The paper presents the function of the starter-generator SG-10-1S as a secondary electric starter of the M-84 tank. The basic principle of the operation of the most basic standard example of an direct current electric motor was outlined and through the operation of the diversity of it and the startergenerator SG-10-1S is described. Through the images of the 3D model of the starter-generator its fundamental parts are shown and their function explained. The SG-10-1S is more complex than traditional electric starters in the automotive industry, as it is both a starter and a generator of electricity for a tank consumption system. The principles of operation through these two modes of starter and generator are described and shown in the electrical diagrams of the tank automation for an easier understanding. Finally, some of the basic failures, their prevention and ways to eliminate them are listed.