Battery Health Beyond BMS

| Environmental Testing

The Cell Guard CAN connected battery monitoring sensor examines a range of battery cell environmental parameters

Health monitoring sensors are being increasingly used to provide greater confidence in the durability of EV batteries

Automotive sensor specialist company, Metis Engineering has launched Cell Guard, a battery safety sensor that aims to make a contribution towards battery health monitoring for electric vehicles (EVs) and Energy Storage Systems (ESS).

Cell Guard is a CAN based sensor that can be easily integrated into almost any battery system and features an accelerometer to measure Shock load and duration up to +/-24G.

The matchbox-sized unit is a unique sensor that provides unrivalled accurate and detailed information on the health of a lithium-ion battery pack by relaying any shock data to the vehicle’s ECU, which can be accessed to provide far greater insight into the battery’s condition.

The battery health information isn’t just constrained to shock however. The general health data available can improve longevity and can detect cell venting, which is an early sign of catastrophic battery failure vastly reducing the risk of thermal runaway.

Battery Environmental Parameter Monitoring

Unlike current battery cell monitoring systems (BMS), which typically only offer temperature and voltage sensors, Cell Guard monitors a range of environmental parameters required to ensure that the battery continues to operate in optimum conditions, including VOCs (Volatile Organic Compounds), pressure change, humidity and dew point as well as shock loads.

This data can be used to crosscheck with other inputs, such as cell temperatures and pressure spikes, to identify cell venting. The sensor relays the data over a configurable CAN interface to a control unit, such as the vehicle’s ECU. This can then raise a warning to alert the driver within seconds that cell venting has occurred. The sensor can also trigger the process to cut the circuit to the battery pack, giving it an opportunity to cool down with the objective of preventing thermal runaway.

The accelerometer can monitor shock loads and impact duration that the battery pack may experience, with the information being able then to reduce the potential for costly scrappage. This information can radicalise the re-sale market of used EVs, with buyers given much needed clarity to be able to make informed decisions regarding battery pack condition, as well as its maintenance. It can also help provide far greater insight into the battery’s condition for repurposing and recycling.

In addition, Cell Guard can monitor the dew point in the battery pack and trigger a warning before condensation settles on the battery terminals, which could lead to shorting and thermal incidents.

The sensor also features a programable pin that can control a relay if a threshold is reached. The Sensor has a low power mode that continues to monitor the pack silently. If a threshold is reached, the sensor starts transmitting on CAN so that it can wake up a vehicle should a problem be detected.

According to Joe Holdsworth, Managing Director at Metis Engineering, Cell Guard makes a big difference to the way batteries are monitored and managed in EVs and Energy Storage Systems. As cells age the chance of one in a pack of hundreds or thousands having a fault increases significantly. The early detection of cell venting is vital to the safety of the vehicle’s passengers and everything in the immediate proximity.

“Our sensor offers far greater accuracy and data than current battery cell monitoring equivalents, and at a much lower cost, up to ten times cheaper than alternatives,” he says.

BMS Limitations

While EV battery packs already have a Battery Management System (BMS) fitted, this system may have limitations when it comes to monitoring the health of the battery pack. For example, temperature sensors may only be present for every few cells, making it difficult to detect issues in a timely manner. Detecting cell issues through voltage fluctuations can also be difficult in the short term because other cells in parallel can prop up the voltage, disguising issues within a cell. Cell Guard can overcome this limitation by supplementing the BMS by providing more detailed information about the health of individual cells.

Consumer Confidence

Holdsworth also believes that Cell Guard also addresses the unsustainable and unnecessary scrapping of used EVs as a result of the automotive market not having sufficient access to vehicle battery health data.

The lack of transparent data on electric vehicle battery health, which is unhelpful in informing consumers, dealers or insurers of the state of the battery condition and is leading to EVs being needlessly scrapped if they are involved in even the most minor collisions.

“Cell Guard not only greatly improves battery health and longevity, but it is also able to provide consumers with valuable and detailed information on used EV battery condition, which is something that is currently lacking and would transform the market,” says Holdsworth.

Until now, the used EV market has not had an effective method to provide consumers with clear data on the health of a car’s battery. Consequently, insurance companies face uncertainty when assessing potential battery damage, often resulting in conservative write-offs even if they have travelled only a few miles. This practice not only raises insurance premiums for consumers but also contributes to unnecessary waste, hindering the circular economy principles that underpin the EV industry.

The information available through the use of CAN attached Cell Guard could have an influence on the re-sale market of used EVs, with buyers given much needed clarity to be able to make informed decisions regarding battery pack condition, as well as its maintenance.

“The unknown risk of poor EV battery health is one of the biggest and most significant barriers hindering the growth of the used electric vehicle market. By providing consumers and insurers with unprecedented insights into battery health, it empowers informed decision-making while minimising uncertainty surrounding minor collision damage. Cell Guard bridges the gap in information between insurers, consumers and the EV industry,” concludes Holdsworth

Based in Bristol, Metis Engineering provides a range of sensors to the automotive industry as well as Cell Guard. These include a CAN-based inertial Measurement Unit (IMU), which monitors 3 axes of acceleration, rotation, quaternion angles and pitch, roll and yaw. There is also a standalone CAN-based Untethered Dead Reckoning (UDR) sensor that outputs latitude, longitude, altitude and course over ground data, which is ideal for when a GPS / GNSS signal is lost and an air quality sensor that measures gaseous parameters to determine cabin HVAC system operation.

Jonathan Newell
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