Otis Singleton
Electric trains are powered by electricity from overhead lines, a third rail, or onboard energy storage like batteries. The simplest version of an electric train involves a sliding wire collecting electric power from overhead lines, which is then fed to a single-phase induction motor connected to the wheels. This basic design can be improved with axle brushes, which transfer current to the wheels through carbon brushes. To ensure efficient power transmission, voltage from the overhead line is stepped down using a transformer. This transformed voltage is then fed to the motor, completing the circuit. Electric trains also benefit from regenerative braking, which recovers kinetic energy during braking and puts it back onto the line. Power supply to each coach within a train can be achieved through self-generation or head-on generation methods. When wiring a model electric train, considerations include the type and size of wiring, wiring connections, and complex wiring situations for multiple trains or functions like parking and reversing.
| Characteristics | Values |
|---|---|
| Power Source | Overhead lines, third rail, or on-board energy storage |
| Overhead Line Voltage | 25 kV |
| Motor Voltage | Much less than 25 kV |
| Motor Type | Three-phase induction motor |
| Power Conversion | Three-phase power conversion |
| Braking System | Pneumatic braking system, regenerative braking |
| Wiring Type | AWG (American Wire Gauge) |
| Wiring Size | 1 AWG (large), 14 AWG (smaller) |
| Track Construction | Parallel steel rails, bolted or welded, with gravel or concrete ballast |
| Track Gauge | Typically 4 feet, 8.5 inches (1,435 mm) |
| Train Control | Throttle, reversing gear, brake |
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Power supply
Overhead lines are wires that supply electricity to the train from above the track. This method is widely used and allows for efficient power transmission. However, it requires careful design and installation to ensure the wires are properly suspended and maintained.
The third rail system involves using a separate rail, in addition to the two running rails, to provide electricity to the train. This rail is typically located outside the running rails and supplies power through contact with the train's shoes or a sliding wire. While this system is simpler and more economical for shorter lines and urban systems, it has limitations in terms of speed and coverage.
On-board energy storage, such as batteries or supercapacitors, is another option for powering electric trains. This method eliminates the need for external power collection systems, providing greater flexibility and independence from infrastructure. However, the energy storage capacity and efficiency of the system are important considerations.
The power supply for each coach's utilities can also be achieved through self-generation. This involves mounting an alternator under the coach frame, driven by a cardan shaft and gearbox mounted on the axle. The output charges a battery, providing a continuous power supply. However, this method may produce fluctuating output power and is less efficient for supplying power to the entire train.
Additionally, electric trains use AC or DC power. AC power is ideal for long-distance transmission due to its ease of boosting voltage and transmitting over longer distances. On the other hand, DC power is preferred for shorter lines, urban systems, and tramways, but it requires a heavier transmission medium and can experience voltage drops.
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Overhead lines
The simplest version of an electric train collects electric power from the overhead lines using a single sliding wire. This power is then fed to a single-phase induction motor, which is connected to the wheels. To complete the circuit, the other terminal of the induction motor is grounded. This grounding connection is made possible by first connecting the wire to the wheels through an axle brush. The wheel is always in contact with the track, and the track is grounded.
Another way to supply power to the coaches is through head-on generation. In this method, an extra winding is added to the locomotive transformer, which supplies power to all the coaches. This method is more common than self-generation, as self-generation produces fluctuating output power. In the self-generation method, an alternator is mounted under the coach frame and driven by a cardan shaft and gearbox mounted on the axle. The output is then rectified and used to charge a 110V DC battery, creating a continuous power supply to the coaches.
The type and size of wiring used are also important considerations. American Wire Gauge (AWG) is the standard used to determine the size of the wiring, with Number 1 AWG being a large size and 14 AWG being smaller. When wiring a simple layout for a single operating train, two wires from the power pack to the track may be sufficient. However, the train's speed may vary depending on its distance from the power pack due to voltage drop. Running feeder wires from the bus to the track, spaced 2-3 feet apart, can help achieve a more even flow of electricity and smoother train control.
Modern shoe systems have remote lifting facilities, which can be used in emergency situations when a shoe breaks off and needs to be isolated from the electrical equipment. Most types of top contact shoes hang from a beam suspended between the axle boxes of the bogie. Soldering can be used to attach the wire to the rails and connect feeder wires to a bus wire. Suitcase connectors, wire t-tap connectors, and spade connectors are also options that do not require soldering and can be easily removed if needed.
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Axle brushes
The brushes are fitted to the rotating wheel, with the current transferred through these brushes, which slip over a disk attached to the wheel axle. This design is simple yet effective and is the standard for electric trains. The brushes are made from a mix of copper and graphite powders, with a high copper percentage to ensure low electrical resistance and the ability to carry a high current without damage.
The flow of current through axle bearings can cause significant issues, reducing the lifetime of the bearings and impacting the safety and reliability of the train. Axle brushes are therefore crucial in preventing this issue, acting as a protective device by directing the current through the axles and wheels, bypassing the bearings. This is known as an Earth Return Current Unit (ERCU).
The number and size of brushes can vary, with different configurations depending on the type of train. For instance, the ERCU can have between one and four brushes, with dimensions ranging from 12.5x32mm to 25x50mm. The brushes are designed to be accessible and easily removable for maintenance and replacement, as periodic changes are necessary to ensure optimal performance.
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Step-down transformers
Electric trains are powered by electricity from overhead lines, a third rail, or onboard energy storage such as a battery. The power collected from the overhead lines flows through the wheels and ends up in the grounding cable of the track. The simplest version of an electric train uses a single sliding wire to collect electric power from the overhead lines, which is then fed to a single-phase induction motor.
However, the voltage used in the overhead line can be as high as 25,000 volts, while motors require much less voltage to run. This is where step-down transformers come into play.
A step-down transformer is a device that reduces voltage and increases current. It transforms voltage and current values in the same way that gear tooth ratios in mechanical gear systems transform values of speed and torque. The voltage "step-down" effect is achieved by having more turns of wire in the primary coil than in the secondary coil, with the specific ratio determining the extent of the step-up or step-down.
For example, a 10:1 ratio of primary to secondary wire turns would result in a tenfold decrease in voltage and a tenfold increase in current. This device is incredibly useful as it allows for the multiplication or division of voltage and current in AC circuits, making long-distance transmission of electric power possible.
Transformers are designed to operate in a specific range of voltage and current, and attempting to use them outside of this range can lead to inefficiency or damage. They are constructed in a way that makes it difficult to distinguish between the primary and secondary windings, so it is important to exercise caution when working with transformers.
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Track wiring
Firstly, decide on the type and size of wiring to use. The standard measurement for wiring is the American Wire Gauge (AWG). The number of the AWG indicates the size of the wire, with lower numbers indicating larger wire sizes. For example, 1 AWG is larger than 14 AWG.
Next, prepare the feeder wires. These are the wires that will connect the track to the bus, which carries the electrical current. Use 18 AWG solid wire, and space the connections roughly every 6 feet. Each connection will consist of a pair of two feeder wires, one on each rail. Strip about half an inch of insulation off the end of the wire and make a small "L" at the end. This bend will make it easier to attach to the rail.
Drill a hole for the feeder wires next to the track and through the roadbed. Use a 3/32" drill bit to reduce the chance of damaging the track. Feed the wire through the hole and bend it to prepare for soldering. Solder the feeder wires to the track and the bus, ensuring a secure connection. You can also use rail joiners with attached wires, but soldering is a more reliable method.
For a smoother train control experience, consider using bus wiring. Install a heavier bus wire following the track, and run the feeder wires from the bus to the track, spaced 2-3 feet apart. This will ensure a more consistent electrical flow and reduce voltage drop-off as the train moves away from the power source.
Finally, test your wiring. Connect the power source to the bus and turn on the electricity. Listen for any short-circuit alarms and adjust as needed. You can also test the voltage by attaching a wire to the common and voltage output terminals and plugging the cord into an electrical outlet.
With these steps, you should be able to successfully wire your electric train track and have it running in no time!
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Frequently asked questions
An electric train is a locomotive that is powered by electricity from overhead lines, a third rail, or onboard energy storage such as a battery or a supercapacitor.
Electric trains use electric traction instead of gears as electric traction is much more flexible than gears. The electricity is supplied through a third insulated rail between the tracks or from overhanging wires. The electricity then flows through the wheels and ends up in the grounding cable of the track.
AC is used for long-distance transmission due to its ease of boosting voltage and transmitting over long distances. On the other hand, DC is preferred for shorter lines, urban systems, and tramways. DC also requires a heavier transmission medium like a third rail or a thick wire.
For a simple layout with a single train, two wires from the power pack to the track may be sufficient. However, for more complex layouts with multiple trains, parking, reverse loops, or Wye's, additional wiring and considerations are needed. The type and size of wiring, such as American Wire Gauge (AWG), should also be considered.
One way to supply power to each coach is through self-generation, where an alternator is mounted under the coach frame and driven by a cardan shaft and gearbox. Another method is head-on generation, where an extra winding is added to the locomotive transformer to supply power to all coaches.
