Help with DC block electrical setup

[Maletrain]

[Not sure what subforum to put this in, so mods may need to move it.]

A friend has asked me for some help planning the wiring for his layout.  He has decided to make it DC, at least for now, because he has only old DC locomotives and 4 DC throttles.  But, I have never wired a DC layout for multiple throttles, and am now using DCC for my own layout.  So, I am looking for some sage advice concerning wiring DC with multiple throttles.

His layout is basically 3 concentric ovals with one end of the inner oval not there.  The ovals interconnect with cross overs between pairs of them.  All 3 ovals actually are flattened into dogbones, so there is parallel trackage from the two sides of the innermost oval running next to each other.  He has put crossovers connecting the two sides of the innermost oval, making the end of the oval that was not cut off into a return loop that needs a reverser.  Only one side of the innermost oval has crossovers to the middle oval, so both sides of that inner oval can be put in the same block and the reversing section on one end does not affect any other oval.  If I get some time tonight, I may make a simplified drawing in Anyrail if this description turns out to confuse.

For DCC, this could all be wired as 1 block except for the reverser loop.  But, it would make more sense to wire it as a block for each oval, plus the reversing section, making 4 blocks.  For DC, the two outer ovals should be wired as at least 2 blocks each, so that a train could be stopped in one block of each oval while another train crosses over between ovals in other blocks for those ovals.  So, I am seeing a minimum of 6 blocks for DC operation.

What I am not experienced with is how to use multiple throttles with multiple connecting blocks on DC.  I am thinking that each block should have something like a rotary switch with 4 positions for selecting which of 4 throttles it is connected to.  I am thinking those rotary switches should have 2 contacts for each position, so that both rails are switched (rather than have a common rail).  That way only one throttle/power supply can be connected to any given block of track, and adjacent blocks can be set to the same throttle when it is intended for a train to cross a block boundary.

What I am not clear about is what happens if a train inadvertently crosses a boundary between blocks that are powered by 2 different throttles?  Is that a potentially destructive situation?  If so, what sort of safety mechanisms have been developed for that situation?  This is where my experience and research have never been focused.

So, I would appreciate those who know either providing a brief explanation or directing me to a reasonably concise reference that I could pass along to my friend.

[rodsup9000]

What I am not experienced with is how to use multiple throttles with multiple connecting blocks on DC.  I am thinking that each block should have something like a rotary switch with 4 positions for selecting which of 4 throttles it is connected to.  I am thinking those rotary switches should have 2 contacts for each position, so that both rails are switched (rather than have a common rail).  That way only one throttle/power supply can be connected to any given block of track, and adjacent blocks can be set to the same throttle when it is intended for a train to cross a block boundary.

That the way we did it back then. The loops may need to be broken into blocks also.

What I am not clear about is what happens if a train inadvertently crosses a boundary between blocks that are powered by 2 different throttles?  Is that a potentially destructive situation?  If so, what sort of safety mechanisms have been developed for that situation?  This is where my experience and research have never been focused.

The overload on one of the throttles would kick or the throttle that is assigned the block the train ran into would have control.

[randgust]

If you're seriously looking at four cabs, and multiple operators, save yourself a lot of grief and do DCC.    If you've got a layout that rarely sees multiple operators, or no more than two, and particularly if you have a multi-track main or separate zones, DC is a good choice.

If you cross blocks and the polarity is the same, no harm, no foul, but whoever has the 'destination' block is now in control.

If the polarity is different, dead short, overload protection will kick in just like you dropped a penny on the rails.  The wheels short out.  Unlike DCC, you won't melt a truck out.   Or damage a mechanism.

One of my good friends built a six-cab basement-sized layout, double track, all DC, and often four operators.  What a complete and total nightmare to operate with rotary switches.   Miles of heavy wire.  Operator confusion yelling from person to person on block sets.  All local panels so you literally had to sprint to the next panel to check your cab assignment.  Runaways.   I hated running on that layout.  And with rotary switches, you can momentarily assign a cab as you 'go by it' to the next one, so every once in a while you may inadvertently pick the wrong one, or set up a dead short in passing.

Now, I'm a DC guy, two-cab layout, medium sized (6'6 x 8 ) layout, very happy with it.  I rarely have a visiting operator, and the room is too small to hold more than two people anyway.  DCC is a waste of time and money there. 

[wm3798]

Without a track diagram, it's hard to visualize what you're describing.
It would also be helpful to understand how he plans to run the layout.
Are there going to be industries to switch or a yard?
Or is he jus looking to park a couple of trains while a few others loop around?
The blocks have to make sense operationally as well as electrically.
Can you shed some light on these aspects?
Also, with three loops, why would there be four throttles? 
And, just how big is the layout?  Is there room for several blocks to exist in each loop?
Lee

[Maletrain]

As I said in the OP, this is not my layout.  And I suspect my friend will eventually go DCC, so I am trying to make sure that it is not a hard conversion.

He is thinking 4 throttles because he has 4 throttles.  But, I think the layout is more a one or two person operation.  With only 2 throttles, he could just use double pole slide switches on the 6 blocks.  But, he might want to have 2 unattended trains "orbiting" on the outer ovals while he putters around on the innermost oval, making up and breaking down trains.  So, maybe 3 throttles and a spare?

Here is a quick AnyRail drawing of his layout in sort of a schematic form - it actually has some passing sidings and spurs on the outer 2 ovals, plus more yard tracks on the inner half-oval.  I made it 6 blocks, as indicated by the six colors, with isolated rail joiners between blocks.

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If I were wiring it for DCC, I would probably make the two outer ovals each one breaker section, so it would be 4 sections.  I would just replace the throttle selector rotary switch and dp-dt reversing switch for each DC block with a PSX breaker and an autoreverser for the return loop on the inner half-oval.

Anybody have any helpful thoughts?

Added: I just read Lee's post and think I have answered his questions except for size.  I didn't measure it, but I an guestimating about 4' x 12'.  He seems to intend to do operations mostly from the cutaway in the middle of the dogbones.  I don't know if he has really considered how he will switch the industries in the spurs in the right hand loop of this drawing.  I think he can easily switch the yard in the left hand loop from the cutaway.  The outer ovals have grades, so that the tracks on the bottom of the drawing are elevated relative to the tracks along the cutaway.  He has Rapido couplers on most of his equipment at this point, which is another thing I have avoided learning how to actually use to do ops. 

[mmagliaro]

As others have said, yep, rotaries for each block and if you cross from one throttle's block into another with opposite polarity, you get a short.  The answer to this in DC world was always, "Don't do that".
From what I see on that track diagram, I would definitely want another block leading into those yellow sidings.  Otherwise, you can't switch them while a train is running on the outermost loop.  I'm assuming he will use power routing turnouts so that any engine parked in a siding will shut off by setting the turnout against it.  I also don't know why the large sections of the outer two loops would both be yellow.  If the plan is to allow two trains to "orbit" the outer loops in roundy-round mode, you want those two trains to always be controlled by different throttles so you have independent speed control of them.  The way it is now, every time either train on an out loop goes into a "yellow" zone, it is controlled by the same throttle.  It's going to make for some weird speed behavior unless you set yellow, red, and blue all to one throttle, and if you do that, the trains speeds won't be independent.  I would make the yellow part of the outer loop into another block to address this. 

[GaryHinshaw]

The outer/lower block is actually orange, not yellow, so it should be fine.  I think the scheme you have outlined is fine, but it won't be very fun for guests to operate.  As Randy notes, he should really go DCC if there are to be 3 or more operators.  Wiring and using all those rotary switches won't be fun.

If the purple section is made polarity reversible, the train traversing it will have to stop in the block to switch polarity, unless he gets really good at simultaneously switching the polarity and throttle direction switches.  All the other blocks can be fixed polarity, so the worst thing that happens at a block crossing is another throttle takes control.  If the other throttle happens to be set in the opposite direction you'll have a short and one or both affected throttles should trip a breaker.

[mmagliaro]

Ah... I see now that outer loop is a slightly different color (it looks like a "dark yellow" on my monitor, not orange, but as long as it's different, yes, it should be fine).

Is this layout drawn with 12" blocks?  So it's about 16 feet long?  What Gary points out about the rotaries being "not fun" to operate could definitely be true.  Either you put the block control rotary switches in near proximity to their respective blocks, so that as you walk around the layout, you can just turn the rotary switches and follow your train, or you have all the rotaries at a central control panel, and you always have one person be a "dispatcher" who assigns the blocks and turns the rotaries.    Since I assume these throttles are not walk-arounds, you are kind of stuck with a central point for the rotaries and that's going to be clumsy unless somebody plays "dispatcher" (which is not an interesting job on a layout with only 7 blocks).

In a system with a LOT of blocks, I always liked the "dispatcher" idea because with all the block rotaries in one place the wiring is easier and it felt more like a real railroad (and more like a DCC system) when the operators don't have to worry about blocks at all.  They get train orders from the dispatcher, the dispatcher assigns the blocks to the engineer's throttle, and everybody just thinks about running trains.  This really only works when there are a good number of blocks and the layout is large and spread out.

I disagree that wiring for 6 (or 7) blocks is hard.   Even if you do everything double-pole as you intend, that's 12 or 14 point-to-point wires from all the blocks over to the rotaries, and then  an 8-wire "bus" you could run from the 4 throttles around the layout, tapping them into the rotaries wherever they are.   This couldn't take more than a few evenings of work to wire up.

My sense is that the owner of this layout is primarily thinking about having something with lots of trains running at once, at least initially, but doesn't want to shut the door on operations (hence future conversion to DCC).  But my other sense is that for operations, they will want to make a whole new track plan at some point because the way this is set up, operations look severely hampered and unrealistic to me.  It's basically a roundy-round layout with some sidings tacked on.

[DKS]

If the owner wishes to operate more than one train on either of the outer loops, then each loop will need a minimum of three blocks. Otherwise, continuous train movement would not be possible.

...it actually has some passing sidings and spurs on the outer 2 ovals, plus more yard tracks on the inner half-oval...

This may affect the number/length of the blocks on the two outer loops, so if block control wiring is a solid given, then these would need to be shown on the plan to move forward.

[Maletrain]

Thanks for the feedback, folks.

I really don't know that my friend has made up his mind on several aspects.  He has been talked into and out of DCC by other people, and seems to be looking to me for "how to" information to understand what his options really are with equipment that he already has (but has never used).  I am not so sure I am the best guy he could use for that, but apparently I am what he has, for now.

Regarding the outer loop operation: He is making the layout pretty high, so I think reaching over from the central cutaway is not going to be feasible for switching those spurs.  So, I am thinking the best way he can get what he wants is to put six (or more) 3-position rotary switches and 3 throttles at a central location in the cutaway, and put the bus wires to the back (bottom) block of the outer loop through a dp-dt switch on that side of the layout, with the input from its central position rotary switch being one option, and the 4th throttle as the other "local" option for when he is on that side of the layout to do switching in that block.  That way, he can run trains on the 2 loops and do switching in the yard from the cutaway without going around the layout, plus go around the layout to switch the industries if and when he feels like it.

Regarding the size of the layout, don't try to scale if from the squares in my diagram.  I just quickly put that together with AnyRail as a schematic to show the logical connections for the track that needs to be controlled.  I put is some convenient curve sizes, but the actual layout has much less smooth curves and some additional sidings.  I put spurs where there are spurs, but not as many as he actually has. 

What he wants to do with ops involving the sidings is not clear to me (yet?), and may require a lot more blocks.  He seems to be thinking about "meets", but I don't know if he intends to be doing "overtaking" meets or "contrary direction" meets - the latter case being much more difficult in DC than DCC.

At this point, I think I have what I was looking for from the crew, here.  Thank you all for helping me think about this.  I may be back with some more questions after I talk to my friend, again.  I think what I am really doing is giving him a better understanding of what he can and can't do with DC.  He seems to be a little uncomfortable with the electronics aspects of DCC, and, so far, doesn't have any DCC equipment, but wants to do things that are much more easily done with DCC.