7 3/8 x 9 1/4 T echnical / Build Your Own Electric Vehicle / Leitman / 373-2 / Chapter 8
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Build Your Own Elec tric Vehicle • Characteristics you should be aware of when buying • Steps you should take during installation • Maintenance you should perform during ownership The intent of this section is not to make you a battery professional, but to provide you with practical knowledge so that you’re prepared to buy, install, and maintain your batteries.
Battery Types As you learned at the outset, there are two major classes of batteries: primary or nonrechargeable, and secondary or rechargeable. Unless your EV’s task is to operate on the moon (like the Lunar Rover you read about in Chapter 3) or some other specific mission, you are unlikely to require the services of a nonrechargeable battery. Among rechargeables, there are lead-acid batteries and there are all the rest. In a nutshell, there are no alternatives to the lead-acid battery for the casual EV converter today, because the disadvantages of the other two choices far outweigh the benefits.
Nickel-Cadmium Batteries
NiCad batteries are the type you’d use in your portable computer, shaver, or appliance, and are unquestionably better than lead-acid batteries in their ability to deliver twice as much energy pound for pound; they also have about 50 percent longer cycles. But the nickel-cadmium electrochemical couple delivers a far lower voltage per cell (1.25 volts), meaning you need more cells to get the same voltage. It is far more expensive (four times as much and up). There are fewer sources for the heavy-duty EV-application batteries (cadmium itself is harder to obtain and has generated environmental concerns). Finally, most of the nickel-cadmium technology development is taking place overseas (England, France, Germany, Japan).
Nickel-Iron Batteries
The “Edison battery” used in early 1900s EVs is even a poorer choice. It offers a higher cycle-life (about twice as many), delivers slightly more energy pound for pound (about a third more), and is very rugged mechanically. But the nickel-iron electrochemical couple delivers only slightly more voltage per cell than a NiCad (about 1.3 volts) and has a high internal resistance and self-discharge rate (10 percent per week). Its performance degrades significantly with temperature (both above and below 78 degrees F). It’s far more expensive (four times as much and up), there are few sources for them (they’re only made in Europe and Japan), and there is little technology development taking place. All the battery development going on in the labs (which we’ll look at briefly later in the chapter) is great, but you can’t buy one. Your choice boils down to the good old lead-acid battery. But all lead-acid batteries are not created equal. Confining our discussion to the larger sizes suitable for the heavy-duty EV application, you have three types to choose from.
Starting Batteries
These are the kind used to start the engine in every internal combustion engine vehicle in the world today. The average starting battery spends only a few seconds of time turning over your vehicle’s electric starter motor and the rest of its time being recharged
