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Re: Cap Confusion
From: Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
Sent: Friday, November 14, 1997 5:16 PM
To: Tesla List
Subject: Re: Cap Confusion
On Friday, November 14, 1997 11:56 AM Andrew Chin
[SMTP:chinny-at-ozemail-dot-com.au] wrote;
> Hey all.
>
> I am trying to build a Tesla coil, and while my mechanical and
> electrical knowledge is fairly sound, I have no idea how to size all the
> capacitors used in a Tesla coil driver.
>
> There are at least 3 capacitors I would like explained:
> -Power Factor Correction capacitors (I think these go on the mains
> side of the transformer)
The formula to calculate power factor correction on neon sign transformers
is;
10^9
C = Corrected kVA ------
2(pi)fe^2
C = required capacitance in microfarads
f = frequency of applied voltage
e = applied voltage
CORRECTED kVA is determined by dividing the corrected power factor output of
the neon sign xfrmr (Volt-Amps below) by 1000
Corrected Power Factor
Secondary Rating Volt-Amps
kV,mA
15,120 900
15,60 450
15,30 250
12,120 775
12,60 400
12,30 200
9,120 600
9,60 300
9,30 150
7.5,120 500
7.5,60 250
7.5,30 125
6,60 200
6,30 100
The power factor correction capacitor is placed in parallel to the primary
of the neon sign trnsformer.
> -Bypass Capacitor (This goes across the High Voltage supply)
Use a .001 ufd. capacitor rated at twice the transformers output voltage and
these should be used in conjunction with a pair of high inductance air core
chokes thus forming a by-pass filter to send R.F. to ground rather than
flowing into the neon sign transformers secondary, your safety gaps should
be placed between the neon sign transformers secondary and the chokes.
> -Tank Capacitor (Forms part of the tuning circuit)
The idea here is to have the largest capacitor possible that your
transformer can fully charge at it's operating frequency. The procedure for
this is;
1. Determine your neon sign transformer's Impedence:
E
Z = ---
I
Z = Impedence
E = volts
I = current in Amps
Note: divide milliamps by 1000 to get Amps.
The Impedence of the primary capacitor should match the Impedence of the
transformer at it's operating frequency.
2. To match Impedence and determine capacitor value:
10000
C = ----------------------
2 x pi x Z x frequency
C = capacitance in microfarads needed for primary capacitor.
Z = Impedence from equation one (Transformer Impedence)
pi = 3.141592654
> There is also the Tesla coil itself which has its internal capacitance or
> something, and the toroid which has capacitance.
The secondary has distributed capacitance which can be calculated using the
Medhurst equation that appeared on this list several times in the past week.
As for the toroid I haven't seen any equation to calculate it's capacitance
thus far.
Sincerely
\\\|///
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-----o00o-(_)-o00o-----
Alfred A. Skrocki
Alfred.Skrocki-at-CyberNetworking-dot-com
.ooo0 0ooo.
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