Subject: Q Values
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Thu, 22 Feb 1996 09:03:00 GMT
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> No, you're not wasting your time if you are having fun.
This is a fun hobby.
> However, if you are trying to build the ultimo secondary, you
> probably are. Any secondary you make on approved materials
> like acrylic or polyethylene are going to produce Q factors far
> above the Q of the primary circuit.
Nothing worth arguing about here.
> These two Q factors behave something like resistors in
> parallel. You know, if you have 1000ohms in parallel with
> 20ohms, the 1000ohm resistor isn't really contributing much to
> the resultant value. The formula for system Q (which I have
> posted many times before) is:
> Qsys = 2 * (1-K) * (Qp * Qs) / (Qp + Qs)
> Qp & Qs are the primary and secondary Q factors
> K is the coefficient of coupling (typically 0.05 to 0.2)
> If you build a really really good primary circuit, you will get
> 50 (about). The typical well made secondary's Qs 150.
> Plugging these numbers into the formula (assume K = 0.1) gives
> Qsys = 68. Now, if you succeed in building an absolutely balls
> out screeeeeemin' secondary with a Qs of 400 (which you
> won't), the SYSTEM Q (Qsys) will increase to 80. This
> translates to a power processing efficiency increase from 72%
> to 75% for all that effort. This is the efficiency
> at which power is coupled from primary to secondary and vice
> versa... My point (as always): INCREASE THE PRIMARY Q and you
> will go much farther in increasing Qsys. The best way to do
> that is to wind a low frequency secondary coil (40-100KHz) that
> will require the largest possible primary inductor to tune it.
And very well put.
Still this arguement should not prevent the coil builder from
constructing the ultimate Q secondary, as long as the price is
both reasonable (time and money) and cost effective (time and
Suppose you are firing an extra coil system, and the coil you
grab for the extra coil (down the line mind you) is that screamin
6" coil you built when you first got going hot & heavy. High Q in
the coil will be directly related to ultimate VSWR.
Suppose you build that "ultimate" balanced tank circuit. Then you
need a decent high Q secondary to match to it...
Suppose you get a nice solid state driver system to base feed
your secondary. The signal is clean & smooth. Will the Q factor
in your old secondary become a performance issue?
Suppose you need a pickup coil to detect ground currents from a
wireless power experiment conducted 1/4 mile away... and you are
not on an earth resonate frequency.
That is a lot of supposition I admit. The fact that I have
encountered all of these circumstances means there is reason to
look at cost effective ways of improving the Q of every system,
sub-system, component, of a Tesla coil for better performance.
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12