Calculator
Example data table
| Unit V | Unit A | Unit Ah | Ns | Np | Config | Total V | Total A | Total Ah | Energy (Wh) |
|---|---|---|---|---|---|---|---|---|---|
| 12 | 10 | 100 | 2 | 2 | 2S2P | 24 | 20 | 200 | 4,800 |
| 3.7 | 5 | 2.6 | 4 | 3 | 4S3P | 14.8 | 15 | 7.8 | 115.44 |
| 40 | 9 | 0 | 6 | 4 | 6S4P | 240 | 36 | 0 | 0 |
Formula used
- V_total = V_unit × Ns (series adds voltage)
- I_total = I_unit × Np (parallel adds current)
- Ah_total = Ah_unit × Np (battery capacity adds in parallel)
- Power = V_total × I_total
- Energy(Wh) = V_total × Ah_total
- R_string = (R_unit × Ns) + R_wire
- R_eq = R_string ÷ Np (identical strings in parallel)
- I_sc ≈ V_total ÷ R_eq (rough surge / short-circuit estimate)
- Safe current = I_total × (1 − margin)
How to use this calculator
- Enter per-unit ratings (voltage, current, and optional Ah and resistance).
- Choose Ns for the number of units in each series string.
- Choose Np for how many identical strings you will parallel.
- Optionally add wiring resistance per string and a safety margin for derating.
- Click Calculate to see totals above the form.
- Use Download CSV or Download PDF to save results.
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Sizing logic that matches real constraints
Start with the voltage your load or inverter expects, then use series units to reach it. When units are identical, series adds voltage while current stays the same within a string. Parallel strings raise available current and, for battery systems, raise amp‑hour capacity. Use the target fields to estimate a starting point, then refine around temperature effects, tolerances, and controller limits.
Balancing current, power, and usable energy
The calculator reports total power as total voltage times total current, which helps compare configurations quickly. For storage, watt‑hours combine pack voltage and total amp‑hours, giving a clearer picture than amp‑hours alone. Use the safety margin input to derate current and power for continuous operation, heat, and aging. A conservative margin also reduces trips from protective devices.
Including resistance for planning and protection
Internal resistance and wiring resistance are optional but valuable for estimating stress. Series resistance adds across units, and wiring resistance adds to each string. When strings are paralleled, equivalent resistance drops, which can increase fault current. The estimated short‑circuit current is a rough indicator for fuse selection, switch ratings, and cable sizing, not a substitute for measurements or datasheets.
Interpreting the Plotly chart outputs
The chart visualizes how totals shift around your chosen counts. Voltage changes linearly with series count, while current scales with parallel strings. By scanning neighboring points, you can see whether a small change in Ns or Np better meets your target. Use the chart to spot overshoot risk, such as exceeding a controller’s maximum input voltage or a connector’s current rating.
Workflow for validating a final configuration
After you compute a candidate setup, confirm it against device limits: voltage, continuous current, surge capability, and thermal conditions. Check that parallel strings are well matched and use balancing and protection. Save the CSV or PDF for documentation, then re‑run with measured resistance values once hardware is selected. This approach improves reliability and reduces rework.
FAQs
What does Ns and Np mean?
Ns is the number of units in series within one string. Np is the number of identical strings connected in parallel. Together they define the configuration, such as 4S3P.
Why does series increase voltage but not current?
In a series string, the same current flows through each unit, so current stays the same while voltages add. Parallel wiring splits current across strings, so total current adds.
When should I enter amp‑hours?
Enter amp‑hours for batteries or storage packs where capacity matters. For solar panels or generic modules, you can set amp‑hours to zero and focus on voltage, current, and power.
How is safe current calculated?
Safe current is the total current multiplied by (1 minus the safety margin). A 15% margin means the calculator reports 85% of total current and power for conservative planning.
Is the short‑circuit current accurate?
It is a rough estimate based on the resistance values you enter. Real fault current depends on cell chemistry, temperature, connectors, and protection devices. Use it for planning, then validate with datasheets and measurements.
How do I use the chart?
The chart shows how totals change near your chosen Ns and Np. Compare nearby points to reach targets with less overshoot, and watch for limits like maximum input voltage or connector current ratings.