So, tell me more about "blocks"

Discussion in 'DCC & Electronics' started by S/390, Nov 12, 2006.

  1. S/390

    S/390 New Member

    I'm still a little confused about blocks in DCC. I thought I had it, but after reading "Wiring for DCC" I'm starting to wonder...

    It was my understandng that you didn't need "physical blocks" in DCC. By physical block I mean a section of track that is insulated from its neighbors, with its own power feed, like with DC. Now I know you need a block for things like a wye, where you have a "physical short". And I can see it in a large layout, where you need multiple boosters and power districts. Are these the only cases where you need a "physical block" in DCC?

    Does it depend on the hardware that I use for block detection? If I'm using a "current flow" detector then I can see the need for insulated blocks. But what if I use IR, or a simple switch as a detector? Doesn't that create a "logical block", and isn't that all I need for things like TrainController?

  2. fsm1000

    fsm1000 Member

    Unless you plan to never make a mistake, use blocks for finding problems later. Also I heard that for LARGE layouts use one block for every 25 feet, each yard and main section of track area. You can keep it all on at the same time all the time but for troubleshooting [like finding a short] blocks will help out that way.
    Except for reverse loops and wyes [as you said] there is no need for blocks though. If you have a small layout I wouldn't worry about it. :)
    Hope that helps.
  3. steamhead

    steamhead Active Member


    Power districts (blocks) are used in DCC to avoid the whole layout from going beserk if a short occurs. If you have power districts, only the affected district shuts down and the rest still operate normaly. Like FSM says, this is a must for larger layouts and multiple operators. A smaller layout can get by without them.
  4. S/390

    S/390 New Member

    Thanks, that's what I figured, just wanted to make sure. :D

    I'll be starting small, a couple or three industry sidings, small yard with about 4 tracks. Maybe I'll try that as a "physical block" and see how it goes. I do plan to have multiple feeds. Only a couple engines active at a time.

    I'll plan on a second block in phase 2, when I get the passenger line going. Theyll run on a second main (mostly) anyway.

    How's that sound? :)
  5. steamhead

    steamhead Active Member

    That sounds just fine.
    Good luck...!!!:thumb:
  6. S/390

    S/390 New Member

    Well, my question may be moot. :oops:

    I'm starting to like Digitrax more than the others. Since they use current flow detectors, and that requires "physical blocks" I may be "forced" into it. :D

    But the good side of that is, I think, I only need one wire pre block for both power and detection. Correct me if I'm wrong. I was thinking a single big block with IR detection would be easier wiring, but that may not be the case...

    I'm sure I'll be back soon with more questions. Thanks for the help so far... :cool:
  7. railwaybob

    railwaybob Member

    As Gus has pointed out, power districts (blocks) can be used to minimize problems. However, minimizing those problems depends on the devices you have at the other end of the block.

    If you are using DCC for your own home layout and you'll only be running a couple of trains at any one time, then you don't need power districts. If you have a large layout and the gang is coming over to the house on a Thursday evening for their usual operating session, then you may want to break your layout into a couple of power districts.

    Remember that one of the limiting factors to the number of trains you can run at one time is the total current draw on the layout. To simplify things, we'll stick with the number of locomotives. If your DCC system is a 10 amp system, and each locomotive draws 1 amp of current, then the maximum number of locos you can run at any one time is 10 (10 locos x 1 amp - 10 amps max). To run more locos at the same time, you will have to add a booster to your DCC system. Assume you have a 10 amp booster. This booster will provide power to a separate power district and the maximum number of locos in that district, if each loco draws 1 amp of current, will be 10 (10 locos x 1 amp = 10 amps). At the same time, you can also have 10 locos in the power district powered by the command station (10 locos x 1 amp = 10 amps). However, if all 20 locos (10 + 10) end up in one power district - assume the power district powered by your booster, then you will have problems (20 locos x 1 amp - 20 amps which exceeds the 10 amp power rating of your booster. Same logic applies for your command station.

    Now, if you're going in for DCC signalling, then we are talking about a different matter here. You will need to break up your layout into blocks so that the signal detection board ( eg a Digitrax BD 4 or BDL168 occupancy detection circuit) that feeds the block, along with the transponder in the decoder in your locomotive (you will need transponding decoders if you want to know the loco ID of the loco in the block), can identify which block the locomotive is in and feed this info back to the command station (which, in turn, can be refed to the signal system which will change the colour aspects of the signal). Again, if you have a home layout, you won't need a separate power district (ie an insulated area that is powered by a booster). But you will need separate insulated blocks so that the DCC system can identify where your loco is on the layout. Are you still with us on this last bit?
  8. fsm1000

    fsm1000 Member

    So eseentially, add up what you think your maximum usage [electrically speaking] will be and add a 'fudge factor' of 10% and that should work for you.
    I know little about DCC but I do know a bit about electricity:D
    Iuse to rewire houses and kinda learned a bit :D
    Anyhow, seems to me that a couple of blocks won't hurt and if you break it down into sections [eg. yard, mainline etc] you will probably have at least 2 maybe 3 sections on an average small to medium layout.

    Nothing is more annoying then trying to find a short [or any problem] when it is all one block. I use to have only one block but I would do work on my layout and accidently leave my pliers on the layout or something and bingo, no power. After a few minutes I found the problem but now a days I find it simpler because if I turn on a block I can isolate it quickly.

    Anyhow, you seem to be on the right track. Have fun and don't fret the small stuff :D
  9. S/390

    S/390 New Member

    Thanks guys, I think I've got the block situation under control.

    I've decided to go with the Digitrax BDL168. It does require insulsted blocks, but overall wiring is easier than IR, switch, or coil detectors, and the total cost is reasonable.

    I appreciate your input on short problems, and it is something to consider. When the time comes I will be looking at things like the Digitrax PM42. And that time may be as soon... But I do think it is a different issue than "blocks" used fo signal / loco control.

    Speaking of signals, I'm now off to attack the DCC signal driver question... :eek:

    Thanks again, I'll be back... :wave:

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