Calculator Inputs
Example Data Table
| Scenario | Equivalent Capacitance (F) | Initial Voltage (V) | Final Voltage (V) | Usable Energy (Wh) | Notes |
|---|---|---|---|---|---|
| Pulse power lab bank | 1000 | 15.0 | 8.0 | 22.87 | Good for short bursts and test benches. |
| Sensor backup module | 350 | 5.0 | 3.3 | 0.76 | Useful where frequent cycling matters more than energy density. |
| Compact robotics bank | 500 | 12.0 | 6.0 | 15.00 | Balances fast delivery and moderate runtime. |
These rows are illustrative examples. Real values depend on temperature, balancing, aging, converter efficiency, and the exact chemistry of the device.
Formula Used
1) Equivalent Bank Capacitance
Ceq = Ccell × Parallel Strings ÷ Series Cells
2) Equivalent Bank ESR
ESReq = ESRcell × Series Cells ÷ Parallel Strings
3) Derated Rated Bank Voltage
Vrated,bank = Vcell × Series Cells × (1 − Derating % ÷ 100)
4) Stored Energy
Estored = 0.5 × Ceq × Vinitial2 × Efficiency
5) Usable Energy Over a Voltage Window
Eusable = 0.5 × Ceq × (Vinitial2 − Vfinal2) × Efficiency
6) Approximate Constant-Current Runtime
t ≈ Ceq × (Vinitial − Vfinal) ÷ I
7) ESR Heating
Ploss = I2 × ESReq
8) Maximum Theoretical Matched-Load Power
Pmax = Vinitial2 ÷ (4 × ESReq)
This calculator applies the classical capacitor energy equation, then adjusts it using series-parallel scaling, operating voltage limits, efficiency, and ESR-dependent behavior.
How to Use This Calculator
- Enter the single-cell capacitance, ESR, and rated voltage from the datasheet.
- Specify how many cells are placed in series and how many strings are placed in parallel.
- Apply a realistic voltage derating for safer chemistry operation and balancing margin.
- Set the starting and ending bank voltages for the discharge window you plan to use.
- Enter efficiency to account for converter losses or other practical system losses.
- Add discharge current, load resistance, leakage, mass, and volume if those metrics matter.
- Press the calculate button to show the result above the form and below the header.
- Use the export buttons to save the result table as CSV or PDF.
Frequently Asked Questions
1) Why is usable energy lower than stored energy?
Stored energy assumes discharge from the initial voltage to zero. Usable energy only counts the selected voltage window and includes the efficiency factor, so it better matches practical operation.
2) Why does series connection reduce equivalent capacitance?
Capacitors in series behave like reciprocals added together. For identical cells, total capacitance becomes the cell capacitance divided by the number of series elements.
3) Why is ESR important in supercapacitor chemistry?
ESR drives heat, voltage sag, and pulse performance. Lower ESR improves current delivery and reduces internal losses during fast charge and discharge events.
4) Should I always use voltage derating?
Yes, derating is usually wise, especially in series banks. It helps accommodate balancing variation, aging, temperature effects, and real-world transients that can overstress individual cells.
5) Is the runtime estimate exact?
No. It is a constant-current approximation. Actual runtime depends on converter topology, cutoff behavior, temperature, rising ESR with age, and changing load conditions.
6) What does specific energy tell me?
Specific energy shows usable watt-hours per kilogram. It helps compare bank designs where mass matters, such as portable instruments, robotics, and experimental mobile systems.
7) What does volumetric energy mean?
Volumetric energy reports usable watt-hours per liter. It is useful when enclosure space is limited and compact packaging is a design priority.
8) Can this replace datasheet validation?
No. It is a design aid. Always verify cell balancing, ripple current, thermal limits, lifetime data, and safety margins against the manufacturer datasheet.