Introduction: Make a SUPER Joule Thief Light!

Picture of Make a SUPER Joule Thief Light!
A joule thief is a simple circuit that can take 1.5 volts and put out as much as 5 volts. It can light an LED super bright! But have you ever heard about getting 120 volts out of a AA battery? The Super Joule Thief can do just that! It is perfect for lighting lights during power outages or just for a desk lamp. It can even charge cameras and cell phones! Watch the video for an overview.

I entered this instructable into the Make it Glow contest, so if you like it, please vote for me!! 

Step 1: The Parts

Picture of The Parts

This circuit requires very few parts:
-TIP31 transistor [HAS to be a TIP31 because it works the BEST :) ]
-10k POT
-0.1uf-1uf capacitor (I used a .22uf)
-Ferrite toroid or rod
-20 to 30 feet of 30 gauge magnet wire
-3 feet of 22 gauge magnet wire
-heatsink? (Do you want to power it with more than 1.5 volts?)
-AA battery and holder
-AC output adapter (A 2 prong to 3 prong adapter works great)

Scissors, solder, and other tools will also help.

Step 2: The Circuit

Picture of The Circuit

UPDATE!! I changed the .22uf capacitor to a .68uf capacitor and I am getting a higher and more stable output.                                                                                                                                                                                                         Here is the circuit. As you can see, the transistor acts as an oscillator and pulses the current into the primary coil. This induces a large voltage into the secondary coil. The two prongs of the AC adapter can be connected to the ends of the secondary coil, or you can solder the ends to a light bulb directly. This setup has a 10 kilo-ohm potentiometer. This controls the current that flows to the base of the transistor. More current means a higher voltage in the secondary, and ultimately a brighter light.  The .22uf capacitor seemed to improve the output of my toroid, so I left it in. You may have to change the value depending on the resonant frequency of your toroid, or you can just omit it and the circuit will still work great. It is a very simple circuit as you can see.

Step 3: The Toroid Transformer

Picture of The Toroid Transformer

Let's take a minute to discuss the ferrite toroid. It does not have to be a toroid. If you open up a radio, you will find a ferrite rod inside that has a layer of wire on it. You can take off the wire and use that. Toroids take up less space and they also look nicer. There are several different kinds.

I used a black toroid from a 1983 television. Mine had a white plastic covering on it, so I popped it off. I found out that these toroids with the plastic covering are the best to use. If you would like to make a giant one, use a giant toroid. But the most common are one inch toroids.

They are also different colors. I have used yellow, black, and green, and these have all worked fine. But BEWARE! Some do not work as joule thiefs. It is best to make a normal joule thief and test if that works before doing all the work winding a secondary to find out that it does not resonate.

Step 4: Winding the Toroid Transformer

Picture of Winding the Toroid Transformer

First, take some 22 gauge wire and wind 11-15 turns. Use a smaller amount for a smaller toroid, and a larger amount for a larger toroid. Cut the wire at the end of the 11-15 turns, leaving a few inches at the end. Scrape off the enamel coating on the ends of the wire. Next, take another piece of wire and twist it with one of the ends that you previously wound. Wind 4 more turns in the same direction. Cut the wire, leaving a couple inches at the end. Scrape off the enamel from the ends. Now you should have 3 connection points: a start, an end, and a center tap. The center tap is where you twisted the two wires together between the 11-15 turns and the 4 turns. This is your primary coil. 

It is a good idea to put a small amount or epoxy over your primary winding to keep it from sliding while you are winding the secondary.

Next, take some 30 gauge wire and start winding the secondary coil. You want to make one layer with the space remaining on the toroid. Then, start winding back over the layer you just wound. Keep doing this until you have around 200-300 turns. More turns = more voltage. I suggest that you wind 50 turns at a time, cut the wire, solder a new piece to it, and wind 50 more turns. This will keep the wire from knotting and breaking and will also let you take breaks without sacrificing coil output voltage. When you are finished, scrape the enamel from the two tips of the secondary and cover the whole toroid in a good layer of epoxy.

Step 5: Solder, Solder, Solder!

Picture of Solder, Solder, Solder!

Now just put the circuit together based on the diagram!

Note what end of the primary connects to the collector, and what end goes to the potentiometer. The longer end will go to the collector.

If you want to get fancy and universal, connect the AC adapter to the secondary's output leads.

The toggle switch should go between the positive input and the center tap.

Step 6: Putting Everything Together

Picture of Putting Everything Together

I epoxied everything onto a piece of perfboard. But feel free to get creative! If you wanted to, you could use a rechargeable AA battery and hook up a solar panel.


It can't kill you, but it is quite uncomfortable. 

Step 7: Using It!

Picture of Using It!

Now find a light bulb less than 4 watts. LED bulbs work the best. I am using a 0.5 watt LED bulb and it lights up 2x brighter than it does in the wall. Plug it in and flick the switch! If you hear a faint high-pitch humming, it is just the transformer resonating. Use the potentiometer to dim the light if you want. The dimmer the light is, the longer the run time. The run time is about 2.5 hours with a fresh battery on full brightness.

You can use this ti charge cameras and phones too! But it is best used as a light.
If you have any questions, feel free to message me and I would be happy to help out.

Thanks for viewing my instructable and happy making!


tjh20 (author)2017-09-07

Can this circuit be modified to power a larger LED? For instance a dimmable A19 size bulb, rated to use 9W@100mA maximum on line voltage (120VAC).

ZEPHER 6 (author)2017-08-12

can i put 2N3055 transistor without putting the above one

DamithaN (author)2017-07-15

Will it work if, a capacitor of 10f(with 2.7v rating) is used instead of 0.22uf capacitor that you have used in this project?

ggarcía-2 (author)2016-12-12

I found two new MOSFET IRFZ44 would it be posible to make it work as oscillator?

ggarcía-2 (author)2016-12-12

Of course, Also I have my tiny 2n2222 as Oscillator, but this time I connected a ceramic capacitor labeled "224" between Collector and emitter, and the LED is bright constantly!!

AS67 (author)2014-01-03

is there a way to make a 13.4v version to jump start a car with a dead battery with (or similar) method?

clevelandstorms (author)AS672014-01-05

Unfortunately not with this circuit. You need something that could supply several amps and this circuit will supply a few milliamps at most.

I will buy the IP31 as you recommend, so I also wanna try to use several of this in parallel. I know that running transistors in parallel increases the power

PhilKE3FL (author)AS672014-02-25

When clevelandstorms says several amps he means around 650 cold cranking amps, meaning in cold temperatures. Car batteries are rated in Cold Cranking Starting Amps or CC: 650 CC or 700 CC for cold cranking amps.

Let's look at using an old standard 4 Watt 120 Volt night-light bulb. This bulb requires about 33 mA at 120 Volts. The circuit we make would still have to supply 4W but, from your 1.5V battery, which means about 2.67 AMPS of current. Which, to say the least, is requiring far more than we normally require from a single AA battery! The thing to remember is POWER, how many Watts does it take? P=I*E or in words, Power (Watts) = Current (Amps) times (*) Electromotive force (Volts) so 4W = I * 1.5V => 4W / 1.5 V = 2.67 Amps yet at 120 Volts 4W / 120V = 0.033 Amps or 33mA. This means to get the 33mA at 120Volts the 1.5 Volt battery (if supplying 1.5 volts) needs to supply about 2.67 Amps of current, and as the voltage drops the battery has to supply MORE current to produce the same power, Watts, to keep the bulb going.

Simply stated, to use this circuit to run an LED night light is, sort of, counter productive. Don't get me wrong, this is a wonderful demonstration of running a very small 120Volt device from a 1.5 Volt battery. But, if all we want is a night light, then using the standard Joule Thief circuit without that large coil (with its shock hazard) to simply run an ultra bright 3V LED directly would be far more efficient. You'll get about a week or more of operation from a dead (~ 1.2 Volt) AA battery instead of only 2.5 hours on a new AA battery for the 120Volt LED night light. It would be the same for charging a cell phone, if we could do it directly with a simple Joule Thief we'd get far more power transferred to the phone battery and far less power wasted just running the conversion circuits.

rah187 (author)2016-06-14

Cool! I haven't made it yet, but I have all of the parts. I am planning to make this circuit with the core on which a CRT tv deflection coil was wound. You're right though; taking off the copper wire absolutely SUCKS! I have been at it for a while, and I still have this much left:

clevelandstorms (author)rah1872016-06-17

Wire gauge isn't critical. I used 22 for the primary and 30 for the secondary.

So Wire gauge isn't Critical?, If found some info and and Amperage/AWG table that said that If you want more amperage to support a heavy load, you need to use a wire with more gauge.

In my opinion, Might be I'm wrong

rah187 (author)clevelandstorms2016-06-17

Does the wire need a heavy coating? I have 24 AWG wire, but it is coated with enamel instead of heavy insulation. Is that okay?

clevelandstorms (author)rah1872016-06-17

Yes definitely you want to use enameled wire

clevelandstorms (author)rah1872016-06-15

For the tape, sure. I think that would work, just be sure to cover it smoothly. As for the windings, I don't really know. I guess keep the 4 + 15 for the primary and do a few hundred for the secondary. I would do the secondary first, winding it all the way around the toroid covering it completely in one layer, then go back over the secondary with some insulated wire and wind the 4 + 15 primary.

rah187 (author)clevelandstorms2016-06-16

By the way: is there a particular wire gauge I have to use?

rah187 (author)clevelandstorms2016-06-16

Thanks for the info on the secondary! As for the tape, I don't think I will be needing it (I bought a can of rustoleum enamal at the home improvement store yesterday).

clevelandstorms (author)rah1872016-06-14

If you can, spool up that wire to use for another project! It comes in handy later on. I Be sure to spray the toroid with enamel or to use good wire with no scrapes in the enamel because when I used a toroid like that the secondary coil would arc to the core and short out. Just a heads up! If you have any other questions let me know I am happy to help.


rah187 (author)clevelandstorms2016-06-15

By the way: how many primary and secondary turns do I need for a giant toroid?

rah187 (author)clevelandstorms2016-06-15

Thanks! I do not have very much wire so I am thinking of using the wire I pulled off for the secondary. As for the coating you were talking about, can I just use electrical tape? I have the feeling that tape may be too thick so I may just purchase something from the hardware store, but if I can use tape it would save me a trip to the Home Depot.

ggarcía-2 (author)2016-12-09

I have a doubt.

I built this one, just for testing. I know that the TIP31 is the best, cuz its a power transistor, so It supports a big load, well might be not so big, for almost make it work a 127v lamp.

But at this time, I don't wanted to risk money if will not work for me. :D

So I have in my hands:

1) 1 2N2222 NPN Transistor (tiny package TO92A).

2) Magnet wire,AWG 20 I think so (I don't know how to know the caliper of a conductor without a tool LOL)

3) Magnet wire (very thin, like hair, red, rescued from a PSU element with two coils).

4) 1 Battery 1.5V

5) 3 inch external Diameter Ferrite toroid.

What I've done?:

--------------------FOR BUILD THE PRIMARY COIL (1.5V)----------------------

1) Cover the toroid with one layer of masking tape.

2) With the "22AWG Magnet Wire" I done 14 Turns and 5 turns then for the Primary coil (in the middle of this turns, I made 1 pin for the TAP center).

3) In one of the extremes of the coil I welded the Colector of the NPN Transistor

4) In the other extreme of the coil I welded the Emitter of the NPN Transistor. Then weld this union with the negative side of the battery.

5) I welded the TAP Center of the coil with the positive side of the battery.

-----------------FOR THE SECONDARY COIL--------------------------------

I made 100 turns of this tiny red wire, I know that will be 300 turns.But I only reach for this :D.

Obviously It doesn't cover all the surface of the toroid.

So, It's showtime!!:

I plug the battery on the battery holder, and voila.

Obviously It will not generate 127V at the secondary coil, cuz i only built 100 turns.

When I plug it, immediately the Toroid transformer starts to "buzzing"

I took my multimeter to make measurements, and I found that it generates 37 volts, but goes to 37VAC to 0 then 5VAC and then 37VAC.

I supposed that this effect is by I don't used a Capacitor, so I see how the coil is being charged and discharged, is that right?.

Then I probe that plugging a rectifier bridge and a LED.

So thats what the circuit does:

Starts buzzing and the LED is very very bright, then gradually the buzzing becomes lower, and the LED lost bright, And keeps turned on but with Low light.

At this time the LED have 2 continuous days turned on.


1) I found that is not really a Joule thief, its more like a classical inverter with a transistor as oscillator, but Instead of using a Classical "E and I" shaped transformer, uses a Toroid transformer, that is more efficient.


If i Use a Ceramical 22uF Capacitor between the collector and emitter of the NPN. Will I solve the Use of charge and discharge the battery?.


pruthvi-in-instructs (author)2016-10-30

can I use a iron core instead of a ferrite core

lego mindstorms made it! (author)2016-07-18

I did five layers of 60turns ,that s 300turns right??, but I only get 34v 1a

Are you measuring the voltage using a multimeter?

yes in ac mode it's 36v

m8ty_com (author)lego mindstorms2016-10-02

I forgot to add that there could be a work around that I haven't tested or confirmed for accuracy, its my theory that you can experiment with to allow you to measure the voltage using your multi meter. For that, you will need a high voltage capacitor with capacitance as less as possible, for example: 600 volts at 0.1 uF or less then connect the capacitor to the output of the joule thief. I theorize that the Joule Thief should charge the capacitor up to its maximum spike voltage and you will have a voltage in terms of Direct Current (DC) that you can, therefore, measure using your multi meter. This only would work if you expect the voltage coming out of your Joule Thief to be no more than 600 volts as most consumer grade multi meter is capped at measuring DC voltages at no more than 600 volts. If you expect that your joule theif would generate more than 600 volts DC and would like to prepare for that possibility, then you will need a capacitor rated for higher voltages, like 1,200 volts DC at 0.1 uF (or less uF) and a multi meter rated for the maximum voltage measurements in terms of DC for your target voltage up to 1,200 volts in this example, you can also use the resistor trick to stick with your 600 volts max measurement multi meter to measure greater than 600 volts DC (in this case, you should google up how to use a multi meter to measure very very high DC voltages, and how to interpret its output readings correctly).

Note about 0.1 uF capacitance value: The less capacitance the faster a joule thief can charge it up and the less likely that you will experience not being able to charge up to the maximum voltage. A Rectifying diode might be needed to ensure the highest voltage retention on the capacitor as possible. Experiment at your own findings with different configurations until you get the most optimal results.

m8ty_com (author)lego mindstorms2016-10-02

You can't measure Joule Thief output using a multi meter for the following reason: Multi meters are configured to measure AC voltages at 60 cycles per second, a Joule Thief, while still being AC, well I wouldn't say AC because in reality its Pulsed DC at a high frequency, that's why you can heat a whistling noise depending on your Joule Thief configuration. A multi meter is not going to be of any use for you to perform Joule Thief based measurements in DC or AC mode. If you would like to measure the irregular wave forms of a Joule Thief to determine their maximum up most voltage spike to get an accurate and correct pulsating voltage readings you will need an oscilloscope.

lego mindstorms (author)2016-07-19

Can I connect a 9v (brick) or 12v 7a battery instead of 1.5v

lego mindstorms (author)2016-07-11

Which TIP31 transistor should I use ,
TIP31A, TIP31B, or TIP31C

the letters A,B,C indicate the range of beta of the transistor, but any should work for you.

rah187 (author)2016-06-25

How much amperage does this device deliver?

ThorMan (author)2014-12-08

Hello my friend!

Can you sell me this?

If yes how much?

DatacorpE (author)ThorMan2016-04-20

yes I can, if u want I will sell for $ 72.

celalboz (author)2015-06-16

will this power a 110v cell phone charger, instead of just a light bulb?

thanks for kind reply in advence.

aangara (author)celalboz2015-11-11

this is DC dude...... you just need a good 5v

ggarcía-2 (author)2015-06-12

You said Using a TIP31 you can use a 4watt Transistor. What do I need to use a 9watt or 13watt led bulb. I've heard about using MOSFET, what do you suggest?

ggarcía-2 (author)2015-06-09

Hi men!!!

This is awsome, I'm thinking to use it with a solar cell or with a dynamo in the bike

Implicate_Order (author)2014-10-29

How is the wiring to the 2 prong adapter connected? And where is the small ring tab on the two prong adapter connected?

Thorofazgar (author)2014-09-07

how long will it run on the 1.5 volt battery ?

mihir.sahu.355 (author)2014-08-02

can you make a step by step video of this.... can omit capacitor have any effect and can i wind toroid cuntinously

mihir.sahu.355 (author)2014-08-02

can you make a step by step video of this.... can omit capacitor have any effect and can i wind toroid cuntinously

TK175672 (author)2014-07-03

Rewound it in a ceramic encased toroid (out of an old CRT monitor) still just buzz but no high voltage. i AM getting output but it is very faint. so i guess i need to replace the transistor

TK175672 (author)TK1756722014-07-03

mosfet* with transistor

TK175672 (author)TK1756722014-07-03

The only NPN i have that is over a tiny logic transistor is a

FJAF6812 (lol i know i have 5v logic transistors then jump to 1500V)

TK175672 (author)TK1756722014-07-03

Lighting up an LED (no resistor) off a 1A 12V power supply -_-

TK175672 (author)2014-06-23

I built one using an IRF630 but i had to use 5-12 windings on the primary and so far i have about 80-90 on the secondary so i decided to test it. i applied 6 volts to it and get a very high pitch wine (that means it is working!) but i don't seem to get anything from the secondary. i have a small neon bulb and nothing happens. i even touched the 2 leads and still nothing.

clevelandstorms (author)TK1756722014-06-24

First off, I wouldnt use a mosfet because this circuit is not meant for a high current output. A normal bjt should be fine. The most likely problem is that the secondary is shorting to the ferrite core or the windings are arcing over. This has happened to me. I covered my toroid in enamel before I wound the coils.

TK175672 (author)clevelandstorms2014-06-25

I will attempt putting some tape on it and re-winding. :( and will the mosfet work? it is all i have that is over a tiny logic transistor
Also i seem to get a very tiny anount out of the secondary beacause i tried connecting a piezo speaker

TK175672 (author)TK1756722014-06-26

Just did it with a flyback and it works fine (tiny arcs compared to my 555/2n3055) but that means my driver is fine so i am going to have to re-wind the secondary :(

TK175672 (author)TK1756722014-06-26

Insulated and the same thing happens.

About This Instructable




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