a more practical capacitor powered


Posted on Feb 5, 2014

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


a more practical capacitor powered
Click here to download the full size of the above Circuit.

and that extracted from it to run the LED was lost as heat - not much heat, but heat just the same. A switching converter to run the LED. The LED didn`t even begin to light until 2. 7-3. 0 volts or so appeared 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 below) was unusable. A simple switching converter would allow both extraction of that additional energy as well as regulate the LED`s current so that its brightness was more consistent over the entire charge range and, in theory, could also be adjusted upwards or downwards as necessary. The efficacy of trying this with a capacitor of high internal resistance would probably be dubious. One of the conclusions in this earlier article was that the back-and-forth shaking motion wasn`t a very efficient means of generating electricity - both in terms of expended muscle energy (since you have to move and stop the entire mass of your arm!) and compared to a conventional crank-type generator - and it would necessarily be larger and heavier in order to be more efficient. By using a conventional spinning generator and gearing up rotational speed, one can more-efficiently rotate a smaller magnet faster in a larger number of poles with a motion that requires less human effort. What`s more, a crank-type generator is quite...




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