Battery has always been an integral component of vehicles. With increased employment of electric vehicles, importance for batteries has increased significantly. Now batteries for automotive industries need not to be large in capacity only, but they must also have high energy density, longer lifespan, and better power characteristic curves.
Batteries in automotive go through varying usage conditions as vehicle is on the road. These usage conditions pertain to vibrations, temperature variations, and water ingression. To ensure safety, longevity of vehicle including battery, and reliable functioning; it is essential to use right battery test equipment for electric vehicles. Various manufacturers have developed multiple solutions to test EV battery systems. Before discussing available solutions, it is important to understand various types of tests, their purposes, and parameters involved.
Why Use EV Battery Testing System?
As mentioned earlier, vehicles and thus batteries face rapidly changing environmental conditions. This, definitely, affects performance of batteries and associated systems. Moreover, over the course of service life connections, installed cooling system, quality of electrolyte, quantity of electrolyte, and other components or systems get affected. These unwanted changes can lead to loss of required battery performance or even total system failure. Consequences can also include financial loss, injury to human beings, and/or loss of life. This is why, it is essential to run a holistic battery testing process before use.
Regulations and Standards for Vehicle Battery Testing: A Guide to Choose Battery Testing Equipment
To provide a consistent method in order to evaluate performance parameters of batteries for various operating conditions, it was necessary to provide requirements to all manufacturers and system providers. Standards serve this purpose well and boost client’s confidence in product and promote innovation. These standards also provide a set of guidelines to manufacturers and technicians for choosing appropriate battery testing equipment complying with their specific needs. Various standards for vehicle battery testing equipment including that of IEC, ISO, and UN are mentioned here:
IEC 62133 Test:
This test is developed by IEC (International Electrotechnical Commission). This is about the safety of rechargeable nickel-ion and lithium-ion batteries. Compliance with this test ensures that battery is capable of operating under various stress conditions and resistant to conditions like overcharging, short-circuiting, over discharging, and high temperature.
38.3 Test:
This test is developed by UN (United Nations) and includes recommendations about transport of lithium batteries through air, land, or sea routes. This test is to ensure that battery could withstand environmental and physical strain like vibrations, pressure, extreme temperatures, and shocks.
ISO 12405 Test:
This test standard is issued by International Organization for Standardization (ISO). This standard is for EV batteries specifically. The purpose of conducting this test is to make sure that battery could retain its performance, be considered safe and durable in stressful as well as normal conditions. This test also verifies that battery could undergo rapid charging and discharging cycles without impacting its own health.
ISO 6469-1:
this standard outlines safety requirements for RESS (Rechargeable Energy Storage Systems) employed in electrically propelled road vehicles. This test is to ensure protection of persons.
Which Performance Parameters are Important during EV Battery Testing?
Batteries in EVs lie at the helm of drivetrain. So it is important to keep checking and controlling (through feedback systems) various performance parameters. Here is a list of all those parameters which are to be checked in normal conditions. Majorly, electrical parameters are discussed in this section. Environmental and mechanical parameters will be discussed in other sections which pertain to special performance tests.
Capacity:
Capacity is measure of energy stored in a battery pack which is represented in Ah (Ampere-hours) or Wh (Watt-hours). Higher capacity means your EV can travel more miles on a single charge so large capacity is desirable. Constant-current testing is employed to determine effective capacity of battery.
Energy Density:
Energy stored per unit mass is referred to as energy density. This is usually given in Wh/kg. Higher energy density means battery is capable of storing more energy per unit mass.
State of Charge (SoC):
SoC is represented in %age and it is ratio of remaining charge (or energy) and total charge (or energy when fully charged) multiplied by 100. It is monitored to be sure that passengers don’t experience unexpected vehicle shutdown upon running out of power.
Output Voltage:
Ideally, cell voltage or output voltage shall be determined by reactions taking place within cell. But, it is not easy to measure this voltage. So, usually, Open Circuit Voltage (OCV) is measured which also gives an estimate of SoC. As SoC decreases, output voltage might drop slightly.
Depth of Discharge (DoD):
During discharging process, batteries don’t get discharged to 0%. In fact, some charge is retained which can be considered as non-dischargeable. As battery life increases, depth of discharge decreases.
This concept is related to SoC (State of Charge) also. To summarize, depth of discharge is ratio of discharged capacity from a fully charged battery by nominal capacity of battery. Higher DoD means better battery health.
Charge and Discharge Rates:
C-rates or charge and discharge rates are also important performance parameters for EV battery. These depend upon input/output current flow and nominal capacity of battery. Higher charging rate means EV users will need to wait for less time to get their vehicles charged. Higher discharging rate means battery is capable of providing higher energy while EV will be climbing a steep road or traction motors will be demanding higher power due to any reason.
Efficiency:
Wherever energy comes in play, efficiency becomes important factor to consider. For EV battery, efficiency can be described as ratio of output power to energy intake.
Special Performance Tests for EV Battery:
Special tests are designed for certain conditions and environments which are
- encountered infrequently
- not relevant to all battery technologies
these tests are related to self discharge, partial discharge, hill climb, special thermal conditions, vibrations, charge optimization, and fast charge. These tests are described briefly here:
Stand Testing:
When battery is not used for longer period of time, it also impacts battery’s capacity. Loss of capacity is, usually, temporary. But semi-permanent and permanent capacity loss can also occur. There might be situations when an EV will not be used for extended period of time and results might include capacity loss among other problems.
Thermal Performance:
Thermal performance of EV battery includes
- Heat management during charging and discharging
- Operating temperature range
EV battery must be able to withstand higher and lower than normal temperatures. Good thermal management for battery system would help prevent problems like demagnetization, efficiency decrease, motor burnout, and aging of insulation materials.
Battery Vibration Test:
EV battery is subjected to vibrations and shocks while on road. This test helps ensure that battery could tolerate these mechanical disturbances. If not, this test could help identify design deficiencies.
Fast Charging Test:
For EV battery systems, fast charging is becoming the norm. This test is made to determine if battery’s efficiency or other performance characteristics are affected upon subjecting to higher charging rates.
Safety and Abuse Testing:
This test is still under development. It is performed to identify design discrepancies in system. It is also to gain public confidence in product and comply with ‘safety’ regulations issued by governments. This test involves subjecting vehicle to accidents, crash, extreme external environments, burning, puncturing, and charger malfunctioning.
A Comparative Guide to Choose from Various EV Battery Testing Solutions
Various manufacturers have designed a range of battery testing solutions which perform various tests to analyze different parameters discussed above. Here some notable brands are discussed briefly.
Sinexcel RE:
Sinexcel RE stands among the top battery testing system providers for EVs. Their test systems accept energy feedback, ensure safety, and provide high accuracy and fast response. These systems give voltage accuracy to the tune of 0.01%F.S. and current accuracy to the tune of 0.02%F.S. Apart from being precise, these testing systems are fast also. Sinexcel’s EV battery testers are capable of performing 50ms roadmap tests, providing 5ms fast current response. On the top, battery testing solutions designed by Sinexcel, can be linked with other system components efficiently like BMS, temperature chamber, water chiller and so on. Various testing solutions by Sinexcel have different power ratings ranging from 14.4kW to 24kW giving its potential buyers a variety of options so they could make appropriate choice according to targeted battery. These battery testing systems come with multiple charge/discharge operation modes including CV, CC, CP, CR, CC-CV, DCIR, drive simulation, and pulse.
Arbin Instruments:
Battery testing solutions by Arbin Instruments provide dynamic drive cycle simulations, include communication with BMS (Battery Management Systems), and contain cell-isolating battery test chamber to ensure temperature stability as per US government regulations. EV battery test systems by Arbin use true bipolar circuitry ensuring that there would be no switching between charging and discharging. Arbin’s Mits Pro Software eases the process of battery testing for constant and dynamic control. It has various built-in functions including mathematical functions, voltage and current ramps, looping, and much more. Arbin also provides helps to its client in calibration, hardware installation and setup, emergency support, software upgrade, remote tech support, and online training. Moreover, Arbin instruments has dedicated teams to support its clients, answer their queries, resolve technical challenges, and assist them in installation to maintenance process.
MTS
MTS provides battery testing solutions for lithium-ion batteries and battery packs for electric cars, off-highway vehicles, trucks, scooters, and all-terrain vehicles. MTS recommends these systems to be used by OEMs, suppliers, and contract test labs while subjecting battery to real-world vibration phenomena. MTS provides MAST (Multi-Axial Simulation Table) available in custom and standard configurations which can be integrated with third-party environmental chambers easily. MTS has also developed its software RPC Connect software which is aimed at optimizing lab efficiency. Their notable testing solutions include Series 295 Isolation Hydraulic Service Manifolds (ISHM), and SilentFlo 515 Hydraulic Power Units (HPU). MTS provides calibration, consulting equipment monitoring, routine maintenance, remanufacturing, and relocation services to its clients. Its technical support and trainings further enhance client’s preference for their battery testing solutions.
AVL
AVL offers ‘plug and play’ solutions for battery testing which could be containerized battery testbeds or free-standing solutions not needing any sort of adaptations. AVL gives options for individual product testing, integrated system solutions, and complete battery test facilities. AVL offers facility services where design, optimization, and development can be realized for a client. It gives full hardware and software package which is complemented by application service and support options.
Keysight Technologies
Keysight in collaboration with Scienlab provide test systems to test battery cells, modules, battery packs, and BMS for e-mobility and other applications. Its hardware and software (ESD – Energy Storage Discover by Scienlab) system helps execute customized performance, aging, function, and environmental tests. ESD includes conformance tests and standards compliance from ISO, DIN EN, and SAE. Its testing solution ensures records measured data in synchronization. Keysight offers technical support,a detailed knowledge center, calibration certificates, and software download center to its clients.
Battery Testing for Lilium eVTOL – A Case Study and a Success Strory
Need for EV battery testing systems led to innovation and research in the field of electronics, controls, prototyping, product designing, and much more. Development of these testing systems is no more confined to EV sector only but it is expanding its horizon in other relevant industries like Aviation industry.
Lilium has been engaged in developing an eVTOL (full electric vertical take-off and landing aircraft). Lilium developed its entire powertrain using batteries, inverter (for DC/AC conversion), motors, and control software. Lilium dreamed its product to be suitable for future Urban Air Mobility having new mechanical, chemical, and electrical design. It was also to meet certification requirements for aviation.
In aviation industry, there is no established testing requirement for batteries. Here battery testing development tools and techniques came in play where Lilium took the task to develop product validation methods for it aviation project but considered established methods of automotive battery testing methods as a basis. To perform battery testing in conditions similar to real-time situations, AVL proposed designing a test facility which was implemented in several stages and included R&D support and production.
Conclusion:
To achieve green energy goals, batteries and thus battery testing solutions are very important. Batteries in automotive undergo a set of conditions and thus a range of tests is needed to ensure that battery and battery packs would withstand those conditions without any compromise in efficiency. Tests conducted on battery would also help identify discrepancies in design, ensure safety, and boost public confidence in product. Moreover, Research and development in the field of EV battery testing would shape many industries including manufacturing, aerospace, and power electronics.