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jamie79512

Solar panels

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I am not the most experienced with electronics and I am just now really getting into any kind of circuits. I had another post about transistors for some robots i am working on and now i need some more help. I can't seem to get my solar panel to charge a capacitor. The solar panel is 3v 25mA. The capacitors I am trying to charge is a 1000uF 6.3 volt electrolytic. Is the difference in voltage the problem? And help much appreciated

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Capacitors don't charge the way you think they do. They're not batteries, they work in a completely different way.

Capacitors store energy in an electric field on two plates separated by an insulator. Applying a voltage forces a number of electrons to one plate and holes to the other. Think of this more of stretching a rubber band than anything else whereas a battery is more like twisting the rubber band, allowing it to release its energy much slower and longer.

In fact, if you use the water analogy, there's a good explanation of capacitors. Some people try to say capacitors are like buckets of water, that somehow store more water than is already in the circuit. This breaks the water analogy entirely. Instead, a capacitor is like a chamber full of water with a rubber membrane in the middle. When you apply voltage (water pressure), the membrane stretches. At a later time when a path is opened up, the membrane can return to its normal state and release that energy. In fact, a capacitor works a lot like the pre-charged water tank you probably have in your basement.

OK, so you can charge a capacitor with a solar panel, but I have to ask: What do you want to do with it? Like I said before a capacitor is not a battery. It can store energy, but when it's released it's released very quickly, like snapping a rubber band.

The voltage is not a problem. The voltage rating on an electrolytic capacitor is the voltage at which the electrolyte (the insulator between the two metal plates, in this case the coiled metal foil) breaks down and becomes conductive. You can charge a 6v capacitor with 3v, but it won't store as much energy.

Charging a capacitor takes time, measured in "time constants." The time constant T is R * C. For every T seconds that pass, the voltage drop across the capacitor increases as it takes more force to hold more electron/hole pairs in place on the plates, the current decreases as the exchange of electrons and holes decreases and the amount of energy stored in the capacitor increases and the total number of electron/hole pairs increases. Generally speaking, in T seconds the capacitor will be 2/3 charged. It will take 5 to 6 * T seconds to "fully charge" a capacitor.

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I understand that capacitors work different than batterys, that they work in quick bursts. I am building a solar engine to use on a "beambot", i can charge the capacitors with a battery but i havent been able to get the capacitors to charge with the solar panel. the design i was working off of is here link

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probably becuse you need a voltage trigger and a transistor, other wise the electricity would go thru the capacitor to the motor and not do anything..

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