Capacitor Charge & Safety Discharge Calculator
Calculate capacitance energy (Joules), charge (Coulombs), and RC discharge time for safety analysis.
About
High-voltage capacitors pose a significant lethal risk in power electronics, retaining charge long after disconnection. Technicians must calculate the stored Potential Energy (E) to assess arc flash risks and design appropriate bleed-down circuits. Neglecting these calculations can lead to life-threatening shocks during maintenance.
This calculator determines the Electric Charge (Q) and Energy based on capacitance and voltage. Crucially, it includes a "Safety Discharge" estimator, computing the time required for a bleeder resistor (R) to drain the capacitor to a touch-safe level (typically 50V or less), strictly following the RC time constant exponential decay.
Formulas
Charge & Energy:
Q = C × V
E = 12 C V2
Discharge Time (to Vsafe):
t = −RC ⋅ lnVsafeV0
Reference Data
| Capacitor Type | Typical Range | Voltage Rating | Dielectric Constant (k) |
|---|---|---|---|
| Ceramic (MLCC) | 1 pF - 100 μF | 6.3V - 3kV | 10 - 10,000 |
| Electrolytic (Al) | 1 μF - 1 F | 6.3V - 450V | ~8 - 10 |
| Tantalum | 100 nF - 1 mF | 2.5V - 63V | ~27 |
| Film (Polyester) | 1 nF - 10 μF | 50V - 1000V | ~3.2 |
| Supercapacitor | 1 F - 5000 F | 2.5V - 5V | N/A (Double Layer) |
| Mica | 1 pF - 10 nF | 100V - 10kV | ~6 |
| Air (Variable) | 10 pF - 500 pF | Variable | ~1.0006 |
| Glass | 10 pF - 1 nF | 500V + | ~3.8 - 14.5 |