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BMS Topology Selector
Tell us the pack and the application; get a recommended BMS architecture, balancing method, number of cell-monitor ICs and the protection features the design needs, with the reasoning spelt out.
Topology
Centralised
Balancing
Passive
Cell-monitor ICs
1
at ~16 cells each
Pack voltage
≈ 56 V
nominal, 3.5 V/cell average
Why
- 16 cells in series fit on one board with 1 monitor IC(s) — the cheapest and simplest layout, typical for e-bikes, 2W and 3W packs.
- Passive (resistor) balancing at 50–200 mA is enough when cells are matched and capacity is modest — it is cheap, simple and proven.
Must-have features
- Cell voltage, pack current (shunt or Hall) and 1 temperature sensor per 4–8 cells
- State of charge by coulomb counting corrected with an OCV table (Kalman filter for higher accuracy)
- Over/under-voltage, over-current, short-circuit and over-temperature cut-off via MOSFETs or contactors
- India L-category vehicles: meet AIS-156 battery safety requirements (cell-level monitoring, thermal-event warning, IP protection)
- CAN or UART telemetry plus a data logger for warranty and field diagnostics
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BMS architecture brief
BMS Topology Selector ·
Inputs
| Application | Scooter / motorcycle |
| Pack | 16S, 40 Ah |
| Priority | balanced |
Results
| Topology | Centralised |
| Balancing | Passive |
| Cell-monitor ICs | 1 |
- 16 cells in series fit on one board with 1 monitor IC(s) — the cheapest and simplest layout, typical for e-bikes, 2W and 3W packs.
- Passive (resistor) balancing at 50–200 mA is enough when cells are matched and capacity is modest — it is cheap, simple and proven.
- Cell voltage, pack current (shunt or Hall) and 1 temperature sensor per 4–8 cells
- State of charge by coulomb counting corrected with an OCV table (Kalman filter for higher accuracy)
- Over/under-voltage, over-current, short-circuit and over-temperature cut-off via MOSFETs or contactors
- India L-category vehicles: meet AIS-156 battery safety requirements (cell-level monitoring, thermal-event warning, IP protection)
- CAN or UART telemetry plus a data logger for warranty and field diagnostics
Estimates for planning — verify against datasheets and supplier quotes before you build or invest. Recalculate or share:
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How it's calculated
Centralised: one board measures every cell. Cheapest and simplest, but sense wires run the length of the pack, so it suits up to roughly 32 cells in series — e-bikes, 2W and 3W.
Modular (master–slave): a slave board on each module measures its cells and reports to a master over an isolated daisy-chain or CAN. The default for cars and larger packs.
Distributed: monitoring at every module or cell group, for very high series counts (buses, large storage) where short wiring and module-level service matter most.
Balancing: passive (bleeding the highest cells through resistors at 50–200 mA) is cheap and enough for matched cells; active (moving charge between cells) pays off for large-Ah cells and long daily cycles. Typical cell-monitor ICs (AFEs) each measure 14–18 cells; the calculator assumes 16.
Results are engineering estimates for planning and learning. Check them against datasheets, supplier quotes and the applicable standards before you build or invest.
Frequently asked questions
What is the difference between passive and active cell balancing?
Passive balancing burns excess charge in the highest cells as heat through resistors until they match the lowest. Active balancing transfers charge from high cells to low cells with inductors, capacitors or transformers, wasting less energy but costing more.
What does an AFE do in a BMS?
The analogue front end (cell-monitor IC) measures each cell's voltage and temperature precisely, runs the balancing switches and passes the readings to the BMS microcontroller, which runs state-of-charge estimation and protection.
Which BMS rules apply in India?
Battery packs for L-category vehicles (2W/3W) must meet AIS-156; cars, buses and goods vehicles fall under AIS-038 Rev 2. Both include BMS-related safety requirements such as protection against over-charge, over-discharge, over-current, short circuit and over-temperature.
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