This is Part 2 of a blog series exploring the factors engineers need to consider when designing a new e-mobility vehicle for their organization.
When designing a new e-mobility vehicle, it’s important to clearly understand how it will operate effectively and efficiently in the environmental and physical conditions it will be exposed to.
E-mobility vehicles—especially those operating in an industrial setting—can be subjected to a range of harsh environments, resulting in various stresses being imposed on their components.
The conditions a vehicle needs to be designed to withstand include: extreme and rapidly fluctuating temperatures and humidity, exposure to dust, dirt, water and/or chemical splashes and sprays, and a wide range of mechanical shocks and vibrations.
If a vehicle is not designed with protection in mind, its components, such as sensitive electronics like motor controllers and on-board battery chargers, can be prone to expensive damage and failures.
It’s also important to consider how the vehicle will be used daily—its expected range and duty cycle—because this will impact battery specifications and charging infrastructure decisions.
The Effects of Heat
Because temperature affects the rate and efficiency of chemical reactions, it significantly influences the performance of the lithium-ion battery cells that power most electric vehicles.
Batteries operate at maximum efficiency of around 68oF (20oC), or just below room temperature. As temperature varies higher or lower, they start to lose capacity, which will reduce the vehicle’s range.
How Heat Affects Battery Performance and Vehicle Range
As a general principle, chemical reactions speed up at higher temperatures, meaning “unwanted” reactions that make batteries degrade will occur faster in hotter conditions.
High temperatures negatively affect the composition and organization of a battery’s protective Solid Electrolyte Interphase (SEI) layer, triggering reactions that use up excessive active lithium or create inert compounds that prevent ions from flowing freely.
While the exact impact of heat will differ depending on the chemistry of a specific battery—and will also vary depending on whether the battery is at rest, charging, or being discharged—it is fair to assume that in most cases, higher temperatures will lead to faster degradation. This means the battery performance and range of an e-mobility vehicle will reduce if it is operated in a hot environment.
How Heat Affects Battery Charging
Batteries can be damaged if they are charged in high-temperature environments. Heat increases the effective force of the electric current that drives lithium ions from one node of the battery to the other, resulting in damage on the receiving end. The higher the temperature—or the higher the current—the more damage the battery node experiences. This can impede the free flow of energy, resulting in an increase in the battery’s internal resistance and a reduction in available power.
Storing E-Mobility Vehicles in the Heat
Batteries will degrade if they (or the vehicles they are mounted in) are stored in hot conditions. As mentioned above, heat increases the rate of chemical reactions, resulting in the degradation of the protective layer around the anode (SEI).
Studies have found that secondary reactions may also occur within a battery at high temperatures, creating new inert compounds and increasing impedance, leading to reduced performance.
The Impact of Cold Conditions on Battery Performance and Vehicle Range
Cold environments have the opposite effect to hot conditions. Reduced conductivity and diffusivity in the cold means slower chemical and physical reactions, resulting in:
- Less battery capacity (due to diminished ion flow), reducing the vehicle’s range.
- Longer charging time (due to increased impedance).
Storing and Charging E-Mobility Vehicles in the Cold
Batteries should be above freezing (32oF/0oC) before they are charged. Ideally, a vehicle should have some form of temperature regulation within its battery management system (BMS) to prevent high voltage or fast charging if the battery is too cold. The BMS will draw energy to keep the battery at a healthy temperature and, in cold conditions, will slow the charge. If battery power is required for temperature regulation, the vehicle’s range will be reduced.
Other Temperature Considerations
If vehicles are operated in extremely high- or low-temperature environments, components may be damaged or fail if they are not rated to withstand the conditions. When designing an e-mobility vehicle, it’s important to choose components that are rated for the temperature extremes the vehicle could potentially be exposed to. This reduces the risk of damage to a vehicle’s battery, charger or other electrical components, which can result in costly maintenance issues.
If an e-mobility vehicle is designed for use in hot or cold conditions, its design should incorporate some form of in-vehicle heating and/or cooling system. Designers need to factor in the increased drain these systems will have on the vehicle’s battery and the resulting reduction in the vehicle’s performance and range.
Protecting Against Humidity, Liquid and Dust Exposure
Batteries and other vehicle components can overheat and fail when subjected to excessively hot and/or humid environments.
Rapid temperature changes—e.g., when a vehicle is driven in hot, humid summer conditions and then stored in a cool, climate-controlled garage—can result in internal condensation leading to electrical shorts and material degradation.
Vehicle components can be damaged if they are exposed to dust, dirt or liquids.
When designing a vehicle, protections against humidity, liquids and solid particles—to a standard appropriate for the environment the vehicle will be exposed to—need to be considered.
The IP (Ingress Protection) rating is an International Electrochemical Commission (IEC) standard for measuring a device’s levels of protection against dust and liquid. It standardizes how sealing is defined worldwide.
The first digit in the two-digit IP code indicates the level of protection against solid objects. IP6x is the highest protection against solid objects and is considered “dust tight”.
The second digit in the two-digit IP code indicates to what degree the device is protected from water and liquids. IPx0 provides no special protection, while IPX9—the highest rating—protects the device against the effects of close-range high pressure and high-temperature spray downs, as well as continued emersion in water.
Fully sealing electronics for submersion is expensive, complex, and unnecessary. Prudent electronics engineers should strive to meet an IP66 standard—dust tight and protected against heavy water jet spray for at least 3 minutes—particularly if water and chemicals are part of everyday activities. This standard is similar to NEMA4 or NEMA4X.
Vibration and Shock Protection
The range of shocks and vibrations a vehicle’s electronics could potentially be subjected to must be considered during the design process.
A vehicle’s components can be exposed to different vibration profiles, which vary significantly in frequency. For on-board battery chargers, vibration can shake the components inside the charger loose or cause damage, leading to charger failure.
E-mobility vehicles need to be designed with adequate suspension to offer suitable protection against the environments and surface conditions where they are likely to operate.
The IEC has developed international methods to test a product’s ability to withstand a wide range of shock and vibration profiles.
Another useful series of tests is defined in GMW3172, an automotive standard created by General Motors to test electrical/electronic devices with circuit boards in stressful environments. These tests subject a large sample of products to extreme shock, bump, vibration, humidity, and temperature cycling at an automotive-grade level. They also accelerate the on-board components’ aging to prove they will meet the design life objectives.
Usage Patterns and Duty Cycle
E-mobility vehicle design needs to consider how the vehicle will be used, including the distance it needs to be capable of covering on a daily basis, and when and where it will be available for recharging during each 24-hour cycle.
Specific questions that need to be considered include:
- Will your vehicle be operated constantly or occasionally? – If it is only intended for occasional use, a vehicle can be designed for overnight charging. If, however, use is likely to be near-constant, an on-board charger may need to be factored into the design to enable opportunity charging at any time.
- What range do you need to achieve? – This will impact decisions about the capacity of the vehicle’s battery.
- Will you need bursts of energy or a more consistent supply? – This may also impact the choice of battery.
- Will you be able to charge slowly or require rapid charging? – If there is not expected to be sufficient vehicle downtime to enable slow charging (e.g., overnight), the design may have to consider the use of charge points for rapid opportunity charging during short-run breaks.
Want To Learn More?
Visit Delta-Q’s e-mobility information and resource hub to learn more about e-mobility design, applications, and the latest technology trends. Topics covered include:
- The regulatory landscape
- The evolution of battery chemistries
- Trends in charging methods
- The future of e-mobility