What is the role of an on board charger?

Above all, the on-board charger allows you to control the current and voltage at which the battery needs to be charged (Voltage or Current Control Mode), thus taking care of the battery lifespan.

The charger offers either constant current or constant voltage charging, both of which are easy to operate. And each of them has its advantages and disadvantages. In the case of constant current charging, there is high efficiency and charging speed, but there is a risk that the battery will be overcharged at a later stage, and its lifespan reduced. In the case of constant voltage charging, there is a risk that too much current will flow into the battery from the beginning, which will heat the battery too much and shorten its lifespan again.

Thus, the charger ensures that it is initially charged with a constant current, thus maintaining speed and efficiency, and when the voltage at both ends of the battery reaches a certain amplitude, it changes to constant voltage charging. This system is called the charging strategy and it is the most important function of the on board charger.

What types of on-board chargers are there?

On-board chargers can be divided according to how many phases they can use (whether one, two or three) and according to their output. The power output of on-board chargers is usually in the range of between 3.7 kW and 22 kW. These two characteristics determine the charger’s price and therefore the price of the whole electric car.

Prospects for the future

Since the charging speed of an electric car always depends on the power of the weakest link, there is a tendency towards increasingly powerful on-board chargers. Current research focuses mainly on reducing the dimensions and weight of the charger with an emphasis on high energy density, high charging efficiency and good heat dissipation.

Research into the first part of the charger (PFC phase) is well advanced and currently achieves efficiency of 98%. So the overall efficiency depends mainly on the design and efficiency of the DC-DC converter in the second phase.

And in addition, electric cars are also equipped with their own power train, which is also able to change the current from AC to DC. But about its functions and future next time in our article on powertrains.