7 3/8 x 9 1/4 T echnical / Build Your Own Electric Vehicle / Leitman / 373-2 / Chapter 8
Chapter 8: Batteries by the alternator under the lightest of loads (unless you are driving at night in the rain with all the electrical accessories on). While they are great for this “high-power output for a short period of time” application, they are not suitable for use in your EV (other than for powering its accessories) because this battery type has thin plates that are only lightly loaded with active material. Used in an EV, it would give you only the shortest deep-cycle discharge life—you’d be lucky to get 100 cycles out of it. Even on a brief trip, if you stomped down too hard (or for too long) on the accelerator pedal, you’d be lucky to make it back to your own driveway.
Deep-Cycle Batteries
These are what you need. The low end of the capacity range might go into a golf cart–type or low-speed electric vehicle. The upper end of the capacity range goes into your EV. They can also be found in manufacturers’ catalogs under the Marine heading. Any of these are a step up from starting batteries; they have much thicker plates and are specifically designed for a deep-discharge cycle-life in the 400 to 800 cycles (and up) ballpark.
Industrial Batteries
These monsters go into forklift pallet and stationary wind- or solar-generation applications. While they give great depth-of-discharge results on paper, have 1,000 cycles and up cycle-life, and make great counterweights for forklifts, their weight and size generally make them unsuitable for EV applications. Your mission is to go after the deep-cycle batteries that might be found under the golf cart, marine, or electric vehicle catalog headings.
Battery Construction From a manufacturing viewpoint, a lead-acid battery is one of the most efficient things going. While lead is definitely something you don’t want in anything you drink or consume (you don’t even want it in the paint on the wall inside your home), the EPA loves lead-acid batteries because more than 97 percent of these batteries are recycled and 100 percent of every battery is recyclable. Battery construction makes this possible. Used lead batteries are gathered at collection points, and then sent to smelting specialists where they are disassembled. The lead is melted, refined, and delivered to battery manufacturers and other users; the plastic is ground up and sent to reprocessors who make it into new plastic products; and the acid is collected and either reused or treated. How a battery is constructed affects which battery you buy. Figure 8-3 shows the details.
Plates
Battery plates are formed on a wire-like grid of lead alloy (antimony is sometimes used to stiffen the lead); a mud-like lead oxide, sulfuric acid, and water paste is applied to them and allowed to harden. An expander is added to the negative cathode plate that prevents it from contracting in use. The plates are then “cooked” in a dilute sulfuric acid solution by sending a forming charge through them that changes the positive anode plate to a highly porous, chocolate-brown lead dioxide material, and changes the negative cathode plate to a gray sponge lead. The positive and negative plates are assembled into a “sandwich” with separators—thin sheets of electrically insulating material that is still porous to the electrolyte—and held in place inside the battery by
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