Pauli writes –
I was assigned to design and implement a battery charger for 12 volt lead acid batteries used to backup WiFi- routers in rural areas of developing countries. Doesn’t sound very complicated a task in the first place, does it? At least that’s what I thought before finding out the facts (most of them using trial and error- method) that makes this task challenging. First of all, in some places here in Dharamsala the mains power can be anything between 80-380Vac + 1000V surges. This big variation puts any kind of power supply under heavy stress. Secondly, I couldn’t have any idea how hard it can be to find proper tools, equipments and components here in Himachal, not to mention the quality of some Indian- (hand) made components…
Jaldi Charger V.1.1 (and newer) is implemented using custom design, one sided printed circuit board that can be quite easily produced using Press’n’Peel technique. All parts are easy to solder (big size, non-smd) and mostly easily available in India (except some of the surge protection diodes). The currently used power supply solution is heavy duty, robust linear transformer with rectifier bridge, big filter capacitor and varistors for surge protection. Charger unit is based on highly reliable, well protected L200 linear regulator, that can efficiently work in this implementation with input voltages between 17 and 26Vdc. LVD unit is based on low cost voltage dual comparator LM393 connected to provide hysteresis and delay on connection and disconnection of the load. Ethernet surge protection is implemented using ultra fast Transient Voltage Suppressor Diodes. All cable connectors used are high quality screw terminals.
Jaldi Charger – safe charging at a reasonable price – Link.