Electric Vehicle Charging: DC or AC?
2021/12/24 By hqt
The main disadvantage of light electric vehicles is the significant charging time of the batteries, usually at least 3 hours. Reducing this time to half an hour makes charging an electric vehicle comparable to refueling a conventional car with gasoline. All the same, you will spend half an hour at a gas station with a cup of coffee and shopping at a local store. Such short charging times have already become a reality when charging the car with DC power. Why, then, haven't AC charging stations become a thing of the past?
Almost any modern electric vehicle (except for some sports models that are not widespread) can be charged from a regular electrical outlet. The presence of such a function allows you not to be left without movement in areas where there are no special charging stations.
You can self-charge an electric car at home if you live in a separate cottage or townhouse. In such buildings, there are usually also three-phase 400 V (according to the old standard - 380 V) AC outlets. You can charge the car at night while you sleep, and during the day it will last for about 500 km.
In the event that the line supplying electricity to a cottage or section of a townhouse is capable of withstanding a current of about 80-100 A, you can further speed up the process by installing a personal AC charging station. It connects directly to your home's electrical panel, so it is not affected by outlet and wiring restrictions. The charging time is reduced to 4 hours.
AC advantages and disadvantages
Batteries are always charged directly with constant current. Therefore, an electric vehicle has a built-in charger that converts the alternating current coming from the station into direct current and adjusts the charging parameters. As already noted, the presence of such a device for any electric vehicle is mandatory, otherwise it will not be able to recharge in a critical situation.
The design of the AC station is extremely simple. It has systems for protecting both the electric vehicle and the electric network from emergency situations, and, if necessary, a billing system that allows you to sell the charging service.
However, placing the main charger assemblies on board an electric vehicle limits the AC charging speed. The higher the charging speed, the higher the amperage. In turn, this entails an increase in the mass and dimensions of the electronic components responsible for charging. Also, increasing the charging speed will require better heat dissipation from electronic components. Limitations on weight, dimensions and heat dissipation capabilities in a passenger electric vehicle have determined the charging current limit of 32 A. It is typical for most mass-produced electric vehicle models.
Constant current charging
You can significantly speed up charging if you connect directly to the battery at the station. With this approach, there are no longer any restrictions on the size and weight of the charger, since all its components are located outside the body of the electric vehicle. Naturally, only direct current can be supplied directly to the batteries.
The operating voltage of the storage battery in modern electric vehicles is usually 400-450 V. Therefore, the voltage of 500 V was adopted as the standard for DC charging.
When charging with a direct current, the interface between the station and the electric vehicle must contain a data link from the vehicle to the charging. Based on this information, the station determines the type and current state of the battery, fine-tuning the voltage and some other charging parameters.
The disadvantages of direct current include the high cost of a charging station complete with a cable. For comparison, charging stations operate on alternating current, taking into account the cost of the cable.
It is also widely believed that DC charging stations will reduce battery life. In fact, battery life will decrease with any kind of boost charging. To reduce the influence of this factor, at some stations ultra-fast charging is limited to 80% of the battery capacity.