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Salvage It!

Building a human-powered LED torch for next to nothing

by Julian Edgar

You’ll need a variety of components from different salvaged goods to make this design, so it’s one to keep in mind as you collect bits and pieces over a period.

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The primary components needed are the turntable motor from a microwave oven, an old plugpack and some high-value, low-voltage capacitors. These salvaged parts shouldn't total more than a few dollars but be careful when salvaging the turntable motor - the bite from the EHT circuitry in a microwave oven can be lethal, even with the power off (see warning in article).

First, you need the turntable motor from a microwave oven. This is an AC synchronous motor that’s about 20mm high and 50mm in diameter. In addition to the motor, inside the package is a system of plastic reduction gears that normally gives an output shaft speed of just 5 RPM (or thereabouts). By turning this shaft with a knob, it’s possible to easily generate up to several hundred volts AC output! There’s our power source.

WARNING! Exercise extreme caution when salvaging parts from a microwave oven. The large capacitors in the EHT (extra high tension) power supply can retain a lethal charge, even after the power has been switched off.

Although these capacitors should be discharged by bleeder resistors when power is removed, don’t take it for granted. Older microwave ovens may not be fitted with bleeder resistors, or the resistors may have gone open circuit. For this reason, always make sure that the capacitors in the EHT supply have been discharged before removing parts from a microwave oven.

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