Wireless Energy Transfer Via Joule Thief Circuit




Introduction: Wireless Energy Transfer Via Joule Thief Circuit

About: Just love to create random stuff...


In this instructable I will show you how to achieve wireless energy transfer with simple joule thief circuit.

Device is able to transmit energy wirelessly, depending of input voltage, to about 15 cm distance.

This little project of mine is result of several conducted “brute force” experimentations. It is created from mostly salvaged components. The design isn’t perfect, and have a plenty of space for improvements.

...and sorry for my English, it’s rusty, a bit....


I have made several JT, all worked well, but I had a problem with acquiring torrid ferrite cores. That stuff is hard to find (at least in my part of the world), and my supplies of malfunctioned electronic is getting short, so after some (re)searching I had decided to try to make air core JT, I did it, and it was functional!

However, despite my limited knowledge about electronic and induction, I had a thought about experiment of using air cored JT for wireless energy transfer. I had a lot of fun time, during my experimentations, all spiced up with good results! So, in this instructable I will present my results.


You are responsible for yourself and your actions.

Principle of operation

JT is basically form of autotransformer, with transistor as active component. Device works on frequencies of tens to about hundred of kilohertz, sufficient to induce current to nearby coil (similar like Tesla coil).

If you interested more in JT ( joule thief), here is link to Wikipedia: http://en.wikipedia.org/wiki/Joule_thief

You can, also search joule thief in instructables, and you will got plenty of “material” on “how to” about JT...

Step 1: Build Your JT Coil

Materials and tools needed:

Enameled magnet wire

1x kOhm resistor

1 x NPN transistor, 2N2222 can do, however I would strongly recommended more powerful one (I used 2n3055 and bu406)

1x led diode ( I used 3 mm blue...)

Super glue

Duct tape

A battery ( I used 1,5 V, and 9V) or wall adapter

*optional 1 old CD

*optional 10 kOhm resistor ( explanation in text)

2 alligator clips




...so let start building....


The coil is most difficult to make, the simplest way is to took enameled magnet wire, ( about three meters should be ok for smaller one ) and wrap it around toilet paper roll, beer can, or something similar ( at least 3 – 5 cm in diameter, bigger diameter of coil – greater range ). Important thing is that when you finish with winding of coil, that you can without difficulty remove coil from form (can or something else).

Try to wrap your coil as flat as you can, flatter coil gives better results.

If you want to make more powerful device I recommend to use thicker enameled wire.

First let some 5 to 10 centimeters of wire free, for connection, and start to wind magnet wire on empty paper roll. Wrap wire of the coil in one, same direction. Wind about 25 turns of wire, then left 10 centimeters of wire free, twist it few times, and back to winding again. Wind 25 more turns, left some free wire on the end, and you almost finish your coil.

Careful remove your coil from paper roll, firmly holding coil, then wrap free coil ends perpendicular around coil, few turns is sufficient. Add a drop of super glue on coil.

Next, you have to clean ends of enameled wire, remove isolation from three terminals – two at ends of coil, and one in the middle of it. I used scalpel for that.....

Step 2: The Circuit

Add resistor and transistor

Connect wire from one side of the coil to a 1 kOhm resistor, simply wrap wire on it.

Next connect free resistor terminal to base of NPN transistor. I connected them directly, just twist them, resistor leads are pretty easy to bend.

Connect other free end of coil to the collector of transistor.

In the end, strip few centimeters of wire, both ends, and connect one end to emitter lead of transistor.

Now your JT is complete, middle, twisted terminal of coil is positive connection, and wire connected to emitter of the transistor is negative terminal.

Step 3: Receiver


Receiver is easier to make, it is just simple coil of wire. I’ve made several receiver coils, however, all of them are missing, or broken accidentally (...I'm crying now...). So I quickly build another one, which is attached on CD, to support it, just because I’m used very thin wire from old, salvaged transformer. And it’s not so pretty...

Took enameled magnet wire, wrap about 50 or more turns, it should be similar size with joule thief coil. You should also wrap your coil in same direction as JT coil. Strip insulation from both ends of coil and connect led diode to ends or receiving coil.

Glue everything.

More turns you have, more voltage/less current will be induced in your receiving coil

Step 4: Try Out!

Try out!

Now connect your battery to joule thief, alligator clips could be useful, although not necessary.

Took receiver coil, and get it near to JT coil, led should emit light, as you get closer to the JT coil.

If you use other DC power sources, like cell phone chargers, wall adapter or similar, instead of 1 kOhm resistor you should connect resistor with greater resistance, 10 kOhm resistor works ok if voltage is in 9 – 12 volts range.

So, what to do with it?

Well this kind of device can have various purposes. It probably isn't most efficient device for wireless energy transfer. Except of lighting up one or few led diodes, it can be used (with some modifications) as a wireless charger, wireless (very) small DC motor power source, wireless relay driver, etc. It also have educational significance.


If you want to play with different power sources, more from 5 volts, I recommend to add a 10 k Ohm transistor instead/or parallel with 1 k, to protect transistor.

Coil can have different number of turns, I recommend at least 20 + 20, if you go lower then that there is loss in efficiency. You can go more than 30 + 30 turns, but you will need more turns on receiving coil.

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    6 years ago

    look for quite large ferrite cores in ATX units (the newer the better)(of course save at least one to use for project power supply first ;). So if there is any one throwing a tower PC: Go fetch!!

    Welcome to instructables, this a neat project! Hope to see more from you in the future!