Power supply for Raspberry Pi

batteriespower supplyraspberry pisolar cell

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I need to power a Raspberry Pi with some electrical equipment attached to it. The Pi needs to run for at least 48 hours and I need at least 2V and 900mAh to be used for the other equipment. The device must be portable, so it doesn't have to weigh too much. I thought about using more than one power source and somehow merge them together (for example using rechargeable Li-on batteries and a solar panel).

What would be the best way to accomplish it?

EDIT: I should be able to see how much power is left.

Best Answer

Add to your 2 V load at 1800 mWh the power consumption of the RPi. Find a good guess on that at RPi@SE. Given the amount the RPi consumes (20 to 45 Wh a day) your load seems to be negligible for your power supply. So the most simple solution would be to pick a suitable power supply for the RPi and use a switching step down regulator to provide the 2 V.

(Depending on the application the RPi might not be best suited for a portable solution.)

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A small 5V latching relay will do it. As it latches, it consumes no power except when changing state.

Battery recharging via solar panel

Vpanel >> Vbattery so panel acts as ~~ constant current source.

2 batteries in series or 4 batteries in series will still be << 9V so charge in the same time.

Imp < Icharge < Isc or
0.33A < Icharge < 0.43A

Say ~~= 350 mA.

T charge ~= Battery_mAh / Ichg x 100 / Battery_efficiency % NimH CURRENT acceptance efficiency probably 80%-90%

= 700 Mah / 350 mA x 100/80 ~~~= 2.5 hours

That's in full mid-day sun with panel square on to sun. Charge for longer than this and you will quickly "cook" the batteries.
Vbattery_max at that charge rate should probably not be more than about 1.5V/cell when charging.

Google: your_city_name gaisma
eg Bangalore gaisma gives

    http://www.gaisma.com/en/location/bangalore.html

to get SSH = sunshine hours per day (= kWh/m^2/day)
Your panel will produce ABOUT 350 mA x SSH mAh per day

Bangalore example -

Half a day on an average day will be more than enough in any month - see below.

enter image description here

Chart from Gaisma entry for Bangalore as above.

Best Answer

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Battery recharging via solar panel

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