Page 132 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

112 Making Things Move

Alternative energy sources provide ways to generate electric power, but you need to
use that power right away or convert it to a form that you can use later. Even if you
use it right away, the unsteady flow of power from something like a solar panel on a
cloudy day or wind turbine might need to be smoothed out before it is useful to
power mechanisms.

Capacitors for Energy Storage
There are many ways to store energy, but only a few that are practical for our
purposes. Gasoline and food store energy in chemical bonds, dams store potential
energy in the elevated water, and flywheels store energy in the movement of a heavy
spinning wheel. However, we’re mostly interested in storing electric potential energy
so we can directly use the electricity in our projects.

We’ve already talked about one way to store electric potential energy: batteries. You
can use an alternative energy source, such as solar power, to charge your rechargeable
batteries instead of using the energy directly. Another electrical component, a capacitor,
can be useful for storing energy as well as smoothing out unsteady flows of energy.
A capacitor is like the water tower in our water analogy (see Figure 5-4). When there’s
plenty of water around, it gets pumped up to the water tower and stored for later
use. When there’s a shortage and the pump stops bringing in water, the water tower
can drain immediately and supply the water it was storing. Capacitors store electrical
energy like water towers store water. Similarly, when electric current is flowing into
one side of a capacitor, it takes in all the energy and stores it. As soon as there is no
current flowing in, the capacitor discharges immediately, until there is no stored up
energy left. (See http://electronics.howstuffworks.com/capacitor1.htm for details of
how capacitors work.)

A capacitor is a little like a battery because it stores electrical energy and has two
connections. But unlike a battery, it doesn’t create energy (it only stores energy), so it’s
much simpler. A capacitor is made of just two conductive plates close to each other
but separated by something nonconductive. There are two kinds of capacitors:
ceramic and electrolytic (see Figure 5-9). Ceramic ones don’t care which way you put
them in a circuit, but electrolytic ones definitely do! Make sure the gray stripe or
minus sign is on the ground side of the current flow.