A set of temperature-triggered switches alerts you to hot batteries.

Li-ion batteries can get hot, which can cause failures or worse in the products they power. Thus, it’s important to monitor their temperature and act before damage occurs. You can monitor temperature with a set of thermocouples, scan them, and write software to produce an action when the temperature exceeds a limit.

Littelfuse has a simpler way, so long as you need just one temperature limit: TTape.

TTape is a strip of ten temperature sensors that you attach to battery packs in EVs, commercial vehicles, and energy-storage systems. The sensors are essentially a series of ten temperature-sensitive switches. When any of the sensors detect an over-temperature condition of 61°C, that sensor will enter a high-impedance state. An external pull-up resistor raises the logic-level voltage that you can use to trigger an action. Hysteresis keeps the switch open until the temperature drops to 55°C. The schematic and voltage plot show how the sensors work. According to Littelfuse, the fixed temperature supports most cell systems for use in degradation management and thermal-runaway protection. The company says that other temperature threshholds will be available later in 2024.

Because the TTape uses a simple single-wire pair and provides a binary output, it doesn’t detect which cell overheated. It can, however, wake up a microcontroller to act when overheating occurs. The TTape’s sensors can break the circuit in less than 1 sec after an over-temperature condition occurs.

The TTape, which attaches to battery packs with an adhesive backing, measures 337 mm in length.

The TTape operates at voltages from V_DD = 3.3 V to 5.5 V with a 200 kΩ (±5%) pull-up resistor. Note: As of this writing, the datasheet also lists a V_DD = 2.5 V to 3.3 V range with a 100 kΩpull-up resistor. EE World pointed that out to Littelfuse. The company will remove that range from the datasheet.