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Solar Powering a FabFi Node

by Chris - June 27th, 2011.
Filed under: Projects. Tagged as: , , , , .

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Slashdot clued me into how residents of censored states are fighting back with the FabFi project. I’ve been thinking about how to build a solar powered wireless router for a while now, and this news article inspired me to figure out how one might solar power their own FabFi Node.


Calculating Power Requirements

One of the devices specifically targeted as a FabFi Node is the WRT160NL. Let’s use the two most useful equations in electronics to figure out the power requirements for this device.

I’m not the first person to think about solar powering this device. According to that project, this router required 8 watts for power. It comes with a 12 volt, 1 amp wall-wart transformer for power. According to the Power equation, there’s now way it could take more than 12 watts:

[math]12(volts) * 1(amp) = 1(watt)[/math]

The other nice thing is that this router runs off of a 12 volt supply, which means it will run directly off of a 12 volt, deep cycle car battery.

Assuming a consumption of 8 watts at an operating voltage of 12 volts, this device takes:

[math]8 (watts) / 12 (volts) = 0.667 (amps)[/math]

Now, assuming 24 hour operation, a WRT160NL running as a FabFi node will use 16 amp-hours (AH) or 192 watt-hours (WH) of energy:

[math]0.667(amps) * 24(hours) = 16(AH)[/math]

[math]8(watts) * 24(hours) = 192(WH)[/math]



Sizing the Solar Panel

Assuming we live in the northern hemisphere and our solar panel only gets 8 hours of direct sunlight a day, our solar panel needs to generate 192 watt-hours of power within those 8 hours. This means the solar panel should be rated for 24 watts or higher:

[math]192(WH)/8(hours)=24(watts)[/math]

If I was to build one of these for myself, I’d probably build a 60 watt DIY solar panel and use a charge controller to ensure it doesn’t overcharge the batteries. If I was to buy a solar panel, I’d probably buy an ET Solar 85 Watt Solar Panel. Either way, I strongly recommend the use of a charge controller. The Sunforce charge controller is very affordable and can handle solar panels up to 85 watts (7 amps).

I’m looking forward to see how the FabFi project develops. With projects like it and the FreedomBox, the citizens of the net may actually have a shot at beating repressive governments.






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