DC layouts

[CNE Runner]

Hmmm, I had 3 other friends over to do some 'group switching' and we all operated our engines at the same time...many times on the same track. My layout has two wires as feeds. No complicated wiring. No throwing switches between Cab A, B, or C. One DCC unit (MRC Prodigy Advance in my case...not that it matters). 'Sounds pretty simple doesn't it? Simple wiring and simple control - isn't that what it should be? The most complicated piece of electronics, on the layout, is a Digitrax AR1 Automatic Reversing Controller that was only needed because I run Peco Electrofrog products - and the Electrofrog crossing required a controller. No powered frogs on your crossings? No AR1 controller needed.

Life is complicated enough...support the KISS principle!
Ray

[Atlantic Central]

Ray,

There is no question that the wiring infrastructure for a small DCC layout is very simple. And that for small layouts, where multiple locomotives will be operated in a small space, DCC has some distinct advantages.

But all newcommers to the hobby and to DCC need to understand that ANY medium sized or larger layout, DC or DCC will involve a somewhat complex and multi layered wiring system for reliable operation.

As layouts become larger, and have both more trackage and more locomotives, the need for power districts, circuit protectors, multiple reverse units, multiple power drops and so forth, can and does easily make the underside of a DCC layout look just like all the large DC layouts I have worked on or built personally.

Ad to that stationary decoder controlled turnouts, signals, radio throttle boosters, etc, etc, and you are WAY past the "two wires" of the advertising hype.

A background with more basic electrical principals is very helpful at that point.

But if your goals only include a 4x8 or two, than true enough, two wires may be all you need. Personally, I have bigger goals, and so might our young beginner - why limit him?

Sheldon

[Jim Banner]

I agree with Sheldon.  As followers of Dilbert well know, the Sales/PR department always overrides the engineering department when it comes to sales brochures.  But it is not an all or nothing situation.

Some people, and I believe this included Sheldon, have the ability to build a medium to large layout all at once.  I have to admire their determination to build the room first, then all the benchwork, then lay all the track, then do all the wiring, followed by all the scenery ...  Well, you get the picture.  Personally, I have tended to "grow" my layouts, starting with something manageable, going through all the steps, then adding to it, section at a time.  Even 25 years after starting my present H0 layout it still has parts running on bare benchwork, other parts with temporary wiring, and still other parts with partly finished scenery.  I suspect from photos in the model press that many layouts are built the same way - they contain everything from beautifully finished sections (that are in the photos) to areas that are only proposed (and for obvious reasons, are never shown in the photos.)  So what is the solution in terms of wiring?

My solution, if there is any chance at all of future expansion, is to use bus wiring right from day one.  And DCC right from day two.  Day one is when you first start adding wiring to make the train run.  The locomotive can be dc or DCC, it does not matter.  In either case, you only need one pair of bus wires, the heavy wires - 12 or 14 gauge - that run from your power pack or command station to the rest of the layout.  Just make sure your risers (short wires from the bus wires to the different blocks of tracks) are heavy enough for 2 or 3 amps - about 20 gauge - and not over 3 feet long.

When day two comes along, you already have suitable wiring in place.  Day two is the day when you want to run more than one train at a time over the same track.  It is the day when you need to upgrade to DCC.  Day two may be weeks, months or years after day one.

As the layout expands, both in area and in the number of trains you want to run at the same time, you will likely get to a point where you do not have enough DCC power to handle everything at once.  The Command Station that once ran two trains now kicks out when you try to run four trains, or six trains, or even more, some of them with lighted passenger cars, some or all of them with sound, and maybe some of them double or triple headed.  Adding one big booster would seem to be a solution, but there is a safe limit to how much current you can safely run through the rails, particularly when a short circuit occurs.  This is usually about 5 amps in H0.  So instead of one huge booster, you could eventually be looking at two or more boosters, each 5 amps or less.  And you would need two or more sets of bus wires to carry all the current.  If your layout was wired with bus wires from day one, it would be easy to divide the layout in half or thirds for an extra set or two of bus wires.  But if you used light wiring from day one onward, you will have to rewire the whole layout if it grows past the two or three train stage.  This is not an easy job, I assure you.

So where does this leave trainsrock?  If he feels he might someday expand his layout, he should probably start off with a main bus running around his layout, with all this main line track connected to it.  Then he can connect his mainline power pack to that bus.  His yard, being a smaller area, should be okay with its feeder or feeders connected directly two his second power pack.  If he expands later on and goes to DCC, he has the option of connecting those yard feeders to his bus wires at that time.  Assuming a 4' x 8' table and an 8' bus, using bus wire from day one would add only abut $3 to the price of the layout.     

[jward]

my solution is a bit different than conventional wisdom.

i don't see dc/dcc as an either/or proposition. i think that any model railroader worth his or her salt should learn how to wire a layout for dc. the basic power feeder circuit is the same for dcc and dc, minus the block switches used in dc. in dcc some substitute circuit breakers for the block toggles. and the wiring is the same for reversing sections, with many in dcc preferring to use auto reversers instead of toggle switches.

keep in mind that nothing is failsafe, even dcc. understanding some basic electric theory as it pertains to model railroading will save you a world of grief when things inevitably go wrong.

my approach is to wire the layout for dc, with the block toggles kept in place. the dcc is connected in place of one of the dc power packs, and the toggles are all thrown to that position. this gives me the ability to quickly isolate any shorts in the wiring by flipping a couple of toggles. once isolated, the rest of the layout still runs as usual, and i have narrowed to location of the problem down considerably.

a second advantage is the ability to quickly revert to dc operation by connecting my dc power packs, should anything go wrong with my command station.

dcc is often touted as simple to wire, and in theory you could get away with two wires to the track. but like most things in life, there's alot more to it than that. taking the time to learn a little more can only help you in the long run......

[Jim Banner]

Jeffery,
There may be a fly in the ointment when you try to use dc wiring for DCC.  And that is the wire size.  It is not a problem in all cases, but let me tell you about one case where it created serious problems.  About ten years ago, I wired a 12' x 24' layout for four CAB dc using two dozen blocks.  Each block was fed by its own rotary switch and the inputs to the rotary switches were linked together by five pair, #20 cable.  This wiring was more than adequate for dc as each CAB was limited to 1 amp by the power packs.  The maximum voltage drop for any CAB was less than one volt.

Then came DCC.  For a layout that was formerly powered by a total of 4 amps dc, a 5 amp DCC booster was in order.  Connecting the booster in place of power pack number one and setting all the block rotaries to CAB 1 seemed pretty straight forward.  Unfortunately, the pair of #20 wires serving CAB 1 had too high a resistance.  The voltage drop between the booster and the trains was as high as 5 volts.  This not only slowed the trains, but interfered with booster shut down in case of a short (those with Digitrax will recognize this as failure to pass the quarter test.)  Even more interesting, certain locomotives would run out of control on certain parts of the layout.

The solution was easy - rip out all the block rotaries and their wiring and replace them with a 12 gauge bus.  The two dozen blocks were reduced to half a dozen, each with a toggle switch and a series lamp to limit current.  With this arrangement, a short in one block did not shut down the whole layout and it was quick and easy to shut off the shorted block before anything melted.

An alternate solution would have been to link the CAB 1 positions of each rotary with 12 gauge wire right from the beginning.  (Isn't hind sight wonderful compared to foresight.)  That would have eliminated the slowing down, the erratic control and the lack of booster shut down, but would not have solved the problem of a short in one place shutting down the entire layout.  To build that into the dc layout would have required adding a series lamp to each and ever block, not just the few consolidated blocks.


If the layout had been smaller, say a 4' x 8' or even a bit larger, then setting all the block rotaries to CAB 1 would probably have worked.  But as we find in model railroading, a good solution in one case is not necessarily a universal solution for all cases.

Jim   

[pdlethbridge]

This sort of reminds me about the guy who was going to build a boat. He started by buying a anchor from a decommissioned air craft carrier

[jward]

i don't use anything smaller than 18 guage in my wiring, and have powered up to a 13 1/2 x 13 1/2 layout in this manner.

unless you have a short in the connection between the command station and the control panel, there is no reason i can see why any problems couldn't be isolated in one block. with the layout mentioned above, i had double track and in some places 3 tracks on the main, with 4 sets of crossovers. removing one block from service for "track amintenance" merely added interest to running the layout. and it is alot easier to find a problem if you know it is contained in 10 feet of track instead of 500.

for me, the attraction of dcc has never been "simple" wiring, but rather the ability to program locomotives to run the way i want them to, and the possibility of having a real working signal system. before dcc, i have gone so far as to regear locomotives that ran too fast, but the signal circuits were an elusive goal.

[Jim Banner]

Jeffery,
I think we are talking about two different kinds of shorts, and I don't mean Jockey versus Boxer.  I suspect you are talking mostly about those "mystery shorts" that sneak into our railways from time to time, the shorts that are causes by gaps closing up or by pinched feeders or by accidental contact between feeders and metallic components of the layout or by the internal failure of track appliances or any other short that still remains even if you remove all the rolling stock from the layout.  Please correct me if I am wrong.

I am talking mostly about operational shorts, the type that occurs when a train operator runs a switch that is set against him or derails his train or tries to consist two improperly insulated locomotives or any other short that disappears when you remove the rolling stock from the layout.

In my experience, mystery shorts are pretty rare because once they occur, they are usually hunted down, repaired, and do not occur again.  With mystery shorts, I see no great problem with having to turn off a dozen or more block switches to find out which block is shorted.  In fact, having a block switch for each operational block (for example, one for a passing siding, another for the main that parallels it) would be a real luxury when mystery shorts appear.

However, operational shorts are much more common, particularly when you have multiple operators.  An operational short on a layout with no short circuit protection other than that built into the booster immediately stops all the trains.  This usually causes bedlam as all the operators start looking at their trains to see why they stopped.  By the time the dispatcher or someone else turns off two dozen block switches to see which train is causing the problem, there is a good chance that one of the innocent operators has meanwhile caused another short by poking and prodding his train trying to get it to run.  Then even more time is spent trying to figure out which two trains are causing problems before operations can resume.

Operational shorts are, in my opinion, better dealt with by having fewer blocks but each block equipped with its own current limiting device and power indicator.  On the railway I talked about earlier, the layout was divided into six blocks and each block has its own current control in the form of an automotive tail light bulb.  This means that an operational short in one of the blocks does not affect operation in any of the other five blocks and the operator using the shorted block knows that it is his train that is causing him problems, not some other person's train.  If he has any doubts, he has a very bright light reminding him of it.  Needless to say it would also have been possible to install a couple of dozen bulbs on this particular layout so that there was one for each operational block.  But dividing the layout into areas where it was unlikely to have more than one or two trains at a time has apparently proved satisfactory.  I have not had the pleasure of leading an operating session on that layout.

On my own H0 layout, I ended up using digital power managers instead of bulbs to divide my layout into four blocks or "sub districts" as the DCC purists like to call them.  When operating trains, it is not at all unusual to have a power manager shut down a block for a few seconds.  I don't keep track, but I would guess it happens once every five to ten minutes with half a dozen operators running trains.  On the other hand, I have had only two mystery shorts occur in the ten years or more since installing DCC on the same layout, both related to 40 year old switch machines going bad.

Jim

[jward]

i didn't have much of a problem with operational shorts. maybe about the same was with dc. my layout was gapped for the eventual installation of signals, which stopped any train far enough back that they wouldn't run through an open switch. the only area of concern for me was the entry of reversing loops, and i had installed polarity sensitive signals at the entrance to the loops so my crews would know whether or not the plarity was correct before they entered the loop. both loops polarity were controlled by toggle switches, same as with dc.

if i had run into issues with operational shorts, i would have put a current limiting bulb in the common return right next to the command station.