With the aim of monitoring the health of a battery pack with greater accuracy, Metis Engineering unveiled the beta version of their Production Battery Safety Sensor. The latter is also capable to detect cell venting, an early sign of catastrophic battery failure.
The beta versions of the Production Battery Safety Sensor are the first of the new streamlined design, optimised for manufacturing in the high volumes required by automotive OEMs. Units are already on trial with a number of EV OEMs and battery manufacturers. Initial feedback has been unanimously positive.
Metis Engineering: monitoring above the BMS
EV battery packs will already have a Battery Management System (BMS) fitted. As well as managing the charging and discharging of the packs, they also attempt to monitor the health of the battery pack, although this is typically limited to temperature sensors, one for every few cells and by monitoring for voltage changes. This system works fine if it happens to be the cell with the temperature sensor that goes bad, but if the cell is a distance away from the sensor in the pack, by the time the sensor registers the change in temperature, if at all, it would very likely be too late. 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 with a cell.
The issue of cooling temperature
Also, battery packs get warm when they are charged or discharged. To prevent overheating, most packs are cooled in some way. If they are cooled below the ambient temperature, they can dip below the dew point (the temperature at which the air can’t carry moisture and it condenses onto cooler surfaces), which could lead to shorting and thermal incidents. The Metis Battery Safety Sensor will monitor the dew point in the battery pack and trigger a warning before condensation settles on the battery terminals.
«The release of the beta versions of our Production Battery Safety Sensor marks another key milestone, as we roll out the technology to enable unrivalled health monitoring of lithium-ion battery packs», commented Metis Engineering Managing Director Joe Holdsworth. «The sensor is already on trial in electric sportscars, buses, aircraft and vans and the feedback has been universally very positive. My team plan to make one or two minor modifications before we sign off the final spec of the Production Battery Safety Sensors, ready for delivery Q3 this year».