How Are Electric Car Motors Cooled? An Engineer’s Explanation


While it seems a bit odd, electric vehicles do require a cooling system. This may seem weird because gasoline engines require coolant to keep the motor cool and electric vehicles obviously don’t have engines. However, they do have electric motors that require some cooling, more like how a transmission fluid needs cooled.

How are electric car motors cooled? Electric car motors are cooled similarly to regular car engines.  Electric motors use pumps to circulate coolant that flows through the motor unit and batteries. Radiator fans also play a part in regulating coolant temperature and hoses and fittings connect the whole system together.

This article will look into more about how the motors are cooled, what kind of coolant is used, and the cooling capacity of an electric vehicle compared to a regular car.

How Are Electric Car Motors Cooled?

Electric vehicles are built with an integrated liquid cooling system. It is mostly similar to the system that is in a regular car, but with a few adaptations. Typically, the motors are designed with passages for coolant to flow through. The coolant absorbs heat away from the motor unit. There is a coolant pump that circulates the coolant so that the heated coolant can flow through the radiator to cool down.

Traditionally, ambient air flows through the radiator and disperses the heat. This requires a grille at the front of the vehicle to allow air to pass through. Also, there is a radiator fan that helps air flow when the vehicle is moving slowly. In electric vehicles, the grille has been phased out mostly due to design. Therefore the radiator fans are critical in proper cooling in electric vehicles.

There can also be a few different valves in the system. These are in place for a couple different reasons. The primary reason is to keep coolant flowing through the motor and battery pack. Secondarily, excess heat from the motor can be routed into the cabin HVAC system to warm the passengers when the weather is cold. The valves can otherwise be opened or closed to increase overall cooling efficiency.

There are also many hoses and fittings to connect the whole system together. There is also a coolant reservoir to hold the coolant as well as allow for some expansion of the coolant. So, aside from the actual engine, the principle is basically the same as a regular vehicle.

What Type Of Coolant Is Used?

The type of coolant used depends on the vehicle. Most BEVs use ethylene-glycol, which is essentially the same thing that is used in regular ICE vehicles. This is typically a 50/50 blend with distilled water to produce the best heat absorption as well as a reduced freezing temperature and raised boiling temperature.

Tesla markets its own brand of coolant, but most formulas can be purchased from an aftermarket brand. This type of coolant does require some volume, which can add a bit of weight and risk for leak, but the thermal management system overall works really well.

Some smaller EV’s are air cooled, such as the Nissan Leaf or Volkswagen E-Golf. Air-cooling goes back a long way to early small engine vehicles that required the ambient air to cool down the engine. Typically there is a built-in heat sink, which consists of intricate fins that increase the overall surface area for the wind to blow across. For small applications, this cooling system can work fairly well, although it can be problematic. If there is no wind or if the air doesn’t offer much cooling, such as a high-humidity area, the vehicle runs the risk of overheating.

There are a few EV models that actually use refrigerant to cool down the vehicle. Refrigerant is a little different from coolant in that it changes from gas to liquid as part of the cooling process. Refrigerant gets pumped through an evaporator which causes the cooling effect.

It is then pumped through a condenser where it transfers the heat and turns back into a liquid. This requires special attention whenever being serviced as refrigerant is harmful to the atmosphere. Also, if a leak is present, it can be difficult to trace down since there will not likely be an obvious location of the leak. 

Of course, every make and model is a bit different. If you suspect your cooling system needs attention, refer to the owner’s manual specific to your vehicle or take it to a qualified repair shop.

How Many Radiators Does An Electric Vehicle Have?

How many radiators a EV has depends on the make and model of the vehicle. As mentioned above, some electric vehicles have zero radiators in a way because they rely on the ambient air to blow past the vehicle and cool things down. But in a vehicle that has some form of liquid cooling, there will be at least one radiator. 

A radiator is the component that allows the heat from the motor and battery pack to be transferred to the ambient air. It’s typically rectangular in shape and is constructed of aluminum and plastic parts. It is designed to be a  grid for the coolant to flow through while being contained and to allow air to blow past and disperse the heat. Hot coolant will come into the top of the radiator and will flow downward as it cools a bit. A hose at the bottom of the radiator allows the coolant to flow back into the vehicle to continue cooling. 

Another key part of the cooling package is the radiator fan. As implied, this is a fan that blows air through the radiator. The radiator fan usually kicks on during slow travel speeds or at idle when air is not otherwise adequately flowing. Most modern radiator fans are electronically controlled as compared to belt-driven fans found in some ICE vehicles.

While it is typical for a vehicle to have one radiator for the coolant, the Tesla Model S has 3 radiators plus later models (since 2011) have a liquid-cooled motor, compared to the previous air-cooled version. There is also ducting in place designed to force air through the radiators to maximize cooling.

Does An Electric Vehicle Have More Cooling Capability Than A Gasoline Car?

A traditional vehicle’s cooling system revolves around the engine. The ignition in the cylinders creates a lot of heat that absolutely needs to be regulated. However, the cooling system can be used for more than just cooling the engine. There are typically a couple of hoses that flow through the cabin to warm up the HVAC system on cold days. Also, in some applications, the coolant can be used to help emissions by cooling down the exhaust before it is rerouted back into the air intake.

In an EV, the main focus is on managing the temperature of the battery. Secondarily, maintaining the temperature of the motor is also very important. But these do not generate as much heat, so the cooling system can be manipulated a bit more.

While coolant can help warm up the HVAC system, most use an electric heater to serve that purpose. Where the real manipulation happens is in electronically controlled valves that direct coolant in different ways. For example, the coolant can be routed away from the batteries to allow them to warm up a bit on cold days. Conversely, coolant can be focused in one area to maximize the cooling capacity. 

As far as the capacity of the type of coolant, the properties of ethylene-glycol are the same whether in an EV or ICE vehicle. Typically referred to as antifreeze, this chemical makes a huge difference for climates that reach below freezing temperatures.

On the hotter end of the spectrum, the water in the coolant does more for bringing the temperature back down (click here to read our article “Does An Electric Car Need Water?”). Also the system is sealed and pressurized. This raises the boiling point and helps cooling at hotter temperatures. Again, in both EVs and ICE vehicles, the chemical properties are the same.

But a big difference is the operating temperatures. An ICE vehicle needs to maintain about 100 degrees up to close to 200 degrees, depending on the vehicle. That is a lot of work required by the cooling system. In contrast, an EV operates at about 70 degrees and wont fluctuate very much. So much less is required by an EV cooling system making it more effective. 

But in an ICE vehicle, there is a little bit of room for error. If an engine is working hard and getting hot, typically it will cool down if the vehicle is driven a bit slower for a while. Overheating is not good for an engine, but it can typically recover from intermittent overheating. However, an electric vehicle does not like to get hot. Those high-voltage batteries can take a lot of damage if they overheat and they typically won’t bounce back. Of course, there is a little bit of wiggle room, but the potential for damage is much more critical since a battery can melt down if it becomes internally damaged.

Conclusion

Yes, electric vehicles do require a cooling system to maintain the temperature of the battery pack and motor. Not all cooling systems are the same, but they each have their benefits. Compared to an ICE vehicle, the electric vehicle doesn’t swing in temperature as much, but it is perhaps more critical to maintain electric vehicle temperatures. As such, automakers have designed comprehensive cooling systems to maximize the cooling capacity.

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