The Super Capacitor Flashlight with Custom Charger and Voltage Booster

Picture of The Super Capacitor Flashlight with Custom Charger and Voltage Booster
Hi Everyone!


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!


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.


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piddy050413 days ago

Hi great project thanks for sharing,just wondering can i use PIC12F683 chip instead

seanmft10 months ago

Pretty cool but I just want to point out that while you lose capacitance by putting capacitors in series, you don't lose energy. J=C/2(V^2). So with two 2.7 V, 50 F caps in series that's 25F/2(5.4V^2) = 364.5 J = 100F/2(2.7V^2). Whether you put them in series or parallel, their energy storage potential remains additive. You are however losing energy through the power converter.

Also, why so many LEDs? You could improve the optics greatly just by arranging the LED bank on a round board, and positioning it centered at the very very bottom of the reflector. Try it with a light meter, you'd be surprised. I'll bet it'll be brighter with half the LEDs running at full power

EngineeringShock (author)  acmefixer2 years ago
Power resistors and a diode to eliminate back powering. Currently, I'm charing my caps at 500ma (In this video). I've got an LM338 based charger at home that can charge up to 2.5A at 12.5v if you have the right resistor. To charge at 12.5v at 2.5A, you need:

R=E/I (12.5v/2.5A) = 5 Ohms
Power = E x I = 12.5v x 2.5A = 31.25 Watts
I'd use a 5 Ohm 40W resistor

I'd use a 16v 4A wall transformer, and a well heat sinked LM338 based variable power supply to tune to my charge voltage.
EngineeringShock (author)  acmefixer2 years ago
The LEDs work at 8v. Tried and tested. They are much dimmer than at 12v, which is nominal. 10v is good because you get good brightness, and it takes much less power. 12v is blindingly bright. However, 8v works too. Much, much less power. No bosting on the board. Parallel strings of 3x LEDs series LEDs with one current limiting resistor. No boost.
EngineeringShock (author)  acmefixer2 years ago
Hi there
i thought I mentioned it? Sorry if not. The booster board takes any voltage between 3.4Min-34vMax at the input, can can boost up to 34VDC.
wooo, jonny 5, 2nd movie is the best.
rimar20003 years ago
Awesome project, but too difficult for me...

Anyway, thanks for sharing it.
EngineeringShock (author)  rimar20003 years ago
I just made a very simple version of this flashlight, and an instructable if you're interested. No software, and no complicated circuitry =) Check out my channel if you're interested!
Oh, thanks. I will see that.
EngineeringShock (author)  rimar20003 years ago
Agreed. It is a bit complicated. I'll make an easier one next week, and cut down on the theory and such =) Thanks for having a look!
I'm really intrigued by the possibility of powering things from capacitors instead of batteries.
ITS CHALLENGING TO ME................