The battery pack is not short-circuit proof on its own (well, practically they are, because the power connector provides well isolation against shorts – however the safety standard does not consider this possibility), so I decided to develop a BMS for it. (And consequently have to redesign the main controller board again.)

The key requirements are chosen to be able to pass all today’s (and hopefully also tomorrow’s) safety tests:

• charge and discharge overcurrent protection
• short-circuit protection
• individual cell overvoltage and undervoltage protection
• separate under- and overtemperature protection for charge and discharge
• cell balancers
• fits to the battery’s front face
• cost effective
• programmable
• remote monitoring and control via I2C
• 15A continuous load current

Intersil has released a new family of full blown BMS IC’s that meets all my requirements: ISL94202 / ISL94203. The earlier is intended for packs with a common charging and discharging port, the latter is optimized for packs with separate ports. The actual difference is subtile, but chosing the wrong one (as I did of course) causes problems in certain conditions. The Intersil support staff is responsive and competent, which helped to sort this out quickly.

Here are some pictures of the first prototypes:

Finished board

Temperature sensor, thickened with heat shrink tubings

Connecting it to the pack

Finished connecting

Packs ready for testing!