DC Generator

First of all it is necessary to familiarize with the concept of term "generator". A generator is an electro-mechanical machine/device which converts mechanical energy into electrical energy. There are two types of generators based on their output. If the output of the generator is AC (Alternating Current) then the generator is known as AC Generator whereas if the output of the machine is  DC (Direct Current) then the same is known as DC Generator.

Marine DC Generator
Photo Credit - www.polarpower.com

A dc generator converts the mechanical energy to DC electrical quantity. This energy conversion is based on the principle of production of dynamically induced emf. Whenever a conductor cuts magnetic flux, dynamically induced e.m.f. is produced in it according to Faraday's Laws of Electromagnetic Induction. This e.m.f. causes a current to flow if the conductor circuit is closed.
A simple DC generator consists of the same basic elements as a simple AC generator: i.e., a multi-turn coil rotating uniformly in a magnetic field. The main difference between a DC generator and an AC generator lies in the manner in which the rotating coil is connected to the external circuit containing the load.