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Re: [TCML] Flat strip primary inductance



Hi Finn,

assuming the 180mm are the outer dia of the coil, and the ribbon width is 50mm, made of 2mm thick sheet, the NBS Circular 74 (of 1918) formula gives 0.83uH for your coil vs. 1.44uH, if the coil were made of wire (~2mm dia). The connecting wires were set to a total length of 10cm only. The formula for flat strip primaries is integrated in my TC-Plan Excel, which seems not having been considered in "All simulators".

Soo... your measured value of 0.8uH seems plausible to me.

I can send you the actual TC-Plan, or the Excel FlatRibbon.xls, which only calculates the primary, - off list, if you like.

TC-Plan can be downloaded from Deano's Terry-mirror-site:
http://deanostoybox.com/hot-streamer/TeslaCoils/Programs/programs.htm
but it's an _obsolete_ version, which not yet contains flat-ribbon type primaries.

IIRC flat strip primaries are not(yet) calculated in JavaTC and Wintesla, while INCA should be able to threat them, because the filament-increment numeric simulation of distributed conductors is contained in the simulator.

Cheers, Kurt

Finn Hammer wrote:
All,

I know this has been up before, but here goes:
A flat strip primary has lower inductance than one made out of round
conductors. This is not new, but here is an extreme example, I think:
I kept hanging tank capacitors on to the primary assembly, without
reaching the desired res. frequency. At last I had to investigate
further.
The primary is an internal flat strip primary, for a BRISG coil, and
it consists of 2 turns 180mm dia with 5mm spacing.

All simulators, INCA, javatc, wintesla predict 1.5µH and since the
primary cap is 7.5µF, the anticipated resonanse was 47kHz.

However, the assembly resonated at 63kHz which corresponds to 0.8µH

It baffels me that such an extreme difference could exist, so I made
up a sanity check:

2Turns of thich speaker wire, and a 7.5µF cap resonates at 43kHz.

Has anybody experienced this before?

A picture posted to see the primary, and the sanity check:
http://www.hammertone.com/sanity.jpg

Cheers, Finn Hammer
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