Joule Theif

Introduction: Joule Theif

A joule thief is a self-oscillating voltage booster. 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 dead.

This circuit uses the self-oscillating properties so the output voltage is increased at the expense of higher current draw on the input.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Materials

Wire about 26 and 30 gauge wires
1k Resistor
A Standard transistor
(Capacitor is optional) But the the output will be more steady
Dead battery

Step 2: Follow the Schematics on the Last Step

Follow the Schematics on the Last step

You don't need any soldering. Just follow the schematics and twist the wires in place.

Now you can use the rest of the battery life with a dead battery.

You can also place this in your electronics to help pull out the remaining bit of electricity that is stored within the battery.

Gadget Hacking and Accessories Contest

Participated in the
Gadget Hacking and Accessories Contest

2 People Made This Project!


  • Backyard Contest

    Backyard Contest
  • Silly Hats Speed Challenge

    Silly Hats Speed Challenge
  • Arduino Contest 2020

    Arduino Contest 2020

3 Discussions


Question 10 months ago on Step 1

So... hooked all this up just as shown. All continuity tests are as expected, checked over and over again. My resistor is showing about .98K, but I suspect good enough. What am I doing wrong if the voltage reading at my LED is exactly that coming from my battery?? In this case, both read .68v???


Question 1 year ago

Hi all, I built a small hobby wind generator that is only generating around 0.2 - 0.4 volts. Would it be possible to use a Joule thief and capacitor to be able to light an LED even with such a low voltage?

Romyr John AndreiP
Romyr John AndreiP

4 years ago

is it ok to use any type of

1.) transistor

2.) Resistor?

And is it ok to use a smaller toroid?