Different types of power.
There two types of power you can supply to the tracks, each type has its own varieties but still come down to the same basic concepts. You either run your layout using a conventional DC supply or use a more modern DCC supply. You must not, as you will see, use both systems at the same time.
Each locomotive may vary in shape, size and design but they all rely on the same basic principle. The locomotive is split into two halves, one side picks up one rail whilst the other side picks up the other rail, at no point must the two sides touch or be connected except through the motor pick ups. If there should be other contact apart from the motor you will create a short circuit and may cause severe damage to the locomotive, so before you do any alterations to a locomotive make sure your are aware of its electrical needs.
Conventional DC supply.
The basic DC supply, as its name states, supplies a Direct Current to the two rails, one being the positive and the other being the negative. The power usually comes from a power box consisting of a transformer to reduce the 240v to 12v, a rectifier to convert the 12v AC to 12v DC and a means of altering the level of this 12v DC to the layout, as well as a means of changing over the polarity for use as a direction switch.
There are several versions of conventional DC controller. The simplest type, the variable resistance controller, a variable resistance is placed in series in the 12v DC output from the transformer and rectifier. This resistance takes part of the voltage, wasting it in the form of heat, leaving the remainder for the locomotive. More resistance means less voltage to the layout, the disadvantage of this is it total relies on total resistance, this includes the motors of locomotives and any wiring. So each locomotive will act differently to the same setting on the controller plus there is little chance of getting a slow, smooth start.The variable transformer type of controller overcomes the basic failing of the resistance type. Here the voltage is directly controlled and the voltage selected determines the speed of the motor. Variations in load do not effect the speed as the extra load is automatically provided by the transformer. As no voltage produced is wasted, there is less heat and the locomotives will maintain a steady speed despite variations in gradients.
The most recent type is the transistor controller. These are vary efficient and produce an almost constant output regardless of load and hence current. In units of this type very sophisticated control can be produced by electronic means. This include the ability to represent inertia and weight of prototypes with slow acceleration and braking. Also with the advancement in the electronics this are no very small.
DCC is the modern way of controlling locomotives. This system does require adapting the locomotive but you can buy these now already adapted. DCC stands for Digital Command Control. The way DCC varies from coventional DC is that it powers the layout using a 12v AC supply. The 12v AC supply is picked up by the locomotive, goes through the decoder, is coverted to DC and pulsed to the motor at 12v DC.
The decoder which sits in the locomotive is fully programmable, this can include identification, acceleration, braking, maximum speed, lights and sound if capable. The decoder will pick its signal up from the signal which is sent out on top of the 12v AC supply, so you actually have two outputs from the main controller. The benefit of DCC is you control the individual locomotive not the layout. This allows you to individually control a number of locomotives on the same piece of track.The disadvantage of DCC is the initial expense, as the equipment is more advanced it costs more. You will also need a means of programming decoders if you want to take full advantage of their capabilities. There is one major bonus though, as you can individually control locomotives the need for sectioning and additional wiring is gone. The layout may only ever need two wires to it.
The wiring rules are the same as DC but they are not treated as a positive and negative, as its AC, but as rail A and rail B, these should only ever meet via the locomotives motor.