DCDC-converter (12 V / 24 V / 48 V / 400 V / 800 V)

  • Although power-hungry components (motor, heating, possibly air conditioning) of electric cars are supplied with the system voltage of the HV network (400 V or 800 V), electric cars still have a low voltage system as well. Mostly 12 V, in some 24 V or even 48 V. This is also live when the car is switched off. It is responsible for ensuring that the HV network can be started up again when the car is switched on. For safety reasons, the HV network is only active when the vehicle is driving or charging.


    Of course, all on-board computers and comfort systems are also powered by low voltage. Radio, navigation system, all lights, heated seats and everything else are also connected to this. To supply the starter battery with power, there is a so-called DCDC converter. Its job is to convert the HV voltage from the driving battery into low voltage in order to then charge the starter battery. This DCDC converter always recharges the starter battery when the HV network is active. Meaning when charging the car and when the car is turned on. In some electric cars, the HV network is also switched on when the 12 V battery goes undervoltage and there is a risk that the car will no longer be able to start if you wait any longer. This happens, for example, if the vehicle has not been driven for weeks or months.

    To ensure that this does not happen while a workshop is working on the vehicle, there is the service disconnect and interlock circuit.


    In early vehicles with an 800 V network there is also a second DCDC converter, which makes it possible to charge at 400 V charging stations. These charging stations are rare now, but they still exist. In more modern vehicles there is no longer a DCDC converter for this. From an electrical point of view, the 800 V battery consists of two 400 V batteries. Depending on whether you are charging at a 400 V charging station or at an 800 V charging station or whether you want to drive, the car then connects both 400 V battery modules in series (-> 800 V system voltage) or in parallel (-> 400 V system voltage).

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