Need some DCC help, please (reverse loops).

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Jacko

Ranulf,
 
I took a look at Allan Gartner's site:
  http://www.wiringfordcc.com/
 
And developed this suggestion:
 

 
I would recommend one reversing section as marked out above in blue and green the way Allan draws his illustrations.  I have drawn it large enough to encompass all the reversing shorts, and a similar train length as would fit on the wye.  As the Darkstorm says though you should avoid trains shorting out in two different places at the same time.  Only one reverser is needed for the reverse section as drawn.
 
Any thoughts, corrections, improvements to my grand idea guys?
 
Thanks,
Charles

 

What I'm referring to is the electrical pickup for the cars.  This affects layout operation even if you have not installed lighting units in those cars.  The internal electronics are irrelevant.  (This is also an issue with block wiring in some cases, it's not just a DCC issue).

Every car has a "footprint" which covers the length that the car must travel to clear an electrical gap.  Until the footprint crosses the gap, the two blocks are electrically connected to each other.  If the blocks are reverse polarity from each other, either a short occurs, or an auto-reversing circuit might kick in.

• For a car with plastic wheels, their footprint is zero: the car does not conduct electricity.

• For a car with metal wheels but no wipers or other pickup, each axle has a small footprint of a small fraction (1/64?) of an inch.  Each wheel will temporarily bridge the gap as it crosses.  (If your gaps are larger than this size, then these cars also can be treated as zero.)
• For a car with wipers or pickup on it trucks, the footprint for each truck is the distance between the axles on that truck.  For passenger trucks, this can be as large as an inch. 
• For some cars, and many locomotives, all the wheels on one side are used for electrical pickup. (Kato passenger cars are the most common example here, where the trucks are connected across the car by copper strips.)  This is desirable for good operation, but it means that the electrial footprint spans the length of the car. 

The DCC problem comes when two different sections of track are connected to the same power district, and two cars bridge gaps between those two track sections and a third common track section (either of these districts could be auto-reversed).  Now all three sections are electrically connected, but no polarity for the auto-reverser can correctly power them.  In this case, a short occurs, and the districts shut off.

Ranulf,
 
What you said about isolating the turnout and length of the reversing section sounds good to me.  Just to be complete I updated the drawing.
 

 
Have fun,
Charles