Page 127 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 5 Mechanical and Electrical Power, Work, and Energy 107

CAUTION Avoid shorting batteries. This is when the positive (+) and
negative (–) ends are accidentally connected, causing the power that the
battery generates to flow back through itself! This will kill your battery and
potentially cause a spark or even a fire. Keep your work space clear of wires
and metal objects—like wrenches or screwdrivers—that could act as metal
bridges and short your batteries. Also avoid using or storing batteries above
80°F. They won’t work as well, and higher temperatures will shorten their life.

The easiest way to incorporate batteries into your project is to use an off-the-shelf
battery holder or snap, as shown in Figure 5-6. These holders can accommodate coin
cells (like those in watches and calculators), 9V batteries, and up to eight AA, C, or D
size batteries. All Electronics (www.allelectronics.com) usually stocks a good assortment
in different sizes and configurations for less than $1 each. Many come with holes
predrilled for easy mounting. All common cylindrical batteries are 1.5V (more like 1.2V
for rechargeable batteries), but the larger and more expensive they are, the more
amp-hours of current they provide.

FIGURE 5-6 Assorted battery holders