Joule Thief 10x10 LED Lamp




About: Maker, student in 10th grade. A Christian. Loves Jesus. Dreams to one day own a house that fully runs on renewable energy. Would like to visit the Maker Faire one day. Plans to be an electronic engineer (or ...

Afraid of the dark? Built a simple Joule Thief circuit and would like to go further? Just want to have a cool blue light to show off to friends? Let me present..... The Joule Thief 10x10 LED Lamp!

The Joule Thief 10x10 LED Lamp! Runs on one to four AA batteries. Lights up 100 LED's, illuminates your night!

This is a simple LED project build with parts I have on hand,

100 3mm LED's (Bought from ebay)

Toroidal core (Salvaged from CFL lamps)

Enameled wire/Magnet Wire (salvaged)

100 ohm resistor (values up to 1k should work)

2N2222A transistor (The TO-92 version of it)

Battery Holder

Step 1: Building the Joule Thief Circuit + Testing

Sorry for the lack of pictures..... I got too excited when building it and forgot to take pictures.....

The Joule Thief is a minimalist self-oscillating voltage booster that is small, low-cost, and easy to build; typically used for driving light loads. It can use nearly all of the energy in a single-cell electric battery, even far below the voltage where other circuits consider the battery fully discharged (or "dead"). Hence the name, which suggests the notion that the circuit is stealing energy or "joules" from the source. The term is a pun on the expression "jewel thief": one who steals jewelry or gemstones.
The circuit uses the self-oscillating properties of the blocking oscillator, to form an unregulated voltage boost converter. The output voltage is increased at the expense of higher current draw on the input.
-Wikipedia (Link)

Anyways, I searched for Joule Thief and got a schematic for it. I built the circuit exactly the same as the schematic but changed the transistor and the resistor value. After its completed I tested it by connecting it to a LED.

Step 2: Build LED Board.

100 blue 3mm LED's are wired in parallel and is connected to the output of the Joule Thief. Some solid core copper wires are use to connect the LED's together.......

Step 3: Test All Connections for Errors.

All connections are tested for shorts and errors. After testing, I put a AA battery in and IT COMES ALIVE!!!!!!

Step 4: Completed.....

The project is completed and it sure is bright! This project is a simple project and it took me about 2 hours to build it. Try making one and just look at it's awesomeness......

I've tested the circuit and it seems to run for about 40 hours before dimming and switching off. That's with one fresh battery connected. (Voltage: 1.5v+/- = start ------ 0.65v end)

Thank you for reading and I hope you have enjoyed reading this instructable!



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    17 Discussions


    1 year ago

    I find it hard to accept that a tiny 2N2222 TO-92 NPN transistor

    (that is instantly destroyed by a current in excess of 1amp)

    could at a working current of only 500ma inject enough magnetic flux energy into the toroid to simultaneously light 100 blue LEDs wired in parallel..

    2 replies

    Reply 9 months ago

    I have yet to measure the actual working current, but as far as I know, while the lights looks bright, its actually quite dim as compared to driving one LED at the full 20mA current. And as it lasted for quite long before the battery runs out, the LEDs are probably driven at a very low current and also switched at a very high frequency.


    Reply 1 year ago

    That's because the transistor is not supplying that much current. The LEDs in the pictures might look bright but it is not running at its full brightness. I've tried lighting up another LED from the same batch with a CR2032 battery and the brightness of the 100 LEDs is around half or quarter of the single LED(this might be confusing but i mean the brightness of a single LED in the whole 100 LED powered by the circuit compared to a single LED powered by the battery). So I'd guess a very low current draw in by the LEDs.

    It does look nice in dark but have no use in terms of lighting anything up.


    4 years ago on Introduction

    What is the purpose of the toroid? As near as I can tell it does nothing. Normally such a toroid is used to filter noise off of the circuit. However this is a pure DC circuit so there shouldn't be any noise to worry bout.

    Also what is the purpose of the transister? Based on your schematic it just shunts power away from the LEDs reduce system efficiency. If you intended to use the transister to regulate the power trhough they leds, it isn't wired in a way that will effectively do that. Besides 1.5Volts is not enough to damage blue LEDs.

    Blue LEDs normally need about 3 volts to reach full brightness. At 1.5 volts they are barrely working. I think you could remove the toroid, transister, toroid, and resistor and the LEDs will still light. Your single battery is not producing enough voltage to damage the LEDs and the LEDs at that voltage will not be able to draw enough current to do any damage. In fact you could power it with 3volts of battery power without any electronics. Without knowing the exact specs of the LEDs I would not exceed 3 volts. Exceeding 3 volts might damage them.

    7 replies

    Hehe sorry for interfering, but your work is amazing,bneo99! I'd like to ask if you can notice the battery getting cold to the touch...whenever I do my Joule thief experiments, I always notice that you have any idea why it happens?


    I never noticed the battery getting cold to the touch in any of my joule thief projects. And as far as i know that shouldn't happen. I'm switching this 10x10 light on and I'll see later if it does get colder than the room temperature or not.

    In your case how cooler is the battery compared to the room temperature? What kind of battery are you using (battery chemistry)?


    Tried running my joule thief and i can only slightly notice it warming up.... Kinda as expected as you're drawing more current from it...

    Bro please study the Joule thief circuit and how it works... the author of this instructable made a Joule thief circuit and not a simple LED circuit only. Hope you understand what you're saying.

    Rolf Gsteven4872

    Reply 3 years ago on Introduction

    To answer your curiosity, I suggest that you take one 1.5V AA battery and connect one LED. The result... will not light up. Now connect one AA battery to joule thief circuit and connect the LED. The result... LED lights as bright as the star. If you don't believe, try making one joule thief first to convinced yourself. The theory behind the toroid, transistor and the resistor is for you to research to add to your knowledge. This parts will not be there if there's no function. This circuit is a voltage booster and not regulator. Remember, we are talking here about one 1.5V AA battery not 3 volts and 10 LED's. Of course ordinary LED (Galium Arsenide) will light in 3 volts but you will damaged it due to over voltage. Super bright LED's will survive 3 volts. I have done a lot of this Joule thief circuit.

    For bneo99, job well done. You are in the right track.

    surya raju

    4 years ago

    Can please update a few details regarding the joule thief circuit, i.e the number of windings,gauge of the wire........ also the schematic shows only a single led as to the entire matrix used in this ible (sorry if u intentionally drew it for representation purpose) :)

    2 replies
    bneo99surya raju

    Reply 4 years ago on Introduction

    Number of windings: 8 - 11. Gauge does not really matter. All the LEDs are wired in parallel.


    4 years ago on Introduction

    I wonder if you could get a nice whitish light if you alternated between R,G and B LEDs?

    So bright, and so futuristic looking! Definitely a way to make sure one never ends up completely in the dark.