A semi-practical capacitor-powered flashlight

Posted on Feb 6, 2014

High-energy capacitors of the type discussed can produce hundreds of amps when short-circuited, possibly causing severe burns, fire and/or property damage! Please be aware of these hazards when using these capacitors and take precautions to avoid accidentally shorting them out. The capacitor-powered flashlight. The white PVC portion at the end contains the inverter

A semi-practical capacitor-powered flashlight
Click here to download the full size of the above Circuit.

circuity to run the LED and the LED itself as well as shielding the positive terminal of the capacitor to prevent accidental short-circuits. You probably remember seeing advertisements for those flashlights whose claim was that they would never need batteries and one simply shook them back-and-forth to generate all the power that was needed. As it turns out many of these same flashlights actually do contain batteries and that while they still worked if they were removed, it took several minutes of shaking to get any usable light and that it was quite an effort to maintain a useful light output with these same flashlights. A better capacitor. The cheap flashlight had a rather small (0. 22 Farad) capacitor for energy storage - not very much energy, really, approximately 6. 6 Joules maximum or less than 1/1000th of what a single AA alkaline cell contains! Being a standard "super cap" its internal resistance was quite high (10`s of ohms) which meant that a large percentage of the energy dumped into it during charging and that extracted from it to run the LED was lost as heat - not much heat, but heat just the same. Switching converter to run the LED. The LED didn`t even begin to light until 2. 7-3. 0 volts or so appears across the capacitor and it isn`t usefully bright until there is 3. 6-4. 2 volts available which meant that a significant portion of the energy in the capacitor (all of that at voltages of 3-ish volts and...

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