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Wifi Repeater solar power

Status: Proposal
January 28, 2017, Latest update: February 9, 2017
Some simple Wifi router can be configure in repeater. This simple Wifi router didn’t need press any button, just start when the USB charger is working. One example I used is TPlink TL-WR802N. After testing, this router need at least 150mA-200mA full time to work. I developed here a board, with 7000mAh batteries and a control charge with an external solar panel.

The board can have 2 control possible. One is with a standard Maxim comparater MAX931 (or equivalent LTC1440), one for low level, one for high level. The second control possible is with a simple uC, PIC 12F1572. Roughly, the functions are the same but with the uC, the voltage adjustment is easier.

For the DC-DC, to convert the 4.2V lithium batteries to 5V USB, I used an LTC3536. This DCDC IC can provide 1A max and has an real disable function, which is mandatory to avoid leakage from the batteries in the USB. - When the voltage is too low, the solar panel will charge the batteries only. USB output is OFF.

- When the batteries level is around 3.9V, the DCDC is ON and provide 5V to the router, which turn ON automatically.
- If the batteries level are more than 4.2V, the solar panel current is redirect to a power resistance. I didn’t want to add a switch in the charging circuit. There is only a Schotcky diod 2A to charge the batteries.
- If the batteries level goes down to 3V, the DCDC is stopped and the router too.

The solar panel is 5V-10W. I tried with a 5W but it is too short. 5h of sunshine cannot give 19h of power to the router. With the 10W panel, it is working well. 4h-5h sunshine are enough to charge the batteries for another 19h.

The efficiency of the DC-Dc is so-so. It is using 200-250mA full time. The batteries are 2 batteries 18650 3500mA in parallel. Take care of the fake... I had some bad experience here. There is some LED to display the status of the charger.

The PCB is done, to solder the DC-Dc chip is little bit tricky due to small pitch and the solder bad under the chip. For the 12F1572, 2 possible format, DIP8 or SOP8. The software for the 12F1572 is not too complex. Power and LED management.

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