Re: DCC Bus distribution and snubbers question


(minor responses interspersed below, then read on here:)
The layout room is 52 x 28; the layout is HO.  Attached is the overall DCC plan. The room is basically a double deck, with three locations where it becomes triple.  Some context: the oval at the bottom is a three tier staging room, 10x28; The three peninsulas are fed from their bases(points A, B, and C), as are the outside walls of the room.  Be aware, there are more subtleties, but this gives you the flavor.  We have built about 30% of the upper deck, as well as the branchline on the third level, upper left (i.e. busses C2 and C3 are in place and in use).  We have been operating with a single DCS100 located at 'C'.  The time has come to build the rest of the upper deck, which requires boosters at A and B, hence my questions.  Once built, A will be the location of the DCS100, B will be a DB210, and C will be a DB150.  Each will have a quad circuit breaker; yes, this could change, but the basic topology doesn't change if I add or remove a breaker or two.

In short,
- There's around 600' of main line, plus two 120' interchange RRs, and a 70' branchline. 
- the topology of the RR lends itself to the chosen booster locations.  There's just a lot of track in excess of 30' from the chosen locations.
- most bus runs go in two directions from the boosters already. 
- Most of those runs are > 30' each way.  All busses shown are planned to be 12 ga. twisted.
- everything installed to date passes the 'quarter' test, and runs fine, with the exception of two reported instances of loss of control at the far ends of busses C3a and C3b.  These could have been operator error (i.e. using a DT400, you can end up with the wrong knob active, and only think you're changing your locomotive's speed...)
- I'm trying to avoid more boosters, as for the operations I plan, more current is unnecessary based on loco and passenger count; two 5A boosters and an 8A booster are enough.  That will service the three yards, and the long mainline country runs.  If I eventually need more, it's likely that the staging yard room will be the reason, and it will be easy to separate it out and add a booster or two.

From what I've read, adding snubbers improves performance to the point where I'll be okay with the longer runs, but how many snubbers to add is the question.  I'm well aware that each one presents an added current load, though not a lot; most recommendations list a 1/2 watt 100 ohm resistor.  If we assume 1/4 watt dissipation, each resistor draws about 50 ma.  (P=I*I*R, R=100, P=0.25, therefore I=0.05).  If I had to install 34 snubbers, I'd be looking at 1.7 amperes just for them.

Sorry for the length of this, but I'm trying to give you all the info you might need, as you seem to want to help.

On 2019-09-21 8:39, Ross Kudlick wrote:

I have 3 thoughts:

"each limiter's output will feed multiple bus segments" my not be convenient for operations.  A short in one segment will stop trains in all other segments which will be frustrating to your train crews..  I suggest having each 'circuit breaker' power a contiguous section so a track short creates minimal train operation disruption.
Already sort of done.  See plan.

"each of those runs will exceed 30' " --  Can you relocate your boosters to avoid exceeding 30' main bus runs?  A 60' length can be powered as 2 30' sections by lacating the booster with a main bus configured as a 'T."  You could power a 60' section on both levels (120' total) with a single booster without exceeding 30' main bus length.   This will mimiize (and possibly eliminate) any need for 'snubbers.'
Already done. 

Circuit breaker selection - consider using 'single' breakers rather than a 'quad' breaker.  Individual breakers can be located along the main bus creating a 'sub-bus' feeding  each section.  This mimimizes the amount of large gauge bus wire needed (and mimizes the 'spaghetti bowl' of wiring under the railroad).  I prefer the PSX breakers; others may offer other suggestions.  (Note - a PSX4 is actually 4 indiviual PSX breakers that can be snapped apart for individual installation.)
Noted.  I have the PM42s, and intend to use them until they annoy me enough, or are inadequate, at which point PSX is likely where I'm going, unless there's a newer product available.  We'll see.

 Designing to 'best wiring practices' now will be benficial in the long run.  You may have to think 'outside the box' for the best solution for your railroad.
Yep.  Already trying to do that, that's why I asked before I proceeded.  Short of spreading boosters all over the place, I would have thought "best wiring practices" would include snubbers, where length dictates.  Not sure which "best wiring practice' you think I'm violating, so please elaborate.

But thinking outside the box requires that one actually know where the box boundaries are...


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