CHECK OUT OUR SUPER CAPACITOR FLASHLIGHT KICKSTARTER CAMPAIGN:
I'm a bit of a super capacitor fanatic, and I've made dozens of circuits that employ them. This circuit is a prototype that I'm turning into a DIY kit. Itis relatively simple, and is pretty darn efficient. There is also a lot of room for customization! When I get my custom PCBs made, I'll be throwing this device into an old flash light housing. For the time being, I'll be talking about the circuit as it is.
This is my entry for the MAD SCIENCE FAIR contest, as well as the MAKE IT GLOW contest, so if you liked this instructable, I'd sincerely appreciate your vote or a rating =) I've done my best to be AS THOROUGH AS POSSIBLE!
HERE IS THE FINAL PRODUCT:
What The Circuit Does:
Unfortunately, super capacitors can only be charged to lower voltages; typically around 2.5v or 2.7v as a standard. If you place some super capacitors in series, you can charge to higher voltages, but you lose a tremendous amount of capacitance. When you plug this device into a wall transformer ((I designed this device around a 9v@1A transformer), the on-board microprocessor turns on a relay that connects power to the capacitor bank. The series super capacitors then charge to 5.2v through the relay contacts. The capacitors an be interchanged to use higher or lower values, depending on how much you want to spend. The voltage on the capacitor bank is constantly being sampled by an ADC (Analog to Digital Converter) that is embedded in the microprocessor. When the voltage exceeds a value of roughly 5.2v, a flag trips in software, and the MCU turns off the charging relay, at which point the green LED indicator will start and continue to blink as an indicator to show the user that the caps are charged. You can leave this device plugged in for as long as you want, and the caps will be very much safe and sound.
When the caps are charged, the user can flip a switch that connects power from the capacitors into a DC-DC voltage booster. The voltage booster takes the 5.2v from the capacitor bank and boosts it to a calibrated 8v. The output voltage from the booster can be boosted anywhere from 3.4v to 34v, and is easily calibrated by an on-board 10-turn variable resistor.
Since I've calibrated the booster to output 8v, as soon as you flip the switch, the output of the booster will provide a constant 8v to the LED bank that acts to emit light. The LED bank is meant for 12v, but works great at 8v, and consumes MUCH less current. However, the LED bank is much brighter at 12v. The booster will continue to source power to the LED bank until the capacitors drain down to 3.4v, at which point the circuit shuts down. At this point, if you can plug it in again, to charge back up to 5.2v.
When the booster is tuned to output 12v, the circuit consumes quite a bit more current, but the light output is much greater. If you're going to consider maximum brightness, you're going to want to use 2x 400f 2.7v caps in parallel with one another. I also took the liberty of hooking up a $1 LED flash light head that I purchased from the dollar store directly to the capacitors as opposed to the booster, and it lasts MUCH longer. See the video.
THE WALL TRANSFORMER CAN BE SUBSTITUTED WITH A SOLAR PANEL! SEE NEXT STEP!