Читать книгу Electronics All-in-One For Dummies - Lowe Doug, Doug Lowe - Страница 59

Most of the projects in this book work with AA batteries, usually two or four of them tied together to produce a total of three or six volts. That’s not enough voltage to do serious harm. Even if you do get a shock with three or six volts, you will probably barely feel it.

However, it’s possible to injure yourself with voltages even as low as three or six volts. If you accidentally create a short circuit between the two poles of a battery, a lot of current will flow very fast. This will very likely cause the wire connecting the two ends of the battery to get very hot, and the battery itself may also heat up. The heat may be enough to inflict a nasty burn.

If the racing current goes unchecked, there’s also the possibility that the battery will explode. Trust me; you don’t want to be nearby if that happens. You really don’t want to make a trip to the emergency room to have fragments of an exploded battery removed from your eyes.

As a result of this danger, you should take the following precautions when working with the battery-powered circuits described in this book:

 Don’t connect power to the circuit until the circuit is completely finished and you’ve reviewed your work to ensure that everything is connected properly.

 Don’t leave your circuits unattended when they’re connected to power. Always remove the batteries before you walk away from your workbench.

 Periodically touch the batteries with your finger to make sure they aren’t hot. If they’re getting warm, remove the batteries and recheck your circuit to make sure you haven’t made a wiring mistake.

 If you smell anything burning, remove the batteries and recheck your circuit.STAYING SAFE BY STAYING DRYWe’ve all seen murders committed on TV crime dramas by throwing a plugged-in electrical appliance such as a hair dryer into a bathtub while the victim was taking a bath. I’ve always wondered how often that really happens, and how likely it’s fatal. For example, how quickly would the circuit breaker kick in and cut power to the hair dryer? Would the special GFCI-protection devices required in all modern bathrooms work as designed and cut power to the hair dryer in time?I’ve never wanted to conduct an experiment to actually find out — nor should you, under any circumstances. Water and electricity are a very bad combination because water is an excellent conductor of electricity, and it flows everywhere.Strictly speaking, pure uncontaminated water is actually an insulator. But pure water is very rare. Most water is filled with contaminates, and those contaminants turn the water into an excellent conductor. Thus, it’s true that you should avoid water when working with electrical current. Here are a few tips for staying safe by staying dry:Make sure the floor is dry. Don’t work on electronic or electrical devices in an area where the floor is wet.Beware of high humidity, especially if it condenses into moisture on your projects.Dry your hands before working with electrical current. Even a small amount of sweat on your hands can lower your body’s natural resistance and accentuate the danger of electrical shocks from lower voltages.

 Always wear protective eyewear to protect yourself against exploding batteries. (Under the right circumstances, other components can explode as well!)