That’s because the supercaps that we had on hand are rated for 2.75 V– not enough to handle the 4.5 V output of the panel when sunlight is present. Instead of adding a single supercapacitor, you might notice that we’ve actually added two. Our next circuit design adds a supercapacitor as a “flywheel” to provide continued power during brief interruptions. For other cases, like powering a microcontroller or other computer, a brief power interruption can be disruptive. For some applications, like running a small fan or pump, that may be perfectly acceptable. They provide no energy storage, and so are quite vulnerable to blinking out when a bird or cloud passes overhead. The “direct drive” circuits work well for their design function, but are rather basic. (The LED is the same type that we used for our high-power LED blinking circuit.) The reason that we’ve used a high-power LED here is that it can easily withstand 50-90 mA from the solar panel– a “regular” LED designed for 20 mA would be destroyed by that current. On the right we’ve hooked one of the panels right up to a high-power blue LED. When you set it out in the sunlight or bring it close to a lamp, the motor starts to spin. On the left, we’ve hooked up one of our little solar panels directly to a small motor taken from an old CD player. Here are a couple of examples of this in practice: The most obvious way to use power from a solar panel is to connect your load directly to the output leads of the solar panel. (While you can solder directly to the terminals, be sure to stress-relieve the connections, e.g., with a blob of epoxy over your wires.) In full sunlight the panel is specified to produce 4.5 V at up to 90 mA, although 50 mA seems like a more typical figure. On the back of the panel are two (thin) solderable terminals, with marked polarity. This is a monolithic copper indium diselenide solar panel, apparently printed on a 60mm square of glass and epoxy coated for toughness. The panel that we’re using for these circuits is this one, part number PWR1241 from BG Micro, about $3 each. To keep things simple, we’re using a single nicely made small solar panel for all of these circuits. The first part of a solar circuit is… a device for collecting sunlight. Use the sun to power small solar and battery powered night lights, garden lights, and decorations for halloween. How to get started adding solar power to your small electronics projects.
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