AWESOME!
It has exceed all expectations. The system was built to provide internet connectivity to public school students in low income neighborhoods so they could do their homework online without a home internet connection needed. It is shuffled from neighborhood to neighborhood, community center to community center and in large, open areas such as parks and empty parking lots in two hour increments, with a published location schedule, where any student can access a 5/5mb symmetric internet connection and complete online homework assignments. Total capacity is 200 simultaneous users with a 100/100 Mb back haul. System turns on at 7:30am and provides internet automatically. System goes into standby at 7:30pm to conserve overnight power. Back haul connects wirelessly to one of my WISP towers, and can also carry backup internet circuits provided by satellite, cell system or any terrestrial wireless provider in the usage area. You can even run an Ethernet cable to it from whatever legacy wireline internet available.
that’s the production part.
The electric part looks like this:
2-24v 55w mono solar panels in series to the tpdin-sc48-20 poe charge controller. A 7P, 14S 18650 pack of Samsung 30q, 3,000mah cells providing 22.75Ah stored energy. Production unit consumes 22w max and about 10w in standby.
it has functioned PERFECTLY for almost three years now. If we get more than two rainy days in a row, morning startup is delayed until the sun gives the system 48v steady (usually by 8a) and it drops into standby when the battery goes below 45v. It has an external charge port that can be connected to the vehicle’s cigarette lighter to fire up regardless of battery condition, but has never been needed. I manually balance the cell pack quarterly and the delta varies with an average of 500 milliohms.
the cooling system is noteworthy as well. This operates in the U.S. Virgin Islands all day long in direct sun. The internal temperature of a black, sealed box initially exceeded 180 degrees. Without robust cooling, the components would all fry and the battery would likely explode. I added passive cooling by isolating components inside the main box in their own pvc container creating a moderate air gap between the exterior and interior cases. Inside the inside box, all components are mounted directly to a large, aluminum plate that is 1/2” thick, leeching the heat from individual devices. I added a 120mm fresh air intake fan which pulls from below the outer shell and blows directly on the aluminum plate, then baffled underneath the plate and added the same size exhaust fan. With these items in place and a thermostat control that turns them on when the temp exceeds 105F, the interior space has never exceeded 110F, and the fans shut down for the night automatically.
I’m now working on V2.0 that increases energy storage to 30Ah, moves from li-ion to LiFePo4, adds a BMS for automated pack balance, integrates a cell phone myfi for our of bandwidth access, stronger hydraulic lift arms for the lid, a pelican case internally instead of the handmade box.
Not only have they allowed hundreds of students daily to get their homework done, I’ve presented the system to a bunch of science class students as an example of how solar power and battery Storage can create fully self contained, fully self sufficient micro power systems that can be designed to run any electrical item indefinitely.
It’s been fun…
