Re: Where to isolate on large loops and wye


I concur with Allen.  As long as

- the normal section is truly longer than the longest single electrical entity crossing it (i.e. if you wired all pickups on two locos together to lengthen their electrical footprint for some reason, that would become your longest single entity), AND

- as long as both reversing sections are long enough to not have anything happening at their far boundaries simultaneously on the same train, and short enough that no other train is going to add confusion to the situation,

then a single separating section of track need not be train length, just longer than the longest single 'footprint'.  The reason is, either AR can align itself with the 'fixed' short zone without 'the sands shifting in the meantime', so they won't start that annoying flip-flop-flip that never ends, and all will be stable.  Neither case 1, nor case 2, below, suffices to begin the flip-flop behaviour.

A good example is the "hoary dogbone with middle crossover", where both loops are fed from separate reversers, and the crossover is wired 'straight'.  No problem.  Whether the crossover is aligned straight, or as an X, both reversers will behave.


On 2/25/2021 3:41 PM, emrldsky wrote:
On 2/25/2021 1:02 PM, wirefordcc wrote:
Does anyone have a scenario you think I need to think about that might be a problem?
Hi Allen,
Two instances come to mind, although I do not know how common they might be.
1. A long passenger train with all lighted cars, and
2 A freight train with helpers in the middle and at the end.
In these situations I would imagine the fixed polarity track to be shorter than the train length, possibly a lot shorter, so the front end would be in one reversing section, the middle in the fixed polarity section, and the end of the train in the other reversing section.
I can see some home layouts, especially those in small spaces, where the fixed polarity track would be small for space reasons because the reversing sections need most of the space for the loop radius to be big enough to make the turns with the longer cars.

Mike G.

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