How to Make Battery Performance Transparent
Global production of Li-ion batteries was roughly 35 gigawatt hours (GWh) in 2013; experts predict the demand will grow to 130GWh by 2020, a 3.7 fold increase. This presents a challenge as batteries need care in the hands of common users. Not enough attention is placed on battery diagnostics as part of work-force-to-retirement; most research goes into developing the super battery.
The capacity of a new battery is (should be) 100%. Lead acid batteries improve briefly with cycling, but all types begin the long gradual decline with usage and age. An analogy is an aging man reaching peak, but declining strength will eventual call for retirement. The condition of a battery should always be known. Device manufacturers tend to gloss over this issue; they wash their hands and wish the buyer good luck with the battery.
Figure 1: Analogy of a maturing man.
A battery reaches peak and then declines like an aging man. Retirement procedures for batteries are often not clearly defined.
Cadex is developing Diagnostic Battery Management (DBM) in the form of an integrated system that manages and diagnoses batteries as part of workforce-to-retirement. The infrastructure includes a web-based application to store data and make battery performance transparent to the user and supervisor. The system comprises of battery chargers, analyzers and monitoring devices that update battery state-of-health (SoH) data with each service to maintain full historic information of the entire battery fleet.
Batteries are often exposed to punitive stresses that include temperature extremes, vibration, harsh loads and fast charging and this applies especially to the electric vehicle (EV). Batteries must perform reliably when in the hands of casual and non-technical consumers.
Many batteries are equipped with a battery management system (BMS) to control voltage and current. The BMS also shows state-of-charge (SoC) but provides little in SoH. This is where DBM takes over by estimating capacity to predict end of battery life. A DBM system can be expanded to also observe internal resistance to assure good power delivery, self-discharge to alert the user of a defect when excessive, and cell balance to protect individual cells from over-use when out of balance.
Attention must be placed on battery aging, and Li-ion is of special concern. Not all batteries will retire quietly; some might depart with a bang; large units may need to be contained to prevent harm. A well-developed DBM cares for a battery alike a doctor who sets limits and raises caution when exceeded.
Without diagnostics, device manufacturers often instruct to replace the battery on a date stamp. To cover most user patterns, a two-year replacement interval is common in healthcare. While this sells batteries, the practice is cost-prohibitive and burdens the environment.
Medical technicians have discovered that the capacity of defibrillator batteries is commonly over 90% at expiry date. Good batteries are discarded prematurely and a manager of the Energy Storage Research Program at DOE reports that “every year roughly one million usable lithium-ion batteries are sent for recycling.”
In spite of this frivolous replacement policy, many batteries stay in service too long. A US FDA survey reported that “up to 50% of service calls in hospitals surveyed relate to battery issues.” Healthcare professionals at AAMI (Association for the Advancement of Medical Instruments) say that “battery management emerged as a top 10 medical device challenge.” A Bio-med Engineer states, “Batteries are the most abused components. Staff care little about them and only do the bare minimum. References to battery maintenance are vague and hidden inside service manuals.”
Battery problems also occur in the military. A corporal serving in the Iraq war checked combat batteries with a voltmeter and marked the “good ones” with tape. Voltage measurement is inadequate because capacity is the leading health indicator. Without proper diagnostics, soldiers may carry rocks instead of batteries as Figure 2 suggests.
Integrating battery diagnostics into daily routines is the goal. DBM does this by verifying the battery capacity with each charge. With
a database, the supervisor also gains access to enable logistics and budgeting. This prevents large quantities of batteries from being dumped into landfills due to of unknown status.
Batteries should receive the same treatment as a critical part in a machine or aircraft where wear and tear falls under strict maintenance guidelines. This is seldom done with batteries for lack of suitable test technologies. Batteries are under-serviced and this is causing system failures under strain and during emergencies.
Figure 2: Soldier carries
rocks instead of batteries.
Battery diagnostics have been lagging behind other technologies and efforts are being made to bring battery care into the 21st century. DBM can be seen as “dressing” a battery that otherwise would go bare. Isidor Buchmann, CEO and founder of Cadex and author of Battery University predicts an industrial revolution in batteries. He states that the time for battery diagnostics is now.
DBM requires capturing the performance of a battery with each service, and this presents a roadblock. Most chargers only charge the battery and show “ready” even if the capacity is low. Cadex has made notable progress in rapid-testing, innovations that will form the building block for DBM. DBM-based products will include battery chargers, analyzers and hand-held testers with a web-based application Battery Embassy.
Battery Embassy communicates over a line or by wireless connectivity with a central database to form the nucleus that connects to the DBM-operated products. Key markets are healthcare, defense, mobile communications, logistics, broadcast, power tools, automotive, mining, as well as as drones, robots and seismic devices. Figure 3 shows Battery Embassy communicating with an intelligent charger, analyzer, SOLI and Spectro™.
SOLI stands for State-of-life Indicator that estimates battery life on delivered coulombs similar to the odometer in a car that reflects distance driven. Spectro™ is a rapid-tester based on Multi-model Electro-chemical Impedance Spectroscopy that scans a battery with a 20–2,000 Hertz signal creating a landscape. Complex modeling fuses the data to estimate battery capacity and CCA. Test time is 15 seconds.
|Figure 3: Battery Embassy is a web-based application that stores test data to make battery state-of-health transparent. The system predicts end of battery life and assists in budgeting.|
FCC measures in-and-out flowing coulombs. An analogy is filling a bottle with water in which the bottle size represents battery capacity and the in-and-out flowing water refers to the coulomb count. The FCC of a new battery is typically 100%; fading as part of capacity loss reflects in a lower reading because of shrinking container size.
The FCC data is stored in the SMBus battery. Available since the 1990s, SMBus stands for System Management Bus, which communicates to the outside world with a two-wire interface. SMBus batteries also include a digital serial number to assist in fleet management.
The FCC data is seldom used as a SoH indicator and the tracking error that develops with use may be to blame. DBM-based chargers and analyzers solve this drawback by requesting a calibration (not a fail) if the FCC reading falls below a user-set pass/fail threshold. Calibration applies a full charge and discharge cycle to measure the true “chemical” capacity and reset the FCC reading. A battery passes if the capacity is above the set threshold; a reading below marks the end of the battery.
Inserting a battery pack into a DBM-based charger or analyzer provides an instant SoH readout. Each service updates the central database to keep a complete history of the battery fleet. Come budget time, the operator simply calls up all packs with low capacity for replacement. Batteries in portable devices are normally replaced at 80%; UPS and traction batteries can often go to 70% or lower; starter batteries may drop to a capacity of as low as 40% before replacement becomes necessary.
DBM can also verify the spare charge on batteries after a long day. An analogy is an airplane carrying extra fuel in anticipation of headwind and to enable a second landing approach. A battery should have a reserve charge of 10%. If the spare charge is always low on a spot check, the pass/fail threshold must be raised. If, on the other hand, plenty of reserve charge is on hand after a busy day, the capacity can drop to a lower threshold before replacement is necessary.
Knowing battery capacity and spare charge reveals the energy consumption for each application. This enables risk management and reduced operational costs. Any calculations must also consider the “what-if.” This level of battery management is not done for lack of technology — DBM will change this.
A RAC-based charger estimates both SoC and capacity. RAC requires a onetime calibration for each battery model; cycling a good battery delivers this parameter that is then stored in the charger or battery adapter.
From the user’s perspective, RAC offers the most simplistic and economical way to manage a battery as it estimates the capacity of regular (dumb) batteries during charge and provides quality control at no added logistics. The green “ready” light assures a full charge and having met capacity requirements; a faded battery is shown the backdoor. Advanced RAC chargers will also feature a display to show SoH in percentage and list battery anomalies.
Simplistic rapid-test methods are based on battery impedance (internal resistance), and as Figure 4 demonstrates resistance does not correlate well with capacity on Li-ion batteries. Improved electrolyte additives have reduced corrosion to keep the internal resistance low while the capacity declines predictably with cycle count. Internal resistance is further affected by SoC, falsifying SoH.
Lead acid batteries behave in a similar way to Li-ion in that resistive values stay low during normal usage (heat-damage is an exception). Nickel-based batteries show a rise in resistance with cycling and age, and here resistance readings can be useful.
QuickSort 4 (QS4) uses Electrochemical Dynamic Response with Multi-dimensional Normalization to estimate the state of health of Li-ion batteries. Spectro™ (mentioned earlier) is based on the more complex Multi-model Electrochemical Impedance Spectroscopy that scans the battery with multiple frequencies. Both are proprietary Cadex technologies.
Figure 4: Relationship between capacity
and resistance as part of cycling of Li-ion.
The full cycle applies a charge/discharge to read the capacity of the chemical battery; it also calibrates the smart battery to correct tracking errors between the chemical and digital battery. A full cycle is also used to prime and condition nickel-based batteries. Performed by a battery analyzer, this provides the most accurate capacity readings but the service is time consuming.
As the world moves from fossil fuel to stored electrical energy, the battery is being promoted as a green solution. This is a noble endeavor, but the battery has not yet matured to assume this important role. Pushing the boundaries exposes many limitations in being a “black box” with unpredictable service and a will of its own that quits at its own terms.
DBM turns the battery into a reliable, safe, cost efficient and environmentally sustainable power source in which each pack can be utilized for its full life. Building a super battery is incomplete without including diagnostic features to predict end-of-life. DBM does this by combining known technologies into a powerful supervisory system. History is full of examples in which connecting known technologies produced powerful products that changed society. Just think of the invention of the Gutenberg press in circa 1440, the Internet and the smartphone.
Isidor Buchmann is the founder and CEO of Cadex Electronics Inc. For three decades, Buchmann has studied the behavior of rechargeable batteries in practical, everyday applications, has written award-winning articles including the best-selling book “Batteries in a Portable World,” now in its fourth edition. Cadex specializes in the design and manufacturing of battery chargers, analyzers and monitoring devices. For more information on batteries, visit www.batteryuniversity.com; product information is on www.cadex.com.
Last updated 2016-11-04
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