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Joule Thief by Beam

INTRO: How to use an 3V LED on the 1.5V of an AA battery?

A Joule thief is a so called “boost” circuit. By cleverly using a fast switch – the transistor – in combination with a coil – using induction effects – it is possible to make 3Volt from the 1.5 Volt of an AAA or AA battery. Just the voltage an LED needs. Of course – there is no free energy. Either 1.5V all the time, or say, 3V half of the time.


Components:

Coil – we make it ourself! Winding two wires around a ferrite ring.
Transistor: NPN, for example BC457c
LED – make it a bright LED
Resistor: 1KOhm
Battery holder: made from aluminium foil fixed with Vliesofix on fabric.
The switch consists of pressing the two sides against the battery.
Battery AA or AAA, 1.5 Volt.
Copper wire for the coil, but it can be done with the “normal” electronic wire too.

 


Joule thief circuit:

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short leg of the LED to the minus of the battery
emitter of the transistor to the minus of the battery
The emitter is the right one of the three legs is you look at the flat side of the transistor.
The coil in this schema is stretched out, in reality these two coils are on top of each other.


Battery holder

The battery holder is made from fabric (a bit stiff) and a conductive material, like Aluminium foil. To glue it together flies-fix is used. at one side a wire is connected with a piece of tape. The two pieces of fabric with one conductive side are   sewn on the supportive fabric to fit the battery. By pushing the conductive sides against the battery, the circuit is closed.

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Winding the coil

To do this the right way is rather important!
Fold a wire in two, keeping the middle at one end, the two ends at the other end.
Wind this double wire around a ferrite ring – or just a big nail – 20 times or so.
Then cut the loop at the one end and reconnect one of these middle wires to the other of the two ends.

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The transistor

A very common transistor is used. A transistor has three legs – with three functions. Depending on the transistor, these legs might be in a different order! S0 we have to know which leg is which. The transistor has one round side, for recognizing the orientation. Here is the schema for the BC547c, which is an NPN transistor. (Transistors are quite complicated devices, with all kinds of details, which can fill an entire encyclopedia…). For the Joule Thief the emitter has to be connected to the Ground.

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Images:

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The Swatch

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about the transistor

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Components

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the battery holder – switch

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the “switching” of the volt made visible with an oscilloscope.


 

This circuit was part of my course “Energy for designers” – Wdka.nl, January 2019, there was a student who used the circuit as part of a geographical map of Russia 1890, the components representing revolution, famine etc. Another student pressed the circuit between two slabs of glass, put it into an oven for ceramics and melted everything, later projecting light through it reflecting it on a wall.

 


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