Supercapacitor Flashlight




About: I am an author and a maker. My current project is Santa's Shop. I'm working on a science fiction type book--more later. @EngineerRigsby

Using a 5 watt MR16 led light, this (50 watt equivalent) flashlight (weighs less than one pound) really puts light in dark places. The capacitors can be recharged hundreds of thousands of times--so there's no worry about wearing them out.

Using a 5 watt MR16 bulb, the light will shine for about six minutes--it can be recharged in 90 seconds with a 5 amp power supply. A 2 watt MR16 would give about 15 minutes of light (and could be recharged in 45 seconds with a 10 amp supply).

Don't be afraid to work with these capacitors--they store less energy than a AAA battery, but they can receive and discharge current quickly--generate some heat on a wire if the wire shorts the terminals (for comparison, an AA battery powered soldering iron can reach a temperature of one thousand degrees in seven seconds).

Step 1:


(2) 350 farad 2.7 volt capacitors Mouser Electronics These cost about $12.00 each at this supplier

(1) 5 watt MR16 bulb Amazon

(1) Boost Converter amazon

(1) Power jack socket Amazon

(1) Power plug to fit jack socket

(1) MR16 light socket

(1) Power supply that can provide constant current up to 5 amps Amazon

(1) On/Off switch

(1) 5 amp fuse and socket

Misc: solder, heat shrink tubing, wire, M3 screws

Print 3d parts

Step 2:

Insert the MR16 socket into the top piece. Secure using M3 screws.

Step 3:

Insert bulb into socket.

Step 4:

Drill hole in back side of switch piece (yes, I should have designed it into the 3d file; but I didn't know that at the time).

Step 5:

Solder wires to switch and secure to switch holder.

Step 6:

Solder wires to jack. It is advisable to have a plug in the jack when soldering--otherwise, the center pin may get too hot and move around off center.

Step 7:

Adjust the DC converter to 12 volts output (using the small screw on the board).

Solder wires to the DC converter. Connect the top of the light and the switch pieces using a soldering iron to melt them together.

Step 8:

Solder remaining wires to the converter, then secure the converter to the upper capacitor holder using an M3 x 8 machine screw.

Step 9:

Solder the wires to the supercapacitors. Use heat shrink tubing when wire connections could move around. Do not allow the supercapacitors to touch each other (some of the older Maxwell supercaps were not insulated on the bottom).

Step 10:

Attach a cable from the jack to the power supply. Set the power supply at 5.4 volts and 5 amps. The supply will limit itself to 5 amps as the voltage rises--you don't want to exceed 5.4 volts on the series connected capacitors.

That being said, I set the voltage at 5.8 volts and watch for the charging current to dip below 1 amp (this gives me a faster charge).

Step 11:

Turn it on. It is really bright and lightweight!

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    8 Discussions


    2 years ago

    What's strange here is the lack of regulation for a working circuit. An empty capacitor is equivalent to a short circuit at the beginning of the charge, that means a very high current. Here it is a several Farad capacitance and, when you know that a 1mF needs more than 1A, I'm quite surprised that the 5A fuse doesn't burn. There are formulas to calculate currents versus voltages and impedance. I only remember these for alternative current.

    2 replies

    Reply 2 years ago

    The power supply is set to 5 amps (maximum) and it reduces the voltage applied to achieve that current level. When the voltage on the capacitor approaches 5.4 volts, the current level drops--these levels have to be "dialed in" to the power supply.


    Reply 11 months ago

    Great project! I wonder why nobody manufactures this! I have a similar project. Even if you limit your power supply around 5.4V there is a risk of burning one of the supercaps with a massive explosion. When in series, you should use balancing circuits. It is good that you use high quality supercaps, they hold the charge and probably have higher overvoltage tolerance. The problem with balancing circuits is - they short circuit your power supply for a moment, when the capacitor reaches max voltage, that is why I charge them only with solar panel in my project. Perhaps USB is also OK, because 5V<5.4V and probably balancing circuit protection will not be activated. But it will be slower than your power supply. Thanks for sharing!


    2 years ago

    rafununu, the power supply is set for 5 amps. That limits the current to 5 amps.


    2 years ago

    A nice mod would be an adjustable current so you had several power levels. Then a cheap wall wart charger, using another regulator module as a current regulator.


    2 years ago

    Wow this is a pretty cool project! Thanks for sharing. It would be ideal to have a charging station where you just put it down on.


    2 years ago

    Please note that when you connect capacitors in series it lowers the total capacitance. The formula is 1/c = 1/c1 + 1/c2


    2 years ago

    I've done a lot of testing on these supercaps and I can tell you this . Each supercap seems different . Some hold a charge for days and then it slowly dissipates ,some lose the charge in minutes. I would say get a few and charge them up first and watch what they do . Then use the one that holds charge best. The cheap black ones from china i have noticed contain quite a lot of duds . Can't even get a charge into them !