A diesel generator is driven by a diesel engine. When useful electrical appliances are connected, the internal coils of the generator and external electrical appliances form a circuit, which generates current. If there is current, electromagnetic resistance torque will be generated. Energy is conserved, and the amount of resistance torque used will require additional work. For a generator with stable speed, more work done by electromagnetic resistance means a greater resistance torque. Simply put, the higher the power of the electrical appliances, the harder it is to rotate. When no electrical appliances are used, there is no current inside the generator coil, and the coil generates electromagnetic resistance torque. However, the bearings and belts of the generator will have resistance torque, which also consumes the power of the diesel engine. In addition, the diesel engine itself is a four stroke engine, with only one power stroke. Maintaining its idle operation also requires fuel consumption. As an internal combustion engine, the efficiency of the diesel engine itself is also limited.

When the power of the generator is high and the power of the electrical appliances is low, the power loss may be greater than the power of the electrical appliances. It is difficult to reduce the power of a diesel engine, so the power of a diesel generator is only a few kilowatts. For electric tools with several hundred watts, this load can be ignored. The above confirms that the fuel consumption with and without appliances is similar.