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Not so, because there is no technical reason why, when the second
gap is bridged, that the first AR doesn't respond at the same time
as the second, which is the same as having the two ARs adjacent
with no fixed zone between. As long as you create a condition
wherein the two AR's see trip conditions from the same shorting
action, the result will depend on the response times and
sensitivities of the devices, resistance of the wiring internal to
the loco, and the occasional interjection from Murphy.
Continue backing your train, repeating your diagram, until you
place LLLLLLLL across all three - AR/Fixed/AR; additionally,
ensure that you acknowledge in your scenario that LLLLL is one
electrically contiguous locomotive, not a 4-diesel consist, for
example, with independent pickups. When your loco hits that
second AR, you have a short, and yes, the first AR does respond as
well as the second one, as that short propagates across the loco
to the original AR. That is the case I described (please revisit
my description earlier in the thread), and the case I have
encountered before on my own layout. If you insist on describing
the second short only in terms of a wired truck, passenger car, or
wheelset that is independent of the locomotive wiring, then yes,
you're correct, but not answering the OP question.
On 2021-05-23 12:27, whmvd wrote:
What you describe is safe. No question. But it will also,
usually, mean that you make a longer intermediate section than
necessary. The 'bridging' you describe is indeed the tricky
bit, but: only when the AR action HAS NOT YET TAKEN PLACE.
Consider a loco that pushes a lighted long wheelbase 4-axle
wagon through the reversing sections, and all axles of the
wagon have power pick-ups. Also assume that the polarity on
entering is the worst it can be.
A = fixed polarity section
B = AR section 1
C = fixed polarity intermediate section
D = AR section 2
E = fixed polarity section
| = isolators
L = loco
W = wagon, with P being power pickup
Initially B has opposite polarity/phase to A, D and E
(which are fixed), but the same as C.
1. Pushing loco moving to the right.
2. A<->B boundary bridged, AR B switches, so A,
B, D and E now have the same polarity/phase.
3. Wagon spans the A<->B boundary. No AR
action. All further bridging of A<->B now
4. B<->C bridged, AR B switches.
5. C<->D bridged, AR D switches, so B, C,
D and E now have the same polarity.
6. C<->D still bridged, No AR action.
7. Nothing bridged, wagon spans entire section C,
but, crucially: there is no problem, because there is
and so on - the rest is trivial..
And this is why only the minimum size of a TRUCK
counts. A longer size becomes necessary only when a
truck is not really a truck but a single axle. In
other words: the long wagon only has one power
pickup at each end (never mind the number of wheels,
the number of pickups is what counts).
Theoretically, it should STILL work. But in
practice, a short on a one-axle truck can be very,
very easily missed as it would be just the wheelset
closing the gap in the rails on its own. See what
happens in the figures above when the short in step
5 is not seen. After that, spanning the C section
(fig. 6) DOES mean trouble, because the B<->C
short has not occurred and the reversers now fight -
exactly what should be prevented from happening.
One solution (yours) is to make the C section
long enough to span the entire wagon, which is fine
and works. However, if that is not convenient (and
the layout might well dictate that it isn't) then
the other possibility is to stagger the cuts in the
rails. That increases the chances of the one-wheel
short occurring by a lot. This is the only advantage
to staggering that I have ever been able to see. But
I repeat: there is ONLY a problem in case of
one-axle trucks (if you can even call them trucks).
On Sun, 23 May 2021 at 12:27,
Think of any single loco as a pair of wires
hovering, one over each rail, drooping to touch the rail
at each point where a loco's wheels do. In order for a
short length between AR sections to do its job, it must be
long enough to prevent the wire from bridging the two AR
sections. So before the wire enters the second AR it must
leave the first AR.
Now generalize this. The user must be aware
of the longest electrically connected "thing" he runs.
For example if you run a dummy loco but wire its wheelsets
to an adjacent engine, then that becomes the longest
That defines the shortest non reversing
section between AR sections.
Hope this helps.
Sent from his
-------- Original message --------
Date: 2021-05-22 22:30 (GMT-05:00)
Subject: [w4dccqa] Minimum length on Non-reversing
I realize that we have addressed the question of
Auto-Reverse (AR) segment wiring extensively in the past ( a
discussion in which I even participated). I understand that
the track of an AR-wired segment cannot be electrically
connected with another AR-wired segment, as the two will go
to war with one another, switching back and forth until
something blows. And I also understand that for similar
reasons, the minimum length of an AR-wired segment must be
as long as the longest train that will run over it (or at
least as long as the length of the train to the last car
with either steel/metal wheels or an electrical pick-up that
would cause a short if the "polarity" is not correct).
What I am unclear about is the minimum length of the fixed
(non-reversing) "polarity" segment that separates AR-wired
segments. I believe I recall a suggestion that the
non-reversing segment be at least the length of a
locomotive, but not sure why that would be required.
In my case, my layout is a basic figure-8 pattern with two
direction reversing segments, each wired with an AR
circuit. Problem is that one of those segments (about 6
feet long) was shorter than my nearly 7-foot long N&W
passenger train (six 11+" MTH passenger cars plus a 13+" MTH
N&W J loco). In reconfiguring, I can lengthen the
AR-wired segments to include portions of the figure 8
(assuring that both AR-wired segments are long enough),
particularly if I do not have to be concerned that the
length of the non-switching "polarity" segment have a
substantial minimum length, e.g., not at least as long as my
I also assume that I can have more than one non-reversing
segment separating AR-wired segments without any problems as
long the "polarity" of all of the non-reversing segments is
Apologies if we have already covered this sufficiently in
previous discussions; but I do not recall the definitive
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