Gasoline and diesel engines generate so much heat that if they’re not properly cooled, they can self-destruct in a matter of minutes. Electric vehicles (EVs) obviously don’t have that engine issue, but their batteries need to be cooled to help preserve their performance and lifespan.
Conventional vehicles pull air in through the front grille, but many EVs don’t even have a grille, and if they do, it’s mainly for looks instead of function. It may seem to you like it’d make more sense to keep the grille and use it for battery cooling, but it generally doesn’t work that way.
Instead, there are different methods for maintaining ideal battery temperature, known as thermal management. Even if air is used, EVs are designed with better ways to get air directly where it needs to be, for the battery and for any other components that require airflow. A front grille usually isn’t the most efficient method. The battery is naturally going to generate heat due to the current flow, and especially when the battery is being fast-charged. Air cooling is simple and relatively inexpensive, but liquid cooling, while more complex, does a better job.
An EV’s traction battery – the big one that powers the electric motors to turn the wheels – generally prefers to be somewhere between about 15 to 25 degrees Celsius.
At lower ambient temperatures, the battery won’t provide as much power, and the vehicle’s range can drop as much as 20 per cent when temperatures outside are below freezing. If the battery gets too hot, it will initially lose some of its power. If its internal temperature continues to rise, it can potentially degrade, suffer partial damage, or experience complete failure, including catching fire.
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A liquid battery-cooling system works somewhat the same way as that of an internal-combustion engine. The coolant fluid is pumped through passages in the battery – usually inside a plate that cools the battery overall, or around the cells themselves.
As with a gasoline engine’s system, the fluid gets hot as it cools the battery, and is cooled in a heat exchanger – basically a small radiator – and then recirculated in a closed loop. That loop may include cooling other electronic components. The waste heat may also be used to help warm the cabin in winter.
While EVs have fewer maintenance requirements than gasoline vehicles, primarily in that they don’t need oil changes, they do need their coolant changed on a regular basis. If it isn’t, then as with a conventional radiator, the coolant can eventually break down, or the passages may get plugged with scale, reducing the system’s effectiveness. If you own an EV, check your owner’s manual for the maintenance schedule.
In addition to thermal management during driving, the liquid system also protects the battery during charging, especially when fast-charging on a DC charger. All charging creates heat, but the extra load of fast-charging can make a lot of it – including in the charger itself, which circulates its own coolant through its charging cable to regulate its temperature. The vehicle monitors its battery’s temperature during charging. If the cooling system isn’t doing enough, the vehicle will reduce its charging rate to bring down the temperature, especially if it’s a hot day. The battery will take longer to charge, but it’ll be better protected.
Air cooling can be achieved by simply letting air circulate around the battery cells, which is least effective; or by using a fan to increase the airflow. Some systems can also use the vehicle’s air conditioning unit to chill the air before it goes to the battery. Air cooling overall is simpler than liquid cooling, and the system weighs and costs less, but it isn’t as good. Not many vehicles use it, but one that does is the Nissan Leaf — although the upcoming Nissan Ariya EV is expected to use liquid cooling.
There are other methods of battery cooling, but they’re not really great for electric vehicles. Fins can be used to dissipate heat, as they are on some electronic components, but they add a lot of weight. There’s also phase change material, which changes from a solid to liquid as it absorbs heat. But it doesn’t then effectively transfer that heat away, and so it’s too inefficient for EV battery use.
Even a liquid-cooled EV uses some air for cooling various components, so why not bring that air in through a conventional-style grille? It’s all about effectiveness. Most EVs have a flat battery in the floor, to maximize cabin space and to lower the vehicle’s centre of gravity, and most of the components sit low in the vehicle as well. Instead of routing air down through the grille, most automakers use designs that incorporate the air intakes lower down and closer to the bumper, so the air comes in closer to what it’s intended to cool. Meanwhile, blocking off the grille area improves aerodynamics, which in turn can help improve range.
When it comes to EV styling, it isn’t just about making sure it doesn’t look like a gasoline car, but doing what’s needed because it also doesn’t work like a gasoline car.