Which cooling system works best in electric vehicles?
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Battery thermal management systems are still a highly researched topic. What we know about them is going to change and develop over the coming years as engineers continue to rethink how our car engines work.
There are a few options to cool an electric car battery: phase change material, fins, air or a liquid coolant.
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Phase change material absorbs heat energy by changing state from solid to liquid. While changing phase, the material can absorb large amounts of heat with little change in temperature. Phase change material cooling systems can meet the cooling requirements of the battery pack. However, the volume change that occurs during a phase change restricts its application. Also, phase change material can only absorb heat generated, not transfer it away, which means that it wont be able to reduce overall temperature as well as other systems. Although not favorable for use in vehicles, phase change materials can be useful for improving thermal performance in buildings by reducing internal temperature fluctuations and reducing peak cooling loads.
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Cooling fins increase surface area to increase the rate of heat transfer. Heat is transferred from the battery pack to the fin through conduction, and from the fin to the air through convection. Fins have high thermal conductivity and can achieve cooling goals, but they add a lot of additional weight to the pack. The use of fins has found a lot of success in electronics. Traditionally, they have been used as an additional cooling system on internal combustion engine vehicles. Using fins to cool the electric car battery has fallen out of favor since the additional weight of the fins outweighs the cooling benefits.
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Air cooling uses the principle of convection to transfer heat away from the battery pack. As air runs over the surface, it will carry away the heat emitted by the pack. Air cooling is simple and easy, but not very efficient and relatively crude compared to liquid cooling. Air cooling is used in earlier versions of electric cars, such as the Nissan Leaf. As electric cars are now being used more commonly, safety issues have arisen with purely air-cooled battery packs, particularly in hot climates. Other car manufacturers, such as Tesla, insist that liquid cooling is the safest method.
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Liquid coolants have higher heat conductivity and heat capacity (ability to store heat in the form of energy in its bonds) than air, and therefore perform very effectively and own advantages like compact structure and ease of arrangement. Out of these options, liquid coolants will deliver the best performance for maintaining a battery pack in the correct temperature range and uniformity. Liquid cooling systems have their own share of safety issues related to leaking and disposal, as glycol can be dangerous for the environment if handled improperly. These systems are currently used by Tesla, Jaguar and BMW, to name a few.
A research group from the National Renewable Energy Lab (USA) and the National Active Distribution Network Technology Research Center (China) compared four different cooling methods for Li-ion pouch cells: air, indirect liquid, direct liquid and fin cooling systems. T
The results show that: an air-cooling system needs two to three times more energy than other methods to keep the same average temperature; an indirect liquid cooling system has the lowest maximum temperature rise; and a fin cooling system adds about 40% extra weight of cell, which weighs most when the four kinds cooling methods have the same volume.
Indirect liquid cooling is a more practical form than direct liquid cooling, though it has slightly lower cooling performance. (Comparison of different cooling methods for lithium-ion battery cells)
The determining features of an electric vehicle battery cooling system are temperature range and uniformity, energy efficiency, size, weight, and ease of usage (i.e., implementation, maintenance).
Each of these proposed systems can be designed to achieve the correct temperature range and uniformity. Energy efficiency is more difficult to achieve, as the cooling effects need to be greater than the heat generated when powering the cooling system. Also, a system with too much additional weight will drain energy from the car as it outputs power.
Phase change material, fan cooling and air cooling all fail at the energy efficiency and size and weight requirements, though they may be just as easy to implement and maintain as liquid cooling. Liquid cooling is the only remaining option that does not consume too much parasitic power, delivers cooling requirements, and fits compactly and easily into the battery pack.
Tesla, BMW i-3 and i-8, Chevy Volt, Ford Focus, Jaguar i-Pace, and LG Chems lithium-ion batteries all use some form of liquid cooling system. Since electric vehicles are still a relatively new technology, there have been problems maintaining temperature range and uniformity in extreme temperatures even when using a liquid cooling system. These are likely due to manufacturing problems, and as companies gain experience developing these systems, the thermal management issues should be resolved.
In liquid cooling systems, there is another division between direct and indirect coolingwhether the cells are submerged in the liquid or if the liquid is pumped through pipes.
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Direct cooling systems place the battery cells in direct contact with the coolant liquid. These thermal management schemes are currently in the research and development stage, with no cars on the market using this system. Direct cooling is more difficult to achieve, due to the fact that a new type of coolant is required. Because the battery is in contact with the liquid, the coolant needs to have low to no conductivity.
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Indirect cooling systems are similar to ICE cooling systems in that both circulate liquid coolant through a series of metal pipes. However, the construction of the cooling system will look much different in electric vehicles. The structure of the cooling system that achieves maximum temperature uniformity is dependent on the shape of the battery pack and will look different for each car manufacturer.
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Making the Decision: Lithium-Ion Battery Supplier
The lithium-ion battery market is in a state of flux. Lithium-ion is a relatively new technology that has taken off in the last five to 10 years and demand for these batteries is high and growing. This has attracted many OEM&#;s and created something of a buyer-beware market for OEM.
Many critical factors must be considered when deciding on a forklift battery supplier. Choosing the wrong lithium-ion battery for a forklift can impact the entire operation of an OEM&#;s business, from procurement to production. An OEM&#;s day-to-day operations depend on forklift transportation, and a forklift's day-to-day operations rely heavily on the battery. Choosing a lithium-ion forklift battery supplier is the first step in determining the success of an OEM&#;s daily processes. OEMs need suppliers who can meet JIT shipping demands, lead technical innovation, and provide extended technical service. Without that, you may end up with a lithium-ion supplier instead of a lithium-ion partner who will be with you for the long run. That can lead to dissatisfied customers and lost time and money.
Ask the manufacturers these questions:
1. To get an idea of how established the company is ask how long they have been in business, how long they have been serving the material handling industry, and whether they have supplied batteries to major OEMs. You could also ask if they offer a full portfolio of batteries including flooded lead-acid, AGM, and lithium-ion. You may want to move on if the manufacturer is a start-up, has been serving the material handling industry for just a few years, or has not supplied batteries to OEMs.
Older, more seasoned companies that understand the material handling industry and manufacture and sell a full line of forklift lithium battery products generally know the issues that can damage batteries and shorten their lifespans. They often engineer solutions to these problems into their products.
2. How long have you been working with lithium-ion technology? Again, the company probably has a lot to learn if the answer is just a few years.
3. What kind of customer support do you provide? Make sure the company has a U.S-based and Europe customer support line staffed by real people who can answer questions and help your technicians troubleshoot issues. Ask if support is available 24/7 and if the staff includes representatives dedicated to lithium-ion products. Many newcomers to the market simply don&#;t have the infrastructure to provide that level of service.
4. How do you support the dealers who carry your products? You don&#;t want to work with a supplier who sells products and then forgets about you. To avoid tag and long hold times, look for a manufacturer with a systematic approach to communicating with dealers. Ask if the manufacturer has an authorized dealer network through which it trains dealers to sell its products and provides them with the information and materials they need.
5. How do you sell your batteries? Many battery manufacturers sell directly to dealerships and are unable to provide the follow-up services dealers may need. Look for a supplier who sells their batteries through a network of trained distributors. These distributors generally know and stand by their products, adding value to your purchase.
6. How is your battery different from others in terms of design and engineering? Look for products with UL certification and at least an IP67 rating. This helps protect the battery from damage from vibration, water and dust and can extend its life. Make sure the battery is embedded and modular expandable.
Ask how the battery is designed to move the damaging heat it generates away from the cells. Most manufacturers do this through inexpensive components called heat sinks because they are easy to make and add on.
But heat sinks should not be the only method of heat management. Well-made batteries reduce the heat generated and allow for natural cooling in the design. This requires more engineering expertise, but it boosts efficiency, improves safety, and prolongs battery life.
7. What range does your battery get? To help OEMs, BSLBATT has developed 43 standard modules for lithium batteries of different capacities, which can form parallel building blocks in forklift battery compartments. Up to 20 of these modules can be stacked in parallel, and the total capacity can be tailored to forklift OEM needs. It's also worth mentioning that OEMs must check usable capacity, not advertised capacity. The stated capacity may be based on the sum of the individual cells within the battery, which does not take into account internal losses like usable capacity. Real-world test data and customer testimonials are the best way to understand the usable range of a battery. This is especially important in the high-capacity, high-current and relatively low voltage batteries used in MHE.
8. What safety features are built into your battery? Look for a battery with lithium-iron-phosphate cells, one of the most stable lithium-ion battery chemistries. Make sure the BMS features several levels of safety redundancy. That way, if one level fails another will step in, catch the issue, and turn the battery off, protecting you and your property. Ask about UL certifications. Is the entire pack UL-certified or does the manufacturer rely solely on the cell provider&#;s UL listing? BSLBATT is the first forklift lithium battery in China to obtain UL certification for its complete product line.
Stocking batteries on pricing alone is a big mistake that can impact your bottom line. Be sure to compare the manufacturers&#; experience, support services, and products. Investing a little time in your decision can have big payoffs in your sales, service, and customer satisfaction.
For details, please click the link below: https://www.lithiumforkliftbattery.com/lithium-ion-battery-supplier.html
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