Capacitor Energy per Bang
ECAP = 0.5 Co (VP / NLINE)2
Where:
ECAP = Energy Stored in
Single Capacitor per Bang (Joules)
Co = Capacitance of a
Single
Capacitor (Farads)
VP = Gap Firing Voltage
(Volts)
NLINE = Number of
Capacitors
per String
Internal Resistance of a Single
Capacitor
RCAP = TANd / (2 p Co F)
Where:
RCAP = Internal Real
Resistance
of a Single Capacitor (Ohms)
TANd
= Dissipation Factor
Co = Capacitance of a
Single
Capacitor (Farads)
F = Fundamental Frequency of Primary
Circuit (Hz)
F (kHz) TANd
10
0.0004
50
0.0008
100
0.0010
200
0.0016
300
0.0024
400
0.0040
Power Dissipation per Small Capacitor
Wo = KSYNC BPS ECAP RCAP / (RCAP + RPRI)
Where:
Wo = Power Dissipation
per Small Capacitor (Watts)
KSYNC = 1 for Synchronous
Gap or 0.5 for Non-Synchronous Gap
BPS = Bangs per Second
ECAP = Energy Stored in
Single Capacitor per Bang (Joules)
RCAP = Internal Real
Resistance
of a Single Capacitor (Ohms)
RPRI = Primary Circuit
Equivalent Resistance (~3 Ohms)
Temperature Rise of Small
Capacitor
To = Wo Ko
Where:
To = Temperature Rise of
Small Capacitor (°
C)
Wo = Power Dissipation
per Small Capacitor (Watts)
Ko = Small Capacitor
Thermal
Dissipation Factor (°
C / Watt)
Lead Spacing
(mm)
Ko
5
250
7.5
167
10
133
15
83
22.5
67
27.5
40
37.5
33
Reliability
To (°
C) Reliability
0 -
5
Very Good
5 -
10
Good
10
-15
?
>
15
Bad
Example:
Total Primary Capacitance = 28nF
Fundamental Frequency = 100 kHz
Firing Voltage = 21000 Volts (15000
VAC)
BPS = 120
Gap = Non-Synchronous
Primary Capacitor = 7 strings of 14
x 56nF small caps whose lead spacing is 27.5 mm and the AC voltage
rating
is 630 VAC.
How reliable would this be?
ECAP = 0.5 Co
(VP / NLINE)2
ECAP = (0.5) (56 x 10-9)
(21000 / 14)2
ECAP = 0.063 Joule
RCAP = TANd
/ (2 p Co
F)
RCAP = 0.0010 / (2 p
(56 x 10-9) 100000)
RCAP = 0.02842 Ohm
Wo = KSYNC
BPS
ECAP RCAP / (RCAP + RPRI)
Wo = (0.5) (120) (0.063)
(0.02842) / (0.02842 + 3)
Wo = 0.0355 Watt
To = Ko Wo
To = 40 x 0.0355
To = 1.42 °
C
The reliability should be "Very
Good".