SERIES AND PARALLEL

Wire cells into a pack

Joining cells in series adds their voltages; joining them in parallel adds their capacities. Packs are described as, say, 96S2P.

Series for voltage, parallel for capacity.

THE BRAIN

The battery management system

🧠

📏

Measure

Voltage of every series group, current, and temperatures

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Estimate

State of charge and state of health

🛑

Protect

Stops charging or discharging outside safe limits

Without a BMS, a lithium-ion pack is not safe to use.

BALANCING

Keeping cells in step

No two cells are identical. In a series string, the first group to hit full stops the charge and the first to hit empty stops the discharge. Balancing bleeds a little charge from the fullest groups (passive) or moves it to the emptiest (active).

A pack is only as good as its weakest group.

KEEPING COOL

Thermal management

❄️

Happy range About 15–35 °C for most lithium-ion cells

Air cooling Simple and cheap, fine for small or gentle packs

Liquid cooling Coolant plates under or between cells, used in most electric cars

Heating Cold cells must be warmed before fast charging to avoid plating

Temperature control adds life and safety.

SIMPLER PACKS

Cell-to-pack and cell-to-body

🚘

Newer designs skip the module and put cells straight into the pack, or even make the pack part of the car's floor. Fewer parts means more cells in the same space and lower cost.

Pack engineering can add as much range as cell chemistry.

UNIT 14 STUDY COMPLETE

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Ready for the Fab Challenge?

You've wired cells into a pack, met the battery management system, and seen why a pack needs cooling.