Supercapacitor Voltage Balancer
Active Switched-Capacitor Cell Balancing Network
Active cell-balancing network using switched-capacitor or flyback topology that equalizes voltage across series-stacked supercap cells, preventing over-voltage of any single cell as the stack discharges or charges.
Purpose
Without balancing, manufacturing tolerance and aging cause divergent cell voltages — pushing the highest-voltage cell into over-voltage damage and limiting useful stack voltage. Balancing recovers full usable energy and extends life.
Context
Embedded in each L3-ESS-SCAP-RACK at module-to-module boundary; supervised by L3-ESS-SCAP-CTRL. Active topology preferred over passive (resistor) balancing because supercaps charge/discharge frequently, making passive dissipation losses unacceptable.
Principles
- ▸Series-stacked supercaps suffer voltage divergence due to capacitance tolerance (~5–10%) and leakage variation
- ▸Passive balancing: resistor across each cell — simple but dissipates energy continuously
- ▸Active balancing: switched-capacitor or transformer-based — transfers charge from high to low cells with >90% efficiency
- ▸Switched-capacitor topology: a 'flying' capacitor transfers charge between adjacent cells via MOSFETs
- ▸Flyback/transformer balancing handles non-adjacent transfers but requires more components
- ▸Balancing current 1–5 A typical; must outpace mean voltage divergence rate
Typical implementations
- ▸Texas Instruments BQ78z100 / EM73D03 active balancer ICs
- ▸Linear Technology / Analog Devices LTC3300 (switched-capacitor)
- ▸Industrial supercap stacks (Maxwell, Skeleton — proprietary balancers)
- ▸Spacecraft battery balancers adapted for supercaps
Lunar considerations
- ▸Long mission life requires balancer components to outlast supercap cells (multiple replacements possible)
- ▸Radiation-tolerant MOSFETs (e.g., IRHF, IRSL) for switched-capacitor network
- ▸Balancing typically active only during charging and during long idle periods
- ▸Cold-temperature operation must maintain switching efficiency — careful MOSFET selection
- ▸Failure mode: any single MOSFET stuck-on causes cell short; redundant balancers needed for critical strings
Specifications
Functional
| primary function | Equalize voltage across series-stacked supercapacitor cells |
| inputs | Cell voltage measurements from L3-ESS-SCAP-MOD, Enable command from L3-ESS-SCAP-CTRL |
| outputs | Balancing currents up to 5 A between cells, Balancing telemetry (currents, MOSFET states) |
| topology | Switched-capacitor (LTC3300 or equivalent) |
| balancing current a | 5 |
| balancing efficiency percent | 92 |
| max cell voltage imbalance mv | 50 |
| switching frequency khz | 200 |
Physical
| mass kg per rack | 0.5 |
| dimensions | 120 × 80 × 15 mm card per rack |
| materials | Rad-tolerant MOSFETs (IRHF series), Ceramic flying capacitors, Polyimide PCB, Conformal coating |
| operating temperature c | -40, 70 |
| radiation tid krad | 100 |
Operational
| power consumption w | 2 |
| thermal range c | -40, 70 |
| lifetime years | 25 |
| mtbf hours | 250000 |
Interfaces
Provides
- Balancing currents to keep cells within tolerance
- Balancer health and current telemetry
Requires
- Cell voltage measurements
- Logic supply (~5 V at <1 W)
Cite this entry
Lunar Ark Codex. "Supercapacitor Voltage Balancer" (L3-ESS-SCAP-BAL). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-ESS-SCAP-BAL
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.