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Overengineered 12V lead battery recharger

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I did a small project that would allow 8 12V batteries taken from an older UPS to be charged from a bunch of photovoltaic panels.


at first I used a charge controller I got from the electronic store, but I was very unhappy by the fact that the controller would discharge the batteries in a few months. it had between 4 and 8 mA of quiescent current, which was much too high given the fact that my pannels almost never get direct sunlight.


so in it comes a msp430 that controls the charging and every once in a while logs to a uSD card the battery and PV voltage, charge current, internal temperature, heatsink temperature and the timestamp of course. all that and it ended up having an Iq of 170uA. that would go down to ~130uA if I drop the status LEDs.


maximum charging current is given by the PB137, so it is arround 2A. I guess two of these could be used in parallel for 4A, but I never get this much sunlight.


it uses a 3V coin cell battery (only for backup when the batteries are unplugged), 8x3w 5V panels from seeedstudio and 8 12V lead batteries all put in parallel.


it has a bunch of optional status LEDs that would either show voltage presence in the input/output/charging circuit, one on the SPI clock and 4 controllable by the uC.

as connectors go there are 5 IO pins - one of them is re-mappable, i2c connector for an optional display, TI spy-bi-wire for programming/debugging, 1 UART for debugging or a serial display, optional USB connection for programming or status gathering.


pictures here: https://plus.google.com/photos/106706955427383613204/albums/5947961264604104321?banner=pwa


all sourcecode and schematics are here: https://github.com/rodan/solar-charger/





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Hi Bluehash,


the 12V battery pack is used to charge all my gadgets via a mock-up USB output, my phone, flashlight baterries and all the 1.2V rechargable AAs I have arround.

it has the same output connector I use on my motorcycle, so I reuse the same cables for all the devices described above. some of them are in the picture on the left side.




also a 220V inverter could be plugged into the unit for those dark moments :smile:




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A few changes have been done to the project:


 - add bash script that parses the uSD log and adds the data into a sqlite database

 - add gnuplot script to generate nice graphs for all the sensors (using the sqlite db)

 - fix bug related to REFVSEL switching in adc.c

 - upgrade to FatFs R0.10 + latest patches (ChaN 2013)

 - added a few more pictures to the picasaweb album


 also discovered that the thermistor used is far from linear so I have to come up with a better calibration for it.

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