Do Ev Charge Faster When Off

Electric vehicle (EV) charging is a hot topic these days, and one question that often comes up is whether an EV charges faster when it's turned off compared to when it's "on," or more accurately, in a state of ready. The short answer is generally yes, but the reasons are nuanced and tied to how the EV's systems manage power and temperature. This article will delve into the technical details behind this phenomenon, explaining the reasons why charging speed can be affected by the vehicle's operational state and offering practical advice for maximizing your charging efficiency.

Background: EV Power Management

Before diving into the specifics of charging speeds, it's crucial to understand the basic components and processes involved in an EV's power management system. Unlike internal combustion engine (ICE) vehicles, EVs rely on a battery pack to store energy and an electric motor to propel the vehicle. Here's a breakdown of the key components:

Battery Pack: Typically composed of hundreds or even thousands of individual lithium-ion cells, the battery pack stores the electrical energy that powers the vehicle. Its capacity is measured in kilowatt-hours (kWh), indicating the amount of energy it can store.
Onboard Charger (OBC): The OBC is a crucial component that converts AC (Alternating Current) power from a charging station into DC (Direct Current) power suitable for charging the battery. The OBC's maximum charging rate is a key factor in determining how quickly the car can charge, especially at Level 2 charging stations.
Battery Management System (BMS): The BMS is the brain of the battery pack. It constantly monitors the voltage, current, and temperature of individual cells and the entire pack. The BMS plays a crucial role in protecting the battery from overcharging, over-discharging, and overheating, ensuring the battery's longevity and safety. The BMS also manages thermal conditioning and controls whether the charging rate needs to be reduced.
Thermal Management System: EVs use sophisticated thermal management systems to regulate the temperature of the battery pack and other components like the motor and inverter. These systems typically use liquid cooling loops and can include heaters to keep the battery within its optimal temperature range. Maintaining the ideal temperature optimizes charging rates, efficiency, and lifespan.
DC-DC Converter: This component converts the high-voltage DC power from the battery pack to lower voltages needed to power auxiliary systems in the car, such as the lights, infotainment system, and other electronic components.

Technical Breakdown: Charging Process and Power Draw

When you plug your EV into a charging station, the following process unfolds:

AC to DC Conversion: For Level 1 and Level 2 charging, the AC power from the charging station flows into the OBC. The OBC then converts this AC power into DC power at the appropriate voltage and current levels for the battery pack.
DC Fast Charging (DCFC): DC fast chargers bypass the OBC entirely. They deliver DC power directly to the battery pack. This allows for much faster charging rates compared to Level 1 and Level 2 charging.
BMS Control: The BMS closely monitors the charging process. It regulates the charging current and voltage to ensure the battery is charged safely and efficiently. It can also reduce the charging rate if the battery is too hot, too cold, or nearing full capacity.
Auxiliary System Power Draw: When the EV is in a "ready" state (even if it's parked), some auxiliary systems are still running, drawing power from the battery. These systems can include the infotainment system, climate control (heating or cooling), battery management system, and communication modules that allow for remote monitoring and control via a mobile app.

Here's where the difference in charging speed comes into play. When the EV is off (completely shut down), these auxiliary systems are typically disabled or significantly reduced in their power consumption. This means that more of the available charging power goes directly to replenishing the battery pack. When the EV is "on" or in a ready state, the auxiliary systems draw power, effectively reducing the amount of power available for charging the battery. The power consumed by the car when in a "ready" state may range from a few hundred watts to over a kilowatt depending on which systems are active. A kilowatt is a relatively small amount of power compared to the 7kW to 11kW that a typical Level 2 charger can supply. However, it is not an insignificant amount, and will reduce the charging rate.

Furthermore, the BMS also plays a critical role. If the BMS detects that the battery needs cooling or heating while charging, the thermal management system will kick in, drawing additional power and potentially further reducing the charging rate. Even when "off", the BMS will usually continue to monitor the battery. It may use some power for this and thermal management, but this is typically less power than is used when the car is fully "on".

Factors Affecting Charging Speed

Several factors can influence EV charging speeds, and it is useful to keep these in mind when assessing the impact of charging while "off".

Charging Level: Level 1 charging is the slowest, using a standard household outlet. Level 2 charging is faster, using a 240V outlet. DC Fast Charging is the fastest, bypassing the OBC.
Charger Power: The power output of the charging station determines how quickly the battery can be charged. Higher power chargers will generally provide faster charging rates.
Battery State of Charge (SoC): Charging speeds tend to slow down as the battery approaches full capacity (typically above 80%). This is because the BMS reduces the charging current to protect the battery from overcharging.
Battery Temperature: Extremely cold or hot temperatures can significantly reduce charging speeds. The BMS may limit the charging current to protect the battery from damage.
Vehicle's Onboard Charger Capacity: The OBC has a limit to the amount of power it can draw from the charging station.

Common Issues and Maintenance Concerns

While charging is generally a straightforward process, there are some common issues that EV owners should be aware of:

Slow Charging Speeds: This can be caused by a variety of factors, including a low-powered charger, a cold battery, or a faulty OBC.
Charging Errors: These can be caused by communication issues between the car and the charging station, or by problems with the charging station itself.
Battery Degradation: Over time, the battery's capacity will gradually decrease due to factors like usage patterns, charging habits, and temperature.
Thermal Management System Failures: Issues with the thermal management system can lead to reduced charging speeds or even damage to the battery pack.

Regular maintenance is essential for keeping your EV in top condition. This includes:

Software Updates: Manufacturers often release software updates that improve charging performance, fix bugs, and add new features.
Battery Health Checks: Periodic battery health checks can help you monitor the battery's capacity and identify any potential problems early on.
Thermal Management System Inspections: It's a good idea to have the thermal management system inspected periodically to ensure it's functioning properly.

Do's and Don'ts / Best Practices

Here are some do's and don'ts to help you maximize your EV charging efficiency and extend the life of your battery:

Do's:

Charge overnight: Take advantage of off-peak electricity rates by charging overnight when demand is lower.
Use a Level 2 charger: If possible, install a Level 2 charger at home for faster charging.
Keep the battery between 20% and 80%: Avoid consistently charging the battery to 100% or letting it drop below 20% to maximize battery life.
Park in the shade: When possible, park in the shade to keep the battery cool, especially during hot weather.
Turn off unnecessary accessories: When charging, turn off unnecessary accessories like the climate control and infotainment system. Specifically, turn the car off.
Check charger compatibility: Ensure the charger you are using is compatible with your vehicle.

Don'ts:

Let the battery sit at 100% for extended periods: Avoid leaving the battery fully charged for long periods, as this can accelerate battery degradation.
Frequently use DC Fast Charging: While DC Fast Charging is convenient, frequent use can put stress on the battery and reduce its lifespan. Use it sparingly.
Charge in extreme temperatures: Avoid charging in extremely hot or cold temperatures, as this can negatively impact charging speeds and battery health.
Ignore warning signs: If you notice any warning signs, such as slow charging speeds or error messages, address them promptly.
Use damaged charging cables: Always inspect charging cables for damage and replace them if necessary.

Conclusion

In conclusion, an EV generally will charge faster when completely turned off because auxiliary systems aren't drawing power. While the exact difference in charging speed depends on the vehicle model and charging conditions, minimizing power consumption during charging is always a good practice. By understanding how your EV's power management system works and following best practices for charging, you can maximize charging efficiency, extend the life of your battery, and enjoy a more seamless EV ownership experience. Therefore, for the fastest possible charging, ensure your EV is powered completely down, minimizing any drain on the battery during the charging process.