DC Generator or DC Dynamo

D.C. generator is a device which converts mechanical energy into electrical energy.

Principle

It is based on the principle of electromagnetic induction i.e. whenever the amount of magnetic flux linking coil changes, an e.m.f. is induced in the coil.

Construction

A D.C.generator has the same parts as that of A.C. generator except for the slip ring which is replaced by split rings or commutator.

The main components of d.c. generator are:

1. Armature
   Armature coil (ABCD) consists of a large number of turns of insulated copper wire wound over a soft iron core.
2. Strong field magnet
   The armature is rotated in a strong uniform magnetic field provided by powerful permanent magnet NS. The axis of rotation is perpendicular to the field.
3. split rings
   The two ends of the armature are connected to a split rings R₁and R₂. The split rings convert alternating voltage into direct voltage across the brushed
4. Brushes
   The two carbon brushes B₁and B₂are pressed against the split rings.

Working

Working of d.c. the generator is almost similar to a.c. generator. Let the plane of the armature coil is perpendicular to the magnetic field. At this position, the e.m.f. across the load is zero.

Now, the coil is rotated through 90^oanticlockwise, the brushes B₁and B₂are in contact with the split rings. The plane of the coil is along the magnetic field and hence maximum e.m.f. is produced in the coil. This e.m.f. is obtained across the load. The direction of induced current is anticlockwise according to Fleming’s right-hand rule.

Again the coil is rotated through 90^o. Now from the brushes B₁and B₂lose their contact from the split ring or commutator and the e.m.f. across the load is zero.

The coil is further rotated through 90^o. Now the brushes B₁is pressed against R₂and B₂against R₁. Thus, it is seen that the direction of induced e.m.f. or current at any position in the coil is same.

The e.m.f. or currently is not smooth as desired. However, the output can be made smooth if another coil of same dimensions as that of first is fixed on the same axis of rotation. These two coils are kept in such a way that their planes are at right angle to each other. Besides, each coil works independently and sends its own current into the load. Thus by increasing the number of coils and the corresponding split rings or commutator, nearly unidirectional smooth current can be obtained across the load.

Reference

Manu Kumar Khatry, Manoj Kumar Thapa, Bhesha Raj Adhikari, Arjun Kumar Gautam, Parashu Ram Poudel.Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.

S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.