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
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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
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