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Should I use a Capacitor or Rechargeable battery for my shake light? Answered

I built a solenoid and am using a neodymium magnet to produce the voltage. I can get 5 volts easily, but I don't know what to use to store it. I am using a LED with a Vf of 3.3 and would ideally like the storing device to discharge slowly. What would be my best bet: A Rechargeable battery or a capacitor?
I still need to get a rectifier, but if a Capacitor is recommended, how many farads should I be looking for?



Best Answer 7 years ago

You'll want a rechargeable battery. "Supercapacitors" (look it up on Wikipedia) do provide slow-discharge, but they're prohibitively expensive for this sort of DIY application.

Make sure you choose a "dumb" battery for recharging, so you don't have to mess with complex control circuits or microcontrollers.

Could I ask what a "dumb" battery is?......and thanks

A lot of the high-end batteries, such as those for laptops and smartphones, actually include circuitry to monitor and report their discharge state, to assist in current-limiting on recharge, and so forth. Those batteries need supporting control circuits in order to be charged properly.

"Dumb" batteries are more like what you buy at the drugstore -- AA's, D cells, button-cells, and so on.

Sweet, speedy reply and thanks

Super caps are not that expensive - a 10F, 2.7V one can cost around 9 USD and can always be used in something else. Put two in series, and you can handle up to 5V. Do some measurements with your cap and generator, and see how fast you can charge it. You don't say what the running current for the LED is, with that you can calculate the time the lamp will light, from fully charged.,