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Capacitor Safety Discharge Calculator

This tool is used for calculations involving the discharge of a capacitor through a fixed-value resistor. Given a capacitance value as well as beginning and end voltages, this calculator solves for either time or resistance, calculating the resulting initial power dissipation in the resistance and the total energy discharged to zero volts.

Many factors need to be considered when choosing a discharge resistor. Safety standards require the voltage across a capacitor to reach a safe voltage before a person is able to touch it. In the USA, standards such as UL, OSHA, NTA, ETL, MET, etc. will have the requirements available for the needs of your product.

Capacitor Value µF
Initial Charge Voltage V
Safety Threshold Voltage V
Resistance Value Ω
Safe Voltage Achieved by
= s
Initial Power Across the Resistor
= W
Time Constant
= s
Energy Discharged to Zero Volts
= J
Desired Discharge Time s
Safe Voltage Achieved by
= Ω
Initial Power Across the Resistor
= W
Time Constant
= s
Energy Discharged to Zero Volts
= J