Placement of (BD20) detectors

[Cajonpassfan]

I’m in the initial stages of installing BD20 detectors and associated block drops/leads, and want to make sure I place the BD20’s in optimal locations. One, they need to be easily accessible (not an easy feat under already scenicked sections), and two, I’d like to minimize the lengths of wire and avoid unnecessary runs and distances between detectors, signal drivers, and signals.

To complicate things, I’ve yet to decide on the control system. In the past, I thought about using MSC Master Signal by Ataras Engineering, because a friend had it on his large layout, but I’m open to other options, with simplicity being very important to me. I will not do JMRI and I’d like to not get into a discussion about why I should.

Bear with me. My signaling system will be very basic, as was the prototype in my era. It’s a simple double track railroad, with an ABS system on each track signalled in one direction only. Westbound, it’s mostly R/Y/G on a single signal head, with an occupied block triggering a red immediately behind it and a yellow one block farther back.

Eastbound, it’s mostly two heads, with a red over yellow indication in addition to R/Y/G, triggering three block signals behind an occupied block. All ABS signals are always on.

There are 14 blocks in each direction. There’s no need for interlockings; the home signals at the entrance to my division yards are manually set by the tower operator, who controls who and when anyone may enter his yard.
(There are a couple of exceptions where a heading-out switch lined to the siding will trigger a red for the main track, but I’ll deal with that another time).

Photos below show typical my east and west facing signals, as well as a BD20 installation that’s generating my questions about placement. Thoughts and ideas, hopefully based on experience, will be appreciated as always.
Otto K.

[Cajonpassfan]

Hmmm, not a single bite. Is it because I was asking for advice based on actual experience? Too much to ask?
Well, I’m placing the occupancy block detectors close to to the protecting signal at this point, must ha=e some protocol and the show must go on...
Otto K.

[C855B]

Hmmm, not a single bite. Is it because I was asking for advice based on actual experience? Too much to ask? ...

No, because you're modeling Santa Fe.   

It's actually because at least two of us here fooling around with detection at the moment, @GaryHinshaw and myself, aren't using BD20s. Gary's using RR-CirKits' system, and I'm using a mix of Model Railroad Control Systems' cpOD and Tam Valley Depot's new detection add-on to their QuadLN controller board. While similar to the BD20 with the remote current loop, there are differences in the wiring requirements and especially limitations among the systems. What works for us may not work for you, and vice versa.

IIRC @John uses BD20s, so he may chime in now that I've pinged 'im.

[John]

Sorry Otto .. I've been distracted by life the last couple of weeks and spent very little time here.

I don't use the BD20s on my layout .. but I would put the detector as close to the section being detected as possible.  Thats the NCE recommendation .. I'd put it as close to the middle of the section as possible.   You will also need to run a connection to your signal system ..  be it the SE8Cs or something else.

https://ncedcc.zendesk.com/hc/en-us/articles/201254549-BD20-Block-Detector





You said you need 14 blocks in each direction of a double track main ..  -- so thats 28 BDLs .. I would also make any crossovers their own detection section ..

It doesn't really matter if you are running ABS or full up CTC ..

[Cajonpassfan]

No, because you're modeling Santa Fe.   
...

Ha! But you’re wrong Mike, I actually have some ugly yellow stuff, too, like the pic below at Cajon station, only about 30 years earlier...as you well know they both ran over Cajon and kinda sorta still do.

Thanks John for the feedback, appreciate the link. I’m not yet ready to install functioning signals, but want to get the rough scenery in place and this would be the time to do the drops and at least detector wiring. I’ve learned the hard way it’s a bear doing wiring under scenery on a double deck layout
All the BD20’s I installed so far are close to their block, I was just asking for advice to make sure I’m not doing something I’ll regret later (been there done that too).

Thanks, Otto

[John]

Even if you don't plan on putting signals in yet .. its also a good time to run the wires from the detector to whatever location you plan on mounting the signal hardware.  I used CAT5 cable I salvaged from a dumpster at work and pulled out the pairs ..

[GaryHinshaw]

Hi Otto.  I'm not really familiar with the BD20's, but I assume the output signal here is some low-voltage switched DC, no?  If so, you should have no trouble feeding that upstream to a signal logic board with CAT5 pairs.  Since you don't know what/where those boards will be yet, I think the sensible option is to put the coils at the head of each block, so as to minimize the need for circuitous power bus loops.  I think that's what you want to do regardless.

As far as scenery goes, my strategy has been to postpone it until I get the under-layout wiring in place and working. Slowly getting there.... You're a braver man than I. 

[jagged ben]

I don't know how many wires each BD20 needs (four?) but on the club layout we found it convenient to group our RR-Cirkits CT detectors in groups connected by one CAT-5 cable.  Maybe pairs, one on each main, would work for you. 

[Cajonpassfan]

Thanks guys! Truly appreciate your thoughts.
Ben, the BD20 only needs two wires, pretty simple. Occupied/unoccupied. The other two terminals light up external LED’s if desired. Not desired here I don’t think. Yes Gary, 5VDC is the plan, and yes, CATS wire is the cats meow; I have some of it left over from a commercial construction job from my previous life. As to being brave, well probably more like unwise, but I’m trying to push toward some kind of ops, even without signaling; it’s been too many years of work without much reward so far and the natives are beginning to be impatient with me. You’ve seen that monster
John, your suggestion about running the two signal wires now is wise...I do need to figure out the signal logic driver locations sooner than later. But it’s yet another step...😜
Thanks again, Otto

[John]

Even if you dont do signalling .. having detection in place would allow you to also automate the train operation ... check ouit the "warrants" in JMRI

[Cajonpassfan]

Oh gosh, noooo, pleeez, no automation here🙀
That would just destroy the ambiance of circa ‘49 I’m trying so hard to recreate. On the Pass, everything was done manually then, and it was slow and took forever. The only “automation” I’d consider would be in hidden staging.
But I do appreciate that different folks have different ways of doing things. I just like it may way
Otto

[John]

Rule #1 always applise .. just pointing out some options 

[Cajonpassfan]

Rule #1 always applise .. just pointing out some options 

And I do appreciate it😎
Otto

[jagged ben]

So to continue the previous thoughts...
What I'd probably do, in the simple example, is put four detectors near a spot where you have block boundaries on both mains, so later you can run one Cat5 cable to your signal logic input board.  You could then probably leapfrog the next pair of block boundaries down the line, and detect the next four blocks one block further down the line.  Make sense?

As mentioned above, turnouts need to be detected separately.  So if you have a crossover at a block boundary you'd detect two turnouts and two blocks with one Cat5.  Of course if/where the track plan gets more complicated you'll have to get more creative.

[jagged ben]

Also in case it's not obvious, you'll probably end up cutting your existing DCC bus into pieces for each block, and you'll run a new main bus that branches off to run through the detectors at each group and power the cut up pieces of the old bus wires.  Terminal blocks with six sets of terminals might come in handy.