Yesterday, the biggest news affecting people’s livelihoods was the heavy rain in Henan and other regions. In the face of the violence of nature, the technology developed by humanity appears to be very powerless. We hope the rain will stop soon and that friends in the affected areas will be safe.
For practitioners in the automobile industry, some shocking scenes are cars parked in underground garages or on the street being washed away by the floods, turning into “boats”. Although this is an extreme situation, it is common for the southern region to encounter heavy rain and strong winds in the summer. Even if the car is parked in the garage, it may still face unexpected flooding. As we all know, for gas-powered cars, water in the engine can cause many potential problems, but for electric cars, a relatively new thing, should they also be afraid of water? And can electric cars still pose new problems such as electric leakage after being inundated? This worries many owners of new energy vehicles.
Today, let’s discuss the safety of electric cars after being submerged in water from the perspective of battery pack design.
Firstly, the high-voltage electrical system of pure electric vehicles is at least around 400V, which is higher than the range of safe voltage for human bodies. It is also for this reason that the safety design of electric vehicles needs to take measures to deal with high-voltage electricity. We usually refer to this as high-voltage electrical safety regulations. Safety issues for electric cars have always been highly valued both domestically and internationally. China has also done a lot of work in this area, such as the “Electric Vehicle Safety Guide” published in 2020, in which I participated in some of the writing work.
The biggest difference between electric cars and traditional gas-powered cars is that electric cars do not have an engine, so there is no issue with intake and exhaust, and they do not need to rely on air intake to drive the electric motor. Therefore, in the design of electric vehicles, the working environment of the electric motor and battery pack is enclosed and will be subjected to waterproof and fully enclosed tests. If designed properly, the waterproof performance of electric vehicles can be said to be very good, which is also a basic requirement of the industry.
According to the GB4208/IEC/EN60529 standard, the dustproof and waterproof rating of the electric vehicle battery system is recommended to be no less than IP67. The IP protection rating is composed of two numbers, the first representing dustproof grade and the second representing waterproof grade. The larger the number, the better the protection level. The battery system’s rating of “IP67” means that “6” represents complete protection from dust intrusion, and “7” represents that it can be submerged in water of at least 1 meter deep for more than 30 minutes while maintaining normal low-voltage monitoring function and no water intrusion inside the shell. In the safety requirements of GB/T18384-2015, three testing rules for waterproofing are explicitly stated: simulated washing, simulated rain, and simulated immersion. In GB/T31467.3-2015, a seawater immersion test is also proposed, which is a testing method that simulates and approaches fault conditions.In the “Electric Vehicle Safety Guidebook,” general requirements for electric vehicle batteries are proposed as shown in Figure 2, which illustrates the requirements and disassembly of the waterproof and dustproof structure of the battery system.
The sealing structure of the power battery housing generally includes two types: O-shaped and irregular. O-shaped seals are mostly used for the seal between the electrical connectors and the housing of the shell, and in some cases, for the lid of the box and the housing.
From a material perspective, rubber products currently have the best sealing effect. By applying pressure, the elastic unit is compressed between the upper and lower mounting surfaces to a certain percentage. The rebound force of the elastic unit is then used to fully contact the elastic unit and the upper and lower mounting surfaces, achieving the requirements of waterproofness and dust resistance. The commonly used compressive sealing elastic materials for battery boxes on the market include foamed silicone or rubber, solid or micro-foamed silicone or rubber injection molding types. Among them, foamed silicone has better compression deformation performance and rebound stress attenuation performance, and has a certain cushioning effect. When the contact friction between the sealing ring and the upper and lower box bodies is greater than the water pressure and the sealing ring is in close contact with the upper and lower box bodies, a sealing effect of waterproofness and dust resistance can be achieved. The sealing effect of the sealing ring is closely related to the effective sealing width and compression of the sealing ring. The common forms of the sealing ring are shown in Figure 3. The effective sealing width refers to the distance from the inner edge of the nut to the inner side of the sealing ring. The round hole is only for positioning, and the effective sealing width needs to be determined based on the sealing protection level of the battery box and the material performance of the sealing ring.
The design of the electrical sealing surface: The high and low voltage connectors of the battery system also have sealing designs. The electrical connection port is an important output, input, communication, and monitoring channel between the battery system and the vehicle or exterior. Due to the diversity and large quantity of interface connectors, designing such interfaces is difficult and is generally the weak link in the sealing of the battery system. If not well done, leakage along the wire core of the system may occur. This is usually caused by the seal not being in place on one end of the high-voltage harness, which leaks along the wire core to the other end. In addition, low-voltage harness sealing plugs may not be able to withstand the corresponding water pressure or may leak due to incompatibility with the connector.
In conclusion, in conditions with water immersion, electric vehicles with an effectively sealed battery system can maintain their power and have certain advantages against extreme environments such as flooding. However, it should be noted that this does not mean that after deep water immersion, electric vehicles can be safely driven like a boat. Apart from the dangers of turbulent water currents, low-voltage systems in electric vehicles, like those in gasoline vehicles, are not waterproof. After the 12V battery and system fail, all control systems, such as electric windows, will be affected.Therefore, when encountering extreme weather, what we ordinary people can do is to maintain a sense of awe and prepare in advance. After all, our level of technology is still too immature compared to nature.
Translated into English Markdown text with HTML tags preserved:
Therefore, when encountering extreme weather, what we ordinary people can do is to maintain a sense of awe and prepare in advance. After all, our level of technology is still too immature compared to nature.
This article is a translation by ChatGPT of a Chinese report from 42HOW. If you have any questions about it, please email bd@42how.com.