1. TopDrive: RP3 Thermal Management of Battery Module 21-09-2010 Unit of Electronics Integration and Reliability Department of Electronics

2. Thermal Management of battery module Steps –Model Development –Experiments –Model Validation Mechanical modeling Material properties Heat Generation in batteries –Cooling Options

3. Experiments Experiments: Discharge only –To validate manufacturer’s data –Discharge at constant current for 4Ah discharge. –Pause for 10 minutes –Then discharge again. –Ten cycles are performed –Discharge is done at 0.5C, 1C, 2C, 3C, 5C and 8C –If the discharge rate is 8C (320A), then first discharge is for (4/320)*3600 = 45 seconds

4. Battery Module Thermal Simulation –7 cells in one module –Uniform heat distribution in the cells –Ambient: 27°C –Cooling with Fan –Fan speed: 6000 rpm –Metal Enclosure Battery Module Enclosure Battery cells in the module

5. Battery model Battery module model in Flotherm Battery cells and the foam pads (in blue)

6. Battery Module Thermal Simulation Heat Dissipation in a battery cell I 2 R, –Where I is discharge current –R is internal resistance –Since R is not measured in the experiments, a value of 0.85m  is chosen from supplier’s data. Material properties (main) used in the model

7. Results 8 C discharge: 320A, 10 Cycles

8. Results Cooling: Fan on Cooling: Fan off

9. Results Flow field inside the module Not enough gaps Between the cells From the fan the flow is blocked by the BMS PWB

10. Cooling options Fan cooling is not enough 2 Liquid cold plates+ high TC pad Saint-Gobain: ThermaCool® R10404 One Liquid cold plate: Bottom 2 Liquid cold plates: Side

11. Cooling options: Results Cooling from 60°C to 30°C Fan only 148 mins Liquid cooling only: 1 plate 135 mins Liquid cooling + fan: 1 plate 110 mins Liquid cooling + fan: 2 plates 98 mins Liquid cooling + fan+ high TC pad: 2 plates 47 mins Liquid Temp: 27°C

12. Drive Cycle simulations Drive cycle of 258 seconds Ambient 40°C.

13. An increase of approx. 2.5°C per cycle. Time to reach 60°C = 2178 sec. –Translates to about 8 cycles Time to cool down to 40°C (liquid temp: 27°C) Drive Cycle simulations: Results Fan only 65 mins Liquid cooling only: 1 plate 56 mins Liquid cooling + fan: 1 plate 50 mins Liquid cooling + fan: 2 plates 42 mins Liquid cooling + fan+ high TC pad: 2 plates 17 mins

14. Cooling options: Results Is liquid cooling the only option?? –Perhaps for passenger vehicles where the power from the battery is drawn constantly for longer period of time –For work machines liquid cooling can be avoided http://www.electronics-cooling.com/2010/07/hybrid%E2%80%99s-liquid-system- allows-chevy-to-offer-cool-warranty/http://www.electronics-cooling.com/2010/07/hybrid%E2%80%99s-liquid-system- allows-chevy-to-offer-cool-warranty/ The liquid heating and cooling system in the Chevrolet Volt battery not only enabled General Motors Co. to offer a long warranty of eight years or 100,000 miles, but it also gave engineers more room for battery cells since it’s more compact than air- cooled systems. Standard auto coolant circulates through 144 metal plates, called fins, between each of the Volt hybrid battery’s 288 cells. The fins are only 1mm thick, but coolant still circulates through channels in them. When the battery needs to warm up, a heating coil warms the fluid. Batteries in electric cars from startup Tesla Motors Inc. are also liquid-cooled. The Nissan Leaf’s batteries are air-cooled.

15. Conclusions Thermal model validation –The trend in the experiments and simulation matches very well. –Some differences in the final result are there, but they could be attributed to the material properties of the battery. –Other unknown chemical reactions might also play some part for the error in the results –It looks like the heat generation estimation method (I 2 R) is suitable for system level simulations. Cooling options –With the current design there is not much we can do to reduce heat. –Fan cooling with the current design is not enough to cool down the module. –High thermal conductivity foam is a must for faster cool down. –Liquid cooling is also an option.