Rechargeable Handheld Capacitor Flashlight




Most flashlights nowadays use store bought alkaline batteries to power them. Battery companies are making their batteries last longer and longer. After a good camping trip, most batteries will run out after the constant use. There are rechargeable batteries such as Ni-Mh and Ni-Cd rechargeable batteries. The problem with these batteries is their toxicity. Instead of using batteries, how about we take a different path. This flashlight is completely powered on energy stored in electrolyte capacitors. They last for a long period of time and can be recharged hundreds of times.

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Step 1: Tools and Materials

I got most of these parts from RadioShack. You can probably find all of these materials at a local electronics store or hobby shop.


  • 4700µf 35v electrolytic capacitor x2
  • 470Ω resistor
  • 3.5v high brightness 10mm white LED
  • large push button switch
  • general purpose perf board
  • red 20 gauge wire
  • black 20 gauge wire
  • female and male banana plugs
  • hard thick plastic
  • 12v DC power source

I got the thick plastic material from a lighter handle. The 12v power source is supposed to be something that you can charge your flashlight from. This can be done from an outlet transformer, a car port, or even a 12v solar cell.


  • screw gun and drill bits
  • soldering iron
  • solder
  • wire cutters
  • super glue
  • electrical tape

Step 2: Connect the Capacitors

First bend the leads downwards so they look like the picture above. Place the capacitors side by side on the perf board. You should have some room on the perf board to solder the LED and the other components there. Bend one capacitors leads to the other capacitors leads and solder them together. It should look like the image above. The capacitors should be connected in a row and not in series. They now have 9400µf to store energy for your flashlight.

Step 3: Add the LED

Place the LED, the switch, and the resistor onto the perf board. Use the leads to connect the parts together. Make sure that all of the components have the right leads going to the right parts and pieces. One lead of the switch will go to the positive lead of the capacitors. This is the side that you will add a positive charge to. The other end of the switch will be connected to the positive lead on the LED. The negative lead on the LED should be connected to one of the resistors leads. The other end of the resistor is then connected to the negative lead of the capacitors. If you have one, I suggest you first test this circuit on a breadboard.

Step 4: Prepare the Charging Section

Cut a piece of the thick plastic about the width of the perf board. Bend the plastic 90% so that it can be glued onto the rim of the perf board. Hold the piece onto the perf board like shown above and mark two points on the plastic piece the lines up with the leads on the capacitors. Then use a screw gun to drill two holes on the points you made. The female banana plugs should be able to fit in the holes.

Step 5: Attach the Charging Ports

Solder wire leads to the female banana plugs. Red is positive and black is negative. Strip the other ends of the wires so they can be soldered to the perf board. Get the wires in place on the perf board. Then super glue the Plastic piece to the perf board like shown above. Solder the wires to the perf board so that the positiven wire goes to the positive end of the capacitors and the negative wire goes to the negative end of the capacitors. You have finished the flashlight.

Step 6: Prepare the Charging Power

To recharge the flashlight you need to get a 12v power source. It should be in DC current. I had a 12v computer charger that plugs into the wall. You can also use batteries, a car port, a 12v solar module, or other alternative 12v power sources. First you strip the wires that come from your power source. Connect the positive wire to the positive male banana plug and the negative wire to the negative male banana plug. If you have some exposed wire you should wrap electrical tape around it.

Step 7: Charge and Run

To charge your flashlight turn on or plug in your 12v power source. Then plug the banana plugs into the flash light. It only takes around one second to charge. Unplug your flash light and push the button. The LED should light up but not burn out. Take your flashlight camping and use it to light up the night. With my power source the LED stayed lit for around 45 minutes before it dimmed and then went out. You can also make this flashlight better by using a voltage regulator instead of a resistor. you can also put the flashlight inside a project box to protect it. I decided to leave mine open.

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    8 Discussions


    Reply 4 years ago on Introduction

    I used 20 gauge solid wire. This means that the thickness of the wire is 0.8 millimeters.


    4 years ago on Introduction

    Thank you for the great comments. I am going to make a new capacitor flashlight. This one is going to be inside a project box using 30,000 micro farads. It will have a bridge rectifier for charging. The power will be brought down by a 5v regulator and a diode. I will also have a potentiometer for brightness control. Here is one of my designs. Sorry about the lighting.


    4 years ago on Introduction

    Great idea, your flashlight recharges very quickly and has a duration sufficient for most applications. Unfortunately, the charge does not stay longtime if you don't use it because capacitors discharges by themselves.

    Allow me to help you improve the project:

    You said it is very fast to charge, but I suggest you to add a small resistor in series, between the capacitor and the power source. It is useful to limit the inrush current an prevent to damage the power supply. You can use a 10Ohm 5W resistor. After few seconds of charge you can bypass this resistor to be sure you have finished charging, if you want (even if it is almost useless).

    A very important thing is the protection against reverse polarity! Use a forward biased diode in series to the circuit, to prevent incorrect connection of the power source. Otherwise electrolytics capacitor may explode, it can be dangerous.

    You put a small resistor in series to the led. It is correct, because leds has to be connected to a limited current supply. Unlike the bulbs which needs a constant voltage and impose the current, leds impose a voltage and have to be driven by a constant current. A resistor is not the best thing you can use but it works. If you use a voltage regulator you will burn the led: you can use a current regulator. The best thing you can do is to increase 2 or 3 time the voltage and to drive the led by a switching regulator, but it is much more difficult and potentially dangerous.



    Reply 4 years ago on Introduction

    The LED Dimmed after around 20 minutes but the light was still able to read by. The LED didn't go out until 45 minutes.


    This looks like a fun, easy to- do build. One suggestion though, it would be a more impressive video demo if it can be illuminated in a darkened room.

    D B Chaudhary

    4 years ago

    What is the charging discharging cycle