Who designs the first DIY LiFePO4 charger?

January 24, 2017 | 00:00
Talk about battery chargers and Elektor has a long record of articles and do it yourself projects always taking the lead. Lead-acid, NiCd, NiMH — we’ve been there and done that and now a new battery composition hails all you Elektor e-zine readers with a challenge to come up with a charger project for ….drumroll… 3.6-V single-cell lithium iron phosphate (LiFePO4). Here is a get-u-going hint.

Intersil’s ISL78693 is qualified to AEC-Q100 Grade-3, leaks only 3 µA, and is suitable for eCall back-up battery charging. In the event of a crash, eCall systems are intended to automatically broadcast location and contact the nearest 24-hour emergency call centre for help. They must “be capable of operating reliably and autonomously from the backup battery at a moment’s notice, even if the vehicle is involved in an accident minutes after being parked for several months,” said Intersil. 3 µA is a maximum, with typical leakage of 700 nA.

LiFePO4 chemistry needs charging at 3.6 V – less than the 4.2 V typically offed by charge chips aimed at more conventional Li-ion cells. Charging is up to 1 amp. A charge current thermal fold-back feature prevents over-heating by automatically reducing the battery charging current, and low-temperature detection prevents charging if the cell is too cold to accept electrons.

The ISL78693 requires only five external passive components. It’s a linear charger, so none of these are inductors. More good news: the 3.6-V ISL78693 is pin-compatible with the 4.1-V ISL78692 Li-ion battery charger. Neither will work from nominal 12-V car voltages though so you have to slap up some dc-dc converter to bridge the gap.

Rise to the challenge! Post your LiFePO4 project on www.elektormagazine.com/labs

 
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