Energy density of batteries. 

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... I NTRODUCTION In the last period, advances in battery technology provide innovative solutions to the consumer market – powering products. Developments are due to increased demands in the field, market demanding large quantities of batteries of different types – Figure 1. The cell phones, laptops and PDAs require small, low power batteries. The major area of application for large batteries is the electric vehicles but also on industrial, medical and military equipment – Figure 2. Different technologies are proposed to obtain as large capacity battery. A comparison of the energy densities of the various rechargeable batteries is shown in Figure 3 [1]. In this direction are remarkable solution offered by lithium- based batteries, the predominant power sources for devices such cars, laptops and telephone cells. Lithium-ion cells usually provide an operating voltage of about three and a half volts, but high voltages require cells in series. Detailed information regarding the operation principle and related technologies for these batteries are presented by Belharouak [2], Root [3], and different specialized companies [4]. A free educational website is dedicated on electrochemical processes, with tutorials evaluating the advantages and limitations of the use of battery [5]. Also, you can highlight the increasing demands for large capacity batteries coming from the field of solar cells and wind power generation. On the other hand, however, this type of battery shows security issues: short-circuiting, overcharging and other factors sometimes cause lithium-ion batteries to become unstable [6]. Therefore, to ensure product safety and reliability, testing is performed to characterize the processes of the charge/ discharge cycle of these batteries to characterize and predict their performance [7]. Some tests are dedicated to certain internal components of batteries, for example, physical evaluation of separators, element with a dual role of preventing short-circuiting between the plus and minus electrodes and shutting off current when heat is generated [8]. Using modern methods of modeling and simulation of electrochemical phenomena specific battery operation provide design optimization and automatic control of batteries. For example, battery block of Simulink software implements a generic dynamic model to represent most types of rechargeable batteries [9]. Different researchers have reported models for predicting the battery capacity or battery service life [10], [11], [12]. After the studies of the influence of different geometries, electrode materials, poor distribution, electrolyte composition and other fundamental parameters, the manufacturer optimize the battery design and simulate performances at relevant operating conditions. A solution for testing Lithium –Ion batteries is presented by Datatranslation Company [14]: TEMPpoint instrument measure and analyze temperature and voltage data with channels for 10 voltages and 36 thermocouples. The charging/discharging process optimization is performed with specialized integrated circuits. For example, the bq24314C (Texas Instruments) is an integrated circuit designed to provide protection to Li-ion batteries from failures of the charging circuit. This device continuously monitors the voltage and the battery current and provides limitation in the case of an overcurrent [13]. Linear Technology produces LTC6804 circuit, specialized for monitoring car battery with 0.04% precision [15]. The graph of Figure 4 shows typical discharge curves for the cells currently used. The Lead acid battery has a pronounced slope, but Lithium-ion has a fairly flat discharge curve. This paper presents a solution tested for a laboratory based on the use of virtual instrumentation, for charging/discharging tests of different types of batteries and for monitoring specific parameters. II. H ARDWARE AND S OFTWARE I MPLEMENTATION OF T ESTING B ATTERIES L ABORATORY Technical solution for the new laboratory was designed for these features: a) Electric parameters a.1. Charger • Charging current programmable with 8 bits of resolution in the range 0 to 2 A (expandable); • Basic accuracy for current: +/- 0.4%, k=2 • Programmable automatic voltage limiter, 8 bits of resolution, with upper voltage in the range of 0 to 10V (expandable); • Basic accuracy for voltage: +/- 0.4%, k=2 a.2. Discharger • Discharging current programmable with 8 bits of resolution in the range 0 to 2 A (expandable); • Basic accuracy for current: +/- 0.4 %, k=2 • Programmable automatic voltage limiter, 8 bits of resolution, with lower voltage in the range of 0 to 10V (expandable); • Basic accuracy for voltage: +/- 0.4 %, k=2 b) Measurements • 4 digits resolution in the range of 0 to 2 A and 0 to 20 V (expandable); • Uncertainty for current and voltage measurements: +/- 0.5 %, k=2 • Accumulator temperature 0-70°C, uncertainty +/- 1°C, k=2. c) Computer control • Software for system control written in LabVIEW; • Access Data Base linked to LabVIEW for inspection of data and visualization of the graphical characteristics of the charging/discharging process; • Serial COM communication emulator system (9600 baud rate) over USB. Principle of measurement in the two phases of testing battery is shown in Figure 5. The charger/discharger is a computer pending current /voltage source and sink aimed to test the charging discharging properties of various battery types, voltage and capacity. The position of the two switches (K1 and K2) allows obtaining specific test circuits in terms of charging and discharging for the battery under test (BUT) – Figure 6. The practical implementation of the hardware solutions of the equipment is shown in Figure 7. The Figure 8 shows an overview of the experimental solution. Hardware design of power circuits includes DC voltage source, power MOS and Charging-discharging mode relay switch. The Stellaris LM4F120xxx microcontroller and the analog control circuits provide operation of the power MOS and relays. Software design is based on LabVIEW virtual instrumentation software linked via USB communication configurated as COM UART for simplicity of usage. There are four operational regions wits controls and indicators on the Panel of the virtual instrument –Figure 10: • General system controls; • Charging/discharging controls; • Battery measurements (voltage, current, temperature); • Configuration and DataBase controls. Uncertainty of measurements is handled bought for compression of random errors and systematic errors reduction: ● Random errors are handled during the microcontroller measurements process performing random sampling with 2000 samples taken on an interval of 200ms for noise and line interferences compression; ● Systematic errors are handled by initial and possible periodic calibration for bought measurements and controls of current and voltage taking in account offset and gain errors. Coefficients generated by the calibration process are entered in the configuration system to be use for correction of every single measurement – Figure 10. Data base register results of the test in progress with a specified rate period and a DB retrieval program may be used to visualize date and graphic results of the tests. Each test is recorded in a separate DB table having indicators of operator, device under test, test type and date. Visualization may be personalized using a data graphic selector Figure ...