Block control and DCC

[rbryce1]

Most of you know that I am about 9 months new to DCC, and have not had a DC layout for over 55 years now.

I understand block control as it applies to DC, but not to DCC.  How does block control benefit DCC, how can Block control let you know where your trains are and why would you need it.

[Joe Satnik]

4 matches for polsgrove power districts

DCC Corner: Understanding power districts
by Mike Polsgrove 
from Model Railroader August 2010  p. 66
dcc  district  Power  wiring

DCC Corner: Wiring power districts and wyes
by Mike Polsgrove 
from Model Railroader July 2008  p. 74
dcc  district  Power  wiring  wye

DCC Corner: Power buses and districts
by Polsgrove, Mike 
from Model Railroader November 2005  p. 94
dcc  electronics

DCC corner: Keep your trains running with power districts
so a short circuit doesn't shut down the whole layout
by Polsgrove, Mike 
from Model Railroader May 2003  p. 104
dcc  electronics

[JerryB]

Block control allows the operation of more than one motive power unit (and its train) on a single track, with the speed and direction controlled by the varying the DC voltage on the track. An engine in one block can be controlled independent of engines in adjacent blocks. The most common arrangements use at least three blocks so the trains can keep moving as they go from one block to another. Larger layouts use many blocks to allow the independent operation of several trains.

DCC is very different. All track is connected to the same constant power source. The power source is a version of AC, with command signals impressed on that power. Speed and direction control is provided by a controller in the engine. The on-board controller has a specific address, and only responds to commands that are sent to that address. That means each motive power unit will operate independent of other units, even those directly on the same track. This capability allows for much more prototypical operation, and also supports the independent operation of all manner of items like turnouts and accessories without the need for individual block or electrical wiring.

See:

http://en.wikipedia.org/wiki/Digital_Command_Control

for a much more detailed explanation.

Happy RRing,

Jerry

[Nathan]

Another good source for information is;

http://www.dccwiki.com/Main_Page

Nathan

[Joe Satnik]

Dear rbryce1,

With separate power districts, you can detect the current flowing into each district. 

A district with no train in it will draw no current. 

A district with a train in it will. 

You can use that detected current to run your track side signals,

or (if you really wanted to get fancy) an automated control system.

Hope this helps.

Sincerely,

Joe Satnik 

[Joe323]

Separating a DCC layout into blocks allows for better operations on a large layout.  For example if a train derails and causes a short on one section the whole layout need not come to a halt while the short is fixed only the affected section stops.  For the same reason it makes for easier troubleshooting when the short does occur.

[jward]

i would add that, if you have an existing dc layout you converted to dcc, that you could often use the existing dc block control switches and wiring. to me the advantages are as follows:

1. by using the dc block switches to isolate certain tracks you can significantly reduce the power draw on your dcc system. think of a roundhouse with 8 or 10 locomotives sitting in the stalls. with those tracks isolated, there are 10 less decoders drawing power from the system.

2. as was said, keeping the blocks allows you to quickly isolate any short circuits. just flip the switches to off one by one until the short goes away. then look in that section for your problem.

3. joe satnick touched on the very real possibility of signals in dcc. you'd have to gap the rails for signals anyway, so why not incorporate blocks into the wiring. there are numerous relatively inexpensive signal detector circuits on the market which are approaching plug n play. this is a far cry from the old dc days when everything had to be custom built except the signals themselves.

4. having the layout divided into blocks makes it easy to add a booster, and have it control half the layout.

[Joe Satnik]

jward,

I am unclear about your point #4. 

Do you mean 2 different DCC signal sources, one for each half of the layout?

The same DCC signal source should be used everywhere on the layout, switched in or switched out of each district.   

The only exception would be a reverse loop or wye,  where polarity reversing switches or an automatic reverser would flip the polarity of the DCC signal to the rails.

Can you clarify?

Thanks.

Sincerely,

Joe Satnik

   

[Ken G Price]

jward,

I am unclear about your point #4. 

Do you mean 2 different DCC signal sources, one for each half of the layout?

The same DCC signal source should be used everywhere on the layout, switched in or switched out of each district.   

The only exception would be a reverse loop or wye,  where polarity reversing switches or an automatic reverser would flip the polarity of the DCC signal to the rails.

Can you clarify?

Thanks.

Sincerely,

Joe Satnik

You would use one or more boosters on a very large club or just really large type layout, but only one command station. I use a Digitrax DB150 as my command station and for track power. I could use another for a reverse loop (though it would be an expensive way to do it) or as a power source for half of my layout, if it was so big that there was a power drop at one end. Running a buss and feeders off of it will still drop power if it runs far enough. It would not be used to control trains. Just for the power.

rbrycel would not need to do this unless, maybe he is building a really huge layout. Lets say, in a 1000 sq ft area.

[jward]

what aboutn phase differences between boosters. basically you'd have multiple ac power sources connected to the same load. unless they are in phase wouldn't they short out?

the way the system is described in the digitrax big book of dcc, breaks between power districts using seperate boosters should be insulated on both rails similar to a reverse loop[.