system's bang energy into the
tank cap. You might find it interesting to note that the magnetic
field within the core of a DC resonant charging reactor will always be
in one direction (due to the de-queuing diode). Knowing this, one can
add a magnetic "bias" in core in the opposite direction as the
winding-generated field by adding a permanent magnet into the magnetic
circuit. The magnet drives the core towards the opposite end of the
saturation curve, allowing the inductor to handle peak currents that
are almost 2X the value that would otherwise cause saturation. This
trick is sometimes used to help reduce overall core size in
high-performance energy storage inductors.
Hope this helped and best wishes,
Bert
Jim Mora wrote:
Hi Bert, Phil,
Not to get too esoteric, but this is of some interest since I am
going to
try and build a reasonable decent one(s). I understand we want the wire
resistance at a minimum, but inductors come in different flavors such
as the
swinging choke used in older (ancient to some) B+ amplifier supplies. It
tends to be a gapped choke to compensate for the DC that is always
present.
Standard inductors are not gapped to my knowledge. Some physics forums
debate if there is energy stored across the gap. More simply put,
would an
inductor sized not to saturate at the extreme current peaks or a gapped
inductor (both assuming low DC ohms) be the more ideal charge inductor?
Indirectly we are entering the gap debate I suppose. I see it as the
energy
stored in the magnetic field which a gap would tend to decrease? I
suppose
it comes down to a compromise. I'm curious how those radar inductors are
designed in this sense. Yours is a beast!
Jim Mora
-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Bert Hickman
Sent: Tuesday, August 19, 2014 8:20 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] How I modified the 3 phase for dual wye 5KV 2xI
Hi Phil and all,
Phil wrote:
(I've jumped around a bit too different emails here, hope you can
follow)
Bert's figures in this vary from what Richie's figures give. Now I know
that
assumes the calculator faithfully reproduces Richie's formulas, but I'm
certain after a lot of testing it does, so who's right, Richie or Burt?
I realise the smoothing cap will vary with 3 phase AC admittedly, but
after
it's rectified it's all DC regardless, so the inductor and tank cap I
would
consider to be the same as for our single phase AC input.
The biggest difference between Richie's model and the spreadsheet
calculator is that I use a lossy charging circuit model that takes into
account charging inductor losses. <snip>
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Bert Hickman
Stoneridge Engineering
http://www.capturedlightning.com
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