The model train transformer is an essential part of the electric toy train and model train kits and without one, the trains will simply not work. This article is ideally suited for someone who is just starting out on train kit building and who still maybe confused about the train transformer.
This is basically how a model train transformer works: 1) The model train transformer is plugged into the wall using a standard 220 volt single phase wall socket (it maybe 110 volts in some areas). The transformer then "transforms" or "changes" the dangerous 220 volt power into a safe level of 12 to 24 volts (normally), depending on type of system. Some systems such as Lego have used 9 volt systems, but which ever one you use, the train transformer converts it down to a safe level so that you do not get an electric shock when using it.
2) The power goes from the transformer down one of the cables to the train track (normally there are two cables) and then connects to the train through the locomotive metal wheels touching the track. This causes the electric motor within the locomotive to turn and the power then continues to the other track and back to the transformer via the other cable. The train completes the connection between the two rails.
3) Note that there are some 3 track systems such as Lionel and Ives and they work in a similar way, except that they take their power from the center rail and pass the current back to the tracks through the outside 2 rails. 4) A model train transformer is also used to power the accessories on the track such as crossing gates, signals, electrical coupling systems and the like although they do not use the same transformer as the train generally. So make a note that you will need more than one transformer if you are adding accessories.
5) If you have a larger model train kit, you will no doubt be using a block control system. This divides up the model into areas or "blocks" and each block is controlled by one transformer. Only one train can run on each block. 6) The final type of system is called DCC or Direct Command Control and is a sophisticated control system that uses one model train transformer generally and sends signal through the tracks to each individual train.
It is important that you understand how to use your train transformer correctly as it will affect the whole running of your model. As the kit grows and you start putting in turnouts (or the point switching systems) to move your train from one track to another track, you will not only need more than 1 transformer, you will also need to use plastic insulating joiners between rails so that the two transformers do not both supply power to the same part of track.
Sources: http://www.youtube.com/watch?v=CTbHXPB6z30 http://ezinearticles.com/?Model-Train-Transformer---6Steps-to-Understanding-How-They-Work&id=3796136