Designing Multi Temperature Thermal Soak Schedules for Commercial Battery Dossiers
Multi temperature thermal soak schedules isolate micro shorts and establish valid cell voltage decay dossiers prior to volume cell procurement.
Thermal Soak Schedule
Meaning
Temporal exposure requirements specify the duration a component remains at a target temperature to achieve internal equilibrium before testing begins. Following a thermal soak schedule ensures that the core of a battery pack is at the same temperature as the exterior surface. Dense materials like lithium ion cells conduct heat slowly, meaning the surface reaches the set point long before the interior does.
Wait periods are a mandatory step in any standardized capacity or power test.
Equilibrium Duration
Sufficient time must pass for the thermal mass of the test object to respond to the surrounding air. In a thermal soak schedule, the duration is often calculated based on the weight and the specific heat capacity of the battery. A small cell might only require two hours, whereas a full automotive pack could need over twelve hours.
Testing conducted before this time has passed will produce inaccurate data because the internal resistance is highly temperature dependent. A pack that is still cold in the middle will show a higher resistance than the specification allows.
Temperature Stabilization
Monitoring sensors placed at the core and on the surface confirms when the gradient has disappeared. Once the difference between these two points is less than one degree, the soak is considered complete. This ensures that the chemical reactions inside the cell are happening at the intended temperature.
Consistency here is the only way to compare results from different laboratories.
Test Readiness
The waiting period is integrated into the automated testing software to prevent premature cycling. After the chamber reaches the set point, a timer starts and locks the test equipment. Once the thermal soak schedule is satisfied, the system proceeds to the next stage of the evaluation.
This rigorous timing is a requirement for all certification tests.