Capacitor Discharge Calculator

A capacitor gradually releases its stored charge through a resistor — the Capacitor Discharge Calculator shows exactly how much voltage remains at any point in that process. Enter your capacitance, resistance, initial voltage, and discharge time (with your choice of units for each) to get the voltage at that moment. Secondary outputs include the time constant (τ), current at time, initial energy, energy discharged, and percent discharged.

µF
Ω
V
s

Results

Voltage at Time

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Time Constant (τ)

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Current at Time

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Initial Energy

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Energy Discharged

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Percent Discharged

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Results Table

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Frequently Asked Questions

What is a capacitor discharge calculator used for?

A capacitor discharge calculator determines how voltage across a capacitor decreases over time when discharged through a resistor. It's essential for safety calculations, timing circuits, and energy storage applications.

How do I calculate the time constant of an RC circuit?

The time constant (τ) equals resistance (R) multiplied by capacitance (C): τ = R × C. After one time constant, the voltage drops to about 37% of its initial value.

What happens after 5 time constants?

After 5 time constants (5τ), a capacitor is approximately 99.3% discharged, leaving only 0.7% of the original voltage. This is considered fully discharged for most practical purposes.

How do I ensure safe capacitor discharge?

Safety standards require capacitor voltage to drop below safe thresholds before human contact. Calculate discharge time needed to reach safe voltage levels using appropriate discharge resistors.

What units should I use for capacitance and resistance?

Common units are microfarads (µF) for capacitance and kiloohms (kΩ) for resistance. The calculator supports various units including picofarads, nanofarads, ohms, and megohms.

How is discharge current calculated?

Discharge current equals the voltage across the resistor divided by resistance: I = V/R. Current decreases exponentially as the capacitor voltage drops during discharge.

What factors affect capacitor discharge rate?

Discharge rate depends on capacitance value, resistance value, and initial voltage. Larger capacitance or resistance increases discharge time, while higher initial voltage increases initial current.

How do I choose a discharge resistor value?

Choose resistance based on desired discharge time and power handling capability. Lower resistance discharges faster but dissipates more power initially. Consider safety standards and component ratings.