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Re: scopes away - mosfet circuits



Malcolm wrote:
> 
>     It seems from my primary musings that part of this might well be
> related to primary cap energy size. I've found that gap losses scale
> rapidly with Ecp. I wonder, has anyone compared an increase in power
> by upping Ecp with an increase in power by upping break rate? Does
> a difference exist? It seems that upping break rate if possible might
> be the more desirable option if it can be done.


One of the most interesting challenges in designing a TC is optimizing 
the primary circuit.  Based on information from other coil designs, 
reference data, and a slew of actual msmts, I have come to a few conclusions
regarding optimum primary values:

Gap Speed - Too low of a gap speed allows the ions to re-combine, and 
excessive gap speed just uses up power that could otherwise be devoted
to increasing the primary voltage.  The published half-life of ions
after an arc is about 4 mS, or 250 PPS.  It appears that the gain in 
spark length starts to level off above 400 PPS.

Primary Impedance [SQRT(L/C)] - Too low of Zpri spoils the Q, and a high
Zpri reduces the secondary voltage [ Vsec/Vpri = SQRT(Lsec/Lpri) ].  For
a 4-gap system (Rgap = 0.65ohm), a good compromise value for Zpri seems to
be around 20 to 25 ohms.

Primary Voltage - More is always better.


Summary:

Gap Speed - Always 400 PPS nominal
Voltage per Gap - 5kV max for good quenching
Primary Impedance - 6 ohms per series gap; (Zpri = 24 ohms for a 4 gap system)
Primary Voltage - Increase until you run out of mains capacity.


For what it's worth, GL