More on my "Ultimate TTRAK control box"

[Ed Kapuscinski]

I've been corralling some thoughts on the plan for building what I'd consider the ultimate TTRAK layout control rig.

The guiding principle is creating something that meets our current needs, is easy to use, and easy to transport.

https://docs.google.com/document/d/1gXFbqMIHtBghBynAfWHWBLAE4GhR1HDFne_FKjPzGd4/edit?usp=sharing

I'd love to hear what you think about what I've put together before I toss it to the wolves of the club membership.

[mmyers]

ED,
 Looks like a comprehensive list. I would delete the PSXX-AR and PSXX1. instead use a PSXX2. That way both outputs to red and yellow would be protected. A short on one line wouldn't stop the other. The need for an auto reverser is probably minimal to none. One could be added inline if the need would arise.

Martin

[Ed Kapuscinski]

ED,
 Looks like a comprehensive list. I would delete the PSXX-AR and PSXX1. instead use a PSXX2. That way both outputs to red and yellow would be protected. A short on one line wouldn't stop the other. The need for an auto reverser is probably minimal to none. One could be added inline if the need would arise.

Martin

Thanks! You're the guy who I'd consider the authority on stuff like this!

I know the reverser seems weird, but it's to address that equally weird quirk of TTRAK where the two tracks are wired backwards to each other. One of the most annoying aspects of running on a TTRAK layout is that you short everything out trying to cross from one main to the other.

I want to prevent that.

I thought about just flipping the outputs to the yellow track, but then I realized that there might be times that I haven't anticipated where that might not be ideal. I figure the auto reverser will cover more of those for relatively little incremental cost.

[Maletrain]

I'm working on the concept for a T-Trak display for our club, so I have been thinking about this issue.

What I am thinking so far is that we will want to support both DC and DCC at various times on various tracks.  I am thinking that a "power input box" with 2 DPDT switches would suffice.  There would be separate feeds from the DC and DCC power both going to both DPDT switches.  The track feed outputs of one switch go to the inner track and the outputs from the other switch go to the outer track.  For DC, the outputs are reversed between the tracks to provide for compliance with the standard requirements to run in opposite directions with one DC controller.  For DCC, the outputs for the inner loop could be wired to allow crossover without shorting the 2 phases (swapped feeds on the inner track compared to the DC setup).

This provides the ability to run DC or DCC on either track, independently, and provides for crossovers with DCC, but not DC.  It does not protect against shorts with DC crossovers, and does not provide for separate DC speed controls on the 2 loops.

A modification to this would be to have 2 DC controllers (or one power pack with 2 output controls) and have separate inputs to the control box for the 2 DC circuits to the 2 tracks. 

With everything labeled clearly, I don't see any problem with this arrangement, except that a set of modules that includes crossovers could cause shorts with DC if people try to use the crossovers when running DC.  And, with DC on one track and DCC on the other track, there could be trouble if there are crossovers and somebody tries to use them.

I think crossovers are going to require some thinking, no matter what the power feed design is, because of the T-Trak standard design.  I could add a "crossover compatibility switch" to the track feed from the DPDT switch that goes to the inner loop, and NOT have the DCC feeds already swapped.  So, thinking about crossovers would be an obviously required step in the setup because of the visible switch and its label. 

But, that doesn't address the issue of somebody trying to use the crossovers when there is DC on one loop and DCC on the other.  Some sort of warning light to detect that situation, placed next to the "crossover compatibility switch" seems like a good idea, but I have not figured out a good way to wire such an indicator light.  I don't think a simple LED wired between a DC track and a DCC track would work if the two different controller power sources are properly isolated from the house current.  Ideas welcomed.

So far, I have zero experience actually running a T-Trak layout, so I am looking to those here with that kind of experience to show me the pitfalls.

[Ed Kapuscinski]

You're onto a lot of the same stuff I am.

I'm not too worried about red/yellow DC mis-matches because it's easy enough to deal with that via the throttle direction controls.

The DCC polarity issue is the reason my plan incorporates two separate circuit breakers, one of which is an auto reverser (that swaps polarity if there's a short like that).

My big concern is that same DC/DCC issue. I haven't figured out a solution to that, and I'd love someone to say "I know just the thing!". It's tough because it's a use case that's very specific.

[Maletrain]

On the DCC inadvertently connecting to DC via crossover issue, the only solution I have been able to conceive of requires more poles on the DCC-or-DC switch for each track feed AND the "crossover compatibility switch, with a separate power source (probably a couple of AA batteries) that feed a couple of LEDs, with the logic set up to light a red LED for situations that we don't want to allow, and a green for situations we do want to allow.

A little more complex, but seems doable.  I just need to sit down and figure out the logic for the LED connections to switch positions.  Or, am I missing something?

Edit: OK, I figured out how to make a 3-lead LED be green when "crossover compatible" is turned off or both loops the same (DC or DCC), and red when "crossover compatible" is turned on and both loops are not the same (DC or DCC).  It requires an extra pole on the crossover switch and one of the loop feed switches, and 2 extra poles on the other loop feed switch.

But, now I am wondering about allowing crossover when both loops are DC, but they are powered by separate controllers.  I don't have any experience with the old-school DC block controls, either.  So, with 2 DC controllers, obviously they would need to be set to the same polarity and voltage to cross over without a short or some sort of speed change.  But, would that be OK, or is there a problem with the short-term double paths to 2 separate power sources?

[peteski]

I don't seem to understand how a crossover wired into double track requires polarity change on DCC.  If you have a layout consisting of a double track loop with a crossover installed somewhere on the loop, there is no polarity change when the trains cross over (there is no reverse loop). Why would that require a reverser? The polarity of both tracks is the same all around the loop.

Maybe I'm just not visualizing it correctly?

[Maletrain]

I don't seem to understand how a crossover wired into double track requires polarity change on DCC.  If you have a layout consisting of a double track loop with a crossover installed somewhere on the loop, there is no polarity change when the trains cross over (there is no reverse loop). Why would that require a reverser? The polarity of both tracks is the same all around the loop.

Maybe I'm just not visualizing it correctly?

Peteski, the problem is the T-Trak standard requires the 2 loops to be wired in opposite polarity, so that a single DC power controller can run trains in opposite directions simultaneously of the separate loops.  So, a crossover is always a short in that design, no matter whether it is DC or DCC.  Standard T-Trak does not accommodate crossovers.

But, people want to do things not envisioned by the standard, so we are trying to accommodate that without creating any smoke.

[peteski]

Peteski, the problem is the T-Trak standard requires the 2 loops to be wired in opposite polarity, so that a single DC power controller can run trains in opposite directions simultaneously of the separate loops.  So, a crossover is always a short in that design, no matter whether it is DC or DCC.  Standard T-Trak does not accommodate crossovers.

But, people want to do things not envisioned by the standard, so we are trying to accommodate that without creating any smoke.

That makes sense now. Still, looks hardwired in opposite polarity? That seems odd to me. So you can only run 2 trains with a single throttle?  Not very "showy" or exciting.

With NTRAK our goal is to run multiple trains individually controlled, even under DC with block control if the layout is large enough. Lots of trains moving around attract spectators.

[Maletrain]

Peteski, Ed and I are probably designing to different criteria. 

Ed is probably thinking about train shows and attracting spectators. 

I am thinking about a club environment display that is intended to draw participants, more like the original T-Trak concept of a bunch of people (some kids) getting together in a person's livingroom to assemble a roundy-round layout on the floor and run their trains for an evening, then take it apart and go home with their modules.

But, the U.S. potential clientele is likely to get bored with such small layouts unless they can do something more than run trains in circles, 2 at a time.  So, DCC is a way to get more trains on the tracks and do more things with them.  And, there is a lot of DC only and DCC only participants that I would like to be able to accommodate at the same time - hence the idea of allowing one loop DC and the other DCC.

None of that is very complicated until you try to accommodate crossovers - especially when those crossovers could be incorporated in a DC, DCC or split DC/DCC configuration.  That is the issue that I am working to optimize for my situation.  With a lot of participants that are getting their introduction to model railroading through participating with this display during one-day events when they can bring their own modules, there is a lot of potential for doing dumb things unintentionally.  So, I am trying to gin up a control board that makes the options and their limitations reasonably clear to the less experienced participants.

[Ed Kapuscinski]

Peteski, Ed and I are probably designing to different criteria. 

Ed is probably thinking about train shows and attracting spectators. 

I am thinking about a club environment display that is intended to draw participants, more like the original T-Trak concept of a bunch of people (some kids) getting together in a person's livingroom to assemble a roundy-round layout on the floor and run their trains for an evening, then take it apart and go home with their modules.

But, the U.S. potential clientele is likely to get bored with such small layouts unless they can do something more than run trains in circles, 2 at a time.  So, DCC is a way to get more trains on the tracks and do more things with them.  And, there is a lot of DC only and DCC only participants that I would like to be able to accommodate at the same time - hence the idea of allowing one loop DC and the other DCC.

None of that is very complicated until you try to accommodate crossovers - especially when those crossovers could be incorporated in a DC, DCC or split DC/DCC configuration.  That is the issue that I am working to optimize for my situation.  With a lot of participants that are getting their introduction to model railroading through participating with this display during one-day events when they can bring their own modules, there is a lot of potential for doing dumb things unintentionally.  So, I am trying to gin up a control board that makes the options and their limitations reasonably clear to the less experienced participants.

Oh no, while my primary use is for BANTRAK's train show usage, the actual use is going to be very similar. I'm not aiming this thing to be the solution for BIG layouts. It's the solution for "typical" layouts.

Here are a couple of examples of the layouts I'm thinking of.

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[signalmaintainer]

Don't forget a "Schnott" trigger, @Ed Kapuscinski. No control is complete without one.

 

[squirrelhunter]

Ed, in my clubs setups we just went with the low tech solution of having the outer loop be DCC, and for any inner loops that have crossovers with the outer loop, we use a cable right where power is put into the bus to make sure it is the same polarity for all DCC tracks. We haven't had any issues but we make sure to do the necessary polarity swap where the power is first added- I could definitely see unforseen issues if it is done closer to where power gets to  the modules or module by module.

[Maletrain]

I haven't seen any comment on my question about whether crossovers between the 2 loops would be a problem if the 2 loops are both DC, but powered by different transformer power packs. 

I am thinking I might want to avoid that.  If so, a switch on the input side of the control box, that selects between a shared DC supply or 2 separate DC supplies, with input to the "crossover compatible" switch light could be added.  And, to make a crossover work, that switch could then be moved to share one DC supply for the duration of the crossover, then returned to the 2 DC supply mode after the crossover move is completed. 

If I do something like that, I think I should include a second indicator light that is visible from the crossover locations that is red unless a crossover is OK at the time somebody running trains looks to see if it is OK to cross over.  That might need some additional poles on some of the configuration switches.

But, that is more complexity that I don't want to add if it is not necessary.  So, any comments on whether it is necessary to avoid crossing over when there are 2 separate DC supplies to the 2 loops?

[peteski]

I haven't seen any comment on my question about whether crossovers between the 2 loops would be a problem if the 2 loops are both DC, but powered by different transformer power packs. 

Yes, that would be a big problem.  Consider what would happen if you took 2 charged 12V car batteries and connected them together with opposite polarities.  That will create lots of sparks and melted cables.

If you think about it, by only connecting one set of terminals (one positive to the other negative) you have no created a 24V battery across the other set of terminasl (since they are connected in series).  Now you you connect the other terminals together, you are creating a dead short across that 24V battery.

Same thing will happen if you do this to 2 power packs at opposite polarities. As soon as both sides are connected together, you short them out.

Even if the 2 power packs are same polarity, any voltage difference between them will cause current ft flow from the higher voltage one to the lower voltage one.  That is not a desired effect.