What Is Overload in Diesel Generator?

All electric generators have a maximum capacity based on two things—the capacity to generate electricity, and the engine that drives that generator.

The greater the load, the more work the engine must do. 1 horsepower is about equivalent to 746 watts. If your motor is capable of one horsepower, the maximum power you can generate is 1 horsepower minus the mechanical losses of turning the generating unit.

Generators are protected by circuit breakers that allow a few seconds of very high current, but will trip if the current stays high for too long. This “surge” allows the generator to start motors which require higher current to go from Zero RPMs to running speed.

The main breaker is sized in accordance with the generator’s ability to produce current without burning itself up.

Example

A Kubota Diesel Generator rated at 12,000 watts (12 kilowatts) has a surge capacity of 14 kilowatts. It is powered by a Kubota D902 3-cylinder diesel engine rated at 20.4 horsepower (or a little more than 15,200 watts).

For a few seconds, this generator tolerates a surge load of 14,000 watts, but to operate continuously it at that level will cause harm to the generating unit because it is overloaded. The voltage will also drop off up to 30 percent and may take up to two seconds to recover once the load drops back in the rated capacity.

At no point will the generator output go much beyond 14,000 watts. The engine’s alternator and water pump, and the mechanical inefficiency of the machine, use up whatever power remains between 14,000 and 15,200 watts. The circuit breaker will trip at higher current draw.

Overload

Operating the generator beyond the rated capacity of the generator causes an overload condition because the generator is overloaded by the demand placed upon it. The breaker will trip. Generator’s with a microprocessor-based controller display the overload condition.