When it comes to setting up a company's own charging infrastructure, fleet managers can't avoid looking at the different charging technologies for electric vehicles.
What is the difference between charging with alternating current and charging with direct current? Which method of charging is better? Should AC or DC charging stations be installed for the EV fleet? We answer these questions in this article.
AC and DC current
What do AC and DC mean?
AC and DC are two different ways that electricity can flow in a circuit.
AC stands for "Alternating Current." With AC current, the electrical power periodically changes direction. AC current is also called "standard current" because it is produced in large quantities in power plants and can be transported more easily than DC current. Alternating current flows out of every common household socket.
DC stands for "Direct Current". DC current always flows constantly in the same direction. The best-known example of a direct current source is the battery.
How does an electric vehicle battery work?
Like any battery, the electric vehicle battery requires direct current. The electric current is stored in the battery through a chemical process.
Storing alternating current in a battery is not possible because AC current periodically changes direction. If the battery were charged with AC current, it would charge during the positive half cycle and discharge during the negative half cycle.
The pole of a battery cannot change polarity at the same rate, which is why the EV battery needs a constant current supply.
AC and DC charging stations in the electric vehicle fleet
AC vs. DC: What is the difference in charging?
The power grid is supplied with alternating current (AC). The vehicle battery, however, requires direct current (DC). To achieve this, the alternating current must be converted into direct current.
To charge an EV with alternating current, it requires an on-board charger that converts the alternating current from the charging station into direct current. The integrated converter in the vehicle is limited in its power, so the EV is not charged very quickly. However, the advantage of AC charging is that, due to the low charging speed and the low amperage, the vehicle battery is not damaged, which has a positive effect on its lifetime.
In DC charging, the alternating current from the power grid is already converted into direct current at the charging station. The EV is therefore supplied directly with direct current, so that the current does not have to be converted in the vehicle. This has the advantage that the vehicle is fully charged within a very short time.
AC or DC charging stations for the vehicle fleet?
Should only AC or DC charging stations be installed for the vehicle fleet? Or should AC and DC charging stations be combined? These questions cannot be answered across the board.
Which charging stations are suitable for the fleet depends on the fleet size, vehicle types and vehicle usage. Generally speaking, vehicles that have a short dwell time should be charged with direct current (DC). Vehicles that have a longer dwell time at the site have the time to be charged with alternating current (AC).
If time is the most critical aspect of electric fleet operations, then DC charging stations are the best option. However, it must be kept in mind that DC charging stations are very expensive to purchase, as well as to operate – they have a high power output that must be taken into account when supplying power to the site: keyword grid connection overload.
If the vehicle fleet is mixed, then it makes sense to combine the charging infrastructure of DC and AC charging stations.
How charging management ensures that AC and DC charging stations are intelligently combined
One of the biggest challenges in fleet electrification is that charging operations are uncontrolled, and vehicle operations are not intelligently linked to energy management.
At IO-Dynamics, we have taken a closer look at this problem. The solution is intelligent charging management software that makes real-time decisions for the electric fleet. All charging stations at the site are automatically controlled depending on vehicle usage and capacity of the power grid.
In this way, our solution optimally combines fleet management and charging management. The IO-ELON platform provides an intuitive overview of the EV fleet and offers the possibility to manage all EVs and charging stations digitally and easily.
Intelligent charging management software helps the fleet management to efficiently and intelligently utilize the available energy for the operation of the EVs and to keep the energy costs as low as possible.
If the fleet is to be electrified, careful planning is advisable in advance. With a site simulation conducted in advance, essential questions can be answered such as: When should vehicles be charged at AC or DC charging stations? How many AC and DC charging stations does my site need?
Read here how simulation software can be used to analyze optimal electric fleet operations.