Design News, May 2013

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Source: Electrochem Solutions Inc. Figure 2: The desirable flat discharge characteristics of available voltage from high-power Li-ion based cells also make assessing their remaining capacity difficult, and so leads to "coulomb counting" measurement rather than simpler voltage measurement. have bans on disposal of lead batteries.There are similar restrictions in place in Europe as well, under the EU Battery Directive. Even production is under stress: China, a leading source of leadacid cells, is shutting down some production facilities due to local environmental issues. Lithium vs. SLA But upgrading from SLA to Li-ion is not simply a matter of just changing to new cells or battery packs, as when you go from standard size AA, C, or D low-energy carbon-zinc cells to alkaline cells in a flashlight. While both technologies embody chemical storage vessels for electrical energy, these two differ in many ways: physical construction, nominal voltage, voltage versus capacity, management and oversight, and perhaps most challenging, charge protocols. There are many different versions of Li-ion chemistry used in rechargeable batteries, and each yields a different combination of performance parameters. In general, the lithium-based electrochemical reaction produces from about 3.0V to a little more than 3.5V, so four cells in series deliver 12 to 14.8. In contrast, an SLA cell produces a little over two volts, so six cells create the well-known 12V battery (actually closer to 12.6V). It is difficult to directly compare performance of SLA and Liion batteries directly, since many of the parameters have different baselines. For example, SLA runtime is a function of inherent capacity, discharge rate, and rest periods between partial discharge (SLA cells recover and partially restore their performance while at rest), but they cannot be discharged fully without damage to their performance. However, rough comparisons are possible.Table 1 shows the key performance attributes of a 12-cell SLA pack comprised Design News | MAY 2013 | w w w. d e s i g n n e w s . c o m –39– magenta cyan yellow black ES244622_DN1305_039.pgs 05.02.2013 07:03 UBM

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