12.3 Battery Analyzers for Maintenance-Free Batteries
In the past, the purpose of battery analyzers was to restore NiCd batteries affected by ‘memory’. With today’s nickel-free batteries, memory is no longer a problem and the modern battery analyzer assumes duties other than conditioning weak batteries. In an environment with nickel-free batteries, the purpose of an analyzer is shifting to performance verification, quality control, quick testing and quick priming.
Common sense suggests that a new battery should always perform flawlessly. Yet even brand new batteries do not always meet manufacturer's specifications. With a battery analyzer, all incoming batteries can be checked as part of a quality control procedure and a warranty claim can be made if the capacity drops below the specified level toward the end of the warranty period.
The typical life of a Li-ion battery is 300 to 500 discharge/charge cycles or two to three years from the time of manufacturing. The loss of battery capacity occurs gradually and often without the knowledge of the user. The function of the battery analyzer is to identify weak batteries and “weed’ them out before they become a problem.
A battery analyzer can also trouble-shoot the cause of short runtimes. There are several reasons for this common deficiency. In some cases, the battery may not be properly formatted when first put in service; or the original charger does not provide a full charge. In other cases, the portable device draws more current than specified. Many of today’s battery analyzers can simulate the load signature of a digital device and verify the runtime according to the load requirements.
Lithium-based batteries are sensitive to aging. If stored fully charged and at elevated temperatures, this battery chemistry deteriorates to a 50 percent performance level in about one year. Similar performance degradation can be seen on NiMH batteries when used under these conditions. Although still considered new, the user will likely blame the equipment rather than the battery for its poor performance. The analyzer can isolate this problem.
Before adding new batteries to the battery fleet, a battery analyzer can be used to perform a spot check to ensure proper operation. If a battery shows low performance due to aging, the inventory practices may be changed to the ‘just in time’ method. Storage facilities with improved temperature control may also be sought.
An important new function of a battery analyzer is the ability to quick test batteries. No longer is it necessary to guess a battery’s condition by reading the terminal voltage, measuring the internal resistance or in enrolling lengthy charge and discharge cycles to determine its performance. Modern quick test programs using artificial intelligence are amazingly accurate and work independently of SoC.
Battery quick testing is finding a ready market niche with mobile phone dealers. This feature saves money because batteries returned under warranty can be tested. Replacements are only issued if a genuine problem is found. Once battery quick testing has been further refined, this technology will also find applications in the fields of biomedical, broadcast, aviation and defense.
12.4 Battery Throughput
The quantity of batteries which an analyzer is capable of servicing depends on the number of battery bays available. The type of service programs and the conditions of the batteries serviced also play a role. Li-ion and lead acid batteries take longer to charge than nickel-based packs. Analyzers with fixed charge and discharge currents require added time, especially for larger batteries.
The four-station Cadex 7400 battery analyzer is capable of processing four nickel-based batteries every 4 to 8 hours on a full-service program. Based on two batches per day (morning and evening attendance) and 20 working days per month, one such analyzer can service 160 batteries every month. The throughput of batteries with ratings higher than 2000mA or those that need to be charged and discharged at lower C-rates will take longer. To allow extra analyzer capacity, including reconditioning of old batteries, one four-station analyzer is recommended for a fleet of 100 batteries.
When first servicing a fleet of batteries with a battery analyzer, extra runtime will be required, especially if a large number of batteries need to be restored with the recondition cycle. Once the user-defined target capacity has been reached, maintaining that level from then on will be easier and take less time. When first installing a battery maintenance program, some older packs will likely need replacing because not all batteries recover with exercise and recondition programs.
Quick test methods require the least amount of time. The Cadex Quicktest™ available on the Cadex 7000 Series takes three minutes per battery. The time is prolonged if a brief charge or discharge is needed prior to testing. A charge or discharge is applied automatically if the battery resides outside the SoC requirements of 20 to 90 percent. Unlike the maintenance program, the Cadex Quicktest™ does not improve the battery’s performance; it simply measures its SoH.
The Ohmtest™measurement of the Cadex 7000 Series analyzer takes ten seconds to complete. Large numbers of batteries can be examined if the packs are charged prior to the test. Measuring the internal battery resistance works reasonably well if reference readings are on hand. However, there are batteries that measure good internal resistance but do not perform well. This is especially common with nickel-based chemistries.
There are a number of factors which affect the accuracy of the internal resistance readings, one of which is SoC and the settling time allowed immediately after a recharge. A newly charged battery exhibits higher resistance readings compared to one that has rested for a while. The increased interfacial resistance present after charging causes this. Allow the battery to rest for one hour or more before measurement. Temperature and the number of cells connected in series also affects the readings. Many batteries contain a protection circuit that distorts the readings further.