Electric vehicles (EVs) rely on electrons rather than petrol or diesel and typically require less maintenance than their internal combustion engine (ICE) counterparts.
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Even so, designing a vehicle to run on an electric car battery pack does not make it immune, and few drivers welcome the sight of unexplained fluid beneath their vehicle.
It’s tempting to neglect regular inspections, as EVs do not require the routine oil changes associated with ICE vehicles. But it is important to check for unusual stains or fluids on the driveway or garage floor to prevent potentially severe and expensive issues.
Many EVs feature a suite of sensors that can check the vehicle’s fluids. Coolant remains central to EV thermal management, keeping batteries, motors, and inverters within safe limits.
Contemporary EVs feature more sophisticated coolant control systems than their ICE predecessors. They use both coolant and refrigerant to manage temperatures via heat pumps, heat exchangers, valves, and sensors.
Fitting precise, dependable sensors is the most effective way to stop minor leaks from becoming major faults. The most advanced electric car battery pack designs can detect coolant leaking into the spaces near battery cells or other areas where this could damage the vehicle.
Potential Leak Sources and the Sensors Required to Monitor These
Leak detection is key to monitoring an electric vehicle’s battery health, whether the vehicle is on the road or charging. Leaks affecting an EV’s battery pack are the most important to monitor because these leaks can affect its thermal management system. These include:
- Coolant
- Refrigerant
- Dielectric oil
- Electrolytes
This article looks at potential sources of these leaks and the sensor technology used to monitor these.
Monitoring for Liquid Coolant Leaks
In EVs, coolant circulates in a sealed loop around the battery, inverter, cabin, and sometimes the motors to maintain a suitable temperature range of 15-45 °C.
The thermal management system ensures that the EV’s battery, inverter, and motors function without overheating, reducing the risk of the system triggering power-limiting mode or complete shutdown.
Sensor(s) Needed for Coolant Leak Detection
Electric vehicles require several sensors to detect liquid coolant leaks.
Coolant Level Sensors
An EV battery’s thermal management system requires a specific level of liquid coolant to function properly, much like an ICE vehicle’s cooling system. Coolant level sensors monitor the amount of liquid coolant present within the battery’s thermal management system, ensuring this is kept at an optimal level.
Coolant Breach Sensors
Coolant breach sensors provide a secondary means of monitoring liquid coolant levels. A coolant breach sensor detects liquid near the battery cells, highlighting a potential coolant leak within the coolant lines inside the battery pack.
They also monitor the presence of water and other liquids in the battery enclosure, which can potentially cause corrosion and short circuits.
Coolant Temperature Sensors
A coolant temperature sensor provides intelligent information on whether or not the coolant is efficiently transferring heat, for example, where the coolant may be unable to circulate properly, or where there may be insufficient cooling or aeration.
Many battery systems feature temperature sensors at both the inlet and outlet of heat-generating devices, such as the battery, inverters, motors, and heat exchangers. These sensors provide key information on heat exchange efficiency.
Monitoring for Refrigerant Leaks
Any EV with an air conditioning system will use refrigerants to keep the passenger space cool, but some manufacturers will also employ this system to maintain optimal battery pack temperatures. Refrigerant-based battery cooling via heat pump systems takes two forms:
- Direct, where refrigerant from the EV’s air conditioning system flows through a series of cooling plates within the battery pack to maintain low temperatures.
- Indirect, whereby the EV’s coolant fluids flow through plates cooled by refrigerant. This more complex cooling system also requires other components, such as a chiller, to keep coolant within an optimal range.
Sensor(s) Needed for Refrigerant Leak Detection
Two types of sensors are required to detect refrigerant leaks in electric vehicle battery packs.
Pressure Sensors
A loss of pressure within a refrigerant system will cause this to stop working. Pressure sensors usually give the first warning of a refrigerant leak, because the compressor, evaporator, and expansion valves all have an expected pressure at different points in the system. The inability to achieve target pressures likely means that some of the refrigerant has leaked from the system.
Temperature Sensors
The ideal gas law also applies to refrigerant, with the combination of temperature and pressure sensing in the gas and liquid phases within the system generally functioning as a reliable indicator of whether sufficient refrigerant is available.
Carbon Dioxide (R744) Sensors
R744 is a carbon dioxide-based refrigerant used in some of the most advanced EV refrigerant systems. This refrigerant leaking into the passenger compartment can result in unsafe levels of carbon dioxide in a breathable air space.
Non-dispersive spectroscopy can pinpoint CO2 levels from a refrigerant leak with precision.
Monitoring for Dielectric Oil Leaks
Dielectric oil cooling boasts superior battery pack temperature control, making it extremely promising for battery pack thermal management applications.
Inside the battery pack, battery cells are immersed in dielectric oil, which circulates in a closed system to keep them cool. The oil, an engineered thermal conductive fluid, not only keeps battery cells cool but also suppresses thermal events.
Sensor(s) Needed for Dielectric Oil Leak Detection
Oil Level, Quality, and Dielectric Sensor
Battery pack thermal management using dielectric oil requires a specific level of fluid to work effectively, must like a coolant system. Monitoring the fluid’s quality and dielectric will also offer insight into the life expectancy of the fluid, providing excellent prognostic tools.
Oil Temperature Sensor
This sensor monitors for spikes in dielectric oil temperature. An oil temperature sensor is a useful indicator of the system’s functionality, highlighting issues with dielectric coolant flow that may signify damaged or kinked lines.
Monitoring for Electrolyte Leaks
Measuring the presence of electrolyte leakage is useful in ascertaining whether cells within an electric vehicle’s battery pack are failing due to stress conditions or age. These leaks would generally be found within the battery enclosure, and it is impossible to observe them from outside the vehicle, so it is imperative that sensors inside the battery pack be used.
Sensor(s) Needed for Detection
Electrolyte Leakage Detection Sensors
A hydrocarbon sensor is ideally suited to detecting electrolyte leakage from damaged cells, because this leakage typically contains volatile hydrocarbons.
Key Considerations for EV Battery Pack Design
Other Signs or Symptoms of an EV Coolant or Refrigerant Leak
Outside of sensor alerts, EV owners might notice physical signs indicating a coolant or refrigerant leak.
One of the most common of these signs is the presence of stains or puddles under the vehicle, which could potentially indicate leaking fluids.
There may also be a sudden drop in vehicle performance, such as the EV’s battery overheating frequently or a notable drop in the air conditioning system’s cooling ability. A strange odor may be another sign of coolant or refrigerant escaping.
These signs are not as precise or reliable as sensor alerts, but they may indicate that something is wrong.
Preventive Maintenance Steps to Reduce the Likelihood of Leaks
EV owners can take a number of preventive maintenance steps in order to minimize the likelihood of leaks. For instance, it is prudent to regularly inspect the vehicle for any signs of fluid leakage, including unusual smells or stains on the ground near the vehicle.
Coolant levels should be kept within the recommended range, and hoses and seals should be maintained to ensure they are in good condition. Checking the vehicle's cooling and refrigerant systems during routine maintenance can help detect potential issues before they develop into major problems.
Overall, keeping the vehicle in good condition and promptly addressing any minor issues is key to helping prevent leaks.
Risks and Consequences of Continued Operation with a Detected Leak
A detected leak in an EV should be dealt with immediately to avoid serious risks.
A vehicle’s thermal management system may fail if the coolant or refrigerant levels drop too low, leading to the overheating of its battery, inverter, or motors. This overheating could lead to a reduction in performance, triggering power-limiting modes, or causing the vehicle to shut down entirely in more severe cases.
A leak involving dielectric oil or electrolytes can lead to corrosion, electrical shorts, or even fires, while refrigerant leaks in the passenger compartment can pose health risks due to unsafe levels of CO2.
These potential consequences mean that it is important to immediately address any detected leaks, ensuring the vehicle's safety and longevity.
Electric Car Battery Pack Thermal Management Performance and Safety
Proper coolant system function is one of the most essential factors in ensuring an EV’s peak performance and safety.
Just as an engine will quickly fail without coolant, an EV without it risks serious battery and electronics damage.
However, most modern electric vehicles have the ‘sense’ to alert their owners when fluid is required. They can alert their owners via alarms, visual alerts, and even text messages thanks to the presence of sensors within the vehicle.
Acknowledgments
Produced from materials originally authored by Amphenol Advanced Sensors.
This information has been sourced, reviewed, and adapted from materials provided by Amphenol Advanced Sensors.
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