Purchase a gift card from this link and funds will help launch our Open Source Solarpad solar USB charger kit for hiking, biking, and camping! https://fundrazr.com/campaigns/5jqBb
This system will combine the power from the sun and dynamo hub to double the power to a USB device like a smart phone and excess energy will be stored in Power Core. When not moving, Solarpad will compensate for the dynamo power loss, and when there's a shadow the dynamo will compensate for Solarpad power loss, which gives a more constant and reliable energy source while riding. Also, the dynamo is connected to an LED circuit that turns on automatically when the bicycle is in motion! During the day, it acts as a great daytime running light. A super capacitor ensures that the tail lights will stay on for a few minutes even after the bicycle has stopped at a stop light. This would be very useful to charge your phone while commuting in the city where lots of shadows and stops are frequent.
Step 1: Build The Circuit and Assemble the Solar Panel Bike Rack
Circuit parts include:
330QBK-ND 330OHM RESISTOR 1/4W 5% QTY: 1
P10791-ND SUPER CAPACITOR 0.1F 5.5V QTY: 1
30BQ015PBFCT-ND SCHOTTKY DIODE 350mV @3A QTY: 3
LM2940T-5.0/NOPB-ND 26Vin - 5Vout REGULATOR QTY: 1
5mm RED STRAW HAT LEDs QTY: 4 (they seem to be very bright and very affordable)
I got the idea for the super capacitor from this website: http://universalelectronix.blogspot.jp/2010/10/sup...
I made a Y-cable to come out of Solarpad and soldered the Schottky Diodes directly to the positive wires on the cable. One end of the Y-cable has a Male connector for the dynamo while the other end has pins that connect directly to the Power Core circuit. I chose to use these larger diodes because they had the smallest voltage drop for higher power output.
I used a hacksaw to slice a thin PCB, soldered the parts to it, and riveted the circuit to the edge of the Solarpad housing. To power the circuit, I spliced a portion of the Y-Cable with the male connector and soldered + and - leads to it. The regulator is required because I noticed that the dynohub can go over 10V at high speed. I also covered the circuit with epoxy to protect it from moisture.
I then modified a Topeak seat post bike rack by inserting Power Core in to the Topeak rack tube and replaced the entire rack with Solarpad. The Power Core female USB output cable and Male USB Y-cable routed inside Solarpad and exited underneath the bike seat where the dynamo and smart phone can connect to. You can test this assembly to make sure that it works by placing the bike rack in the sun and seeing if the Power Core LED turns on.
UPDATE 2/27/2014: The LEDs are supposed to be connected in parallel not series. The schematic has been updated to show the parallel LED connections.