This simulator models a four-cell series string of 3 Ah teaching cells that starts with an unequal state of charge. Run passive resistor bleed balancing, active energy-transfer balancing, or disable balancing entirely, and watch how the SOC spread, string voltage, balancer loss and dissipated or delivered energy evolve over time.
• A real-time 3D workbench of the series cell string — vented cylindrical cells in an insulating cradle, welded busbars, a bleed-resistor and active-transfer balancer module, and a four-channel cell monitor — with toggleable enclosure, auto-rotate, exploded view and selectable, callout-labeled parts. • Experiment controls: initial SOC and initial SOC spread for a new trial, a balancing-method selector (passive bleed, active transfer, disabled), and a balance-channel current control from 50 mA to 1 A. • Start/stop actions to begin the trial or open the external circuit, plus pause, single-step (1 s) and 60 s advance, with playback from real time up to one hour per second. • A live sequence readout, switch-state tokens and a per-cell SOC readings table. • An Analysis tab with SOC/voltage/loss history charts, the model equations for passive bleed and active transfer, and snapshot measurements of SOC spread, string voltage, mean SOC, balancer loss, dissipated energy and charge delivered to the low cell. • A Test & diagnose tab with four guided experiments (passive equalization, active equalization, balancing disabled, small balance current), a model-verification bench, and a timestamped event log with trial report export. • A Learn & assess tab with four lessons, a two-question knowledge-check quiz, and a written model-scope statement with a reference link.
Passive balancing selectively discharges the highest-SOC cells through bleed resistor channels. That excess energy becomes heat, so mean string SOC decreases over the balancing period — dSOC/dt = −Ibleed / (3600 × Q) for each bled cell.
Active balancing instead uses a bidirectional converter to move energy directly from the highest-SOC cell to the lowest, modeled at 85% conversion efficiency: Ireceive = 0.85 × Isource × Vhigh / Vlow. The lowest cell's SOC rises while the difference between input and output power appears as converter loss. Balancing stops once the SOC spread across the string reaches the 0.2 percentage-point stop band.
In a series string, every cell carries the same current, so the string must stop charging or discharging as soon as any single cell reaches its voltage or SOC limit — even while its neighbors still have usable headroom. This is why cell-to-cell mismatch, whether from manufacturing tolerance or uneven aging, directly caps a pack's usable capacity, and why balancing exists at all.
This lab intentionally balances against a modeled SOC value rather than measured terminal voltage, to make the comparison between bleed and transfer unambiguous. Real balancing systems commonly rely on voltage and state-estimation logic instead, which is subject to additional chemistry-dependent limitations that this simplified model does not include.
Passive (resistor bleed) balancing discharges the highest-SOC cells through resistor channels, converting the excess energy to heat and lowering mean string SOC. Active (energy-transfer) balancing uses a bidirectional converter, modeled at 85% efficiency, to move charge directly from the highest cell to the lowest, raising the low cell's SOC while dissipating only the conversion loss.
Every cell in a series string carries the same current, so the whole string must stop charging or discharging once any one cell reaches its limit, regardless of how much headroom the other cells have. Balancing equalizes state of charge across cells so the pack can use more of its total capacity before any single cell becomes the bottleneck.
No. The energy delivered to the low cell equals the energy drawn from the high cell times the modeled 85% converter efficiency — the remainder is dissipated as loss, exactly as the simulator's Balancer Loss and Dissipated Energy readouts show.
The lab uses four isolated 3 Ah series cells with no external pack load, no capacity mismatch between cells, and no self-discharge. The active converter's switching behavior is averaged rather than simulated in detail, and SOC-based cell selection is idealized rather than based on measured terminal voltage.