Factors Affecting the Charging Times of Electric Vehicles

Factors Affecting the Charging Times of Electric Vehicles

Electric vehicles (EVs) continue to gain popularity in our country and around the world. Since the introduction of EVs, various aspects such as charging, battery capacity, acceleration, range, and comfort have been discussed. In this article, we plan to provide you with useful information about the charging times of electric vehicles and the factors that influence them.

When charging an electric vehicle, the time it takes to charge can vary depending on the maximum DC charging power it can receive. Charging from 20% to 80% battery capacity can take anywhere from 15 to 45 minutes, or it can vary between 3 to 10 hours for AC charging based on the on-board charger power within the vehicle.

Factors affecting the charging times of electric vehicles include:

1) Battery Charge Capacity

The size and capacity of an electric vehicle's battery can vary among different makes and models. Larger battery capacity may result in longer charging times. However, it's not a strict rule, as some EVs with lower battery capacity (e.g., 50 kWh) can be charged at 1C, while a vehicle with a 65 kWh battery can be charged at 2C rapid charging. Looking at the charging times of two different vehicles, it can be observed that the vehicle with the larger battery capacity finishes energy transfer earlier. The reason for different charging powers lies in the battery chemistry and technology used.

What is the difference between kW and kWh?

Kilowatt-hour (kWh) and kilowatt (kW) are related units of measurement but serve different purposes. Kilowatt is a measure of power and 1 kW is equal to 1000 watts. Kilowatt-hour measures the energy consumed in kilowatts per hour. For instance, if you charge your vehicle for one hour with a 60,000-watt charging station, you will consume 60 kWh of energy.

NOTE: For electric vehicles, one kilowatt-hour (kWh) represents the amount of energy stored in the battery. The higher the number, the more power the electric vehicle's battery can store.

2) Output Power of Charging Station

The charging speed of a charging station is measured in kilowatts (kW). The higher the kW, the faster the charging process. However, the maximum charging power your vehicle can accept depends on what the battery management system allows. Various details such as battery quality, battery chemistry, thermal analysis, and cable thickness between battery groups have been determined by the manufacturer to ensure user safety and longevity of the battery cycles.

3) Electrical Grid Connected to the Charging Station

The energy stored in the batteries of electric vehicles demands an instantaneous draw from the grid, equivalent to the energy consumption of an average family of four over two weeks. To meet this demand, charging stations should have dedicated transformers to provide power exclusively to the station. However, in the current situation, stations may not always be able to deliver the desired power during times of high electricity usage, especially during peak hours such as lunch and dinner. This is because the charging station may not be able to draw enough power from the transformer when companies are operating their ovens at full capacity during meal times, resulting in a reduction in charging power and longer charging times. Another example is the fixed stations in major cities, which may not operate at full capacity during certain hours due to insufficient local grid power. As a result, they may not be able to provide the expected charging power throughout the day and can blow the fuse of businesses when stations suddenly draw high power.

4) Battery State of Charge

The state of charge (SoC) of your vehicle's battery indicates how full it is in terms of percentage, similar to a fuel gauge in internal combustion engine vehicles. When batteries are nearly empty, at a low SoC, they are charged most quickly. The higher the SoC, the slower the charging rate. This is because the charging process slows down as the battery approaches its maximum capacity to prevent fast charging and potential battery damage. It has been observed that the power diminishes after around 90% in AC charging and after around 80% in DC charging. In both cases, changes in the charging curves can be seen in the battery management system (BMS) software.

5) Simultaneous Charging

When multiple electric vehicles use the charging sockets of five different stations at Station X simultaneously, it can extend the charging time. The reason for this is that these five stations are powered by a single source (transformer). The allowed power is shared among the five stations.

For example, a 180 kW charging station may have two DC sockets. When a single vehicle uses it and if both the vehicle and the grid allow, it can draw the full 180 kW power to charge the vehicle. However, when another vehicle arrives and wants to use the unoccupied socket, the charging power is distributed either equally (90 kW - 90 kW) or proportionally based on the state of charge of the batteries, depending on the station's software. As a result, the charging power of the first vehicle plugged in is reduced, at best, by half (90 kW), thereby extending the charging time.

The infrastructure of charging stations can place an excessive load on the existing electrical grid connection. In other words, the total maximum power of the charging stations can exceed the grid connection capacity. To address this issue, companies may use solutions such as load management or centralized management software to ensure optimal use of the grid connection.

6) Battery Temperature

Electric vehicles are equipped with cards called Battery Management System (BMS), which serve as the "brain" of the battery. The battery management system is responsible for ensuring the safe operation of the battery. It reads data from temperature sensors placed at critical points within the battery pack based on thermal analysis. When temperature data is received, the battery management system decides on measures to be taken to ensure fast but safe charging in cases of extreme temperatures, whether it's too hot or too cold.

The temperature of the battery can have a significant impact on the charging process. Charging a battery when it's too hot or too cold can lead to reduced charging efficiency and potentially damage the battery. Therefore, the BMS takes into account the battery temperature to optimize the charging process and protect the battery from adverse temperature conditions.

7) Energy Consumption of the Vehicle

During charging, using systems such as air conditioning, lighting, radio, and other in-vehicle systems consumes a portion of the energy sent to the battery. The thermal management system operates based on the temperature within the battery pack. This system can use a portion of the charging power to heat or cool the battery as needed. As a result, there can be a difference between the power displayed on the vehicle's screens and the power actually delivered by the charging station.

The energy consumption inside the vehicle, especially with climate control and other electrical accessories, can impact the overall charging process. To optimize energy usage and maintain the battery's temperature within the ideal range, the thermal management system actively manages the power distribution within the vehicle.

It's essential to be aware that using these in-vehicle systems during charging can extend the overall charging time because the available power is being used not only for charging the battery but also for powering these systems.

8) Battery Health

Li-ion batteries have a specific cycle life, and over time, their useful lifespan can decrease, leading to a loss of battery charge capacity. As a result, their fast-charging capabilities can be adversely affected.

Electric vehicle manufacturers typically offer warranties for their batteries that last 8-10 years or cover a specific mileage, often ranging from 160,000 to 200,000 kilometers. Some electric vehicle manufacturers anticipate a usage lifespan of 15-20 years without the need for battery replacement.

For more detailed information about NMC (Nickel Manganese Cobalt) and LFP (Lithium Iron Phosphate) battery chemistries commonly used in electric vehicle batteries, you can refer to our previous post: https://www.ev-bee.com/article/11-factors-affecting-the-charging-times-of-electric-vehicles