Make the voltage window visible.
Turn farads and operating voltage into usable energy, then see how much of the stored energy a converter can actually reach.
How much energy can the supercapacitor actually release?
Supercapacitor energy falls with the square of voltage. Set the voltage where discharge starts and the lowest voltage your converter can still use.
Backup time includes the converter efficiency entered above. It still excludes ESR voltage sag, temperature, balancing, aging and control reserve. Confirm current and voltage limits against the manufacturer data sheet.
The supercapacitor energy formulas
A capacitor stores energy in its electric field. Unlike a battery, its terminal voltage declines continuously during discharge, so the converter voltage floor matters as much as the capacitance.
Why the voltage floor changes the answer
- Capacitance (F)
- The electrical capacity of the cell or module. More farads stores more energy at the same voltage.
- Start voltage
- The voltage at the beginning of discharge. It sets the total energy initially in the supercapacitor.
- Minimum usable voltage
- The lowest voltage the downstream converter and load can accept. Energy below this voltage is not available to the application.
- Voltage squared
- Energy falls with V², not in a straight line. Reducing voltage by half leaves one quarter of the energy in the capacitor.
Voltage-window reference
| Minimum voltage | Energy released | Energy left in the capacitor |
|---|---|---|
| 0% of start voltage | 100% | 0% |
| 50% of start voltage | 75% | 25% |
| 70% of start voltage | 51% | 49% |
FAQ
How do I calculate supercapacitor energy?
Stored energy in joules is E = 1/2 × C × V², where C is capacitance in farads and V is voltage. Divide joules by 3,600 to convert the result to watt-hours.
Why is the usable energy lower than the stored energy?
A converter normally stops drawing energy before the capacitor reaches zero volts. The energy below that minimum operating voltage remains in the capacitor, so usable energy is E = 1/2 × C × (Vstart² − Vmin²).
Does half the voltage mean half the energy remains?
No. Energy follows voltage squared. At half the starting voltage, 25% of the original energy remains and 75% has been released.
Does this calculator include ESR or converter losses?
The entered converter efficiency is applied to estimate delivered energy and backup time. Final designs must still allow for ESR, temperature, balancing, aging and the permitted voltage limits of the selected cells or module.
Turn the calculation into engineering intuition.
Compare voltage windows, pulse loads and storage behaviour with the guides and definitions behind this reference calculator. Use it to make the next physics question more concrete.