Why is my Ev Charging so Slow? A comprehensive analysis of the causes and ways to speed up

It is undoubtedly frustrating when you plug your electric car into the charging station with great expectations, but find that the charging speed is abnormally slow. The charging speed of electric vehicles (EVs) is one of the key factors affecting the user experience. A charging process that was originally expected to be completed quickly, if it takes twice or more time, will not only disrupt your travel plans, but may also make you question the convenience of using electric vehicles. So, what factors cause your electric car to charge slowly? Is it a problem with the vehicle itself? A problem with the charging equipment? Or are there other external factors at work?

This article will delve into the various potential causes of slow electric vehicle charging, from the most common factors to some easily overlooked situations, providing you with a detailed diagnostic guide. At the same time, we will also provide practical solutions and prevention suggestions to help you understand and optimize your EV charging experience.

Understanding the Basics of Electric Vehicle Charging

Before we delve into the reasons for slow charging, we first need to talk about an issue that is easily overlooked - people ignore the type of charging. Common types of chargers are: AC Charging and DC Fast Charging. If you are used to the speed of DC fast charging, then using AC slow charging will definitely feel slow to you, but this is actually normal. What we need to compare is whether the charging speed is lower than expected under specific charging conditions.

Common reasons why electric vehicles charge slowly

Now that we know the basics, let’s break down the specific reasons why your electric car may be charging slowly. These reasons may be related to a variety of factors such as the vehicle itself, the charging equipment, the power source, the environment, or the software.

1. Limitations and problems of charging equipment itself

The type and power of the charging pile (EVSE) do not match

This is one of the most common reasons.

Charging with a Level 1 Charger: If you are using the portable 120V charger that comes with the car (i.e. Level 1 charging), it is designed for emergency or overnight slow charging, so its speed is naturally very slow. Compared with Level 2 charging or DC fast charging, it will be extremely slow.
Level 2 charging piles have lower power: Even for Level 2 charging, different charging piles have different powers, with common ones being 3.5kW, 7kW, 11kW, etc. If you are using a lower-power Level 2 charging pile, the charging speed will naturally be slower than using a high-power charging pile. You need to confirm whether the charging pile you are using is the speed level you expect.
Charging pile failure or current limiting: The charging pile itself may have an internal fault, causing it to be unable to output the designed power. Sometimes, in order to manage the load or for operational strategies, public charging stations may limit the current of the charging pile, making its output power lower than the nominal value.

Charging cable capacity and specifications

Charging cables also have their rated current and power capacity.

Using an incompatible cable: If the charging cable you use is rated for a lower current than the maximum current that the charger or vehicle can accept, the charging speed will be limited by the cable. For example, if your vehicle and charger both support 40A, but the cable you use can only carry 30A, the charging speed will be limited to 30A.
Cable aging or damage: If the wires or connectors inside the charging cable are aging, worn, or damaged, resistance may increase and transmission efficiency may decrease, thus affecting charging speed. Severe damage may even cause charging interruption or safety hazards.

2. Your car is the key factor

The vehicle itself is another core link in the charging process, and its internal system has a decisive influence on the charging speed.

Capacity of the on-board charger (for AC slow charging)

When using AC charging (Level 1 or Level 2), the power first passes through the onboard charger inside the vehicle, where it is converted from AC to DC before entering the battery. The capacity of the onboard charger is the upper limit of the AC charging speed.

Low onboard charger capacity: Different models of electric vehicles have different onboard charger capacities, with common ones being 3kW, 6.6kW, 7.2kW, 11kW, etc. Even if you connect to a Level 2 charger with a power of up to 11kW, if your vehicle's onboard charger is only 7kW, the actual charging speed can only reach a maximum of 7kW. This is a limiting factor that many users tend to overlook but is very important.
On-board charger failure: If the on-board charger fails, it may also cause the AC charging speed to slow down or even fail to charge.

Battery State of Charge (SoC) and Charging Curve

Lithium-ion batteries do not charge at a constant rate, especially when using DC fast charging.

Charging "Tapering" Effect: To protect the battery and extend its life, the Battery Management System (BMS) allows a higher charging rate when the battery charge is low, but gradually reduces the charging rate as the charge increases (usually above 80%). This phenomenon is called "trickle charging" or "reduced charging speed". This is a normal working characteristic of the battery and is for safety and health reasons, not a malfunction. Therefore, if you are charging a vehicle that is close to full, it is completely normal for the charging rate to be slower.
Battery Management System (BMS) control: BMS is the "brain" of the battery pack. It monitors the battery's voltage, current, temperature and other parameters in real time, and dynamically adjusts the charging speed based on these data to ensure a safe and efficient charging process. The BMS algorithm design and the judgment of the battery status will affect the final charging speed.

Battery Temperature Management

The temperature of the battery has a significant impact on the charging speed. Lithium-ion batteries will have lower charging efficiency in an overly cold or overheated environment, and may even limit the charging speed to protect the battery.

Low temperature environment: In cold weather, the internal chemical reaction activity of the battery is reduced. The BMS will limit the charging current to prevent damage to the battery. Many electric vehicles will start the battery preheating system before charging in low temperatures, but this takes time, and even after preheating, the charging speed may still be lower than the speed at ideal temperature.
High temperature environment: In hot weather or after long-term high-power charging, the battery temperature may be too high. To prevent permanent damage to the battery due to overheating, the BMS will also limit the charging power or even suspend charging until the battery temperature drops to a safe range. The working state of the vehicle's battery thermal management system (heat dissipation or heating) will also affect the charging speed.

Vehicle settings and charging modes

Sometimes, slow charging may be caused by your own setting.

Charging limit setting: You may have set a charging limit in the vehicle settings (for example, only charge to 80%). When the power reaches this limit, charging will stop. If you mistakenly think that the vehicle is still charging but the speed is very slow, it is necessary to check the charging limit setting.
Scheduled charging or off-peak charging mode: You may have set scheduled charging so that the vehicle will only start charging during a specific time period. Or you may have turned on off-peak charging mode so that the vehicle will automatically adjust the charging time or speed based on the peak electricity prices. Please check whether these settings are what you expected.
Economy or Eco Charging Mode: Some vehicles may offer Economy or Eco Charging Mode, in which the vehicle may actively limit the charging speed to reduce the impact on the grid or optimize battery life.

3. Power supply problem

Whether charging at home or in a public facility, problems on the power supply side can also cause charging to be slow.

Insufficient household circuit capacity or wiring problem (for slow AC charging)

When installing a Level 2 charger at home, you need to make sure your home circuit has enough capacity.

Circuit overload or shared with other devices: If the circuit connected to the charging station is shared with other high-power appliances (such as air conditioners, ovens, water heaters, etc.), when these devices are running at the same time, the circuit current may exceed the limit, thereby triggering the circuit breaker or limiting the charging current, resulting in slower charging or even interruption.
Insufficient or aging wire specifications: If the wire specifications used in home wiring are not sufficient to carry the maximum current required by the charging pile, or if the wires are aging or the connectors are loose, the voltage may drop and affect the charging efficiency.

Load and current limiting in public charging stations

At public charging stations, especially DC fast charging stations:

High charging pile load: When multiple vehicles are connected to the same charging station's charging piles at the same time, if the total power supply capacity of the charging station is limited, or some charging piles are designed to share power (such as a pile has two guns, and the power is halved when two cars are plugged in), then the power allocated to each vehicle will be reduced, resulting in slower charging speed.
Current limiting by charging station operators: For reasons such as grid load, operating costs or equipment protection, charging station operators may proactively limit the current of charging piles during specific periods or under certain conditions.

4. Environmental factors cannot be ignored

As mentioned above, ambient temperature has a great impact on battery performance, which in turn affects charging speed. Two common extreme weather conditions can easily cause battery performance to be greatly affected:

Extremely cold weather: Battery activity decreases and charging speed drops significantly.
Extremely hot weather: The battery is protected from overheating and the charging speed will be limited.

5. Software or communication failure

Communication between vehicles, charging piles and background management systems is the basis for normal charging.

Incompatible or faulty communication protocols: The vehicle and the charging station need to negotiate charging parameters through communication protocols (such as CCS, CHAdeMO, GB/T, etc.). If the communication fails or is incompatible, charging may not start or can only be performed at a lower power.
Vehicle or charging station software bugs: There may be bugs in the vehicle's battery management system software, the charging station's control software, or the background system software, which may cause abnormal charging process, including slower speed.
Network connection issues: For smart charging piles or remote control functions of vehicles that require Internet access, if the network connection is unstable or interrupted, it may also affect the charging process and speed monitoring.

How to Diagnose and Fix Slow Electric Vehicle Charging Problems

If you are facing the problem of slow charging speed, you can follow the steps below to diagnose and try to solve it:

Step 1: Confirm the charging type and expected speed

First, determine the type of charging you are using (Level 1, Level 2, DC Fast Charge) and the expected speed of that type of charging under normal circumstances (check the vehicle manual or charger information). This will help determine if the current speed is abnormal.

Step 2: Check the charging device and cable

Change charging station: If you are at a public charging station, try to change to a different charging station to see if the speed returns to normal. If you are at home, check whether your charging station is working properly and whether there is a fault indicator light on.
Check the charging cable: Check the cable for visible damage, cracks, or loose connectors. If possible, try charging with another compatible cable to see if that improves the situation. Make sure the cable is rated for the correct charging capacity.

Step 3: Check the vehicle's charging status and settings

Check the vehicle dashboard or APP: Check the current charging power (kW) or current (A) displayed on the vehicle dashboard, central control screen or mobile phone APP. Compare it with the maximum charging power theoretically supported by the vehicle to determine whether the current speed is far below the normal level.
Check the battery level (SoC): If the level is already high (e.g. over 80%), then a slower charging rate is a normal trickle effect.
Check the vehicle charging settings: Confirm whether a charging limit, timed charging, or off-peak charging mode is set. If so, try to cancel or adjust the settings. Check whether an economy or eco mode that limits charging speed is enabled.
Check the battery temperature: If the vehicle provides a battery temperature display, check whether the temperature is too high or too low. If the battery temperature is abnormal, try to wait until the temperature returns to normal before charging.

Step 4: Consider the power supply side (for home charging)

If you are charging at home, make sure the circuit the charger is connected to is not shared with other high-power appliances and that the circuit capacity is sufficient. If you suspect a circuit problem, you may need to ask an electrician to check your home wiring and circuit breakers.

Step 5: Consider environmental factors

If charging in extremely cold or hot weather, slow charging may be a normal battery protection mechanism. Try to charge in a temperature-friendly environment or use the vehicle's battery preheating/cooling function.

Step 6: Restart your device or vehicle

Restart the charging station: Some charging stations can be restarted by cutting off the power and then turning it on again.
Restart vehicle systems: Try restarting the vehicle's entertainment system or main control system (please refer to the vehicle manual for specific operations). This can sometimes resolve temporary software or communication-related failures.

Step 7: Consult professionals or after-sales service

If you have tried the above methods and the problem persists, or you are not sure why, we recommend:

Contact the charging station operator: If you encounter problems at a public charging station, contact the customer service number on the charging station to report the problem and consult.
Contact the vehicle manufacturer or authorized service center: If you suspect that the problem is with the vehicle itself, or the charging station works normally on other vehicles, contact your vehicle brand after-sales service. They can perform more professional diagnosis, including checking the on-board charger, battery management system, etc.
Contact the charger installer or supplier: If there is a problem with the home charger, contact the company that installed the charger for inspection and repair.

Tips to prevent slow charging

Now that you know the possible causes, there are some preventative measures you can take to minimize future slow charging issues:

Understand your vehicle's charging capabilities: Know the maximum AC charging power (onboard charger capacity) and maximum DC fast charging power supported by your vehicle. This will help you choose the right charging equipment.
Choose the right charging equipment: Choose a home Level 2 charger with the right power based on your charging needs (daily commuting, long-distance travel, etc.) and home circuit conditions. For users who often need fast charging, learn about the types and powers of chargers at the public charging stations you often visit.
Regularly inspect and maintain charging equipment: For home charging piles and onboard cables, regularly check whether their appearance is damaged and whether the connectors are clean and free of foreign matter. Follow the manufacturer's maintenance recommendations.
Pay attention to vehicle software updates: Vehicle manufacturers occasionally release software updates that may include optimizations to the battery management system or charging control logic, which can sometimes improve charging performance. Make sure your vehicle software is up to date.
Plan your charging: On long trips, plan your charging stops ahead of time and try to fast charge your battery when it’s low (taking advantage of the fast-charging “sweet spot” speed). Avoid fast charging when the battery is high, as speeds will drop significantly.
Pay attention to battery temperature: In extreme weather, if conditions permit, try to charge in an indoor parking lot. For vehicles that support the battery preheating function, use this function appropriately.