Help! DCC VS DC common rail cab a/b wiring questions

[Anonymous]

I have recently invested in an atlas master dcc system. I already have my layout wired in block section with insulated rail joiners and a common negative rail through out the entire layout . I have all 10 blocks wired on an separate atlas cab a cab b swithes including a yard and xy turntable switch and 2 dc power packs. My question is can I run the main line with dcc on cab a and the old dc power packs on cab b. I thought it might be useful to have the ability to isolate dc power packs in the switching yards while running dcc engines on the main lines. Or should I just pull out all the cab switches and just run the whole layout dcc. I didnt want to waste all those cab swithes plus I think I should keep the block sections in case I need to trouble shoot for shorts later on they will be easier to track down. What is the best way to wire this with all the equipment I have in order to provide maximum flexibility. I have about 30 engines and only one is DCC so far so it will be awhile before I get them set up

[Anonymous]

If i understand you correctly, the common rail is the entire railroad? If so, you have no way to separate the dcc from the dc. I originally had a had a Atlas master system and everytime i just switched from DC to dcc i had to reset the controller. I would not recommend trying to run both at the same time, even if you had each block totally isolated from the other. Having blocks to test for electrical problems is a good idea if you have large areas that you are trying to isolate a problem in. Depends upon the size of the railroad.

[nfmisso]

Bob is spot on with his advice.

With common rail, do not ever mix dc and dcc. Even with both rails blocked, there are risks that could severely damage your dcc system and dc power packs; such as a locomotive bridging both systems: lots of smoke is likely.

[mcouvillion]

Ween,

Every time I hear that someone uses common rail I cringe. Something that was supposed to be so easy to do and save you all this wiring is an albatros when you want to upgrade your control electronics. I rewired an entire layout for a club that had a "genius" wire it with common rail, then tell them that it would be OK to run DCC on it. Not going to happen. Bite the bullet and convert your "common" rail to a parallel blocked buss and get your DCC going. You will be glad you did.

Mark C.

[Anonymous]

Mark What do you mean by convert your "common" rail to a parallel blocked buss and get your DCC going. I am not sure exactly how to convert it. Right now it is set up in common rail blocks with each block separated by an insulated rail joiner on one rail.

[rrinker]

With a small layout and only a single DCC booster, it really doesn't matter. I DO hope that common rail has more than one feeder to the track though, or you will likely experience loss of power.
Do NOT mix DC and DCC ont he same layout, common rail or not - unless you wiere it such that it is one or the other, not "this block is DC and tha block is DCC". The chances of damaging something (DCC unit, loco) are too high.
Common rail is particularly bad when trying to mix DC and DCC, or when you have more than a single DC booster, because situations can exist where the voltage across the gap is DOUBLE the normal voltage, which means fried light bulbs and fried DCC decoders.
Three reasons to even have blocks in DCC: Multiple boosters, multiple power districts with individual circuit breakers (so a short in one part won't shut down the entire layout), and for detection circuits to use for signalling. If your layout is small and you won't have more than one booster, and you aren't going to implement a signal system, you can wire all the blocks together for DCC.

-Randy

[Anonymous]

With my new DCC set up should I put insulated rail joiners on both the positive and negative rail and wire each block directly to the next block underneath the benchwork? Or do I still need an on off switch between each block section? Also how do I wire a reverse loop with dcc?

[rrinker]

QUOTE: Originally posted by Ween

With my new DCC set up should I put insulated rail joiners on both the positive and negative rail and wire each block directly to the next block underneath the benchwork? Or do I still need an on off switch between each block section? Also how do I wire a reverse loop with dcc?

You don't HAVE to insulate anything, except live-frog turnouts, reverse loops, or wyes. The only reason to insulate sections with DCC is to prvide for seperate power districts - that is a section of track powered by its own booster or via an electronic circuit breaker. Each power district would have its own bus running under it, and one or more sets of feeders to the tracks. At the boundaries of these you would insulate both rails. For track that is all part of the same power district, that is all the feeders go to the same bus wire, there is no need to use insulated track joiners other than the above special cases. No toggles required unless you really need to turn off the power to a particular section of track. This can be useful in staging yards to prevent unexpected train movement, or in an engine terminal to shut off all the sound locos, but otherwise the whole point of DCC is to get rid of block toggles and wacky wiring.

--Randy

[MisterBeasley]

There is a gadget called a "DCC Reverser" used to automatically control power to reverse loops, wyes and turntables. It senses the polarity conflict when something "bridges" the gap between oppositely-set regions, and automatically flips one so they match.

I have a lot of old (and I do mean old) DC equipment, plus a couple of new units for my mass transit system. I had planned to run both DCC and DC, either half-and-half or switched, for a while. An hour after I started running with DCC, I removed the track connections from the DC power pack forever. Your DC locomotives will likely be gathering dust until you convert them, I predict.

[mcouvillion]

Ween,

Sorry I didn't get back to you sooner. Randy's suggestions are essentially what I would do. Apparently, your idea of "common rail" is a little different than what I envision, but it still makes converting to reliable DCC problematic. My experience is that the most reliable wiring is from a wire pair bus with feeders to the rails from the bus. Color code the feeders and the bus wires and you can't go wrong. Do not rely on rail joiners to carry track power, do not solder the rails at the joiners. For setting up power districts or "blocks" for signaling, use insulated rail joiners on both rails, or just gaps in the rails. Insulated rail joiners are needed at frogs so that the frog can be powered, at the beginning of reverse loops, and wyes. Circuit breakers protect the railroad from total shutdown if something causes a short. Only the affected power district shuts down. Do it right once and never have to do it again.

Mark C.

[Anonymous]

How does the signal going to the decoder in the engine cross a power district or "block if it is separated by gaps in the rails?

[Anonymous]

also, how do you know if a frog needs to be powered and how can you tell if it is or not I thought there were two types of frogs?

[rrinker]

The signal works between power districts just fine. You just have to keep the 'polarity' of the wires straight, otherwise you will get a short.
As for the switches and frogs - if you are using Atlas or Peco Insulfrog, there's no issue, they are already insulated. Powering the frogs is optional, if you have a lot of really small locos it's probably a good idea, but larger locos will never have all pickup wheels on the frog at the same time and so should always be able to get power. Other problem types are the kinds that pick up with one side of the front truck and the other side of the rear truck (for a diesel). Locos with all-wheel pickup are usually ok even with non-powered frogs.

--Randy

[Anonymous]

I'm in a very similar position to Ween. I've got a DC layout with one common rail running through it all. My guess is I need to break this up into several power districts by adding some insulators. Luckly I haven't ballasted the track yet. What I'm wondering is the mapping between boosters and power districts. I'm under the impression it's a 1-to-1 mapping, that each power district needs its own booster. For a layout my size, a 4x8 N-scale, that seems like overkill.
It is nice, however, that I've got blocks pre-made for block detection.

[rrinker]

No, each power district does not need a seperate booster. You can use an electronic circuit breaker like Tony's PowerShield to break the one booster up into seperate power districts with their own short protection. This way a short on one portion of your layout won't shut down everything all at once.

--Randy

[Anonymous]

QUOTE: Originally posted by rrinker

No, each power district does not need a seperate booster.

Very, very cool. I was hoping that would be the answer. I'm feeling better and better about this DCC stuff, and I really appreciate all your response, Randy. Very helpful. Any advice on how to break up the power districts? I've got, essentially, four loops, so that seems like a logical place to break power districts, which would give me six, I think, four for the loops, one for the yard, one for the two interchanges. Too many? Too few?

[rrinker]

Probably don't need one for the interchanges. It also depends on how many trains you can run - are they 4 true loops, in that you can have 4 trains runing around without runnign into one another? If so, make them seperate districts. If not - it's probably overkill to make each one seperate. Keeping the yard by itself is a good idea, that's the most likely place to derail something and cause a short.
For an example, the completed portion of my layout is essetially two loops connected with crossovers, plus a yard and switching area inside the two loops. I was planning to make 3 power districts, one for each loop and one for the yard area.

--Randy

[Anonymous]

It's pretty much a stock Atlas N-18 layout. I made some changes to the yard design to better fit the modeling I want to do, but the rest of it is as they described. There's a double-tracked oval on the outside that can run two trains with no problem. In the center is a double-tracked figure eight, so only one train can run unattended there. Two can run fine so long as they're watched closely (learned that the hard way!). There's two sidings on the upper level, the figure eight, and two on the lower plus the yard on the lower. The two interchanges shift from the upper level, the figure eight, back to the lower oval on the outside.
From what you're saying it sounds like five power districts. I'm thinking of wiring up a control boad to mount under the layout and using terminal strips to join in the connections. so that the board is removable and all the wiring stays relatively neat. Wish I'd done that when I did the DC wiring!

[Anonymous]

Thanks Everyone for all your help. I now have my layout converted to DCC and am running three trains simultaniously on the main line and it is awesome!!. Now I have to figure out how to wire my reverse loop, yard and my turntable for dcc. Should all the track around the turntable, into the round house and, any sidings be wired with an on off switch so I can leave engines parked on them. I was concerned about leaving an engine parked on the powered track and causing the decoder to overheat

[Anonymous]

also I am still debating wheather I should have went with digitrax instead of atlas. Does any one know what software I can use to program decoders on a computer. and what type of hardware I can use to interface with a pc?

[rrinker]

You won't overheat the decoders, but providing a way t shut off power to storage tracks isn't a bad idea - it can prevent accidents if someone selects the wrong address, or you get one of those rare 'runaway' events. Also saves power and noise if you start running sound-equipped locos if you can just turn off all the parked ones.

Check the JMRI group on Yahoo. I think there are some issues using the Lenz computer interface with the Atlas (and Lenz Compact, which is the same system). If you want to do standalone programming, there is the SPROG which is a standalone programmer that works with JMRI and DecoderPro and since it connects directly to a programming track, it doesn't matter what your DCC system is.

--Randy

[Anonymous]

I am totally ignorant about DCC, so please tell me if this is whacked out thinking: If you have Atlas controllers and selectors, the old 1960's style of common rail cab control wiring, and you want to convert that DC system to DCC, couldn't you just throw all the Atlas switches to cab "A" (or cab "B"), and then remove that cab "A" DC pack, and connect your DCC power source to the same wires that fed out of the DC pack? By throwing all the Atlas switches the same direction, you would be creating one big electrical block, right? Why won't that block work for DCC? Again, I admit my ignorance. Please tell me what I'm missing here. Thanks.

[Anonymous]

I think that way you are right. The key is that you can't have any right track touching left track, reverse loops still need to be dealt with. The big problem with what was proposed at the beginning of this was that he wanted to run DC on part of the layout and DCC on part, and keeping them separate is more than a challenge.

[rrinker]

That will work - provided you're talking a smaller layout and will only ever have 1 booster. I would also hope that common-rail wired layout would have more than one feeder for the common rail, otherwise you might have power problems at the furthest points. You already have multiple feeders for the other rail, from all the lines going from the Selector to the blocks.
It's never a good idea to mix DC and DCC in a situation like that, where one flip of the switch changes the block from DCC to DC. Bad Things happen when a loco crosses the gaps between a block set for DC and one set for DCC, common rail or not. Common rail just makes it worse.

--Randy