How to test EV batteries safely and efficiently.
Did you know that when it comes to EV battery manufacturing, there are about 100 different opportunities for something to blow up? When working with such a powerful tool there is a lot of power, a lot of voltage, complex connections, high current and many considerations that need to be met.
What is Inside an EV Battery?
A complete battery is made of individual cells, and these cells are then packed into a module. Multiple modules are combined to achieve the intended battery power and that forms a full pack, the final product. Most batteries will have a base plate with a heating and cooling system because batteries don’t work as well in high or low temperatures. This connects to the car’s heating/cooling system.
All modern (Li-Ion) batteries have a battery management system (BMS) that ensures the battery can’t be under or overcharged. It also confirms that all the cells and modules are working properly and are balanced correctly, and all temperatures are in operational range. In the battery there is of course a high-voltage connector and there is a high-voltage relay found between the battery and the inverter. That is there to ensure the high-voltage circuit is switched off when it is not used, or if the car is in an accident.
EV Battery Testing Requirements
There are many considerations that need to be made when testing a battery. When a product has that much voltage and current running through it, a lot can go wrong very quickly.
- Extensive electrical tests need to be run and they need to exceed what the battery is designed to handle. This power needs to be managed safely and efficiently.
- In R&D, batteries need to withstand extreme temperatures ranging between -40°C – 150°C, so a thermal chamber must be developed.
- The cooling/heating systems need to be simulated to emulate low-high temperatures and pressures and check for any leakages. Cell, modules, and packs need to be tested for failures. Failure can include:
- Overheating
- External short circuiting
- Punctures and leakage
- Swelling
- Over-discharging
- Thermal runaway
- Dendrite formation
All these considerations, amongst others, must be made in the design of a test station, and that station must be able to manage these hazards. Each potential consequence has been associated to a danger level by the European Council for Automotive R&D. These are the EUCAR hazard levels and are used to gauge the level of danger associated with handling batteries and the outcome of tests performed on the cells and packs. While these apply to European passenger car and commercial vehicle manufacturers, they are globally regarded as a reliable guideline. The range is from No Effect (Level 0) to Explosion (Level 7). Battery testing therefore takes place inside a safety chamber or thermal chamber that can manage these consequences.
| Level | Description | Effect |
| 0 | No effect | No effect. No loss of functionality. |
| 1 | Passive protection activated | No defect; no leakage; no venting, fire or flame; no rupture; no explosion; no exothermic reaction or thermal runaway. Cell reversibly damaged. Repair of protection device needed. |
| 2 | Defect/Damage | No leakage; no venting, fire or flame; no rupture; no explosion; no exothermic reaction or thermal runaway. Cell irreversibly damaged. Repair needed. |
| 3 | Leakage, mass change <50% | No venting, fire or flame; no rupture; no explosion. Weight loss <50% of electrolyte weight (electrolyte = solvent + salt). |
| 4 | Venting, mass change ≥ 50% | No fire or flame; no rupture; no explosion. Weight loss ≥50% of electrolyte weight (electrolyte = solvent + salt). |
| 5 | Fire or flame | No rupture; no explosion (i.e. no flying parts). |
| 6 | Rupture | No explosion, but flying parts of the active mass. |
| 7 | Explosion | Explosion (i.e. disintegration of the cell). |
EUCAR Hazard Levels
Source: https://www.batterydesign.net/eucar-hazard-levels/
A Common Core Solution
Additionally, the mechanical design of the fixtures needs to be very specific to factor in the complex connections on a battery. By designing a generic test station that includes the high voltage, high current, and highly reusable test instruments in the core, but swappable fixtures, one station can accommodate multiple devices under test (DUTs) and test standardization can be simplified.
SMART Safety Monitoring
With a product as complicated as a battery, there are a lot of separate components required to fully test it and they each have their own safety system. There’s the BMS, the thermal chamber, the battery cyclers, and the thermoregulation safety systems to consider in addition to the overall factory system. Each one works independently, but it is not part of an independent process. It is key to have an over-coupling monitoring system to gauge each component on its own as well as the overall impact. If something were to happen to the battery cycler, the monitor can go ahead and safely shut it down, along with any other part that may be affected.
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Compliance Matters
Due to the potential safety risks, there are at least a dozen standards to consider in battery manufacturing. These standards vary between packs and modules, cells, whether the battery is portable whether it is for North America, Europe, or Asia. By understanding these standards up front and designing the product for test will certainly accelerate compliance and overall manufacturing.
For questions on safer battery testing and compliance strategies, please contact Averna.
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