Battery Power - Spring 2014 - (Page 18)

Feature Managing Fleet Batteries and Knowing When to Retire Them Isidor Buchmann, CEO and Founder Cadex Electronics, Inc. Batteries have become our trusted travel companions; they serve important functions but are a poorly understood as a power source. Batteries work well when new and confidence falls after the first packs fade and need replacing. In time, the battery fleet becomes a jumble of good and bad batteries, and that's when the headache begins. Batteries exhibit human-like qualities. They need good nutrition, prefer cool temperature, but suffer from abuse. Care begins by operating them at cool temperatures, using moderate charge rates and going easy on discharge. It is better not to run batteries down too low but to charging them more often. Avoid ultra-fast charging and harsh loading conditions. There is some truth to why well-cared batteries outperform neglected ones; studies can back this up. Battery charging is generally well understood, but the "ready" light is misconstrued. Ready does not mean "able." There is no link to battery performance, nor does the green light promise a full runtime. Batteries always charge completely, even the weak ones, and ready simply means that the battery is full. With age, the ability to hold charge shrinks and the charge time shortens. This causes faded batteries to gravitate to the top, disguised as combat ready. System collapse is imminent when workers scramble for freshly charged batteries in an emergency. Those glowing ready may be deadwood. (The charge time of a partially charged battery is also short.) Figure 1. The "Ready" Light Lies The Ready light indicates that the battery is fully charged. This does not mean "able." There is no link between "ready" and battery performance. The amount of energy a battery can hold is measured in capacity. Capacity is the leading health indicator that determines runtime and predicts end-of-battery-life. A new battery is rated at 100 percent, but few packs in service deliver the full amount. A workable capacity bandwidth is 80 to 100 percent. As a simple guideline, a battery on a portable device having a capacity of 100 percent typically provides a runtime of ten hours, 80 percent is eight hours and 70 percent seven hours. The service life of a battery is specified in number of cycles. Lithium- and nickel-based batteries deliver between 300 and 500 full discharge/charge cycles before the capacity drops below 80 percent. Cycling is not the only cause of capacity loss; keeping a battery at elevated temperature also induces stress. A fully charged Li-Ion kept at 40°C (104°F) 18 Battery Power * Spring 2014 loses about 35 percent of its capacity in a year without even being used. Ultra-fast chargers and punitive discharging is also harmful, causing a cut in battery life to half, and hobbyists can attest to this. Battery Maintenance Batteries are commonly serviced on a battery analyzer. These instruments became popular in the 1980s to restore nickel-cadmium batteries affected by "memory." With memory absent in Li-Ion, the purpose of a modern battery analyzer is to keep fleet batteries at an acceptable performance level and to retire them when low. Device manufacturers endorse battery analyzers, knowing that well-performing packs reflect positively on their devices, a win-win situation for both parties. Conventional battery analyzers measure capacity by discharging a fully charged battery and tracking the elapsed time. This procedure is time-consuming and stresses the battery. Rapid-testing is preferred but this only provides estimated state-of-health values and the degree of accuracies varies with the method used. Public safety, medical and defense organizations still rely on periodic full discharge/charge cycles. Most battery analyzers feature multi-bays to service a diverse group of batteries. Custom battery adapters configure the analyzer to the correct setting and smart cables enable programming on the fly. With PC software, the computer becomes the host from which all functions are entered. Clicking the mouse on a battery listed in the database configures the analyzer to the correct setting. The user can add, remove and edit the batteries. Figure 2 illustrates Cadex battery analyzers running on PC-BatteryShop displaying battery test results in real time. Figure 2. Battery Analyzers with PC Software With PC software, the computer becomes the command center. PC-operated battery maintenance systems offer several services, one of which is marking all batteries with a permanent ID number. A printer generates these labels in bar code format. To service a battery, the user simply scans the label and inserts the battery into the analyzer. Past battery performance data are made available that may also include purchasing dates, vendor information and pricing. Figure 3 illustrates such a system. www.BatteryPowerOnline.com http://www.BatteryPowerOnline.com

Table of Contents for the Digital Edition of Battery Power - Spring 2014

NREL Model Licensed to Improve Accuracy of Battery Simulations
Companies Collaborate to Make Wireless Power As Commonplace as WiFi
Improving the Coulombic Efficiency and Lifetime Of Li-Ion Cells Demands High Precision, High Accuracy Testing
Rapid Charging for Battery-Powered Portable Devices
Managing Fleet Batteries and Knowing When to Retire Them
Batteries
ICs & Semiconductors
Charging Systems
Industry News
Research & Development
Marketplace

Battery Power - Spring 2014

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