Brief Explanation of DCC

DC Train POWER: Until about 1990, most model trains were powered by "direct current" -the same stuff that comes from flashlight batteries. A "transformer" or power pack converted house current (AC) into DC, and fed it to the tracks. The amount of power being fed was controlled by the throttle (speed knob) on the power pack. No power -train doesn't move. Full power: train may fly off at a curve and land in your neighbor's outdoor grill. And so, the amount of power applied to the track is what ran the train slow or fast.

The Problem with DC: Sounds easy enough -until you put more than one loco on the track. They can't be controlled independently because they both are controlled by whatever power is applied to the track. Exactly the same as having two light bulbs controlled by one dimmer, or two garage doors controlled by one remote -they BOTH go up and both go down. So, on the railroad, one throttle (light dimmer) is powering 2 loco's with the exact same power setting going to both locos at the same time. And even though they both get the same amount of juice, one loco will go faster because it has a different motor in it, or maybe they'll run in opposite directions. Bottom line: it is a hassle. The solution is to put gaps in the rails so you have basically two isolated portions of track -and get a separate power pack for each section. But that gets complicated -and expensive.

How DCC is Different: But these days, there's a way to get around the problems of plain vanilla DC. Apply FULL power to the track ALL THE TIME, and THEN put little micro-chips (called "decoders") in each loco that control how much power the loco will use and which direction it will go. Talk to the decoders by sending commands to them through the rails. Give each decoder its own unique "address," so that ONLY the commands sent out to that address will control the loco where the decoder is located. Thus, decoder #1 won't respond to commands sent to decoder #2; and #2 won't do what you command #1 to do. This is like a set of remote control garage doors; each one has its own address, so the remote for door #1 won't open door #2, and vice-versa. Simple concept. BRILLIANT concept, in fact.

How DCC is Better: NOW you can have 2 or 50 locos on the same track, and as long as each has a decoder with a unique address, you can run each of them independently of the other. The power pack itself has an array of buttons sort of like a push-button phone -that's how you select an address. So, you punch in "301" to get one loco going, then punch in "401" to start another -and meanwhile, 301 just keeps doing the last thing you told it to do. And, as long as you've got decoders for the locos, why not use them to throw switches and do other things on the layout as well? Exactly -you use "stationery decoders" for those tasks -and they get their power from the rails, too -same as the locos. The rails, because they carry full power ALL the time, are really just like a circuit in your house or an extension cord.

Converting DC Locomotives to DCC: This is all very well and good -but what about the existing investment people already HAVE in plain DC operations? The answer is to retrofit existing DC locos with decoders, so they will now run on a DCC powered layout. And as a matter of fact, most DCC systems will allow you to run ONE (just one) DC loco while you also run DCC equipped locos at the same time.

Running DCC Equipped Locos on a DC Layout: Some decoders are made to sense what kind of rail power they are getting, and switch themselves to adapt to that kind of power. Such decoders may be programmed to allow or to forbid this auto-sensing feature. Other locos are equipped with a switch; flip one way for DCC, flip the other for DC. Still others won't tolerate DC power and can be spoiled by feeding them pure DC. Some DCC commandunits will allow a regular DC transformer to be "slaved" to the DCC unit so it can control one train. But generally, your old DC transformer can't be deployed to run DCC trains because it has no way to "talk" to the decoders. It CAN however, be used a source of power for other things -such as lighting or small DC motors which run accessories -like a merry-go-round or a crane. Bottom line: if you are just getting started, be SURE of the capability of your equipment.

Wiring for DCC: The wiring for DC and DCC is basically identical -two wires go to each of two rails; and so, you can usually swap out a DC transformer with a DCC unit, hook up the existing wiring -and everything should work. Well, of course it should -the electricity is still electricity, with the same physical properties it always has. In general, experienced modelers will install a main wiring system called a "bus" under the table. Each bus wire is attached to the terminals of the command unit or booster, same basic way you'd hook up a DC "transformer." The bus runs under the table, more-or-less following the tracks above. At intervals of every few feet, run "feeder wires" from the bus to the rails. Just scarpe off some insulation from the bus, wrap one end of the feeder around the exposed metal, and send the other end of the feeder through the table to the rails, and solder it in place. The idea is to make a really solid and redundant power feed to the layout.

Like DC, it is essential to keep power for one one rail ALWAYS to that one rail, and power for the other rail ALWAYS to that other rail. Thus, many modelers will designate "rail A" and "rail B," and use one color of wire for A, and a different color for B.

How to Tell Which Rail is A or B: If your tracks makes a lot of turns and involves a number of turnouts, diverging routes, siding, reversing loops, etc., it can be difficult to visually figure out which are the A and B rails at any given point. Here's the fail

There's more to it than that -but now you have the basic idea. Search the 'net for model railroad DCC -and start your research.

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