Metis Engineering – Revolutionary electric vehicle battery health monitoring goes into production in the UK

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Metis Engineering – Revolutionary electric vehicle battery health monitoring goes into production in the UK.

Metis Engineering announced the successful certification of its production battery safety sensor, designed to monitor the condition of a lithium-ion battery pack and detect cell ventilation, an early sign of catastrophic battery failure.

The sensor was developed using ISO26262 processes and tested to ISO automotive standards by an independent test house, Applus+ 3C Test and in-house testing capability.

Manufacturing of the production version of the Battery Safety Sensor begins in the UK under strict quality control conditions to satisfy orders from a growing number of OEMs and Tier 1 where they are used in ASIL applications B.

Joe Holdsworththe Managing Director of Metis Engineering said:

Our battery safety sensor measures pressure change and volatile organic compounds (VOCs) for the detection of cell ventilation, which is an early stage of thermal runaway.

“It also monitors the humidity, dew point and air temperature parameters needed to ensure the battery continues to operate at optimum conditions, as well as many other useful features such as a low power mode and configurable CAN parameters.”

He continued. “Fortunately, electric vehicle battery fires are very rare, but when they do occur they are usually catastrophic to the vehicle. As cells age, the risk that one cell out of hundreds or thousands deteriorates increases dramatically.

“Early detection of cell ventilation is vital to the safety of vehicle passengers and anything in close proximity, we hope this sensor will provide an affordable part of the solution.”

In April 2022, Metis released the first beta versions of the new simplified design, optimized for manufacturing in the high volumes required by automotive OEMs. The beta units have been tested by a number of EV manufacturers and battery manufacturers and their feedback has informed the minor changes implemented in the units now certified to ISO automotive standards.

The unique sensor is designed to detect a range of environmental parameters necessary to ensure the battery continues to operate at optimum conditions, including VOCs, pressure changes, humidity, dew point and features an accelerometer optional to record shock loads. This data can be used to cross-check with other inputs, such as cell temperatures, to verify cell ventilation.

The sensor relays data through a configurable CAN interface to a control unit, such as the vehicle’s ECU, to alert the driver that cell ventilation has occurred. The sensor can also initiate the circuit breaking process to the battery, giving it the opportunity to cool itself in an effort to prevent thermal runaway.

Limitations of current battery management systems

EV battery packs will already be equipped with a battery management system (BMS). As well as managing the charging and discharging of packs, they also attempt to monitor battery health, although this is usually limited to temperature sensors, one for a few cells, and monitoring voltage changes.

This system works well if it is the cell with the temperature sensor that goes bad, but if the cell is some distance from the sensor in the pack, at the time the sensor registers the temperature change, if any, it would most likely be too late.

Detecting cell problems through voltage fluctuations can also be difficult in the short term because other cells in parallel can sustain the voltage, masking problems with one cell.

The Metis Battery Safety Sensor typically detects breakdown within seconds.

There are several stages for a cell to enter thermal runaway. First, there is an increase in temperature, often caused when a battery is overworked, has a manufacturing defect, or ages. The increase in temperature leads to an increase in pressure inside the battery cell. Eventually this pressure, if high enough, will cause the sealed battery cell to vent. If the load is not removed from the cell, thermal runaway can occur.

If a battery fails after being vented, it can catch fire in an auto-oxidation reaction, which will most likely result in a runaway reaction, triggering the cells around it and resulting in the total loss of the vehicle.

The Metis Battery Safety Sensor also includes an optional accelerometer, so it can monitor shock loads up to 24G and how long the battery may be impacted. If the electric vehicle is involved in a collision, the sensor will indicate if the pack has been subjected to loads above safe levels and for how long.

This can inform decisions about whether the battery requires service, a second life in a home or industrial energy storage system (ESS), or sent for recycling and any subsequent insurance claims.

Batteries heat up when charged or discharged. To prevent overheating, most packs are cooled in some way. If cooled below room temperature, they may drop below the dew point (the temperature at which air cannot transport moisture and condenses on cooler surfaces), which could result in short circuits and thermal incidents.

The Metis Battery Safety Sensor monitors the relative humidity as well as the dew point in the battery and can trigger a warning before condensation deposits on the battery or other components.

Strong points:

  • Battery safety sensor to detect cell ventilation and provide early warning of thermal runaway – certified to ISO automotive standards
  • Monitors the health of a battery with greater accuracy and data
  • Low power consumption (~7mA in CAN sleep monitoring mode)
  • Configurable CAN address, speed and update rate
  • Configurable 500mA LSD pin triggered on threshold detection
  • Fully certified sensor enters production in UK

Metis Engineering – Revolutionary electric vehicle battery health monitoring goes into production in the UK, Bristol, 5 October 2022

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