Thermal Management in EVs and Power Electronics: Where Vacuum Brazing Makes the Difference

Modern EVs have tremendous power demands, and where there is power, there is heat. The power electronics that control and convert energy in EVs and numerous other applications like industrial motor drives, renewable energy inverters, aerospace electronics, all require sophisticated cooling systems to disperse the large quantities of heat that they generate. 

The more power that is charged, discharged, converted, or regenerated, the more heat that is generated. That heat needs to go somewhere. 

It’s a major engineering challenge, but the entire field of thermal management in electric vehicles and power electronics cooling exists to solve this problem. 

One of the most reliable ways to cool EVs and power electronics is through cold plates, and the process of vacuum brazing enables engineers to build highly reliable and efficient cold plates that stand up to the rigors that EVs and power electronics demand.

Why EV Thermal Management is Crucial

Every EV faces two major cooling challenges: the battery pack and its power electronics (the inverter, motor controller, onboard charger) all produce great quantities of heat. 

Thermal management in electric vehicles uses cooling systems to capture excess heat, transfer it away from critical components, and cool it before releasing it into the surrounding environment. 

In practice, it’s not very different from a traditional vehicle with an internal combustion engine. A gas powered vehicle uses a radiator, coolant, water pump, and fans to manage and release the heat generated by the engine. 

EV battery cooling systems use a similar premise, except they use cold plates, coolant loops, and heat exchangers to help the vehicle maintain an ideal operating temperature. 

Without these cooling systems, an EV would simply not be able to perform. Drivers would experience a reduced driving range, poor battery performance, and shorter battery lifespans. In extreme cases, unmanaged or improper cooling could also create an extreme safety hazard. 

Cooling both the battery and its power electronics rely on a common approach: liquid cooling, cold plates, and heat exchangers.

Understanding Power Electronics Cooling

Power electronics are an essential part of EVs. They function as inverters, devices that control and convert a battery’s DC electrical energy into AC power used to turn the motor itself. Inverters accomplish this task using devices called insulated gate bipolar transistors (IGBT), which are essentially high-power semiconductor switches. 

EV inverters are very efficient, often operating in the 94-98% efficiency range. However, those small inefficiencies create significant waste heat when energy isn’t successfully converted from DC to AC.

To put it in perspective, if a 100kW inverter operates at 96% efficiency, it loses 4kW of energy as heat. That’s a substantial amount of heat that is concentrated within a relatively small electronic package, and that heat needs somewhere to go.

To safely redistribute that heat, power electronics cooling systems use cold plates. 

Cold plates are designed to be mounted directly beneath or adjacent to the IGBT module, allowing heat to be transferred away from the semiconductor and into a circulating coolant loop. The coolant fluid absorbs the excess heat from the IGBT, which flows through the microchannels in the cold plate. 

The heated fluid is pumped to a heat exchanger, which functions much like a radiator in a gas powered vehicle, where ambient air removes the heat from the coolant fluid and releases it back into the environment. 

The cooled fluid is pumped back through the cold plate, where the cycle begins again.

Battery Thermal Management Systems in EV Battery Cooling Systems

Power electronics cooling is a crucial part of EV thermal management, but the vehicle’s battery itself is one of its biggest sources of heat. 

Whether the battery is being charged, rapidly charged, or when the driver rapidly accelerates, the battery cells generate heat. 

Lithium-ion batteries used in modern EVs operate best within a narrow temperature range. The battery thermal management system (BTMS) is what keeps its temperature within that range. 

When a battery becomes too hot, it accelerates degradation. Its capacity can drop, and the charging rates are reduced. Likewise, when an EV battery gets too cold, the vehicle’s range decreases and charging slows down significantly. The BTMS is designed to keep the battery within its optimal operating window.

Much like the IGBTs in the vehicle’s power electronics, EV batteries often rely on large cooling plates integrated into the battery pack to remove heat from the cells. Heat is transferred from the battery, to the cooling plate and its liquid coolant. As the coolant absorbs the heat, it is pumped into the heat exchanger, which releases it into the ambient air. 

The process itself is nearly identical, though the scale is much larger with EV battery cooling systems. A cold plate designed for an IGBT may be roughly 3”x5”, while one designed for an EV battery cooling system can be around 30”x50”. 

Whether cooling EV battery packs or power electronics, both applications require cold plates and heat exchangers that can safely and efficiently remove heat, while containing pressurized coolant. This is where vacuum brazing makes a significant difference.

Where Vacuum Brazing Fits Into EV Thermal Management

If you’re a manufacturer developing hardware for thermal management in electric vehicles and their power electronics, you know that your components require several key features. 

They require:

• Exceptional thermal transfer
• Leak-tight, hermetic seals
• Complex internal cooling channels
• High-volume, repeatable production 

Vacuum brazing makes each of these requirements possible in the construction of cold plates and heat exchangers.

Leak-Tight Seals

To successfully absorb the heat produced by EV batteries and power electronics, both cold plates and heat exchangers often contain intricate internal flow passages, including microchannel designs, that move the coolant through the assembly. 

That fluid absolutely cannot leak. Leaking coolant prevents these devices from absorbing heat and channeling it through the system properly, which can potentially damage the components and cause systems to fail. 

Vacuum brazing allows the internal channels that carry the coolant to be completely sealed. It does this by permanently joining the walls of these microchannels to the cold plate or heat exchanger, forming a single monolithic structure. The process creates a hermetic seal that greatly reduces the chance of leakage.

Performance Conditions

The conditions under which a finished assembly is intended to perform play a large role in determining the right type of joining method to use. 

Industrial metal joining applications that must support large structural loads often benefit from welding, while critical metal assemblies like heat exchangers favor vacuum brazing. Environmental exposure as well as repeated stress cycles all need to be taken into consideration when choosing the right metal assembly joining method. Thermal loads are particularly important, as the repeated heating and cooling cycles create expansion and contraction stresses that affect the joint over time.

Efficient Heat Transfer

EV cooling technology also benefits from vacuum brazing’s excellent thermal transfer capability. Vacuum brazing creates a metallurgical bond between the components that make up the cold plate or heat exchanger. This allows heat to transfer efficiently away from batteries and power electronics, and through the structure with minimal thermal resistance.

Complex Internal Cooling Channels

Vacuum brazing also helps with complexity of the internal cooling channels in an EV cold plate. The narrow internal passages and complex flow paths are very difficult to achieve with standard joining techniques like welding. Inside of a vacuum furnace, assemblies of multiple pieces with complex geometries can be joined together into a single structure through one cycle.

High-Volume Production

Vacuum brazing furnaces are capable of producing large batches of assemblies. This makes them ideal for producing mass quantities of cold plates, heat exchangers, and cooling manifolds.

Hermetic Sealing

Whether a joint requires a leak-tight seal is a major decision point. While welding can produce leak-tight joints, brazing is often preferred for creating hermetically sealed joints while minimizing distortion. Vacuum brazing is preferred for assemblies where gases cannot enter or escape the system, such as heat exchangers, semiconductor equipment, electronic sensor packages, and aerospace components. 

Why Vacuum Brazing is Becoming Increasingly Important in Cooling Solutions for Power Electronics and EVs

As the technology becomes more ubiquitous, thermal management in electric vehicles becomes more important.

Growing Power Densities

Newer generations of EVs have more horsepower and more torque than their predecessors. At the same time, electronics packaging is becoming smaller and more efficient. As a result, power electronics are converting more power in smaller spaces, which increases cooling demands. 

Thermal management solutions for EVs and power electronics will only become more important as cooling demands increase. 

Faster Charging Requirements

EV manufacturers are constantly trying to push faster and faster charging speeds for their vehicles. The faster an EV battery charges, the more heat it generates. 

Think of your smartphone or laptop. Most modern devices have lithium-ion batteries, which can become hot to the touch while charging. Now consider an EV battery that weighs over 1,000 pounds, receives hundreds of kilowatts in a single charge, and must do so in less than an hour. That creates a significant thermal load that needs to be distributed away from the vehicle. 

Manufacturers will look for any advantage they can find in keeping these batteries and vehicles cool, and vacuum brazed cold plates and heat exchangers help them do that. 

Increased Thermal Loads 

More powerful vehicles, faster charging requirements, and higher performance electronics means that the amount of energy that must be dispersed is only going to keep increasing with every generation of EVs. 

As thermal loads increase, manufacturers will need better cold plates, more efficient heat exchangers, and more sophisticated microchannel flow paths.

Vacuum brazing for EV cooling systems enables thermal management solutions that can be difficult or impractical to achieve with many conventional metal joining methods. The process enables the production of leak-tight cold plates and heat exchangers that can withstand the intense thermal loads of next-generation EVs, with the flexibility to be mass produced.

Vacuum Brazing: The Key to Thermal Management in Electric Vehicles

For component and parts manufacturers for EVs that require advanced thermal management, vacuum brazing techniques offer the ideal solution for building robust cold plates and heat exchangers needed to provide thermal management solutions for EVs and power electronics. 

Vacuum Process Engineering (VPE) has been a leader in advanced metal joining technologies, including vacuum brazing for over 50 years. 

We have an extensive set of capabilities, including multiple vacuum brazing furnaces capable of mass-producing cold plates and heat exchangers with the precision and endurance needed to meet the challenges of today’s EV and power electronics. 

To discuss how vacuum brazing can help provide superior EV cooling technology for your project, contact the team at VPE today.

FAQs: Vacuum Brazing and EV Thermal Management

How does vacuum brazing improve EV thermal management?

Vacuum brazing improves thermal management in electric vehicles by enabling the production of leak-tight cold plates, heat exchangers, and cooling manifolds used in EV cooling systems. The process creates a strong metallurgical bond between components while supporting efficient heat transfer and complex internal coolant channels designs. The vacuum brazing process is also highly repeatable and reliable, enabling mass production of components needed for thermal management. 

How does vacuum brazing help battery cooling systems?

Battery thermal management systems use cold plates to remove heat generated from lithium-ion battery packs during charging and operation. The vacuum brazing process enables the construction of hermetically sealed cold plates containing internal coolant passages. Vacuum brazed cold plates are extremely durable and feature exceptional thermal performance, well suited for EV battery cooling applications. 

What impact does vacuum brazing have on heat exchangers for EVs?

Manufacturers use vacuum brazing to build heat exchangers with durable, leak-tight assemblies and complex geometries that provide excellent thermal conductivity. This combination of characteristics enables heat exchangers to efficiently transfer heat from the coolant fluid to the surrounding air. 

What is the role of vacuum brazing in EV manufacturing?

As EVs become more powerful and charging speeds continue to increase, they require greater thermal management capabilities. Vacuum brazing allows manufacturers to build cold plates and heat exchangers capable of withstanding the increasing thermal loads of modern EVs. The vacuum brazing process is also highly scalable, capable of mass producing these devices to meet the demands of EV manufacturing.