Capacitor Safety Discharge Calculator

This calculator helps you select the correct bleed resistor or determine the waiting period required before a circuit is safe to handle.

Use this tool to:

• Calculate Discharge Time: Determine how long it takes for a capacitor to drop from its peak operating voltage to a safe threshold (typically 50V or less).
• Size Bleed Resistors: Find the appropriate resistance value that balances safety (fast discharge) with efficiency (minimal power waste during normal operation).
• Visualize Voltage Decay: View a real-time chart of the exponential decay curve to understand the “safety window” of your specific setup.

Safety Considerations

• Resistor Wattage: The “Resistor Power Dissipation (Peak)” value is crucial. If you use a standard 1/4W resistor for a 400V discharge, the resistor will likely fail or ignite. Ensure your bleed resistor is rated for the peak power calculated.
• Safe Threshold: While 50V is a common industry standard for “touch-safe” DC voltage, extra caution should be used with high-energy banks.
• Redundancy: In critical power supplies, it is common to use two bleed resistors in parallel so that if one fails open, the capacitor still eventually discharges.

Expand your toolbox

Simplify hardware and firmware development using the Quickboards Library. Eliminate R&D uncertainty and cut design time by assembling subcircuit schematics from a library of Processors, Sensors, Power Management, ADC/DACs, Memory, Interface circuits and more. Download the full library here.