Instructables
Picture of 2600 Farad Capacitor Flashlight
UPDATE:

My newest 400 farad super capacitor flashlight made with the latest readily available components here:

 

http://www.instructables.com/id/400-Farad-Super-Capacitor-Flashlight-Build-This-/?ALLSTEPS

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This “how to” deals primarily with the 2600 farad capacitor “flashlight” I made (NO BATTERIES). I will not go into a lot of detail on how to make it in regard to details like “cut this size circle out of this kind of plastic” “drill four holes here”. What I will provide is simple circuit diagrams and explanations along with some pictures that will provide enough information to make one of these flashlights. Your “flashlight” will probably look different than mine depending on what you use as an enclosure. You can put it in a chassis box or a lunch box or a tool box or a shoe box. You can even glue it to a piece of wood. In any case you will still have a usable source of light for TWCS or TEOTWAWKI (No grid? No problem). As you will see I used the “LEGO” design philosophy when I built mine. I like thing that snap together with a variety of easily interchangeable parts. I plan on doing plug in upgrades as new technologies arise. I don’t want to have to tear it apart and rewire my flashlight just to try something new. In addition to providing the basic design I will also suggest some options for charging and options for drive circuits and LEDS. I will also provide a little bit of test data so you can decide if this project is worth your trouble.
One last thing before getting started, If you think you would like to make one of these someday, you may want to buy a couple of capacitors now rather than later. I bought two of the 2600 farad capacitors earlier this year when they were on sale. I got them for under $10.00 each. The individual 2600 farad capacitors are currently unavailable from Electronic Goldmine. As of this writing you can purchase two of them bolted together for $34.00 (plus shipping). Who knows what the cost or availability will be in the future. Here is the link for the capacitor page:
 http://www.goldmine-elec-products.com/products.asp?dept=1471

 2600 Farad Flashlight

This project has three distinct parts:
The power supply /charger.
The capacitor enclosure and wiring
The LED Driver Circuit
Let’s start with the enclosure and wiring. I had used this type of plumbing part (see pics) for another project and luckily the capacitor fit in it. I made the round plastic part for the two ends and wired it up, per the wiring diagram. The test points are used to monitor when the capacitor is fully charged. If you utilize this feature you will need a volt meter. If you build electronic circuits you probably have one of these already. I chose an RCA (phono) jack for the output of the capacitor. The speaker connector with the spring loaded contacts is the input for charging. You may want to go with the more common barrel connector for input power. I decided against this to prevent plugging in the wrong power supply. I plan on making a polarized 3 pin connector to plug into the speaker connector. The enclosure has an on/off switch also. (easy so far).
Next let’s look at how to charge up the capacitor. The main thing you don’t want to do is over charge the capacitor. If you connect the capacitor to a power supply that supplies less than the maximum rated voltage, you can leave it connected all day long. You should not connect it to a power supply that will deliver a voltage higher than the maximum voltage rating of the capacitor. These capacitors can be charged with a very high current and can deliver a very high current. So high in fact that you can melt small gauge wires and circuit board traces. Be careful. Don’t short out one of these capacitors. It could be quite unnerving unless you are expecting very large sparks (think arc welder). In fact eye protection during assembly would not be a bad idea. You may want to take a look at the data sheet for any capacitor you intend to rapid charge for the maximum current rating. Staying within the maximum rating of the capacitor will help insure decades if not lifetimes of LED run time with minimal degradation of performance.
Since the intended purpose of this flashlight (among other things) is to insure that I have at least some available lighting if the power grid becomes temporarily off line and if I were to hypothetically run out of batteries. Not that I will be using to many batteries since I have three capacitor flashlights. So I decided to use a solar panel to charge the capacitor. I decided to go with a 5 watt panel since they are relatively cheap. I waited for a sale over at UL Solar and bought one:
http://www.ul-solar.com/default.asp
I chose the LM317T adjustable regulator to limit the charging voltage to 2.47 volts. Here is a link for an LM317 resistor calculator:
 http://www.dimovi.net/toma/stuff/LM317.htm
Remember to test the output voltage after you wire it up since the actual voltage the regulator puts out may vary from what the calculator says it should be. By the way my actual resistor values used are not 200 ohms. I had to connect lower value resistors together to dial in 2.47 volts. Also if you type in 2.47 volts into the calculator it shows two resistors in the 240 ohm range. I used a chart from another web site. What determines the output of the regulator is the ratio between the two resistors.
I also included a 6 ohm current limiting resistor to keep the charger from loading down the solar panel too much. A 5 watt resistor would have worked fine but all I had was s 25 watt resistor. I tried connecting the charger to a car battery and it works great but the regulator gets frying hot since it is burning off 80 percent of the input voltage. You may want to use an ac adapter to supply current to the regulator circuit. If you go with a lower voltage you can minimize the heat problem. A higher current adapter will be helpful to charge the capacitor quickly. Some tweaking of the current limiting resistor value may be necessary. In the future I plan on trying a 6 volt panel. I will also try a dc to dc converter if I can find one on sale / for cheap. By the way, my charger works ok even on cloudy days since I am burning off almost all the voltage anyway.
Next let’s look at the LED driver circuit. I decided to go with one capacitor (2.5 volts) instead of two in series because my flashlight would too big. Also, the capacitance gets cut in half with two capacitors in series. Besides, there are plenty of ways to run LEDS on less than their rated voltage. I made one flashlight that uses a 1/2 watt mag light LED upgrade “bulb”. It has a tiny built in circuit so it can run on two to six batteries. The bulb can be connected directly to the capacitor but I decided to put a variable resistor in the circuit to control brightness and extend run time. The bulb does not put out as much light with 2.5 volts as it does with 3 volts (2 batteries) but it does put out a usable amount of light and it is as easy to use in this circuit as any LED. Here is the link to the LED upgrade:
http://www.niteize.com/collections/flashlights/products/led-upgrade-kit-cd-cell
I made another flashlight with a Joule Thief circuit. Some very smart wire head (smarter than this one anyway) came up with a circuit to power a LED off of a battery that is basically dead. There are different variations on the circuit so it is worth looking around at some of them before jumping in. You may have to make a coil but it is easy. Here are a few links:
 http://www.ledsales.com.au/kits/joule_thief.pdf
 http://www.evilmadscientist.com/article.php/joulethief
 http://www.joulethief.com/kit.php
 http://www.emanator.demon.co.uk/bigclive/joule.htm
Since the circuit I built was designed to run on less than 1-1/2 volts I added a current limiting resistor and a variable resistor.
For the 2600 farad flashlight I took apart a solar powered lawn light. I used the type that has no photo cell (only the solar cell) to detect ambient light and switch on the LED when it is dark. If you use one with a photo cell you will need to test if shorting the wires together going to the photo cell will make the LED stay on all the time. I got my lawn lights for cheap when they went on sale last year at the end of summer. As you can see from the drawing of the circuit all you are doing is:
Taking the solar cell out of the circuit altogether.
Connecting the output RCA jack to where the led was (Cut the end of the led off and solder to the leads).
Connecting the capacitor in the circuit where the battery used to go.
Oh yes, and adding a current limiting resistor since you are running the circuit at over 1.5 volts to start.
I added a high low switch and resistor also.
You can do a lot of tweaking of resistors values. I tried the circuit momentarily with no resistors using a 10MM, narrow angle, 4 element LED. It was impressively bright. I may have been over driving it. I will have to try that again. My selection of resistors will deliver over 30 milliamps to a LED with the switch in the high position. This is too much for many low power LEDS. I will be using only higher current LEDS like the 10mm multi chip LEDS or two and three LEDS wired in parallel. My personal favorite so far is two high flux piranhas in parallel.
Here is yet another way to produce light with a supercapacitor: I bought a couple of the AAA Rayovac flashlights from Wal Mart ($3.00, see pic). The metal part with the lens, LED, and driver circuit can be removed.
By soldering wires to the contacts, this assembly can be connected directly to a capacitor if the capacitor is charged to about 1.6 volts or less. If the capacitor is charged to a higher voltage, a resistor is needed in the circuit. I used a 10 ohm resistor for testing.
Runtime
My goal in making this flashlight was to get a runtime of at least 12 hours of useable light from a fully charged capacitor. I started the test with the two piranha LEDS mentioned above, with the flashlight in “high” mode. I tested the current going to the LED by putting a 1 ohm resistor in series with the led and measuring the voltage. The voltage across the resistor is divided by the resistance of the resistor to calculate the current in the circuit. The current was 32 milliamps at the start of the test. That would be 16ma per LED. I tested the current after 13 hours and it was 10ma (5 ma per LED). The intensity between 30 ma and 10ma did not look that different. This is due to two factors. Most LEDS are the most efficient at producing light at around 7 – 10ma. You get more light by running two LEDS at 10ma each than one at 20ma. Also the human eye is progressively less sensitive to light as the light intensity increases. So, I met my goal of 12 hours but I continued the test for a total of 18-1/2 hours. At that time the current in the circuit was 7ma and it did look a little dimmer. But I continued on with testing by using the flashlight (and only the flashlight) to make an eat breakfast at 5:30in the morning. It worked fine. Also tried reading and it worked fine although reading for an extended period of time would be better with the flashlight at 10ma.
I think if I were to run the flashlight for a full 24 hours I would run it for about 14 hours on low and then switch to high for 10 hours. That will be a test for another day.
In a grid outage situation 12 – 14 hours of run time between charges should be all I need.
Here are some links for where you can buy LEDS:
 http://www.niktronixonline.com
 http://www.superbrightleds.com
If you want to buy a capacitor flashlight, here is the link (It costs $179.99. It has 120 minute run time (60 min @ 90 lumens, 30 min @25 lumens, 30 min @ 14 lumens). 90 second charge time):
 http://www.511tactical.com/All-Products/Flashlights/Light-for-Life-Flashlight-UC3400.html
 
 
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luxstar (author) 1 year ago

Since this was published I have made an improved charging circuit using a DC to DC converter.

It’s here:

 

 

http://www.instructables.com/id/93-efficient-DC-to-DC-Converter/

Better still to use a constant current AND constant voltage circuit, just like a NIcad charger.
luxstar (author) 2 years ago

UPDATE

Goldmine Electronics is not currently stocking the 2600 farad capacitor. You can get the 400 farad capacitors I made my other two flashlights with here

 

http://www.futureelectronics.com/en/Technologies/Product.aspx?ProductID=DB5U407M35060HASAMWHAELECTRICCOLTD8382301&IM=0

Good project--excellent link to supplies!