Myths and rumors

Throughout the electrical and electronic world, there are a multitude of inaccurate stories about how things work, that complicate things and intimidate potential users of some equipment or ideas. Some are due to ignorance, some are an attempt to appear knowledgeable, and some are just fun, harmless stories. We will make an attempt here to correct some of the more common ones.

Conductor Properties - There are concerns that Direct Current (DC) flows on the outside of a wire only. There would be no reason for that to occur at any amount of voltage or current. The amount of electrons in a conductor does not increase when current is flowing, they merely move. Electrons move relatively slowly through a conductor (certainly not at the speed of light as some think) and should the voltage be increased, they are forced to move faster. Consequently, there is no tendency for the electrons to be adversely affected by the electrons around them. The larger the wire, the more electrons are present so, consequently, the resistance to the current flow decreases.

In Alternating Current (AC) there is a phenomenon called "skin effect" that does cause the current to move toward the outside of the wire as the frequency of the AC increases. This has caused some concerns, rumors and even phony formulas about the effect on DC conductors. There is no skin effect in DC conductors. While DC circuits do have inductance (electrical inertia), they do not have the property of inductive reactance present in all AC circuits. Skin effect is caused by the inductive reactance being created unevenly through the wire causing the inner part of the wire to oppose current flow to a higher degree than the outside. This effect gets more and more noticeable as the frequency of the AC increases until eventually, at very high frequencies, the majority of the current travels near the surface of the conductor. Since even pulsed DC never actually reverses direction, it has no inductive reactance and the inductance that is there has only a smoothing effect. Needless to say, skin effect does not affect model train operation.

Track Switch (turnout) Motors - There is a rumor that the motors that control the switches in a track layout will be adversely affected in some way by operation on AC or smooth DC. While the application of AC directly to the motor could, after a while, weaken the motor's internal magnet (it would never move anyhow), there is no reason to suspect that DC operation would ever adversely affect the motor or the switch itself, and the voltage necessary for reliable operation is only half of conventional control methods. The switches on the TP&W have always operated on DC.

Motors and PWC (PWM) - There are always rumors that certain common type motors, as well as some sound systems, will be permanently damaged by the use of some power supplies utilizing Pulse Width Control. Most of these stories are false. Most brush type motors actually run better on PWC. However, check with the manufacturer. If they say you should only use one certain type of supply with their stuff, then buy another brand of stuff until they get around to fixing their problem. This kind of thing was acceptable in the last century, but not anymore.

	Myths, Magic and Rumors Throughout the electrical and electronic world, there are a multitude of inaccurate stories about how things work, that complicate things and intimidate potential users of some equipment or ideas. Some are due to ignorance, some are an attempt to appear knowledgeable, and some are just fun, harmless stories. We will make an attempt here to correct some of the more common ones. Conductor Properties - There are concerns that Direct Current (DC) flows on the outside of a wire only. There would be no reason for that to occur at any amount of voltage or current. The amount of electrons in a conductor does not increase when current is flowing, they merely move. Electrons move relatively slowly through a conductor (certainly not at the speed of light as some think) and should the voltage be increased, they are forced to move faster. Consequently, there is no tendency for the electrons to be adversely affected by the electrons around them. The larger the wire, the more electrons are present so, consequently, the resistance to the current flow decreases. In Alternating Current (AC) there is a phenomenon called "skin effect" that does cause the current to move toward the outside of the wire as the frequency of the AC increases. This has caused some concerns, rumors and even phony formulas about the effect on DC conductors. There is no skin effect in DC conductors. While DC circuits do have inductance (electrical inertia), they do not have the property of inductive reactance present in all AC circuits. Skin effect is caused by the inductive reactance being created unevenly through the wire causing the inner part of the wire to oppose current flow to a higher degree than the outside. This effect gets more and more noticeable as the frequency of the AC increases until eventually, at very high frequencies, the majority of the current travels near the surface of the conductor. Since even pulsed DC never actually reverses direction, it has no inductive reactance and the inductance that is there has only a smoothing effect. Needless to say, skin effect does not affect model train operation. Track Switch (turnout) Motors - There is a rumor that the motors that control the switches in a track layout will be adversely affected in some way by operation on AC or smooth DC. While the application of AC directly to the motor could, after a while, weaken the motor's internal magnet (it would never move anyhow), there is no reason to suspect that DC operation would ever adversely affect the motor or the switch itself, and the voltage necessary for reliable operation is only half of conventional control methods. The switches on the TP&W have always operated on DC. Motors and PWC (PWM) - There are always rumors that certain common type motors, as well as some sound systems, will be permanently damaged by the use of some power supplies utilizing Pulse Width Control. Most of these stories are false. Most brush type motors actually run better on PWC. However, check with the manufacturer. If they say you should only use one certain type of supply with their stuff, then buy another brand of stuff until they get around to fixing their problem. This kind of thing was acceptable in the last century, but not anymore.

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