hey ^-^ hmm recently I've taken apart one of my old toy cars from way back when. The main reason being that I wanted to make a sort of hand crank flashlight using the motor. The motor originally took five double A batteries, so I assumed, perhaps incorrectly, that it would be able to put out about that much. The real question is, would it be possible to put a capacitor on it in order to store the electricity generated to power a few leds hmm I'm pretty sure I can figure out what kind of resistor to use, its just the capacitor I don't know about. Hmm so basically, I need to know how I would go about choosing a capacitor, how long I would need to crank in order to fill it without overloading it, and so on hmm. Well I hope this was wall coherent hmm if it wasn't my apologies, let me know what's wrong with it and I'll try to make it clearer what I need to know. Thanks in advanced.

There are some 1 Fahad capacitors that will hold a reasonable amount of energy.

Capacitors are rated by voltage. If the rated voltage exceeds the applied voltage, you won't overload the capacitor. Basically, when you connect a voltage to the capacitor, the voltage at the capacitor will read very low. As it charges, the capacitor charges, the voltage rises until it reaches the applied voltage.

The biggest problem is that even a 1 Farad capacitor doesn't hold a whole lot of power. In order to determine how long it would last, you need to specify the voltage (7.5 V?) and the current that the flashlight would draw.

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Originally Posted by saboo4800

i need to know how i would go about choosing a capacitor, how long i would need to crank in order to fill it without overloading it, and so on hmm. well i hope this was wall coherent hmm if it wasn't my apologies, let me know whats wrong with it and i'll try to make it clearer what i need to know. Thanks in advanced.

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It's more : can your motor be used as generator (not always possible).
As to the circuitry : I would not use a resistor, but a rectifier to charge something.
And instead of a capacitor I would charge a small rechargeable battery bank.
There are many LED types, some needing only 20 mA, other bright LEDs can require up to 1 Amp. You feed small LEDs via a resistor (to limit the current), and via a current regulator IC for bright LEDs.

Charging time for a capacitor of 1000 uF is 1 or 2 seconds, depending on the cranked power.
But note : full is full in capacitor world !

As to the values :

I x t = E x C

E = supply voltage in Volts
C = capacity in miliFarads.
I = discharge current in mA
t = discharge time in Seconds

If E = 7,5 V and C = 1000 uF and I = 20 mA, than t = 7,5 x 1 / 20 = 0,375 seconds

A rather short discharge time, reason for replacing the capacitor with a rechargeable battery bank, which you can load by cranking much longer for more power storage !

Thanks very much all. I've begun making the light, and I've successfully gotten the motor to generate electricity. As for how much I cannot be certain, but enough to light four orange LEDs 20ma I believe in parallel. With a 330 resistor. Now I just need to make a crank to attach to one end of the motor for easier charging, and connect a battery pack before the leds along with a switch. Thanks again for your time, and my apologies for getting back to you two so late >< hmm