DC MOTOR AND ALTERNATOR CONSTRUCTION
The D.C motor gets current from the battery to turn the alternator ordinarily, an electric motor is a machine which converts electric energy into mechanical energy. its action is based on the principle that when a current carrying conductor is placed in a magnetic field , it experience a mechanical force whose
direction is given by Fleming’s left hand Rule and whose magnitude is given by F=BIL Newton
Where b =magnetic flux
L =Length of the conductor
Constructionally, there is no basic different between a dc generator and a dc motor. In fact the same DC machine can be used interchangeably as a generator or as a motor. D.C motors are also like generator, in that they can be shunt wound or series wound or compound wound.
For the construction of the 2.5KVA fuelless generator, a D.C motor of 4hp is used because it produces a speed greater than the alternator speed and this makes it to drive the alternator.
NOTE: The alternator will not rotate if the speed of the D.C is lesser than the alternator speed.
AC generator or alternators (as they are usually called) operate on the same fundamental principles of electromagnetic induction as D.C generators. But there is one important different between the two; Whereas in D.C generators ,the armature rotates and the field system is stationary, the arrangement in alternator
is just the reverse of it .In their case standard construction consists of armature winding mounted on a stationary element called stator and field windings on a rotating element called rotor. Alternator comes in different sizes , revolution per minute [R.P.M], single phase and three phase.
Alternator has low speed and high speed ,low speed alternators such as those with power rating of 3.5KVA and above operated with diesel engine always have a revolution of about 1,500 rpm to 2,500 rpm. High speed alternators on the other hand have rpm of 2,500 to 6,000 and they are normally operated with premium motor spirit (fuel) engine. With this a low speed alternator needs a low speed device to rotate it for it to give 230vac.
The alternator size used for the construction is 1.5KVA, 4pole with a speed of 1,500 rpm and that is why a dc motor of 4hp, 3,000 rpm is needed to rotate it.