Reasons for dual power supply and DC low voltage in automotive electrical systems

When you say dual power supply, do you mean generator and battery?

When the car is working, the electrical load is heavy and needs to be powered by a generator, which cannot be driven by the battery alone.

The battery is used to power some of the electrical equipment in the car when the engine is off, as well as to power the electric ignition when the engine is started, a process that consumes battery power very quickly, so there is a generator to charge the battery after the ignition is on.

The reason for the use of DC low voltage is to reduce the electrical insulation standards and reduce personnel injuries.