Picture of Battery Free, USB Powered LED Torch

A rechargeable, battery-free LED torch which gets it's power from USB and stores it in a capacitor.


I reckon USB stuff is cool. I also reckon LED stuff is cool. I HATE paying for batteries. I love my shaky torch. Putting all this together, I thought I'd make a LED torch, simmilar in form to those keychain types, which stores it's power in a capacitor. The capacitor is charged from the USB port.


This is only a "proof of concept", and is intended to show it works. I doubt it will have the best performace, but that's not the point. I think I should be able to do it fairly cheaply, for about the cost of a keychain coin-cell LED light.
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Step 1: Gather Parts

Picture of Gather Parts
Here are the parts I used. The link directs to the product page where I purchased them to give you an idea if you are unsure what you are looking for (or to see how much/if I got ripped off). All prices in AU$ at time of posting.

Obviously substitute parts and suppliers where applicable for your location. I think you can get pretty much everything here from SparkFun, but I listed Altronics as they are a good source for parts in Australia.

- 1 x 5.5V 1F Supercap - Altronics - $4.25
- 1 x 5mm Blue High Intensity LED - LSDiodes $0.75ish depending on exchange rate
- 1 x 18 Ohm resistor - DSE - $0.04
- 1 x mini push button toggle switch - SparkFun - $0.30ish
- 1 x Verobaord, 310mm x 95mm, 0.1" spacing - DSE - $7.99 - OK I didn't actually buy this, I used leftover scraps, but this is what you'd buy. You only need a small bit, so I'll count 1/10th of the price (even that's way too much)

So total is AU$6.13. Definately acheived goal.

Yes the capacitor looks like a coin-cell battery. Trust me, I'm not trying to cheat, that's what it looks like.

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nkrishna33 months ago
this is very nice.... can we add a 1 watt led instead of 5 mm led??
Articas5 years ago
wtf the picture has a battery

it's not a battery, its a flat super capacitor, you can get super capacitors even thinner if you look hard enough!

trialex (author)  Articas5 years ago
wtf I don't think you read the description
 Look at the parts list, that "battery" is a capacitor.
RtyQ1 year ago
nice, i will just add some (a rondom lot) of capacitors in paralel to it and see where it gets me using a lm regulator and a dvd drive laser :D btw thanks for al the calculations and stuff, realy helped me out with another projectof mine
XOIIO3 years ago
Here's a tip, digikey has them for a shitload cheaper, I ordered 18 for 57 bucks, from altronics it's 69.30
trialex (author)  XOIIO3 years ago
Ah yes, but things have changed in the last 5 AND A HALF YEARS since I posted this instructable! (Wow, I feel old...) . In general, super capacitor prices have come down, but this altronics are still charging about the same for the 1F version. It doesn't surprise me that digikey has them cheaper - in general component prices in the US are cheaper than in Australia.

Altronics now has a 220F (yep, 220 times larger!) for $23.

eelco_g7 years ago
This is my first comment, but I think I should warn you guys about this: You CAN use more capacitor in parallel to increase the charge but that also means you'll be putting the internal resistance of the caps in parallel. Meaning you'll draw more current out of your USB port. To be safe, put a resistor between the positive lead and the capacitor to limit the charging current to about 100mA. Charging will take longer, but thats a minor inconvenience compared to frying your mother board.
a480641 eelco_g3 years ago
might be a good idea to keep it around 400 mA just to be safe.
would also be cool if someone made one with a potentiometer to change the brightness or to select b/tw using 1-5 leds
(removed by author or community request)
by the way, you can only draw 500ma from a USB port if you use extra circuittry that "asks" for 500ma, not 100ma. Anyway I think if you try and use too much, you'll get a popup on your screen saying "USB is taking too much current" or something. I had that message once - nothing happened, i just unplugged a homemade usb device!
trialex (author)  davidprosser6 years ago
True in theory you need to properly ask for the full 500mA, but a lot of USB ports will supply 500mA from the get-go.
what determines which usb ports will?
think it depends on the age of the computer as theyre built to accomodate newer devices... but i really dont know and thats just a guess
DYLEGO trialex6 years ago
Hey Trialex, I was wondering how exactly you wire a four-lead tact switch, as in what does each lead do? Where is the NO and C?
raykholo DYLEGO6 years ago
real easy -- the 2 next to each other are already wired together, on both sides... if u only need 2 contacts, just use any 2 diagonal from each other
trialex (author)  raykholo6 years ago
rak - nice; good rule of thumb.
thanks -- thats the easiest way to remember it
I didn't know that ;) I like to play it safe when it comes to my computer.

Resistorvalues are in Ohm, not amps. To calculate the required resistor: USB voltage is 5 volts, max current is 0.5A. If you've got a lot of capacitors in parallel, and they're fully discharged, they behave like a short circuit, or resistance of 0 ohm (not really true, but to keep things simple...)
Resistance=Voltage/current, so to limit current to 0.5A the resistor would be 5V/0.5A = 10 ohm.

Time (in seconds) to fully charge the capacitors then would be 5*R*C, where R is the 10 ohm resistor, and C is the total capacitance in farads. 5 is not the voltage, just a constant.
Taran6064 years ago
What resistor would I use if I used a 25v resistor with 100 nf or uf
trialex (author)  Taran6064 years ago
Sorry mate but your question doesn't make sense. Can you try re-phrasing it? Resistors aren't (typically) rated for a "voltage" - normally they have a resistance (like 100 ohms) and a power rating (eg 1/4 watt).
I meant to say capacitor not resistor I'm using a 25v cap with 100 uf or nf
that cap wont work for more than a second. uF is Micro-Farads or millionths of a Farad. you need a one-Farad supercapacitor. you won't find one of those in a radio shack any time soon, I'm pretty sure. you could also use a bigger cap like 5-15 Farads for longer-lasting light.
reywolf5 years ago
what do the other two usb wires do? i just need to know which wire does what, i already know what to use it for. I'm too lazy to test.
trialex (author)  reywolf5 years ago
Ah but it takes so little effort to google!

The middle two pins of the usb A connector are for D+ and D-.
Wesley6665 years ago
ha this is great but mine is better. I bought 100 polyacene batteries off electronics goldmine. They are rechargeable, half the size of the capacitor in this instructable, they will each, when charged, power an LED for an hour, and they take no time at all to charge. They are rated for 3.3v only so a few other components have to be added, but they work really well!
That's not better, that's completely different. Did you read the description? This wasn't supposed to be an effective model. It's a proof of concept.
Ya, but you can make it an effective model...
Yes, I get that, just pointing out that Polyacene batteries last longer, about an hour on one charge. 

However, just follow me on this thought, if you mixed this Instructable, with Polyacene Batteries, with this Instructable:

You would have one wicked flashlight! 
Thanks for this proof of concept. I was just reading up on resistors and wondered if this were possible.
XOIIO5 years ago
Where did you get a capacitor like that? it really looks like  battery.
trialex (author)  XOIIO5 years ago
Did you check out step 1? It's got a link to Altronics, which is where I got mine from.

The idea and concept is great. This design can be made in many ways. With a larger Capacitor and a different charging point, not necessary USB charging.Some add-on would further improve the design.
Like Charging Indicator.
The Power level left in Capacitor , as when being used .
The concept of not using batteries justifies the project.
Thanks for this wonderful project.

Another idea would be to put a smaller, lower power led to indicate "charging" or you  could just use the smae one, but then taht might slow the charging, hence why i suggested using slower post one. and you could probaly just put the additional LED in parrelle to the capacitor with a small resistor too.
Does anyone have that LED array calculator? I am making a similar project.
I found it, but this is a great project, good job!
usb i need to say anything else?
u mean like the AA and AAA batteries recharged from a usb port? huge!
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