Transformers

One of the most useful devices that rely upon the Mutual Inductance effect is the Transformer. The Transformer is capable of transforming energy from one circuit to another without a direct connection. It is comprised 2 coils of wire wrapped around an iron core. The input coil is known as the Primary and the output coil is referred to as the Secondary. Electrical energy (voltage) is supplied to the primary causing a change in magnetic field at the iron core. The magnetic core enhances the mutual inductance between the coils. This causes an electric field, which induces an output at the secondary. The transformer is an alternating current (ac) device only. See sketches  below.

Top sketch is a physical representation & the bottom one is the schematic representation.

Mathematical Relationships associated with Transformers -

The input voltage to the primary and the output secondary voltage relate as follows:

Vsec = Vpri multplied by (Nsec/Npri)  where:

Vsec = the secondary output voltage

Vpri = the primary input voltage

Nsec = number of turns in the secondary winding or coil

Npri = number of turns in the primary winding or coil

Example:

If  Vpri =120 vac;

Nsec = 100 turns;

Npri = 10 turns;

Then Vsec = 120(100/10) = 1200 vac

Note that if  in the above sketch we can consider the Secondary as a Primary and vice-versa, we get inverse results. In other words 1200 vac input will result in 120 vac output.

The input current to the primary and the output secondary current relate as follows:

Ipri = Isec  (multplied by (Nsec/Npri)  where:

Isec = the secondary output current

Ipri = the primary input current

Nsec = number of turns in the secondary winding or coil

Npri = number of turns in the primary winding or coil

Example:

If  Isec = 1 amp

Nsec = 100 turns

Npri = 10 turns

Then Ipri = (1)(100/10)  =10 amps

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

In the Model train hobby, Transformers can be used in lighting applications as a source of voltages.
Point Of Interest:  The Lionel O gauge trains use a power pack which contains a transformer of the variable type.

In general, the following vendors are recommended for any of the above electronic components:

Radio Shack (Local Store or on-line at  www.radioshack.com)

Futurlec at  www.futurlec.com

DeMar Electronics at  www.demarelectronics.com/