130 CHAPTER FOUR
against using rechargeable batteries in the toy. The following sections discuss some of the things that can go wrong with batteries. Leakage Batteries contain chemicals that can leak out and ruin portions of the robot. In the case of a car battery, for example, this would be a real possibility if the batter is turned upside down. Liquid acid will ruin anyone’s day. Other batteries contain other more solid chemicals that still present leakage hazards. Treat batteries like a container of chemicals. Make provisions outside the battery to contain any leakage that might occur. If serious concerns exist about leakage, search for a type of battery that will not “leak,” if such a battery exists. Explosion Some batteries are capable of releasing their energy very rapidly. This can happen if they are shorted or if the robot’s power supply shorts out. When this happens, energy is dissipated inside the battery and an explosion can ensue. If the design calls for a type of battery that can explode under these circumstances, then consider the following safety steps: ■ ■ ■ ■
Read and understand the manufacturer’s warnings. Determine just how big such an explosion might be and treat the batteries as an explosive. Consider housing the battery in an explosion-proof container so it will not cause damage during a catastrophic event. Educate all the engineers about how to handle the batteries, or restrict the number of people authorized to do so.
Jewelry I include this section in addition to the following warning about fire for a very specific reason. Some batteries can release massive amounts of current in a very short time period. If a designer is wearing a ring that shorts out the battery, the ring can heat up sufficiently to take off a finger. Do not wear jewelry when working with batteries. For that matter, designers working with electronics should consider removing jewelry during work hours. I would include rings, watches, and necklaces in this category. Freak accidents happen much more often than expected. Fire Just as batteries can heat up jewelry, they can also start fires inside the robot’s wiring. Consider putting a suitable fuse or circuit breaker in with the batteries. If a short circuit someplace within the robot should occur, this may help. Don’t forget to use ULrated wire and PCB components that are somewhat fire resistant. Trauma Don’t drop batteries on your foot! I’m just waiting for such a warning label to show up. I think it’s only a matter of time.