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Electric Car Battery Pack Design & Sensors for Leak Detection

electric car battery pack

It’s the last thing any owner wants to see -- a small puddle of mysterious fluid underneath their vehicle. Given that EV’s use electrons instead of petrol or diesel as fuel and require significantly less maintenance than their Internal combustion engine (ICE) counterparts, it is easy to get complacent regarding observation and maintenance.

Just because you design a vehicle to run on electricity doesn’t mean it’s immune to one of the most common issues owners face in maintaining their car or truck -- leaks. 

As EV’s generally don’t have frequent oil change intervals like their ICE counterparts, regular maintenance and observation for any unusual stains or fluids on the driveway or garage floor can prevent expensive and potentially catastrophic issues later. And, just in case you forget,  many EV’s contain a suite of sensors that will check your fluids for you.

Electric vehicles typically contain coolant to provide thermal management (cooling or heating) of the various high energy electronics systems, including the motors, inverters, and the battery pack.  Modern electric vehicles contain substantially more complex coolant control systems than their ICE predecessors, using both coolant and refrigerant to control the temperatures of various components through the use of heat exchangers, heat pumps, various valves, and sensors.

The best way your design can prevent a small leak of any sort from becoming a big problem is to have reliable, accurate sensors to monitor for fluid level, temperature, pressure, and quality.  Several advanced EV designs are even capable of sensing whether the coolant is leaking into an area where it can cause damage to the vehicle, such as near the battery cells.

4 Leaks to Watch for in Electric Vehicle Battery Packs (Plus the Sensors Needed for Monitoring)

In monitoring an electric vehicle’s battery health, leak detection is an absolute necessity, whether the vehicle is charging or on the road. The most important leaks to monitor for in an EV’s battery pack are those that affect its thermal management system, such as:

  1. Coolant 

  2. Refrigerant 

  3. Dielectric oil 

  4. Electrolytes

Electric Vehicle Battery Pack Leak: Liquid Coolant

Rather than circulating through an engine block like in an IC engine, coolant is circulated in a closed-loop around an electric vehicle’s battery pack, inverter, cabin, and possibly even the motors to keep temperatures within a suitable range of 15-45°C. The thermal management system allows the battery, inverter, and motors to function without overheating and triggering power-limiting mode or shutdown.

Sensor(s) Needed for Detection: 

To detect liquid coolant leaks, electric vehicles need:

  • Coolant level sensors: Like an ICE vehicle’s cooling system, an EV battery’s thermal management system needs a certain level of liquid coolant to function properly. As its name indicates, this electric vehicle sensor type monitors the amount of liquid coolant within the battery’s thermal management system.

  • Coolant breach sensors: This sensor provides a secondary method for monitoring liquid coolant levels. Should a coolant leak occur within the coolant lines inside the battery pack, a coolant breach sensor detects liquid near the battery cells.  A coolant breach sensor also monitors for the presence of other liquids, such as water intrusion into the battery enclosure, which can cause short circuits and corrosion.

  • Coolant temperature sensors: If the coolant is unable to circulate properly, or if there is insufficient cooling or aeration, the coolant temperature sensor can provide intelligent information on whether or not the coolant is efficiently transferring heat.  Many battery systems will include temperature sensors at the inlet and outlet of heat-generating devices, such as the battery, motors, or inverters, as well as the heat exchangers, providing information on the efficiency of heat exchange.

Electric Vehicle Battery Pack Leak: Refrigerant 

While all EVs with an air conditioning system use refrigerants to keep the passenger space cool, some manufacturers use the same system to keep battery pack temperatures in check. Using heat pump systems, refrigerant-based battery cooling takes two forms:

  1. Direct, in which refrigerant from the vehicle’s air conditioning system flows through a series of cooling plates within the battery pack to keep temperatures down.  

  2. Indirect, in which a vehicle’s coolant fluids flow through plates cooled by refrigerant. This cooling system is more complex and involves other components, such as a chiller, to keep coolant within an optimal range. 

Sensor(s) Needed for Detection: 

To detect refrigerant electric vehicle battery pack leaks, you’ll need two types of sensors:

  • Pressure sensors: Put simply, when there’s a loss of pressure within a refrigerant system, it doesn’t work. Pressure sensors are often the first indicator of reduced performance and leakage within the system, as the compressor, expansion valves, and evaporator all have an expected pressure at various points in the system. When the system cannot attain target pressures, it can be assumed that some of the refrigerant has leaked from the system.

  • Temperature sensors: As in high school physics, the ideal gas law applies to the refrigerant.  The combination of temperature and pressure sensing in the gas and liquid phase within the system is a good indicator as to whether or not there is sufficient refrigerant.

  • Carbon dioxide (R744) sensors: In some of the most advanced refrigerant systems for EVs, R744, a carbon dioxide-based refrigerant is used.  If the refrigerant leaks into the passenger compartment, there can be unsafe levels of carbon dioxide levels released into the breathable air space.  Non-dispersive spectroscopy allows for accurately measuring the CO2 levels in the passenger compartment to determine if a leak of refrigerant has occurred.

Resource: Visit our EV/HEV Sensor Resource Hub to learn more about our suite of sensors for next-generation vehicles:

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Electric Vehicle Battery Pack Leak: Dielectric Oil

A newer battery pack thermal management system with promising applications, dielectric oil cooling boasts superior battery pack temperature control. 

Inside the battery pack, battery cells are immersed in dielectric oil that’s circulated in a closed loop through the unit. The oil -- an engineered thermal conductive fluid -- not only keeps battery cells cool, but also suppresses thermal events.

Sensor(s) Needed for Detection: 

Oil level / Quality / Dielectric sensor: Like a coolant system, battery pack thermal management with dielectric oil requires a specific level of fluid to work effectively. In addition, monitoring the quality and dielectric of the fluid will provide an indication of the life expectancy of the fluid and provides excellent prognostics tools.

Oil temperature sensor: An indicator of the system’s functionality, this sensor monitors for spikes in dielectric oil temperature that may indicate issues with dielectric coolant flow that may indicate kinked or damaged lines.

Electric Vehicle Battery Pack Leak: Electrolytes

In monitoring an electric vehicle’s battery health, measuring the presence of electrolyte leakage is useful in determining if cells within the pack are failing due to age or other stress conditions. These leaks would typically only occur within the battery enclosure and cannot be observed outside the vehicle, so it is critical that sensors inside the battery pack are used to detect this event.

Sensor(s) Needed for Detection: 

Electrolyte leakage detection sensor: The electrolyte leakage from damaged cells typically contains volatile hydrocarbons, which can be detected by a hydrocarbon sensor.

Electric Car Battery Pack Thermal Management Performance & Safety 

Maintaining proper coolant system function is one of the most important elements in maintaining peak performance and safety of an electric vehicle. 

Running a combustion engine without coolant is a sure way to destroy it.  Likewise, an EV without coolant can damage the battery and power electronics. The good news is that most modern electric vehicles have the “sense “ to know when they need fluid and to tell their owners.  Your car may even send you a text, letting you know you need to pick up a gallon of coolant for them!

Take a Deeper Dive Into Detection and Prevention of EV Battery Pack Thermal Management

Explore our resource center for EV thermal management sensors: