Matching commercial cap
Subject: Matching commercial cap
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Sat, 18 Nov 1995 01:36:00 GMT
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Quoting Don Froula <froula-at-cig.mot-dot-com>:
> As far as capacitors, I like the Richard Hull's rolled cap
> design. Homemade flat plate caps also work well. Scott Myers'
> recent deal for the .025 MFD 20kvac pulse caps -at- $198.80 would
> work flawlessly on your coil. (Richard Quick)
> Richard, your recent comment to Ryan on the suitability of the
> group purchase commercial caps got me to think a bit more
> analytically about how well the cap (I purchased one!) will
> match my 15KV, 60 ma neon xformer. Using the formula for
> capacitive reactance, 1/(2*pi*f*C), I come up with a value of
> about 106K at 60 Hz. The neon should have a secondary
> impedance of 15Kv/60 ma or 250K. The fact that the impedance
> of the transformer is twice that of the cap suggests to me
> that the transformer may have difficulty in charging our
> commercial caps. In your experience, do you think that this
> mis-match is of any practical concern?
Yes. If there is not a rough match between the cap and the power
supply the tank circuit performance does suffer. It is better to
have too much transformer than too little.
There are couple of ways to get by this. The first is to reduce
the voltage of the transformers. You will find the circuit will
match well with 90 ma supplied from 9000 volts secondary neons.
If you stick with your 15000 volt supply you will need to gang
some more transformer outputs in parallel to increase your
current to around 150 ma, more than doubling your existing
Both methods work very well for obtaining the correct match.
However, if you look at your input powers you will easily see
that the best spark is going to be produced by adding more 15 kv
neons in parallel to your HV buss. Dropping the voltage down to
90 kv 90 ma is going to match with only 800 VA input, adding more
15 kv neons to build up a 150 ma supply will input 2250 VA (over
2 kVA). Either way you be scrounging for some more neons to build
up a paralleled bank neon power supply this capacitor.
... If all else fails... Throw another megavolt across it!
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