Capacitors  Stored Energy
Potential power and energy stored in capacitors.
Capacitor  Energy Stored
The work done in establishing an electric field in a capacitor, and hence the amount of energy stored  can be expressed as
W = 1/2 C U^{2} (1)
where
W = energy stored  or work done in establishing the electric field (joules, J)
C = capacitance (farad, F, µF)
U = potential difference (voltage, V)
Capacitor  Power Generated
Since power is energy dissipated in time  the potential power generated by a capacitor can be expressed as
P = dW / dt (2)
where
P = potential power (watts, W)
dt = dissipation time (s)
Example  Capacitor, energy stored and power generated
The energy stored in a 10 μF capacitor charged to 230 V can be calculated as
W = 1/2 (10 10^{6} F) (230 V)^{2}
= 0.26 J
in theory  if this energy is dissipated within 5 μs the potential power generated can be calculated as
P = (0.26 Joules) / (5 10^{6} s)
= 52000 W
= 52 kW
Be aware that in any real circuit, discharge starts at a peak value and declines. The energy dissipated is a very rough average power over the discharge pulse.
Capacitor  Time to Discharge at Constant Power Load
The time to discharge a capacitor at constant power load can be expressed as
dt = 1/2 C (U_{s}^{2}  U_{f}^{2}) / P (3)
where
dt = discharge time (s)
U_{s} = start voltage (V)
U_{f} = final voltage (V)
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