How does a 2 rail system work? I understand a 3 rail, pretty straight forward, power in the center rail, two outside rails ground, but how can a 2 rail do the same? Thanks, Jake
Power on one rail, return on the other. AF used two rail AC, most two rail systems do use DC in which one rail is positive and the other negative. This means track geometry beomes problematic when you try to create a revering loop and you will need some type isolation and electrical switching to avert short circuits when/where the track will cross back on themselves.
By the way, the right-hand rail is positive when going forward.
And the wheels must be insulated from each other, too.
Very important point. This is why you can’t just take three rail rolling stock and use it on a two rail system without modifying wheelsets (unless you already use plastic wheels).
3 rail is to 2 rail as a lamp is to a car battery…
Alternating current, electricity flows both ways. i.e. “Alternating direction”
Direct current only travels in one direction, i.e. “unidirectional”
But there is no reason why either number of rails must be used with either kind of voltage. American Flyer uses AC with two rails; and Lionel has used DC with three rails.
So an engine must have some sort of seperation between wheels or sides of the loco? What about cars? Seems as if a regular metal car would short itself out somehow. I don’t know why after all these years I want to know, but it bothers me I do not understand. Jake
Any three rail metal wheeled car can not be used on a two rail system, the wheels will short out. Modern cars usually have delrin pockets for the needle point axles so they won’t short out even if you have die cast truck frames but you still need to isolate the left and right wheels. Higher end two rail wheel sets use metal wheels and either isolate the axles from the wheels (plastic sleve) or use plastic axles.
The two rail as stated can be either AC or DC. Typically the “outside” rail is the “base” or common.
There was an ingenious device called the 695 reverse loop rely that would allow you to create a revrse loop. It would change the polairity via a coil activated switch.
Jim
Normally the axle on one side passes through a plastic bushing that separates the metal wheel from the metal axle. Spacing on the axle is far enough from the truck sides or locomotive frame to prevent contact. Steam locomotive drivers may be rim insulated between the driver tire and the driver rim holding the spokes. This prevent the rods/valve gear from causing a problem for all metal locomotives, with plastic super structures this method isn’t required. Since insulation is usually only on one wheel, care must be taken to put all the insulated wheels on the same side. For cars with metal floors, insulating metal couplers from the floor is required to prevent a possible short when coupling 2 cars together - plastic coupler boxes accomplish this for most couplers.
Some cheaper trucks use plastic wheels and/or axles to solve the problem.
Enjoy
Paul