Re: DCC Bus reversing question


Jim Betz
 

Blair/Don ... and all,

  You don't need to re-invent the wheel.  DCC works just fine as designed.  DCC wiring - if
you follow Gartner's recommendations - is also easy and fool proof (if you follow them
correctly).  Specific responses:

  1) No you don't need to swap railsync wires - and you shouldn't do so.
  2) Yes, you can use some kind of physical switch to "rewire" reversing
       sections.  Most guys like the automated aspect of a Reversing DCC
       circuit breaker.
  3) The best (in my opinion) DCC circuit breakers are the PSX series.  They
       work and work well.  They were designed with sound in mind.  They are
       electronic (which makes them fast).  Yes, they cost a bit more than 
       other brands of DCC circuit breaker - yes, they are worth it.
  4) A reversing section should not be up against another reversing section if
      you are using DCC circuit breakers.  They end up trying to out guess each
      other - and that competition usually goes on forever.  You can, with some
      breakers, set a different trip speed to prevent this ... but it is better to not
      have two reversing sections next to each other.  This is almost always
      possible thru careful selection of where your breaker boundaries are.
  5) A reversing section should be "longer than the longest train you will
      ever run thru it".  It does not have to be "the entire loop" - but most guys
      will set it up that way and it's usually easier.  Another way to say this one
      is "you don't want both ends of the train - or two trains at once - crossing
      the reversing section".  Again, the breaker gets confused and, in this case,
      ends up competing with itself.

  Reversing breakers work like this:

  a) Situation normal.
  b) A short occurs.
  c) The breaker -temporarily- tries reversing the polarity of the reversing
      section.
  d) If that works it leaves it alone and the train continues to run.
  e) If it didn't work then you have an "actual short" and the breaker goes
      into "there's a short" status.
  f) Most modern DCC circuit breakers also have an automated Retry.
     They will wait a second or two and then retest to see if the short is
     still there - this is what allows you to throw the switch and "clear the
     short".

  On my layout I have just one reversing section - it is the huge loop in
staging - the staging is 5 tracks wide and 3 trains long.  All trains enter
(and exit) staging thru just one track that goes to a switch.  All of the
track past that switch is both Staging and the reversing loop.  I have it
wired with just one circuit breaker.  If it ends up that there are too many
trains in staging (amp draw too high) I will cut the power to some of the
tracks (the ones that the turnouts make "unavailable".
                                                                                                - Jim

  

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