How to keep your battery pack cool while delivering high power output
Keeping the batteries in a battery pack within their temperature range is very important for the battery performance and lifespan. Operation outside of the temperature range can cause a reduced range, reduced power and above all it can cause safety hazards. A question that rises is how to assemble a battery pack and keep it cool while still delivering high power. In this article we'll talk you trough the different battery cooling methods for electric vehicles.
Air cooling
The easiest way to cool is with airflow. But in high-power applications air cooling will not be enough. With air cooling you rely to much on the temperature of the air and the airflow. Even when optimal, this will still not be enough to cool the batteries.
Liquid cooling
The next logical step that follows is to it with fluid. A fluid cooled system needs way more components than an air-cooled system. But because you have way more components, there is also the possibility to improve your cooling system by upgrading one or more of these components.
The Power Battery modules have the possibility to add cooling pipes through the modules. In this way, a fluid can run through the modules to cool the batteries. Another way of cooling batteries is by mounting a cooling plate on top of the main poles of the modules. Because a cooling plate is usually made of a conducting material, an isolation layer must be added to separate the cooling system from the electrical system. When cooling the top of the main poles, it is very important to make sure that the heat from the batteries can be conducted very well to the top of the poles. Because it is a long distance between the place where the heat is generated and the place where the heat is absorbed, this method is not the most ideal. It is best to have your cooling system as close to the heat source as possible.
But one way or the other, the system is fluid cooled. The difference between the temperature of the batteries and the temperature of the cooling fluid will determine the amount of heat transfer between the two. The higher the temperature difference, the higher the heat transfer will be.
In a regular petrol car, the cooling fluid is cooled by a radiator. This works very well because the temperature difference between the cooling fluid and the surrounding air is high enough. The cooling fluid in a battery pack will not reach the temperature of the cooling fluid in a petrol car. The usage of a radiator in the cooling system of a battery pack will still work, but it will not be that efficient. Because we are talking about a high-power application, the temperature of the batteries will get close to the maximum of 60-70 degrees Celsius. Operation of the batteries above 70 degrees Celsius is very dangerous, so we need to make sure the temperatures does not rise to that level.
As said before, the radiator will not be that efficient in transferring the heat in this situation. Measures need to be taken to increase the cooling performance. We will explain a few examples of how one can increase the cooling performance of a cooling system.
Increase the flow of the cooling fluid
When the flow of the cooling fluid increases, the increase of the temperature of the cooling fluid will slow down. The temperature of the cooling fluid will still increase, but this will happen slower. In technical terms, the difference between your inlet temperature and outlet temperature will decrease. When the increase of the temperature of the cooling fluid is slowed down, the cooling of the batteries will improve.
A pump with a higher flow rate can provide a higher flow. Also, more parallel string of cooling tubes can decrease the difference between the inlet and outlet temperature.
Lower the temperature of the cooling fluid
The lower the temperature of the cooling fluid is, the higher the heat transfer will be. There are cases where dry ice is added to the cooling system to lower the temperature.
Change the type of cooling fluid
The most common cooling fluid is water, but there are other cooling fluids as well. There also are additives that you can add to the water to increase the heat transfer.
Spray the radiator with a fluid that evaporates
In racing they sometimes spray CO2 or pure alcohol on the radiator to increase the heat transfer form the radiator to the air via evaporation.
Add an air-conditioning system to your application
By adding an air-conditioning system to your application, the heat transfer will increase very much. The air-conditioning system enables you to achieve a higher temperature difference between the cooling system and the heat source.
Submersion cooling
Another way of cooling a battery pack with liquid is to submerge the complete battery pack in the cooling fluid. This technology is already used in the world of supercomputers. However, this method is very expensive. The cooling liquid needs to be electrically insulated and thermally conductive. In nature, these two characteristics act the same. So, good thermally conductive materials are most of the times also electrically conductive. To combine materials in a fluid that will result in an electrically insulated, but thermally conductive fluid is not easy. Also, this fluid must not affect the materials it cools in a bad way. Summarizing, this fluid is not easy to create, therefore it is expensive.
Summary
The best and most achievable way of cooling a battery pack is to use liquid cooling. The parts to assemble the cooling system are very common thus relatively not expensive. It is also very suitable for trying a number of different subsystems on the cooling system to improve its performance.
When your application will draw maximum power from a battery pack during a long time, it is suggested to optimize this cooling system the best you can.
Custom advice for your EV project
Choosing the right cooling method for your electric vehicle can be quite a challenge. At Power Battery we develop a unique cooling method for high-power battery packs. Please contact us if you have any questions regarding your project, or request consultation.
