Battery Pack Thermal Management: Match the Cold Plate to the BTMS

When selecting a battery thermal management system (BTMS), one must not rely solely on cooling capacity as the sole criterion. The battery cold plate and the BTMS must be based on a unified set of operating specifications, including: thermal load, the permissible temperature range of the battery, coolant operating conditions, and the resistance of the installation circuit. Even if the cooling unit itself meets its rated performance specifications, the battery may not necessarily achieve its temperature control targets.

In coach or lorry projects, it is essential to clarify the interface requirements between the battery supplier and the thermal management system supplier before approving samples. The key issue is not the rated power of the cooling unit in kilowatts, but whether the unit can effectively remove the required heat under actual battery installation conditions.

Starting from the battery interface

Require the battery supplier to specify the coolant connection points and their required operating conditions. Record the heat that must be removed whilst the vehicle is in motion, during charging, and during relevant stationary operating conditions. Care must be taken to distinguish between these operating conditions: the peak thermal load during charging is not equivalent to the thermal load requirements during sustained vehicle operation.

Obtain the permissible coolant inlet temperature, the required flow rate range, pressure limits and the criteria for determining battery temperature. A single ‘target temperature’ specification is incomplete without specifying the measurement location and operating mode. It must be confirmed whether this limit refers to cell readings, module sensor readings, the surface temperature of the cold plate, or the coolant temperature.

The battery supplier should also specify the exact configurations to which the above data corresponds. Changes in the number of battery packs, modifications to the cold plate version, or adjustments to the connecting hoses will all alter the actual installation environment served by the BTMS.

The cold plate forms part of the heat transfer path

Heat must be transferred from the cells through the battery assembly to the coolant. Consequently, the performance of the cold plate depends not only on the temperature of the fluid supplied by the cooling system, but also on the contact conditions between the battery and the cold plate, as well as the thermal interface properties.

In its battery materials guide, Boyd states that thermal interface materials form part of the heat transfer path between the module and the cold plate. This is not intended to define the specific performance of the EVLINK system, but rather to illustrate that specifying requirements based solely on coolant parameters leaves certain engineering issues undefined.

Battery suppliers should be required to provide thermal performance data under the proposed coolant operating conditions. If the cold plate’s performance testing was conducted using different fluids, flow rates or thermal distribution conditions, it must be confirmed which test results remain applicable. Generic heat transfer coefficients must not be used as a substitute for measured data specific to the configuration in question. Thermal performance and pressure drop should be assessed comprehensively. Components that improve temperature uniformity often also alter fluid resistance; therefore, both sets of data must be considered when making design decisions. Boyd’s characterisation analysis of its cold plate geometries demonstrates this trade-off; however, its findings cannot be directly used as universal reference values for the selection of other battery packs.

For systems comprising multiple battery packs, a distinction should be made between the total pump flow rate and the flow rates in each branch circuit. Branch circuits with hoses of the same diameter or similar appearance do not necessarily imply uniform flow distribution. Please provide a complete circuit diagram, including manifolds, valves, fittings and the connection methods between the individual battery packs.

When conducting an assessment, reference may be made to the guidelines on coolant flow rate and pump head provided in the BTMS (Battery Thermal Management System). The specific requirements of each branch circuit ultimately depend on the selected battery design. Under no circumstances should simply increasing the pump speed be used as a substitute for verifying the actual flow distribution.

Use one interface record for both suppliers

A clear distinction must be made between estimated values and actual measured results. For input parameters that have not yet been finalised, a responsible person must be designated and a final confirmation date set; it is strictly prohibited to include such parameters directly as finalised values in a quotation without explicit confirmation.

Verification of system operation following integration

Prior to testing, consensus must be reached on the initial temperature, state of charge (SOC), load conditions and acceptance criteria. Battery temperature, coolant inlet and outlet temperatures, flow rates in each branch, and the commands and feedback from the battery thermal management system (BTMS) must be recorded on a unified timeline.

Compare the actual cooling conditions with the battery’s response. If the cooling conditions meet the agreed requirements but temperatures in localised areas of the battery remain elevated, the distribution of coolant, thermal contact conditions and measurement coverage should be investigated first; under no circumstances should the conclusion that ‘chiller capacity needs to be increased’ be drawn before carrying out the aforementioned investigations. If the equipment fails to meet the agreed cooling conditions, its rated operating limits and heat dissipation conditions in the actual installation environment should be verified.

Strictly adhere to established electrical operating and fluid handling specifications. Do not bypass protective devices or dismantle the battery pack without authorisation, even when referring to this planning guide.

Conduct a joint assessment (EVLINK)

Provide EVLINK with the battery supplier’s interface requirements, cold plate technical parameters, thermal load conditions and complete circuit schematics. Additionally, provide information on installation space, available power supply and controller architecture.

Request that the other party conduct a BTMS configuration assessment based on the above conditions and draw up a list of items requiring further validation at the vehicle level. The assessment deliverables should include a correlation analysis between battery requirements and the selected equipment, rather than merely listing two sets of independent rated parameters.

Discuss your battery thermal management requirements with EVLINK