Temperature Based Termination Methods

During the battery charging process, it is important to monitor the cell temperature to prevent cell failure. Some batteries during the process of charging may lack the drop in voltage a commonly displayed phenomenon, which is usually used to detect full charge (refer to Figure 4-6). In case this drop is not noticed, the charge will not be discontinued. Therefore, a temperature-based termination method should be used as an alternate charge termination method. Three methods of charge termination...

Traction Battery Pack Design

Before commencing battery pack design for EV applications, it is important to understand the behavior of the battery chemistry. It is important to start with the requirements to ensure that the battery design falls within the boundaries of the technology. It is important to determine the maximum discharge rate of the battery in addition to the operating and storage temperature ranges. Consider the cell configuration Pb-acid, NiMH, and Li-ion batteries can be configured in the series or parallel...

Definition Of Nimh Battery Capacity

NiMH batteries are rated with an abbreviation C, the capacity in Ahr. The C rating for the NiMH battery is obtained by thorough conditioning of the individual NiMH cells. This can be established by subjecting the cell to a constant-current discharge under room temperature. Since the cell capacity varies inversely with the discharge rate, capacity ratings depend on the discharge rate used during the discharge process. For NiMH batteries, the rated capacity is normally determined at a discharge...

Highvoltage Cabling And Disconnects

EVs have two different wiring systems high-voltage and low-voltage. The high-voltage wiring system is used primarily to provide energy to the motor to propel the vehicle. However, some vehicle manufacturers use high voltages to power heating cooling systems, power steering pumps, and EV sensors. The Society of Automotive Engineers (SAE) has specified that orange cables are the standard color for high-voltage wiring in EVs. At present, EVs have high-voltage systems ranging from 250 to 360 V DC...

Storage of an NiMH Battery

The common rule of thumb for NiMH batteries is that an increase in storage temperature halves the time required to self-discharge to a given depth. Traction batteries will provide full capacity on their first discharge after removal from storage and charging with standard methods. Batteries stored either for an extended period of time or at elevated temperatures may require more than one charge discharge cycle to attain prestorage capacities. It is advised that special storage procedures should...

Capacity Discharge Testing Of Vrla Batteries

As recommended by most manufacturers and also industry standards (IEEE 450), a VRLA battery should be replaced if it fails to deliver 80 of its rated capacity. There is a very simple reason for the 80 of the rated capacity value. Based on the typical battery life curve of a lead-acid battery, once the battery capacity begins to deteriorate, the fall-off occurs at a rapid rate. A fully balanced, new traction battery pack will exhibit up to 95 of its rated capacity upon delivery because the...

Temperature Sensing of Traction Battery Packs

Temperature of a traction battery can be measured using an NTC thermistor or other temperature sensing device that is attached to the surface of the cell. This method of temperature sensing relies on the transfer of heat due to conduction. The heat generated inside the cell is measured by the sensor attached to the surface of the cell. However, this measurement is often skewed by loss of heat from the cell surface due to convection and radiation, and depends upon the ability of the battery to...

Introduction To Electric Vehicle Batteries

In the early part of 1900s, the EV design could not compete with the plethora of inventions for the internal combustion engine. The speed and range of the internal combustion engines made them an efficient solution for transportation. By the middle of the 1900s, discussions about the impending oil supplies, the growing demands of fossil fuels began to rekindle the inventions of alternate energy systems and discovery of alternate energy sources. By the mid-1970s, oil shortages led to aggressive...

Definition Of Vrla Battery Capacity

As part of a battery pack configuration, a major problem experienced with the EVs is the premature decline of battery capacity, which ultimately leads to battery failure. The primary cause of the battery pack failure is owing to repeated nonuniform discharging and charging of the cells. Both the battery charging and discharging are highly dependent upon temperature. Owing to the large temperature difference between the coolest battery or batteries on the outer edge of the battery pack, and the...

Thermal Runaway

When a traction battery is operating on float or overcharge in a fully recombinant mode, the net chemical reaction is minimum. Virtually all the energy (V x I) results in heat generation. During the design of the system, the heat generated during the charge-discharge process should be dissipated without raising the battery temperature. In case the temperature of the battery pack rises during the charge-discharge process, more current will be required to maintain the float voltage. The...

Coldweather Impact On Electric Vehicle Battery Discharge

As seen with temperature characteristics of the traction battery, low temperature limits the battery discharge and useful available capacity. For commercial viability and customer acceptance, EVs need to operate reliably over a wide climatic range. The cold weather deterioration of range is well known, however, it is important to identify and quantify the causes of battery pack degradation. Once the solutions have been identified, it is important to pursue the solutions to eliminate the causes....

Cell Unit Internal Impedance Conductance

AC impedance and AC conductance tests are performed to determine battery pack internal impedance or internal conductance of the traction battery. The impedance and conductance tests provide baseline information from similar cells in the battery. The internal cell impedance of the traction battery cell consists of the physical connection resistances exhibited by battery terminal to battery plate welds and similar plate-to-plate connections. The ionic conductivity of the electrolyte and the...

The Battery Performance Management System

A typical electric vehicle (EV) traction battery system consists of a chain of batteries connected in a series, forming a battery pack with nominal voltages ranging from 72 to 324 V and capable of discharge charge rates of several hundred amperes. Owing to the fact that no two batteries in a pack are alike, or even that no two cells in a battery are identical or manufactured exactly the same, their parameters such as capacity may vary by a few percent. In the case of a new battery, these...

8 Testing And Computerbased Modeling Of Electric Vehicle Batteries

As the electric vehicle (EV) development continues, it is important to simulate and validate the development of advanced batteries for electric and hybrid-EV applications. From an end-to-end system perspective, it is important to validate the performance of the batteries by defining the performance envelope of the battery pack. This includes subjecting the traction battery pack to in-vehicle testing for electric and hybrid-EV applications. Integrated with the computer-based simulation, the...

Effects of Current Density on NiMH Battery Formation

The electrical capacity of NiMH batteries exceeds that of nickel-cadmium (NiCd) batteries by about 40 . The NiMH battery is environmentally friendly and contains no toxic cadmium. It provides high-energy storage with reduced weight and volume. During the charging process, hydrogen is generated at the nickel hydroxide anode. The bivalent nickel hydroxide is oxidized to trivalent state by electron removal. At the same time, protons are discharged at the cathode's metal electrolyte boundary layer...

Effects Of Vrla Battery Formation On Electric Vehicle Performance

The formation process of batteries converts unformed paste masses to the charged state, which is stored as energy. In the case of lead-acid batteries, this involves the formation of lead dioxide (PbO2) with lead on the positive plate and sponge lead on the negative plate. This process of conversion of the unformed paste to an active mass is carried out in the presence of sulfuric acid. At the end of formation, the battery gains its final strength and the active mass exhibits a porous structure...

Advances in NiMH Charging

In case the NiMH battery pack is charged too quickly, it can result in permanent damage to the battery and, in some cases, can also cause battery fires and explosions. Combining efficient battery charging circuits and intelligent algorithms can improve the battery life and reduce the battery charging times. Battery designs must account for the variations in the vehicle design to allow for effective utilization of battery charging algorithms. The market for intelligent chargers is expected to...

Model of the BPMS

BPMS, including the defined components, requires a self-adjusting battery model. The algorithm for determining the residual useful battery capacity and the miles-to-go includes calculation of the actual battery pack capacity with respect to the nominal battery pack capacity. The Peukert constant is replaced by 10 representative points. Based on the average load current iav, a linear interpolation is applied from the beginning of the battery pack discharge current to the most recent discharge...

Table Of Contents

Electric Vehicle Operation 2 Battery Basics 4 Introduction to Electric Vehicle Batteries 4 Fuel Cell Technology 14 Choice of a Battery Type for Electric Vehicles 18 2 ELECTRIC VEHICLE BATTERY EFFICIENCY 23 Effects of VRLA Battery Formation on Electric Vehicle Performance 23 Effects of Current Density on Battery Formation 25 Effects of Excessive Heat on Battery Cycle Life 35 3 ELECTRIC VEHICLE BATTERY CAPACITY 43 The Temperature Dependence of Battery Capacity 44 State of Charge of a VRLA Battery...

State Of Charge Of A Vrla Battery

The state of charge (SOC) of a sealed VRLA battery is defined as the percentage of full charge capacity remaining in the battery. This information is identical to the combustion engine fuel gauge. In case of the EV, the SOC provides an indication of the amount of electrical energy remaining in the battery pack. The SOC is accurately determined by the measurement of the stabilized open circuit voltage (OCV). Unfortunately, the VRLA batteries require at least five hours to stabilize after the...

The Liion Battery

Li-ion batteries are the third type most likely to be commercialized for EV applications. Because lithium is the metal with the highest negative potential and lowest atomic weight, batteries using lithium have the greatest potential for attaining the technological breakthrough that will provide EVs with the greatest performance characteristics in terms of acceleration and range. Unfortunately, lithium metal, on its own, is highly reactive with air and with most liquid electrolytes. To avoid the...

Failure Modes of VRLA

Most battery manufacturers prefer not to discuss or talk about the possible failure modes of battery failure. Rather they are interested in talking about the length and the dependable life of the batteries. However, it remains to be a fact that batteries do fail. In VRLA lead-acid batteries, grid corrosion is the leading cause of battery failure. It is the corrosion of the positive grid that limits the life expectancy of the battery. As the battery cycles and ages, the grid gradually begins to...

Charging A Single Vrla Battery

The constant current-constant voltage CI-CV algorithm is the suggested recharge method for the 12 V VRLA battery. It is recommended that this recharge be applied to the battery once every 20 to 30 battery charge-discharge cycles. The correct charging methods and optional values of current and voltage are presented in Figure 4-1. The value of the charge current Ic depends on the output power delivered by the battery charger, the maximum and the minimum values of Ic, the corresponding values of...