Category Archives: Automotive

Webinar: EV Battery Thermal Management

Maintaining the proper operating temperature for electric vehicle (EV) batteries is a critical component of the spread of EV across the world. If batteries are too hot, then the batteries will degrade faster, and safety becomes a concern. At lower temperatures, battery capacity and performance suffer.

EV Battery Thermal Management
The webinar below will cover techniques for maintaining proper battery temperatures in electric vehicles. (Wikimedia Commons)

Thermal management of batteries is important for EV to live up to the potential that manufacturers promise and that consumers desire. But, how can the temperature be maintained at the proper operating levels during use and how can manufacturers cope with the varied environments that the vehicles will operate in?

As an earlier post on EV battery thermal management explained, the main concerns for engineers are:

  1. At temperatures below 0°C (32°F), batteries lose charge due to slower chemical reactions taking place in the battery cells. The result is a significant loss in power, acceleration and driving range, and higher potential for battery damage during charging.
  2. At temperatures above 30°C (86°F) the battery performance degrades, posing a real issue if a vehicle’s air conditioner is needed for passengers. The result is an impact on power density and reduced acceleration response.
  3. Temperatures above 40°C (104°F) can lead to serious and irreversible damage in the battery. At even higher temperatures, e.g. 70-100°C, thermal runaway can occur. This is triggered when the runaway temperature is reached. The result is a self-heating chain reaction in a battery cell that causes its destruction while propagating to adjacent cells.

This hour-long webinar from thermal management expert Dr. Kaveh Azar, founder and CEO of Advanced Thermal Solutions, Inc. (ATS), presents some of the techniques that design engineers have employed to keep EV batteries within the proper temperature range both during operation and charging.


For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.

Industry Developments in Thermal Management of Electric Vehicle Batteries

By Norman Quesnel
Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc. (ATS)

Electric vehicles (EV) fall into two main categories: vehicles where an electric motor replaces a combustion engine and vehicles that feature a combustion engine assisted by an electric motor. All EV contain large, complex, rechargeable batteries, sometimes called traction batteries, to provide all or a portion of the vehicle’s propelling power.

Electric Vehicle Batteries

(Wikimedia Commons)

In EV batteries, current flow, both charge and discharge, generates heat inside the cells and in their interconnection systems. This heat is proportional to the square of the flowing current multiplied by the internal resistance of the cells and the interconnect systems. The higher the current flow the more the heating will be produced. [1]

Battery manufacturers and researchers routinely investigate how the rate of heat generation in cells varies over the course of charging and discharging. Heat can be generated from multiple sources including internal losses of joule heating and local electrode overpotentials, the entropy of the cell reaction, heat of mixing, and side reactions. [2]

Figure 1. Structure of a basic lithium-ion battery. [3]

Proper thermal management of EV batteries (lithium-ion is the most common) is essential to maintain adequate and consistent performance of the battery and the vehicle. Excessive temperature will negatively affect an EV’s battery and its performance. Features that can be impacted include its electrochemical system, charge acceptance, power output, safety and life cycle/replacement cost and the vehicle’s driving distance.

From a thermal point of view, there are three main aspects to consider when using lithium-ion batteries in an EV:

  1. At temperatures below 0°C (32°F), batteries lose charge due to slower chemical reactions taking place in the battery cells. The result is a significant loss in power, acceleration and driving range, and higher potential for battery damage during charging.
  2. At temperatures above 30°C (86°F) the battery performance degrades, posing a real issue if a vehicle’s air conditioner is needed for passengers. The result is an impact on power density and reduced acceleration response.
  3. Temperatures above 40°C (104°F) can lead to serious and irreversible damage in the battery. At even higher temperatures, e.g. 70-100°C, thermal runaway can occur. This is triggered when the runaway temperature is reached. The result is a self-heating chain reaction in a battery cell that causes its destruction while propagating to adjacent cells.

The ideal temperature range for an EV’s lithium-ion battery is akin to that preferred by human beings. To keep it in this range, the battery temperature must be monitored and adjusted. A battery thermal management system (BTMS) is necessary to prevent temperature extremes, ensure proper battery performance, and achieve the expected life cycle. An effective BTMS keeps cell temperatures within their allowed operating range. [1]

As defined by engineers at the U.S. Department of Energy’s NREL (National Renewable Energy Laboratory), EV battery pack thermal management is needed for three basic reasons: [5]

  1. To ensure the pack operates in the desired temperature range for optimum performance and working life. A typical temperature range is 15-35°C.
  2. To reduce uneven temperature distribution in the cells. Temperature differences should be less than 3-4C°.
  3. To eliminate potential hazards related to uncontrolled temperature, e.g. thermal runaway.

Figure 2. Chevy Bolt EV battery pack is liquid cooled via a base plate below the cells. [6,7]

Various cooling agents and methods are in use today as part of the thermal management of EV batteries. Among these are air cooling, the use of flowing liquid coolants, or direct immersion.

Air Cooling

The lowest cost method for EV battery cooling is with air. A passive air-cooling system uses outside air and the movement of the vehicle to cool the battery. Active air-cooling systems enhance this natural air with fans and blowers. Air cooling eliminates the need for cooling loops and any concerns about liquids leaking into the electronics. The added weight from using liquids, pumps and tubing is also avoided.

Figure 3. The Nissan Leaf’s battery pack is cooled by air. [8]

The trade-off is that air cooling, even with high-powered blowers, does not transport the same level of heat as a liquid system can. This has led to problems for EV in hot climates, including more temperature variation in battery pack cells. Blower noise can also be an issue.

Figure 4. Air cooler battery thermal management system used in Toyota’s Prius. [9]

Still, air-cooling solutions have their roles and value. An example is the custom-built Volkswagen EV race car that finished first in the Pikes Peak International Hill Climb in Colorado Springs, Colo. To optimize performance, the car was designed to combine minimum weight, as much downforce as possible, and maximum power. Volkswagen used air-cooling systems to reduce weight. It used thermal software in virtual driving tests along the entire race to ensure the air-cooling system would perform sufficiently. [10]

Figure 5. Volkswagen’s EV won a grueling race while powered by air-cooled batteries. [10]

Liquid Cooling

Piped liquid cooling systems provide better battery thermal management because they are better at conducting heat away from batteries than air-cooling systems. One downside is the limited supply of liquid in the system compared with the essentially limitless amount of air that can flow through a battery.

Tesla’s thermal management system (as well as GM’s) uses liquid glycol as a coolant. Both the GM and Tesla systems transfer heat via a refrigeration cycle. Glycol coolant is distributed throughout the battery pack to cool the cells. Considering that Tesla has 7,000 cells to cool, this is a challenge. [11]

Figure 6. Tesla uses a metallic cooling tube that snakes through the EV battery pack. [11]

The Tesla Model S battery cooling system consists of a patented serpentine cooling pipe that winds through the battery pack and carries a flow of water-glycol coolant; thermal contact with the cells is through their sides by thermal transfer material.

Figure 7. GM’s Chevrolet Volt uses cold plates interwoven with battery cells as liquid cooling system. [12]

General Motor’s Chevrolet Volt features a liquid cooling system to manage battery heat. Each rectangular battery cell is about the size of a children’s book. Sandwiched between the cells is an aluminum cooling plate. There are five individual coolant paths passing thru the plate in parallel, not in series as the Tesla system does. Each battery pouch (cell) is housed in a plastic frame. The frames with coolant plates are then stacked longitudinally to make the entire pack. [12]

Thermodynamic engineers at Porsche develop and optimize each vehicle’s entire cooling system. This includes the battery, of course, and one example is the liquid-filled cooling plate from the traction battery in the Boxster E. [13]

Figure 8. Thermal model of a battery cooling plate in the Porsche Boxster. [13]

Based on the results of the analysis in the thermal model described above, the cooling plate was designed geometrically and optimized using computational fluid dynamics (CFD). The result is a highly efficient and lightweight heat exchanger, optimally tailored and adapted to the battery pack, with low pressure losses, high cooling performance and a very even distribution of temperature.

Liquid Immersion

Instead of snaking coolant through lines and chambers within a battery pack’s case, XING Mobility takes a different approach by immersing its cells in a non-conductive fluid with a high boiling point. The coolant is 3M Novec 7200 Engineered Fluid, a non-conductive fluid designed for heat transfer applications, fire suppression and supercomputer cooling.

Figure 9. The XING Battery has 4,200 individual lithium-ion cells encased in liquid-cooled module packs. [14]

XING’s batteries take the form of 42 lithium-ion-cell modules that can be put together to build larger battery solutions. The complete XING battery houses 4,200 individual 18,650 lithium-ion cells encased in liquid-cooled module packs. [14]

Simulation Technologies

Design of thermal management solutions requires extensive knowledge of cooling systems and the amount of heat generated by cells throughout the battery pack. Engineers must also weigh various tradeoffs and factors such as cost, packaging, manufacturability, efficiency, reliability of heat dissipation components, and battery pack as an integrated, modular system.

Figure 10. Simulation tools speed the development of EV batteries and their thermal management systems. [2]

Batteries require a unique range of issues be taken into consideration. First, detailed models and sub-models are needed to simulate the chemical and physical phenomena inside battery cells. Then, these models need to be tied into a system-level model of a battery pack, which can comprise hundreds of cells and cooling circuits. Finally, the battery pack model needs to be integrated with the system model of the entire powertrain and vehicle.

Engineers must consider the physical placement of the battery pack within the EV, not only to minimize the effects of ambient temperatures and maximize heat dissipation but also to avoid excessive mechanical stresses, structural fatigue from road vibrations, and potential impact from road debris. The team also must consider crash scenarios in which passengers must be protected from toxic acids released from the battery pack.

References:
1. https://avidtp.com/what-is-the-best-cooling-system-for-electric-vehicle-battery-packs/
2. Hu, X., Battery Thermal Management in Electric Vehicles. Ansys, Inc., 2011.
3. https://www.mpoweruk.com/chemistries.htm
4. Wang, Q., Jiang, B., Xue, Q., Sun, H., Li, B., Zou, H. and Yan, Y., Experimental Investigation on EV Battery Cooling and Heating by Heat Pipes, Applied Thermal Engineering, 2015.
5. Rugh, J., Pesaran, A. and Smith, K., Electric Vehicle Battery Thermal Issues and Thermal Management Techniques, NREL, SAE Alternative Refrigerant and System Efficiency Symposium, 2011.
6. https://www.hybridcars.com/chevy-bolt-evs-battery-is-as-big-as-a-teslas/
7. https://cleantechnica.com/2018/07/08/tesla-model-3-chevy-bolt-battery-packs-examined/
8. https://www.greencarreports.com/news/1064332_nissan-leafs-battery-pack-should-last-as-long-as-the-car
9. http://synergyfiles.com/2016/07/battery-thermal-management-system-review/
10. https://www.theverge.com/2018/6/24/17078544/volkswagen-ev-race-car-pikes-peak-hill-climb-record https://media.vw.com/en-us/releases/1008
11. https://insideevs.com/tesla-or-gm-who-has-the-best-battery-thermal-management-bower/
12. https://www.youtube.com/watch?time_continue=113&v=h4nM7rXpsJg
13. Thermal Management in Vehicles with Electric Drive System, Porsche Engineering Magazine, January 2011.
14. https://www.greencarreports.com/news/1114188_new-approach-to-electric-car-battery-cooling-immerse-cells-in-coolant

Advanced Thermal Solutions, Inc. (ATS) is hosting a series of monthly, online webinars covering different aspects of the thermal management of electronics. This month’s webinar will be held on Thursday, Oct. 25 from 2-3 p.m. ET and will cover the cooling of automotive batteries. Learn more and register at https://qats.com/Training/Webinars.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/Consulting/Custom-Cooling-Solutions or contact ATS at 781.769.2800 or ats-hq@qats.com.

ATS Collaborates on SAM Car Featured on the CNBC program ‘Jay Leno’s Garage’

On Jan. 6, 2000, champion race car driver Sam Schmidt crashed his vehicle at the Walt Disney World Speedway in Orlando, Fla. The accident severely injured his spinal cord, leaving him paralyzed from the neck down and with doctors telling him that he would never walk again, let alone get behind the wheel of a car.

SAM Car

ATS partnered with ARROW Electronics to devise a thermal solution for the computer system in the semi-autonomous car that allowed Sam Schmidt to get back behind the wheel. (Advanced Thermal Solutions, Inc.)

Colorado-based neurosurgeon Dr. Scott Falci had other ideas and enlisted the aid of several technology companies, including ARROW Electronics, the Air Force Research Laboratory (AFRL), and Ball Aerospace and Technologies Corp., to make his dream of helping Schmidt drive come to fruition 17 years after the accident.

The result was the SAM Car. Using infrared sensors, cameras, on-board GPS and other next-generation technologies, the team created a semi-autonomous vehicle that Schmidt could power by simply moving his head. Leaning right or left would steer the car, tilting his head back would cause the car to accelerate, and biting down on a special mouthpiece would cause the car to break.

Watch this CNBC video with Jay Leno to learn more and see the car in action:

Advanced Thermal Solutions, Inc. (ATS) was brought in by ARROW to assist with the challenge of providing thermal management for the car’s on-board computer system. ATS designed an enclosure that cooled both sides of the board without the need for a fan and protected it from dust and other debris.

ATS engineers Bahman Tavassoli, Vineet Barot, and Anatoly Pikovsky are proud to have collaborated with these other innovative pioneers to provide Mr. Schmidt with the ability to get back behind the wheel where he belongs.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.

Electric Car Batteries Are Topic of Presentation by ATS CEO Dr. Kaveh Azar

Electric Car Batteries

ATS CEO Dr. Kaveh Azar will deliver a presentation on the thermal management of electric vehicle batteries on Thursday, Sept. 22. (Photo courtesy of Wikimedia Commons)

On Thursday, Sept. 22, Advanced Thermal Solutions, Inc. (ATS), a leading-edge engineering and manufacturing company focused on the thermal management of electronics, will host the New England Section of Society of Automotive Engineers International (SAE NE) for a tour of its Norwood campus and a presentation by ATS founder, President, and CEO Dr. Kaveh Azar.

Dr. Azar’s discussion is entitled, “Battery Thermal Management – The Gateway to the Successful Operation of Electric Vehicles.” He will review the role of temperature in the longevity and performance of nickel metal hydride (NiMH) and lithium-ion electric vehicle batteries; drawing analogies between battery temperature and the junction temperature of modern electronics. As Dr. Azar notes, “Both play an identical role in successful operation of their respective systems.”

There will be a discussion of the analytical methods and design criterion for predicting battery temperature and establishing safe temperature limits. Dr. Azar will present high-level possibilities for thermal management in the electric vehicle sphere as well as cooling options that are deployed for battery thermal management. Current cooling designs can be active or passive. There are forced air, liquid cooling, natural convection and conduction systems used by manufacturers.

Several thermal solutions that engineers have incorporated include increasing the thermal density of the battery, using phase-change material to store transient heat loads and graphite-impregnated paraffin waxes as gap fillers. It is also important for the designs to control temperature distribution across the battery to avoid degradation of cells.

Thermal management is crucial in the design of electric vehicle batteries because temperature has a direct correlation on battery life and performance. It will affect the battery’s ability to store and deliver a charge, weaken polymer- or fiber-based cell dividers, and could potentially lead to thermal runaway.

“The engineers who will design the next hybrid vehicle battery packs will need to be cognizant of the growing need for thermal management,” read a recent article on coolingZONE. “The increased need for thermal protection, due to safety considerations; the reduced thermal capacity, due to lesser mass; and the reduced workable volume are among the challenges to be faced. The hybrid vehicle we may soon drive must have reliable and intelligent cooling systems to cool down their high-density battery packs.”

Why is this topic of particular relevance now?

Electric vehicle sales worldwide have jumped 57 percent from 2015 to 2016, according to data reported by Bloomberg New Energy Finance. The article referenced a Bloomberg report stating that electric vehicle sales could be as much as 47 percent of the automotive market by 2040 (dependent on factors such as oil prices). In the U.S., manufacturers have been urged by President Barack Obama’s EV Everywhere challenge to make electric cars as affordable and convenient as gas-powered vehicles by 2022.

Like cell phone technology in the past two decades, electric vehicles have the potential for widespread usage and to wide-ranging effects inside and outside of the automotive industry. The “digitization of the transport system” will effect, among others, oil companies, car dealerships, maintenance services, and utility suppliers.

“If it is hard to predict when phase change in complex systems begins, it is even harder to predict where it ends,” said Michael Leibreich and Angus McCrone, the authors of the Bloomberg article. “No list of potential impacts of the ‘Transformation of Transportation’ can be complete. However, one thing is for sure: if our predictions for the uptake of electric vehicles are anything like correct, there is no part of the global economy which will not, in some way, be affected.”

Currently, electric vehicles cost an average of $30,000 and travel 100 miles or less on a single charge. Tesla (Model 3) and Chevrolet (Bolt EV) have both promised electric vehicles that will travel 200 miles on a charge within the year. Other car makers, such as Volkswagen and BMW, have announced plans to turn a large portion of their production to electric vehicles in the next few years as well.

While the changes in infrastructure and the length of time that most car owners keep a vehicle (11 years on average) have limited electric vehicle sales to this point, according to Christopher Mims of the Wall Street Journal, the next vehicle that most consumers purchase is likely to be electric.

Mims explained, “It is the nature of disruptive technological shifts that it seems like nothing is changing—until it seems as if everything is changing at once. Electric vehicles have been a long time coming, but they now represent such a clear and present threat to the gasoline engine that Mr. Fox, of the service-station association, now recommends that members signing long-term contracts for fuel include an option to renegotiate if more than 10 percent of a state’s fleet goes electric.”

Electric vehicles offer a smooth drive with better acceleration, less moving parts requiring less maintenance, better air quality, and a better platform for autonomous driving, said Bloomberg. Electric vehicles are the future and that means designing better, longer-lasting, higher-performing batteries will be the future as well.

Cooling those batteries will be critical. As Dr. Azar will explain, without proper thermal management the electric vehicle battery will be inefficient and unable to provide the performance that consumers demand.

The Sept. 22 event is free for SAE NE members and $5 for non-members. It runs from 6-9:15 p.m. with tours of the ATS campus from 7-8:00 p.m. and Dr. Azar’s presentation at 8:00. Register online at http://www.sae.org/servlets/sectionEvent?PAGE=getSectionEvents&OBJECT_TYPE=SectionEventAdmin&HEIR_CODE=MS045#249128&saetkn=w1aFMMls8Y or contact SAE member Jeff Mobed at jeffrey.mobed@gmail.com or 508-367-6565.

Some Help for Thermal Engineers Working in Automotive

Think about thermal management of automotive electronics like this:   A control system you’ve carefully engineered is subjected to grime, dirt, mud, crazy temperature cycles, flooding rain and no maintenance.  Oh and it has to work every time it is turned on, regardless of the condition.  That’s thermal management of automotive electronics.

We wrote on this topic a couple of times in our Qpedia Thermal eMagazine.  We also published an article in EE Times on this topic.  For the thermal engineer new to that space, they can form helpful primers on the topic.

Siemens PLM is weighing in with their own thoughts on this topic with a free webinar tomorrow, July 15th.  As the Siemens team notes, “systems integration is one of the current challenges faced by car manufacturers and suppliers, especially in the field of engine thermal management.” We couldn’t agree more! You can hear and see their thoughts on this topic by registering at their webinar here: “Siemens 7/15 Webinar on Automotive Thermal Management”.

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