Supercapacitor USB Light




For those who never heard about supercapacitor, you can check for more info about supercapacitor here. Supercapacitor is basically a capacitor with very high capacity, and the capacity rating is normally around few Farads. With the “super” capacity, it basically can store a lot of charge, and I am going to use the “super” capacity to store charges for a 5mm LED. Let’s see how long will the 5mm LED last.

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Step 1: Components Needed

The components you will need for this project is basically a supercapacitor (I am using 5.5V 0.1F supercapacitor which I bought from Farnell), a White LED, a 1K Ohm resistor and a USB male connector (I get this from an broken pendrive).

Step 2: Supercapacitor Polarity

Make sure you know the polarity of the supercapacitor, or refer to its datasheet

Step 3: Soldering

The first step is to cut the 2nd and 3rd pin of the USB male connector, we will need only the 1st and 4th pin (5V and 0V pin).

Then solder the negative pin of the supercapacitor to the 4th (0V) pin of the USB male connector.

Now, try to connect the positive pin of the supercapacitor to the 1st pin (5V). For the connection I am using a resistor leg.

Step 4: Soldering

Next, connect the positive pin of the White LED to the 1st pin (5V) of the USB male connector.

Finally, connect a 1K resistor from the negative pin of White LED to the 4th pin (0V) of the USB male connector.

Step 5: Schematic

Please check the diagram below for the complete schematic. You are actually free to use higher Farad supercapacitor, but voltage rating must be larger or equal to 5V, and you can have your creative way to connect all the components together.

Step 6: Testing

Now, plug it to your computer for around 10-30 seconds to charge up the supercapacitor.

You should see the White LED turned on (if it doesn’t turned on, there are some mistake in the connection), then after 10-30 second, you can unplug it and you should have around 10 minutes of the LED light.


Step 7: Circuit Update

Circuit Update (6 Oct 2010)

I made some changes to the circuit, adding another resistor to limit the current consumption from USB port, and an ON/OFF switch to control the white LED.

The circuitry is simple, when you plug it into PC, the USB port will start charging the Supercapacitor, and there is a 10Ohm resistor (R1) limiting the current from USB port to 5V/10Ohm = 500mA maximum, but the R1 will also slow down the charging time. For large capacitance Supercap, you might need to let it charge for around 1 to 2 minutes. At the LED side, the S1 will let you turn ON or OFF the LED, and the 1KOhm resistor (R2) is to limit the current for the LED. If you use smaller value for R2, like 330Ohm, it will increase the brightness of LED but will also reduce the operating time of the LED for one charge. By using larger value for R2, you will increase the operating time, but reducing the brightness. I found 1K to be the balance value for the brightness and operating time.
Talking about the brightness and the operating time balance, I created another circuit that let you choose 3 level of brightness.

Step 8: Circuit Update

In this circuit, the charging and USB port part is still the same, but I add in S2 and R3 at the LED side. So, the S1 and R2 will still function like the previous one, that by switching on S1, you will get the 1KOhm resistor brightness. By adding S2 and R3, it means that if you switch on S2, you will get 330Ohm brightness, which is brighter than 1KOhm brightness, because the resistor that limiting the LED current is now smaller and higher current on the LED means higher brightness. I say you will have 3 level brightness, so, the third level brightness is by switching ON S1 and S2 at the same time.
When S1 and S2 is being switch ON, the R2 and R3 form a parallel pattern, and you need some calculation to get the total resistance for the White LED.

The total resistance from the parallel of R2 and R3:
1/R = 1/R2 + 1/R3
R = 1 / ( 1/R2 +1/R3 )
R = 248.12Ohm
So, the total resistance at the White LED if you turn ON both S1 and S2 is 248.12Ohm which is 3rd level of brightness for the White LED.
- 1st level (S1 ON) – 1KOhm Brightness
- 2nd level (S2 ON) – 330Ohm Brightness
- 3rd level (S1 and S2 ON) – 248.12Ohm Brightness


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130 Discussions


2 years ago

would a 0.1 farad capacitor work? It's the cheapest one- 20 for $4


3 years ago

How long does the light stay on?


3 years ago

Look up AliExpress. You can get up to 4 F capacitors at bargain prices, delivered free any where in the world.I have a bunch of old ball point pens with built in batteries and single led torch. These originally cost me like 5 ¢ each. Practically don't have to spend any money.


4 years ago on Introduction

A white led would probably handle 5V (+- 0.5V), and would be nicely bright. If you don't want to risk it, still, 1K ohm resistor seems to be too much.

I just made mine and it is so awesome!! I did add a modify it though, instead of using just one LED I used two, and used a slide switch to alternate between them.

9 replies

Awesome! I wanted to incorporate something like this into a bracelet but didn't want to use a battery! Now I don't have to! Thank you a lot for making this!

Very nice! You can use "3 step slide switch" (not sure the exact name of the slide switch with 3 steps), and you can choose to ON LED1, ON LED2, or OFF both LEDs.


Reply 8 years ago on Introduction

3 stage slide switches really hard to get a hold of, I've looked several times. Do you know anywhere good?


8 years ago on Step 8

it would be great to put a couple of supercap in paralel to get a larger capaticance, and you forgot that if not healty for supercaps to charge them with unlimited current, the USB port has a limmited current to 500mA , and it would be great to add some PWM to circuit, it's more efficiant than a ressistor, besause the ressistor turns the unused energy to heat, so the NE555 SMD in C-mos used like PWM would be perfect for this project

PS, there are supercap that has a capaticanse of 7F but only 2V , add a hand generator to charge it and a 1,5V LED driver and ingoy your hand rechargeable flash light.

sorry for bad english, I'm from Serbia :)

3 replies
htetkyawlwinCallum Snowden

Reply 7 years ago on Step 8

I never heard that much of capacitance before. 150F supercapacitors, that's monster size... I wonder what kind of circuit will need that amount of capacitance.