AC Charger vs DC Charger
When you understand the terminology related to charging electric vehicles, you will probably come across the abbreviations AC or DC, and the more common terms "fast" and "slow" charging are also often used. Let's see what it is and how they differ.
Let's start with a school physics course:
- AC (Alternate Current) - Alternating Current,
- DC (Direct Current) - Direct Current
The household and industrial outlets you encounter on a daily basis provide alternating current. You meet a constant in everyday life when it comes to personal household appliances, in which there are AAA batteries and accumulators and other common ones.
An EV battery is made up of many interconnected cells, often reminiscent of home appliance batteries, that are charged with DC only and therefore feedback DC. When charging, a rectifier is used that converts alternating current to direct current. All-electric vehicles have such a device "on board".
But in view of the dimensions of these converters (devices grow in size and weight with power), trying to fit a massive device on the chassis of an electric car that can pass and convert enough power to charge in an hour, or even more so in 10-20 minutes, does not make any sense. Therefore, rectifiers installed directly in an electric vehicle or "on-board chargers" have a limited capacity, while powerful and massive converters remain "overboard".
Slow AC Chargers
AC or slow charging stations are just "smart" AC switches that feed the available AC (without affecting or converting it in any way) via cable into an electric car to an onboard charger. They control the charging process via special signal wires and implement the following important functions:
- Coordination of the charging process with an electric vehicle, only after which the current is turned on, and at the end of charging it is turned off;
- Power control - indicates the maximum allowable current to the electric vehicle and controls it so that the electric vehicle does not overload the network and does not "cut down" the machines;
- Safety - is responsible for the emergency shutdown of current, in case of detection of its leakage on the charging cable or station body, as well as in the electric vehicle itself. Tracking the quality and performance of grounding.
Advanced AC charging stations often have additional features: kilowatt counters, delay timers, intelligent load management functions (dynamic balancing), connection to cloud management and monitoring systems, and many others.
Fast DC Charges
Powerful AC converters (40-200 kW and even more) remain standing on the ground and are connected directly to the battery through special connectors that contain power and signal cables. What is the DC station responsible for?
- Coordinates the charging process with the electric car and only after coordination turns on the current, turns it off at the end;
- Limits and regulates the current on commands from the BMS (Battery Management System - battery management system) in order to carry out the charging process without overloads and overheating;
- Monitors the safety of the charging process - turns off the current in the event of current leaks on the charging cable or station body, in the electric vehicle itself, or grounding problems occur;
- Monitor the temperature of the connectors to avoid overheating.
All DC charging stations have meters, balancing functions, and connect to cloud management, monitoring, and settlement systems using the worldwide OCPP ( Open Charge Point Protocol).
- Mode 2 is charging through a small portable AC station;
- Mode 3 - charging with a more powerful current through a stationary one;
- Mode 4 are already DC charging stations.
The current DC charging standard for electric vehicles is designed for batteries with an operating voltage of 450 V. This is the current vision of the situation by electric vehicle designers. But studies are already underway showing that to increase the efficiency and driving performance of electric vehicles, it will be necessary to increase the battery voltage, up to 900 V. It is also expected that batteries in electric vehicles will be replaced by supercapacitors soon. Both events will require rework or simply replacement of DC charging station equipment. At the same time, AC charging stations will be able to service both 900V battery-powered cars and supercapacitor electric vehicles without any problems. Therefore, the development of networks of charging stations on the alternating current will be of interest to investors for a long time to come. Such stations are not only inexpensive but also protect the investment, as they are compatible with the electric vehicles of the future.