How are electric cars cooled?

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Generally, the part of an electric car that needs to be cooled the most is the batteries. As you discharge a battery and take energy out of it, it creates heat. The quicker you discharge the battery the hotter the battery will become. Its the same story for charging batteries, the hotter they become, the shorter lifespan they have. This is why batteries are generally monitored and managed closely by the battery management system (BMS) if your car has one. If batteries become too hot they can damage themselves, they degrade and lose range. Battery management systems aim to keep the batteries at an optimum temperature level between 68ºF to 104ºF (20ºC to 40ºC). Coolant can also be used to cool the batteries of some cars and this is operated by the BMS. Cars that don’t use coolant to cool the batteries have an air-cooled system (passive system), such as the Nissan Leaf. Whether this passive cooling is enough from this to suitably cool the batteries to a more optimal temperature remains to be seen and could cause more long term degradation to the battery than a controlled and monitored coolant system.

You will probably notice that some car manufacturers design their electric cars with a grille at the front of a car. This is typically part of the design process for an internal combustion engine (ICE) car, as the engine gets very hot and cold air is pushed through the front of the grille whilst driving along. This is not required for electric cars as the electric motor does not reach very high temperatures when compared to an ICE engine. Cars designed without a BMS such as a Nissan Leaf cool the car battery with air whilst driving, in this design the air passing underneath the car helps to cool the battery. The creation of the grille is something purely done by the designers, but the reality is that having a grille reduces the aerodynamic efficiency of a car, meaning it uses more energy to move. This front grille look is something which we have all become accustomed to in our experience of cars and will be something that you will see less and less over time. Efficiency is now the aim of the game for electric cars, the more efficient it is the more range you can achieve from your battery.

Electric motors do require coolant for them to be cooled down, but due to the efficiency of an electric motor, a very small amount of heat is created when compared with an ICE. An ICE can create heat upwards of 1300ºF (700ºC), this can be useful in the winter when you want to use this excess heat of your internal car to warm up the passengers. But this is a lot less efficient and useful when you are driving in the summer and don’t need the heating up.

In Tesla’s it is true that the computers inside the car need to be cooled, there is a lot of heat created by the electronics and the central console is attached into the dashboard making it pretty well insulated. Another way of cooling the computers inside the car can be with air conditioning. There is a fail-safe feature that if your Tesla is left out in the sun whilst you are away from the car, the air conditioning will turn on automatically and lower the temperature to keep the computer at a reasonable temperature and avoid any damage to the electronics.

Can electric cars overheat?

Electric cars can overheat, they normally, reduce the amount of power to the engine and then eventually, shut themselves down when they are overheating. This is a way of protecting the car from permanent damage, discharging your batteries quicker also creates more heat. This means the quicker your speed or if you drive with lots of heavy acceleration you will discharge the batteries quicker than normal. The same can be done with charging rates when charging your electric car, the batteries begin to heat up a lot. Reducing the speed that you are charging the car at, will reduce the temperature in the batteries. If your car has a BMS, there is a lot less chance of your battery overheating as the cars onboard computers will monitor and prevent this.

What happens if an electric car battery overheats?

Generally, within a battery pack, there are various modules which are all connected together, in the event that some modules heat up a lot more than others it can cause: battery degradation which means your battery has less range. Fires can also occur due to batteries overheating generally there will be some kind of small explosion followed by a fire. Fire services have had to receive special training in dealing with battery fires in electric cars. Battery overheating can also cause different charging speeds, within your battery packs and different discharge speeds too. A battery works best when all the battery modules are charging or discharging at the same speed so that no single battery pack is working harder than the other.

Cooling system in a Tesla explained

Tesla uses pipes filled with propylene glycol to cool the batteries, electronics, and electric motors. This is circulated throughout the car using pumps and prevents important parts of the car from overheating. Tesla uses a patented snake-shaped cooling system in their battery packs, see the diagram below (the coolant pipe is shown in blue). This allows the batteries to be cooled sufficiently due to the glycol having access to all of the batteries. A similar liquid cooling process is used for the Jaguar I-Pace and the BMW I3 also.

This type of liquid cooling we have described above can be referred to as indirect cooling because liquid is circulated in pipes next to the batteries. ICE cars also use pipes to help cool the engine. The other type of liquid cooling is called direct cooling, which is where the batteries are fully submerged in a liquid solution. The liquid solution needs to have little to no conductivity so that the batteries do not conduct electricity in the liquid. So far, direct cooling is only something that has been achieved in a lab environment, but in the future, it will hopefully be implemented into the industry. The direct cooling method can potentially be a lot more efficient at cooling batteries when compared to the indirect solution. The downside of liquid cooling is that any kind of leak could cause major problems to the car.

What is Propylene Glycol?

Propylene glycol is an organic chemical compound that has antifreeze properties, which allows it to lower the freezing point of water. When Propylene glycol is dissolved into water it combats the formation of ice crystals so that a lower freezing point of the water can be achieved. The previous chemical used for antifreeze purposes in the car industry was Ethylene glycol, but this was a toxic substance. Propylene glycol is not more efficient than its predecessor ethylene glycol but it is a lot less toxic, which is why the industry moved in this direction. The antifreeze properties are a must for any kind of liquid that circulates the car for cooling purposes. If the temperatures dropped low enough outside it would mean your cooling system for the car would be frozen and not work. Just because the temperature is cold outside does not mean that various parts of a car still need to be cooled down.

Air cooled electric vehicle

We have talked before about the Nissan Leaf, which uses air to cool the battery. It uses convection to remove heat from its battery using the movement of air. The problem with this is that it cannot be controlled very much, especially if you want to have the battery cooled more than usual. What we have not talked about is various air cooling methods, several are available to car manufacturers for cooling batteries and electric motors, etc. A method that has been used on ICE cars is to attach fins to the engine and effectively increase the surface area and transfer the heat to the fin. The fin is then cooled by the air after taking the heat away from the engine. Electric car manufacturers no longer want to use fins to cool the battery packs as the additional weight for this reduces the range of the car and they prefer other cooling methods. Another option is to use fans to cool the battery pack but this also adds excess additional weight which reduces the range of the car.

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