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power disticts

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power disticts
Posted by steamfreightboy on Saturday, March 01, 2008 12:17 PM
I am very new to DCC and am wondering how power districts work. Could you please explain so an advanced 5th grader can understand?
"It's your layout, only you have to like it." Lin's Junction
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Posted by selector on Saturday, March 01, 2008 2:22 PM

Are you familiar with the concept of a rebroadcasting facility in radio and microwave networks?  A power district is much the same thing.  It is a separate booster to provide full power to a defined and isolated section of your layout.  Note that districts are intended for larger and more complex layouts where there may also be many users needing power.  So a power district improves the signal to noise ratio in a given area of the layout and also provides short protection to that area since that is all it is sensitive to.  By protecting only its child area from shorts, the other parts of a layout also controlled by their own boosters keep running.  They don't "see" the short, so they keep their rails powered up and the trains there-in running while someone fixes the short in the one district that has the problem.

Again, these make sense on larger and more power hungry layouts, not so much on the typical room-sized layout in the 6X8' range.

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Posted by MisterBeasley on Saturday, March 01, 2008 3:04 PM

A basic DCC system consists of a power supply, a control station, one or more throttles, and one or more power boosters.  Depending on the manufacturer, two or more of these components may be combined into single physical box, but they are still all there.

The power supply plugs into the wall and takes your house power, normally 120 volts, and lowers it down to the 12-16 volt range.  It may also rectify the power, or convert the AC signal to DC.  The control station is the heart of DCC.  It builds a signal which goes out to the tracks, containing not only the power, but also the control signals which tell the engines what to do.  It uses what's called a modulated square wave signal to do this.  When the signal leaves the control station, it's weak, and needs more power.  For that, the signal goes to a power booster, which gives the signal not only enough power to travel around the tracks, but also provides enough power to actually run the engines.

Each power booster has a rating, usually in amps (or amperes, the real electrical name.)  Low-end boosters may provide 1 amp, and high-powered ones up to 8 amps.  Each engine on your track uses some of that current, more when running.  If you have more engines than your booster can run, you need to add another booster.

Each power booster should be connected to its own isolated block of track, called a power district.  So, while everything in your system is connected, and they all share the same control station, you may divide your layout into power districts to distribute and manage the power, and to allow you to run more engines.

It takes an iron man to play with a toy iron horse. 

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Posted by UpNorth on Saturday, March 01, 2008 3:07 PM

Lets say you have a 4 x 8 loop of track and you have your  DCC controler hooked up, two engines running.  All the track is powered from the one DCC controler. You have only one siding turnout.

If a short occurs because of an operator error (ie: rolling into a wrongly thown turnout) this will cause the stopping of all engines in operation as the DCC controler cuts the power supplied while the short is present.

A power district is, simply, cutting both rails (double gap)  of the loop into 2 districts,  isolating them from each other. You then add a power management device  (ie: Digitrax PM42) that will sense a short circuit  but this time cutting power ONLY to  the section of track (district) that encountered the short. The other half loop is not affected and any  engine present keeps chugging along because the DCC controler was not affected by the short (the PM42 handle it) until it enters the shorted district. 

Other option is  drop the power management device in favor of adding a second DCC controler for the 2nd district. This  doubles  the availlable power to your layout and you can run more trains.

Digitrax makes the PM42. Powershield is another option.

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Posted by MisterBeasley on Sunday, March 02, 2008 10:20 AM

Well, we have a difference of opinion about the definition of a Power District.  I've always believed that a Power District requires a separate booster.  Thus, the power used within a district is counted only against that booster's rating.  The idea of a Power District separated by PM42's, which is a "power management device," is not the same.  The PM42 is a circuit-breaker and auto-reverse module, but all of the power consumed within the individually controlled sections would go against the same booster.

Can somebody clear this up for us?  Thanks.

It takes an iron man to play with a toy iron horse. 

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Posted by UpNorth on Sunday, March 02, 2008 4:27 PM

As per Digitrax. 

Power district: the power wiring, components and equipment attached to that wiring, driven by a single properly isolated booster.

Power sub-district: a subdivision of a power district. Usually controlled by a power management device like a PM42.

As it is difficult to determine the audience involved in a forum, I was simplifying a tad. You are correct

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Posted by steamfreightboy on Sunday, March 02, 2008 6:17 PM
thanks for the infoWink [;)]Bow [bow]
"It's your layout, only you have to like it." Lin's Junction

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