Primary Q factors
Subject: Primary Q factors
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Sun, 22 Oct 1995 22:37:00 GMT
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Quoting Scott Myers <102505.61-at-compuserve-dot-com>:
> Hi Richard,
> As you know, I've been discussing Pulse Discharge capacitors
> with a couple of manufacturers. This is in order to get a
> quantity discount and the best design possible.
Yeah, I know a few people out here (including myself) who are
always interested in picking up some high quality, commercially
manufactured, HVAC rated, pulse discharge capacitance at a
> One question arises that I don't have an answer for. What is
> the Q of a high Q primary. The heart of the question is really
> this; When the primary is (dis)charged <in> one pulse, how
> long does it take it to ring down? What is its time
> constant ? Inquiring capacitor design engineers want to know.
> I realize that this will differ with the construction of each
> circuit. I guess what I'm asking is what is the Q of yours?
> Gauging by your video, your would be typical of a high Q
> primary, maybe even better than most. The reason that this is
> asked of course is that the better the Q, the higher the
> resonate rise. Therefore a higher voltage rated capacitor
> is required for a higher Q primary.
> Any feedback you can provide would be greatly appreciated.
Wow, what a question... I have never actually sat down and
calculated the tank circuit Q into values that might be of
assistance to you. I have directly measured the Q of many,
many tank circuits with the O'scope and signal generator.
Unfortunately, as you already realize, there are lots of
different variables involved. Some we can eliminate, others we
can reference, and the others I can probably make a reasonable
First let's tackle the question about ring times in spark excited
LC oscillators. This is directly related to the quench time of
the spark gap, the coupling coefficient between the primary and
secondary, the tune, the Q of: the capacitor, the spark gap, the
primary coil and the tank circuit wiring; and to a certain extent
the Q of the secondary coil that is coupled to the primary.
A typicical ring time would probably be around .0001 seconds. I
would guess that the tank circuit Q factor on a well designed
coil is probably going to be a bit higher than the Q factor of
your typical secondary coil. Figure a Q factor around 100 - 150
... If all else fails... Throw another megavolt across it!
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