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[TCML] Question for solid-staters

Bert (et al)-

Thanks much for the analysis. It's quite interesting that k drops so markedly. Turns out that I'm planning to use 6-8 twisted strands of doubly-varnished 20 awg solid wire for the primary (or primaries), since I have a spool of it and the primary voltage is relatively low. With my scheme, it happens that that will be divided into 2 actual conductors, one conducting current CW and the other, CCW. From what you write, it appears as if, with my 4 driving modules connected either in series or in parallel and using one physical 12"-dia coil-layout, either of the modes of connection will work. If between-turn k seems too high, I'll just spread them out a tad.

Parallel module-connection will be easier since I'll not need to choke-isolate the mains-power inputs, each from the others.

Right now, I'm laying out a new board. I still get too-high of a ringing spike between MOSFET conductions, even after adding a decent 10 uF snubber capacitor across my big, fat 4000 uF supply-electrolytic, which tells me that my present board layout is too spread out. (I'll also use another of the snubber cap's for the actual snubber.) My circuit-board manufacture consists merely of hand-grinding away isolation-paths through the copper laminate rather than etching away everything but conduction-paths. Easier, at least for me, for 1-up or even 4-up fabrication.

And BTW, I specified a fractional turn since for series connection, such is necessary, to reach either the drive module just preceding the starting one or just following it. The individual primaries would each have 3-4 turns, I suppose; will have to determine that after I fire up the new board & crank it up to full power at the ~300VDC+ input. Will expect to draw from the mains ~ 1/4 the current that will pop the breaker.

Also BTW...it goes slowly due to too much socialization of late not to mention advanced age.


Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx>
4/16/2015 9:02 AM

Hi Ken,

It looks like you could also use coaxial stacked or coplanar single-turn primaries in your system and still achieve the desired multiplication of ampere-turns. It looks to be quite difficult to achieve coupling coefficients much above 0.85 using single-turn air-core coils without resorting to things like bifilar winding.

To quantify this, I used Antonio's Inca program to solve for the individual winding inductance, mutual inductance, and coupling coefficient between a pair of identical primary windings. Looking at the photo of your coil's 24" x 24" base, I estimated that the diameter of your primary is about 12". I also assumed #4AWG (about 0.20" diameter) insulated primary wire with 1/16" thick insulation. I also assumed two identical single-turn primary windings, one stacked above other the other (configuration 1) and one tucked outside the other (configuration 2). Windings were assumed to be separated just by their two layers of insulation (assumed to be a total of 1/8", for a center-to-center turn separation of 0.325". All primaries were assumed to be about 6" above the floor.

Configuration 1 (vertically stacked):
L2 (upper winding) = 0.759 uH
L2 (lower winding) = 0.754 uH
M = 0.574 uH
k = 0.759

Configuration 2 (nested planar):
L1 (inner winding) = 0.759 uH
L2 (outer winding) = 0.811 uH
M = 0.595 uH
k = 0.758

The coupling coefficient is relatively insensitive to primary diameter at 12" or above. For example, doubling the primary winding to 24" only increases k to ~0.79 for either configuration. If we reduce the insulation thickness to about 30 mils (between 24" turns), k increases to about ~0.85 - higher, but still below 0.90.

So, it looks like you have a wide degree of latitude for either stacking or nesting primary turns while still achieving the desired ampere-turn scaling. No need for using partial turns.

Bert Hickman
Stoneridge Engineering, LLC
World's source for "Captured Lightning" Lichtenberg Figure sculptures,
magnetically "shrunken" coins, and scarce/out of print technical books

Ken Herrick wrote:
> Hi, Greg (et al)-
> Thanks for the comments.  A question remains, though

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