Supercapacitor Energy

Calculate stored energy and usable energy (Vmax→Vmin) for a single supercap or a series/parallel bank.

How to Use

  1. Enter capacitance and your charge voltage (Vmax).
  2. Optional: set a minimum voltage (Vmin) to compute usable energy.
  3. Optional: set series/parallel counts to model a supercap bank.
  4. Open “Show Work” for formulas and steps in base units.
Energy View
Stored vs usable energy from voltage range.
Ceq
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Vmax
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Vmin
—
Eusable
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Indicator: —
Supercap Energy (J) Energy (Wh) — — Usable energy uses: Euse = 1/2·C·(Vmax² − Vmin²)
Inputs & Settings
Works for a single cap or an equivalent bank. Outputs update instantly.
Common: 10F, 100F, 3000F, 500F bank
Use the charge voltage (rated max)
Optional: set cutoff voltage for usable energy
Optional: affects peak power estimate only
Bank only: Ns ≥ 1
Bank only: Np ≥ 1

Bank math uses equivalent values: Ceq = C·Np/Ns, Vmax,eq = Vmax·Ns, Vmin,eq = Vmin·Ns.

Show Work (step-by-step)
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Work is shown in base units (F, V, J, Wh) for clarity and consistency.

Reference Formulas

  • Stored energy: E = ½ · C · V²
  • Usable energy (Vmax→Vmin): Euse = ½ · C · (Vmax² − Vmin²)
  • Charge moved: ΔQ = C · (Vmax − Vmin)
  • Bank equivalent: Ceq = C · Np / Ns, Veq = V · Ns
  • Wh conversion: Wh = J / 3600
  • Peak power estimate (optional ESR): Ppk ≈ V² / (4 · ESR)
These are idealized equations; real systems depend on ESR, balancing, wiring, and load profile.

FAQ

Why does voltage drop fast on supercaps?

Because stored energy scales with V². As voltage drops, available energy drops quickly unless you regulate it.

What’s “usable energy”?

It’s the energy between your max charge voltage and your cutoff voltage: ½·C·(Vmax² − Vmin²).

Series banks confuse me—what changes?

Series increases voltage but reduces capacitance: Ceq = C/Ns. Parallel increases capacitance: Ceq = C·Np.

Is peak power estimate reliable?

It’s a rough ideal estimate using ESR only. Real limits include current ratings, thermal rise, interconnect resistance, and balancing circuits.

Tool Info

Last updated:

Updates may include additional unit support, bank edge-case handling, and export improvements.