A system comprising a direct current power source and a controlling unit for controlling an electrical power system in a motor driven vessel or vehicle, the power system comprising the direct current power source which comprises a direct current power generator comprising an engine driven dynamo combined with one or more first battery assemblies, the power system being configured for delivering power to an alternating current power consuming device, the alternating current power consuming device being an electrical driving engine in the motor driven vessel or vehicle and driven by modulatable multiple phase alternating output current at a first voltage provided by the controlling unit, the controlling unit comprising: a. an electrical current transformer, capable of transforming direct input current of the first voltage to modulated multiple phase alternating output current, b. multiple outlet conductors for connecting the transformer to the alternating current power consuming device, the outlet conductors being designed to deliver modulated multiple phase alternating current from the transformer to the electrical power consuming device in a monodirectional way, c. command input means to receive controlling commands from a controller interface, designed to modulate the electrical power to be delivered to the alternating current power consuming device by the transformer, d. battery power input means designed to receive direct electrical current from a second battery assembly having the first voltage for conducting said direct current to the current transformer in a monodirectional way, e. direct current power source input means for receiving direct current from the direct current power source in a monodirectional way, f. a voltage converter, the voltage converter being connected to the direct current power source input means, the said direct current power source input means being designed to receive said direct current power from the direct current power source at a second voltage in a monodirectional way, the second voltage being lower than the first voltage, the voltage converter being designed to convert the direct current power of the second voltage received by the direct current power source input means to converted direct current power having the first voltage, g. first conducting means connecting the voltage converter to the current transformer in a monodirectional way, allowing the converted direct current power having the first voltage to be received by the current transformer, and h. second conducting means connecting the voltage converter to a converted direct current power outlet, designed to be connected with the second battery assembly and to allow the converted direct current power to be received by the second battery assembly in a monodirectional way a. an electrical current transformer, capable of transforming direct input current of the first voltage to modulated multiple phase alternating output current, b. multiple outlet conductors for connecting the transformer to the alternating current power consuming device, the outlet conductors being designed to deliver modulated multiple phase alternating current from the transformer to the electrical power consuming device in a monodirectional way, c. command input means to receive controlling commands from a controller interface, designed to modulate the electrical power to be delivered to the alternating current power consuming device by the transformer, d. battery power input means designed to receive direct electrical current from a second battery assembly having the first voltage for conducting said direct current to the current transformer in a monodirectional way, e. direct current power source input means for receiving direct current from the direct current power source in a monodirectional way, f. a voltage converter, the voltage converter being connected to the direct current power source input means, the said direct current power source input means being designed to receive said direct current power from the direct current power source at a second voltage in a monodirectional way, the second voltage being lower than the first voltage, the voltage converter being designed to convert the direct current power of the second voltage received by the direct current power source input means to converted direct current power having the first voltage, g. first conducting means connecting the voltage converter to the current transformer in a monodirectional way, allowing the converted direct current power having the first voltage to be received by the current transformer, and h. second conducting means connecting the voltage converter to a converted direct current power outlet, designed to be connected with the second battery assembly and to allow the converted direct current power to be received by the second battery assembly in a monodirectional way