joule thief

Posted on Feb 6, 2014

The joule thief is an electronic circuit that allows you to make use of batteries normally considered dead. A battery is often considered `dead` when it can`t power a particular device. But what`s really happening is that the battery voltage is no longer high enough for the device when it`s used directly. The joule thief circuit massages the volta

joule thief
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ge and current coming from the battery so that the voltage is high enough, for periods of time, for the device to work continuously. The LED in the above photo requires 1. 85 volts but as the photo below shows, the battery voltage is only 1. 27 volts. When run through the joule thief circuit, the voltage is as high as 24 volts, as shown in the oscilloscope output n the photo on the right. Notice that the LED is not always getting power, but it`s often enough to keep it lit. People, including myself, have gotten it to run a compact fluorescent lightbulb (CFL) by adding an extra coil of wire to the toroid core. Also, the electronics has to be removed from the CFL so that the joule thief circuit is powering the fluorescent tubes directly. i. e. it must be a gutted CFL. Transistor - The legs of the transistor can be determined by noticing that there`s a flat side to the transistor case. See the diagram above. A large number of transistors have been reported to work: 2N4401, NET123AP, BC547B, 2SC2500, BC337, PN2222, to name just a few. Resistor - The diagram says use a 1 kilo ohm resistor but I`ve used an 820 ohm one just fine. I`ve also seen a 2 kilo ohm one in use. Use whatever works for you. You can also use a potentiometer (a variable resistor) so that you can easily adjust it to select the resistance that gives the best light. Toroid ferrite core - Some people have gotten these by opening up compact fluorescent lightbulbs...

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