Page 119 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

100 Making Things Move

one point in a wire is like the amount of water flowing past one point on a water
pipe. Most components in this book will use less than one amp of current, so are
rated in milliamps: 1,000 milliamps (mA) = 1A.

Sometimes batteries have a current marking, which will say something like 3000mAh
for a size AA (see www.ladyada.net/make/mintyboost/process.html). The mAh stands
for milliamps × hours. This means it will give you up to 3,000mA for 1 hour, or
1,500mA for 2 hours, or 750mA for 4 hours—get it?

NOTE This is the technical definition of mAh, but the internal chemistry of
the battery will limit how fast you can get current out of it (see “Powering
Your Projects” later in this chapter).

Motors and other components will often have a current rating that tells you how
much current they need to operate, which is just as important as hooking them up to
a battery or power supply set to the correct voltage.

If you connect two AA batteries end to end, so the (+) sides are facing the same way,
you get 3V. When batteries are put together end to end like this, we say they are in
series. Their voltages are added together, so there is more “water pressure” we can
put to work. However, batteries in parallel add currents while the voltage stays the
same. Figure 5-2 illustrates these concepts.

There are two flavors of electrical current:

1. Direct current (DC) is a constant flow of electricity from high energy to low
energy. A battery supplies DC.

FIGURE 5-2 Batteries in series and parallel