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Re: [TCML] was: How I modified the 3 phase for dual wye 5KV 2xI; Now charge inductor physics.

Hi Bert,

your idea with the permanent magnet bias remembers me of my current limiting experiments with saturable reactors some years ago. So you could make a special charging reactor for DC resonant charging: take a gapped 3-phase core, put the high voltage reactor coils on the outer legs and put a DC coil onto the middle leg. Then you crank up the DC bias field and see what happens :-)


----- Original Message ----- From: "Bert Hickman" <bert@xxxxxxxxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Wednesday, August 20, 2014 3:03 PM
Subject: Re: [TCML] was: How I modified the 3 phase for dual wye 5KV 2xI; Now charge inductor physics.

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:


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,


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
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
it's rectified it's all DC regardless, so the inductor and tank cap I
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
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