The Top Reasons Why Charging Slows Over Time

There are always new energy car owners reporting: "Why is it that a certain brand of fast charging stations with hundreds of kilowatts only has a maximum of tens of kilowatts at the car end?" "Every time I feel that charging becomes slower as time goes by, why can't it always be maintained at a higher rate?" High charging power? Did the company deliberately limit the power of the charging pile?" Today, Longduo will talk about the things behind "charging speed" based on these common confusions among users~

01 Correctly understand the “fast charging” process

Before we start talking about charging speed, we might as well first understand the whole process of charging new energy vehicles. Taking DC charging piles at public stations as an example, the entire charging process can be divided into the following steps:

• The physical connection between the car end and the pile end is also known as "inserting the gun".
• The charging pile provides low-voltage auxiliary DC power to the electric vehicle to activate the vehicle's built-in BMS (battery management system);
• Just like two people meeting for the first time, shaking hands and exchanging business cards, after the BMS is activated, the vehicle terminal and the pile terminal will send charging related parameters to each other;
• The exchanged "business card" information also includes parameters such as the vehicle's maximum charging power demand and the charging pile's maximum output power. After both parties confirm that they are "adapted" to each other, they wait to start charging;
• After charging officially starts, the vehicle's built-in BMS will send charging power demand information to the charging pile. The charging pile will adjust its output voltage and current in real time based on this information to ensure that the entire charging process proceeds smoothly. At the same time, they will also monitor each other in real time. Charging status to ensure safety;

Therefore, it is not difficult to find that the process of "fast charging" is actually a process in which the vehicle end meets the needs of the vehicle end and controls the output voltage and current of the pile end in real time. Longduo charging engineers also vividly compared this process to "drinking water": the car end is like a thirsty person who needs to drink water, and the pile end is like a water outlet. The speed of drinking water depends on the amount of water consumed in each sip. There is a certain relationship between the amount and the instantaneous water output, but it depends more on the thirst and drinking ability of the water drinker.

02 After SOC reaches 80%, the charging speed decreases

After understanding the charging process, it will be easy to understand if we look at the problem reported by users that "charging becomes slower and the charging power becomes smaller and smaller". Longduo engineers vividly divided charging into three processes: "excitement zone", "happy slide" and "waiting zone". For example, during the charging process of a certain brand of electric vehicle SOC (battery remaining capacity) from 0% to 80%, we can observe the changing curve of charging demand voltage and charging demand current. According to P=UI (ie power = voltage x current ), we can see that: in the more than 20 minutes after starting charging, the battery is in the preheating stage, the battery activity gradually increases, the charging power required by the battery continues to increase, and the charging speed continues to accelerate. When the SOC reaches about 50% (results vary depending on brands and models), the charging power will gradually begin to decrease. When the SOC reaches 80%, the charging speed will further decrease and enter the "trickle charging" stage until it is close to full state. This is why many car companies choose to use the expression "X%-80% fast charging time" as a selling point when promoting. Therefore, the feeling of "charging becomes slower and the charging power becomes smaller and smaller" does exist. The main reason is actually the limitations of the car end and the power battery, not the pile end.

03 Follow the principle of “recharge as you use, charge shallowly and discharge shallowly”

Generally speaking, we can follow the principle of "charge as you use, charge shallowly and discharge shallowly", especially at public charging stations, charging to 80%-90% each time, and at the same time, keep the SOC daily at no less than 20% . Doing so can not only fully protect charging safety, but also reduce the waiting time for charging. Even for lithium iron phosphate batteries, they can be charged at most once a week to correct the cruising range. Seeing this, someone will definitely say: "If I follow your recommended method and increase the number of charging times, won't it affect the battery life?" There is actually a misunderstanding here. Battery life is indeed related to charging, but it is not determined by the amount of charge or the number of charges per time, but by the complete cycle of the battery: a battery is discharged from 100% full charge to 0%, and then charged to 100% %, it is considered a complete cycle. Therefore, whether it is due to considerations of charging efficiency or the actual situation of daily travel, "full" is not the best choice~

04 Conclusion

Of course, in addition to vehicle end restrictions, battery materials, battery temperature, charging pile technology, etc. will also have a certain impact on the charging speed . Especially as the weather continues to get cooler, the charging speed will also decrease in some areas with lower temperatures. Oh, today’s science popularization ends here. If you have anything else you want to know, please leave a message in the comment area~