Resettable fuse carries 20A for Li

Bourns has introduced a series of miniature resettable thermal cut-off (TCO) devices for dense, high capacity lithium-ion battery packs.

The Model AC series offers five trip temperatures: 72, 77, 82, 85 or 90°C (all +/-5°C) – the latter of which “is capable of carrying up to 20A at 60°C, making it the highest current-carrying TCO device Bourns offers,” said the firm. Contact rating is 1,000 cycles (9V 35A). Reset is at 40°C min. Leakage (through parallel resistance (see circuit below) is 200mA max at 25°C.

Rather than being thermistor-based, these devices are real thermostats with metal contacts (see cross section below) – un-tripped resistance is very low, 2mΩ max (1-1.5mΩ typ) Other devices in the range are listed here.

Devices are 7 x 4 x 1.1mm (plus leads) – 0.12mm thinner and 16% lighter than the existing Model AA series, introduced in January 2017.

Applications are expected beyond traditional laptop, tablet and smart phone applications, to power tools, electric vehicles, e-bikes and grid storage.

Model AC devices are available now, and are RoHS compliant and halogen free – the last of which Bourns commendably actually defines. Max levels are: Br 900ppm, Cl 900ppm, Br+Cl 1,500ppm.