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.


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).


Make sure you know the polarity of the supercapacitor, or refer to its datasheet 190820101400

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.190820101402 Now, try to connect the positive pin of the supercapacitor to the 1st pin (5V). For the connection I am using a resistor leg.

190820101403 Next, connect the positive pin of the White LED to the 1st pin (5V) of the USB male connector.

190820101404 Finally, connect a 1K resistor from the negative pin of White LED to the 4th pin (0V) of the USB male connector.


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.

image 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.


Right after the charging.

190820101409 After 2 minutes.


After 4 minutes.

190820101411 6 minutes.


8 minutes.


10 minutes.

190820101414  And after 20 minutes.



This Supercapacitor USB Light is basically not an useful light or torch light that you can use, but it is  definitely a very fun project for your free time. So, have a try and share your experience here.


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.

Supercapacitor USB Light Schematic 2

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.


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

26 thoughts on “Supercapacitor USB Light”

  1. Is it really a 0.1F cap or is it 1.0? I just saw a 1.0F super cap for sale, and im thinking about buying it since it should last 10 times longer than yours if its 0.1F. But im not sure if its a 0.1F you have or it really is a 1.0F. Thanks!

    1. The spec for the Supercap I use in this project is 5.5V 0.1uF. For your project, make sure that the Supercap’s voltage is larger than 5V, because the USB port will be use as the charger for the Supercap. And maybe you will need to add an 10 Ohm resistor between the Supercap and the USB male port, to prevent the 1F Supercap from consuming too much current from your USB port.

  2. Sorry for double comment,

    but is it possible to put a “slide” switch on this so it can turn off and save power?
    If it is, could you teach us?

    Thanks from a new electric beginner.

  3. Thank you very much! This helps me a lot!
    To the slide, i just have a little question, when i turn the slide switch “off” will the capacitor still use power or will it save it? – Thats pretty much what i want to achieve, that the capacitor stops using power when the slide is off, so that I can use the USB Light anytime i want for a little period of time.


    1. Arda, after you turn off the slide switch there should be no wasted current through the slide switch, however, normal Supercap will have its self discharge rate, which will slowly reduce the stored energy in the Supercap. If I am not wrong this self discharge rate is lower in Supercap compared to rechargeable battery, so, don’t worry about it.

  4. i have a question: given a very large supercapacitor, is there a simple way to know how much it’s charged ? There are cheap capacitor up to 10 Farad, they could require more than 15 minutes to charge if i’ve done my math well. It could be useful to know when it’s charged (or even better a percentage :P)

    1. nicola, I also not very sure on how to know the charged up capacity in the Supercap. The voltage of the Supercap might be able to help in getting the capacity, but from what I tested, the voltage you read just after the charge is not accurate. For example, if I charge it using my USB port, right after the charge, the voltage will be very near to 5V, like 4.8V, but the voltage will slowly drop to the real capacity voltage if you leave it there (without applying the LED load to the Supercap) for some time, maybe after one minute you will get 3.5V. So, I think the charged up capacity in the Supercap is only 3.5V/5V*100% = 70%. If you repeat the same charge process, maybe this time charge it for longer (which should also result in higher charged up capacity), then the voltage after one minute will be higher. But I can’t have a confirmation on this theory, it is just my assumption.

  5. hello I have one question related with this post> I want to make LED array to use it like light about 15 cm long. I need to know How many led lights can i add to one array. I want to use USB port as power supply. So please can you write me here or Email me with some info how to do this what parts I need to buy and some schematic. Thanks in advance

    1. Marjan, to help on your design, you should better understand the basic concept on how to power up a LED. If you are using 5V (from USB) to power up one LED, you will need to add a resistor (maybe around 100 Ohm) to limit the current for the LED. So, why 100 Ohm? and how if I am using 12V? Basically there is a fix forward voltage for every type of LED, for the white LED I have, the forward voltage is around 3V. The equation for the current running through the LED is I= [(V Supply) – (LED V Forward)]/(Resistor). From the equation, you will get the current (I) running through one set of LED and resistor, I = (5 – 3)/100 = 20mA. 20mA is quite sufficient for a bright output from one LED. From the current for each LED, you can calculate on how many LED you can add to the array. Normal USB support up to 500mA (safe rating), the max number of LED is 500/20 = 25 pcs. So, for your design, the max number of the LED is 25 pcs, simply parallel 25 pcs of LED set (LED set refer to one LED plus one resistor) with the 5V supply from USB port. Hope my suggestion do helps and good luck in your project.

  6. Hello!

    Could you make pictures step by step for the switch idea? It seems really awesome, but I dont really know how to make it since its hard to know how to really set it up. Im new to electric’s and I cant read schematics and get a picture of how things should look.
    Also the capacitor i have bought is not like yours, mine is like this:

    And because of that Im having a REALLY hard time doing this. I really really, REALLY want to complete this as this just the most awsome thing I have seen and this is my first project and my goal. Could you help me with that?


    1. Hi Jose, thanks for reading my blog. I will try to take some time to redo the project that include the switch idea, but I think it is not within these few days. I will do it maybe around next week because I am currently busy with something else. I will send an email to inform you once I have completed the update.

  7. Thanks for this really cool page! Towards the end of the page, you say:

    “This Supercapacitor USB Light is basically not an useful light or torch light that you can use, but it is definitely a very fun project for your free time.”

    ~ Why did you make this comment? Are you meaning the circuit is not stable, or do you just mean that 10 mins of light is not useful… If instead of using just a 0.1F supercap, a person used (1 or 2) 5.5v 4F supercaps, would you not get a pretty “usable” project?

    Wondering about the context of your statement?

    Also, could you use a 555 timer / transistors / diodes / resistors… to pulse the LED’s such that a 60Hz pattern was established, saving even more energy (think Joule Thief).

    Great article!!! Thanks

    1. What I mean is the 10 minutes of light is not very useful, for a torch light, and the original project is without a push button, means it is only a 10 minutes light after you unplug this from your PC.
      This is just a very basic part of a complete torch light where you can add in bunch of features like the 555 timer, and On/Off button. Anyway, hope you enjoy making it.

  8. You know what this is brilliant for and just what I was looking for? A model railway carriage lights that stay on when the train is stopped! a bit of adaption to 12v and off you go!
    thanks a million!

  9. Hey admin, please help

    I can’t find 5.5V 0.1uF capacitor.
    I have used, 2.2uF, 50 V capacitor, what to do. LED is glowing only when it is plugged to the computer and i have left 1 minute, its not glowing after it is unplugged.

    Plz help,

    1. Hi Adarsh, please take note that the capacitor used in this project is 5.5V 0.1F Super capacitor. It is different from electrolytic capacitor. The capacitance for Super capacitor is much higher compare to electrolytic capacitor. The reason your LED turned off after short time is because of the small capacitance in your capacitor compare to 0.1F.

  10. Hi, this is a nice project, is it true, that the higher the Farad value is, de longer it takes to discharge, but i guess it also takes longer to charge the super cap ? i guess when put in parallel, they discharge on their internal resistance ? or does is this very little ?

    Eric Jan.

  11. hi. is this still active?
    ive been wondering. can i keep this plugged to my pc, and make it act as an emergency light in case of power failure? thank you very much

  12. Very nice. I’ve not been doing anything like that for more than 20 years, and my knowledge seems very rusty at best. I have a simple question : How much power (Watts) does the current limiter resistor R1 need to have?
    Is it 1/2 A * 5V = 2.5W or am I completely wrong?
    Somehow this looks obscure to me.


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