Basic Capacitor Formulas
I. Capacitance (farads)
English: C = .224 K A
T
D
Metric: C = .0884 K A
T
D
II. Energy stored in capacitors (Joules, watt - sec)
E =
1
⁄
2
CV
2
III. Linear charge of a capacitor (Amperes)
dV
I=C
dt
IV. Total Impedance of a capacitor (ohms)
R
2
+ (XC - XL )
2
S
V. Capacitive Reactance (ohms)
1
xc =
2
π
fC
Z=
VI. Inductive Reactance (ohms)
x
L
= 2
π
fL
VII. Phase Angles:
Ideal Capacitors: Current leads voltage 90°
Ideal Inductors: Current lags voltage 90°
Ideal Resistors: Current in phase with voltage
VIII. Dissipation Factor (%)
(loss angle) = E.S.R. = (2
πfC)
(E.S.R.)
Xc
IX. Power Factor (%)
P.F. = Sine (loss angle) = Cos (phase angle)
f
P.F. = (when less than 10%) = DF
D.F.= tan
X. Quality Factor (dimensionless)
Q = Cotan (loss angle) = 1
D.F.
XI. Equivalent Series Resistance (ohms)
E.S.R. = (D.F.) (Xc) = (D.F.) / (2
π
fC)
XII. Power Loss (watts)
Power Loss = (2
π
fCV
2
) (D.F.)
XIII. KVA (Kilowatts)
KVA = 2
π
fCV
2
x 10
-3
XIV. Temperature Characteristic (ppm/°C)
T.C. = Ct – C
25
x 10
6
C
25
(T
t
– 25)
XV. Cap Drift (%)
C
1
– C
2
C.D. =
C
1
x 100
XVI. Reliability of Ceramic Capacitors
V
t
L
0
X
T
t
Y
=
L
t
V
o
T
o
( ) ( )
XVII. Capacitors in Series (current the same)
1 = 1 + 1 --- 1
CT
C
1
C
2
CN
C
1
C
2
Two: CT =
C
1
+ C
2
XVIII. Capacitors in Parallel (voltage the same)
CT = C
1
+ C
2
--- + CN
XIX. Aging Rate
A.R. = %
Any Number:
D
C/decade of time
XX. Decibels
db = 20 log V
1
V
2
METRIC PREFIXES
Pico
Nano
Micro
Milli
Deci
Deca
Kilo
Mega
Giga
Tera
X 10
-12
X 10
-9
X 10
-6
X 10
-3
X 10
-1
X 10
+1
X 10
+3
X 10
+6
X 10
+9
X 10
+12
SYMBOLS
K
A
T
D
V
t
Rs
= Dielectric Constant
= Area
= Dielectric thickness
= Voltage
= time
= Series Resistance
f
L
= frequency
= Inductance
= Loss angle
L
t
V
t
V
o
T
t
T
o
= Test life
= Test voltage
= Operating voltage
= Test temperature
= Operating temperature
f
X&Y
L
o
= Phase angle
= exponent effect of voltage and temp.
= Operating life
2
ETC [ ETC ]
