Capacitor energy and reactance calculator
A capacitor stores energy as the square of voltage, and its impedance falls as frequency rises.
microfarad
V
Hz
ohm
Stored energy
1.25J
- Stored charge
- 0.05 C
- Capacitive reactance
- 3.1831 ohm
- Current at that voltage and frequency
- 15.708 A
- RC time constant
- 1 s
- Time to 99% charged
- 5 s
Show the working
- Capacitance = 1000
- Voltage = 50
- Frequency = 50
- Series resistance = 1000
- farads = 1000 * 1e-6 = 0.001
- Stored energy = 0.001 * 50^2 / 2 = 1.25
- Stored charge = 0.001 * 50 = 0.05
- Capacitive reactance = 1 / (2 * pi * 50 * 0.001) = 3.1831
- Current at that voltage and frequency = 50 / 3.1831 = 15.708
- RC time constant = 1000 * 0.001 = 1
- Time to 99% charged = 1 * 5 = 5
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- E = (1/2) C V^2
- Q = C V
- Xc = 1 / (2 pi f C)
- tau = R C; the capacitor reaches 63.2% in one tau and 99.3% in five.
A charged 1000 microfarad capacitor at 50 V holds 1.25 J — enough to give a real jolt, and enough to weld a screwdriver tip.