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Re: [TCML] Secondary Coil: Wire Gauge and Number of Turns



On 7/2/13 3:48 PM, Brandon Hendershot wrote:
Phil,

Not too sure what you meant by "(... while keeping the required primary
inductance to about 90% of the primary coil's capacity.)".

Basically I was wanting to design the secondary to require almost all of
the available primary coil when tuned properly.

It's all about having a balance, that's why using an aspect ratio that has
been determined as sensible by countless coilers over the years (4 / 5:1),
combined with a turns ratio centred around 1200  (900 - 1500), means the
both the secondary inductance and inter-turn capacitance should work out
ok.

Based on this (and other advice) I'm thinking of making it like this:
1237 Turns of 24 AWG, 28" x 6.6" (4.25:1) yielding 54.5 mH Inductance and
12.0pF Capacitance.
Based on popular opinion I believe we can all agree on this being somewhat
optimal, right?




I would go for fewer turns of a heavier wire.

Taking your 6.6x28 inches and running some different wire gauges..
ga	tpi	turns	L	Rdc

24	40	1120	44	48
22	32	900	28.2	25
20	25	700	17	12

at 100 kHz, skin depth is 0.008", AWG20 is 0.032" in diameter, so AC resistance is going to be pretty close to dc resistance (current flows in pretty much the whole cross section of the wire)

To a first order, current is proportional to 1/sqrt(L)
since loss is proportional to I^2*R, the loss is going to go as R/L


L	R	I	R/L
44	48	0.15	1.09
28.2	25	0.19	0.89
17	12	0.24	0.71

This pushes you to fewer turns of larger wire.
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