A good (and free) resource on line is the NMRA (National Model Railroad Association) site's Beginner's Page. Here's the electrical section that describes dual cab control:
http://www.nmra.org/beginner/extended.html
Dual cab control is simplest to understand if you understand what the switch abreviations mean. DPDT is a double pole-double throw switch. The wire side of the switch has 6 terminals, for this purpose, the two outside pairs go to each of the power packs, the center pair goes to the rails for that block. I used the DPDT with the center off position, giving each one three positions, Cab A, Off, and Cab B. You can have either Cab A or B control that block, or set the switch to the center position to turn the block off. If you have two blocks, you do this twice, 10 blocks do this 10 times, etc. Although it may sound complicated, think of one block switch at a time.
The other links on the NMRA's Beginners Pages are a good place to start for basic information on just about any facet of model railroading.
Enjoy.
Sheldon,
Thanks for your guidance. I will be installing a "bridge block" as you (and AlienKing) suggest. I believe that will solve my problem and, particularly, allow me to remove the staging yard and operate it entirely separately, which is what I have set out to do.
I am interested in your comments and suggestions about "more advanced DC cab control systems" than the common rail/wire system I am using.
Thanks,
edwardjIII
TomDiehlSeems we have another OP that has flown the coop, so we may never know.
Seems we have another OP that has flown the coop, so we may never know.
I hate when that happens!
Jeff But it's a dry heat!
I don't believe the flywheels and coasting has anything to do with it. The locos stop because the common rail isn't tied together. When the new locos cross the gap, the loco itself makes the connection. As long as the polarity of the two packs is the same, and the settings are close to the same neighborhood, the locos will move right across. There will be some current through the frame of the loco on the high side to equalize the voltage.
I think things would be more graceful with cabs, but if the common is tied together there's no reason it can't work as it is. That's what common rail wiring gives you.
Phoebe Vet At the risk of spilling my cool aid, I don't understand the need to stop and change power packs. I thought the object in blocked DC is to change the block to the power pack that is controlling the particular engine not to change the control of the engine to the power pack controlling the particular block. I agree that a third block that switches between the two power packs would do what you describe, though I do not believe the lack of a flywheel is relevant, but I just have to ask: Why not just switch the yard to the power pack controlling the layout and then just drive the engine out? You can then switch the yard lead off or back to the other power pack.
At the risk of spilling my cool aid, I don't understand the need to stop and change power packs. I thought the object in blocked DC is to change the block to the power pack that is controlling the particular engine not to change the control of the engine to the power pack controlling the particular block.
I agree that a third block that switches between the two power packs would do what you describe, though I do not believe the lack of a flywheel is relevant, but I just have to ask: Why not just switch the yard to the power pack controlling the layout and then just drive the engine out? You can then switch the yard lead off or back to the other power pack.
What you're describing is Cab Control, the "Cab" being the power pack and the "Block" being the section of track. With two power packs, this is easiest when done with a DPDT center off switch for each block. My overall recommendation to the OP is to have this set up through the entire layout, so that either pack (Cab) can control any section of track (block). This would totally eliminate the need for the transition track. Since he sounds like a novice, I was trying to keep the answer simple.
In the OP's question, the flywheel is relevent. It causes the locomotive to coast over the gap to the section controlled by the other pack. Lacking a flywheel, the older locomotives come to a screaching halt when one set of wheels crosses the gap.
I agree, and have never understood the reasoning behind expecting a train to go from one power supply to another under power. Every time I have experimented with that concept it performs poorly.
I suggested that the OP should simply make the stagging selectable to either power supply.
Sheldon
Dave
Lackawanna Route of the Phoebe Snow
Phoebe Vet Welcome to the forum. I agree that the problem engines are picking up power from the left rail on one truck and the right rail on the other truck. Since you are using two different power packs, when you are bridging the gap you don't have a complete circuit. Blocked DC is too much trouble for my taste, so I use DCC.
Welcome to the forum.
I agree that the problem engines are picking up power from the left rail on one truck and the right rail on the other truck. Since you are using two different power packs, when you are bridging the gap you don't have a complete circuit.
Blocked DC is too much trouble for my taste, so I use DCC.
Since the original poster hasn't drunk the DCC Kool-Aide yet, we should keep the answers in the DC realm. The problem is you need a transition section when going from one power pack to another. I'd be willing to bet that the newer locomotives that glide across the gap are flywheel equipped and the older ones that don't glide across are not. The flywheel compensates for the lack of a transition section. What that means is you need to have a section at least as long as your longest engine that has a selector switch that can select between your mainline pack and your yard pack. Set the switch for side that the locomotive is on and run it into this section. Stop the engine in this section, flip the switch, and off it goes on the other pack. This is essentially what Alienking suggested above.
Just reading that, it sounds complicated, but it isn't.
Edward,
The others have correctly found your problem, When picks are strattled over the gaps, the loco is not seeing a complete circuit to either power supply.
On my DC system we actually use this feature to advantage to prevent operators from overrunning their assigned territory. We stagger the rail gaps between track sections (blocks) and everything is double gapped/swittched. Two sections not assigned to the same throttle creates a dead spot between the double gaps. As soon as both sections are powered by the same throttle, the section is powered. This is SO old, it was used by John Allen.
Dispite its popularity over the years, common rail/wire wiring systems have fallen out of favor with those of us using more adavanced DC cab control systems. I will not expand on why unless you are interested.
Also, I understand your desire for seperate control, but systems that require locos to transition from one power supply/controller to another are less than ideal as well.
Being able to assign the stagging yard to the same throttle as the main layout would be a better approach and would eliminate your problem.
Or you could add some rail sliders or do some other modification so your older engines are picking up from both sides of the rail for both trucks.
Lehigh Willie I have separated the staging yard trackage from that of the original layout wih gaps in both rails at the point where the new base for the staging yard "drops-in" to connect to the original layout.
I have separated the staging yard trackage from that of the original layout wih gaps in both rails at the point where the new base for the staging yard "drops-in" to connect to the original layout.
There it is!
You can gap the rail, but you need to wire the supplies together with some kind of connector that you can disconnect when you pull off the staging. (Just the common rail side!)
I think I disagree. If the common rails are tied together, then the voltage difference is preserved. I think it is more likely that the common rail is actually gapped. That way when a newer loco with power drawn from all the wheels crosses, it completes the common rail circuit, and everything is good. When the old locos cross, the reference is lost, and the train stops.
I'm guessing your older locos are picking up one rail of power from the front truck, and the other rail from the rear truck. The "common" rails voltage is not guaranteed to be be an absolute value from ground, but a relative value from the other output. When your engine crosses the gap, its sees the opposite rails connected and does the easiest thing, makes them the same. Your newer engines bring both rails so it forces the opposite rails to be vdiff apart (where vdiff is the output voltage from the dc pack).
Could you make a short section isolated section, say 1 piece of flex track, at the throat of the staging yard which has a double pull double throw toggle switch to change between the two power packs? Match the two packs and flip the switch while you are on the transition track.
I have recently added a six-block staging yard to my small, seven-block HO DC layout. I have set it up to operate from a separate power pack than that used on my original layout (though both power packs are MRC Railpower 1370s), and I have separated the staging yard trackage from that of the original layout wih gaps in both rails at the point where the new base for the staging yard "drops-in" to connect to the original layout. I have done this, including operating the staging yard section with a seoarate power pack, so I can remove the staging yard portion for portability and to be able to operate it as a separate layout, if I so choose. I am using standard Atlas wiring technique with one common rail and gapped power rails for each block on each portion of the layout - the original portion and the staging yard portion.
I have used my recent-vintage Atlas and Bachmann locos on these connected portions of the overall layout without any problem. They flow smootly across the gap between the two sections (so long as I set the polarity correctly, of course). However, my thirty year-old plus locos (including a SOHO steeplecab North Shore Line "Pup", a Walther North Shore Combo Coach and Suydham Brass Pacific Electric MOW car, all of which are out of production) won't go across the gap without stopping with one set of trucks on each side of the gap. Fiddle with the polarity and amperage as I may, the locos just won't make the transition.
What's the problem and what can I do to fix it? Must I re-power the ancient locos - which I definitiely don't wan to try because of the difficulty of getting motors which will fit, particularly in the SOHO Steeplecab? I'll appreciate your help.
Regards and Thanks,
EdwardjIII