Re: Reverse Polarity at Edge of Power District

Mark Gurries

On Jul 17, 2015, at 5:26 AM, pbeinert@... [WiringForDCC] <WiringForDCC@...> wrote:
    I am not sure I completely understand your answer ("Yes") in relation to the OP's question.

On my layout, I have 1 DB150 for power and it feeds 2 PSX-ARs and 3 PSX's. With this configuration, I do believe that I have just 1 power district.

We have a common terminology problem here.

Power Districts are created by DCC circuit breakers.

Booster Districts are create by Boosters.

The above description shows you have 1 booster districts (DB150) powering 5 power districts (PSX…)

The confusion comes with the most common layout that only has the need for 1 booster.   There is never a need to talk about booster districts.  We only talk about power districts.

Only when a second booster or more introduced, do we need to talk about booster districts.

(Ancient DCC history:  Before DCC circuit breaker existed, the only solution for the creation of power districts was to use multiple boosters even if you did not need the extra power)

If instead, I add a DB150 as a booster and move the two PSX-ARs to it, then I would have 2 power districts and the reversing loop would be at the edge of a power district.

You now have two booster districts 

Booster District 1 has 3 power districts consisting of PSX's
Booster District 2 has 2 power districts consisting of PSX-AR

Your text diagram was very confusing….Its not your fault…text diagrams do not work do to proportion spacing AND a lot of blank spaces are involved.

Here is what I think you have:

I appear you have a double track main feeding into a double track reverse loop.  The two parallel reverse loop tracks are their own power districts (PSX-AR)

If you have two parallel main lines with EACH feed by its own PSX-AR —AND--- you have a crossover between them, then you have a special problem.  You normally cannot have two back to back reversing sections because when the train crosses, they will fight each other often resulting in shutdown like a short circuit.  Why?  Because they are each chasing the other in figuring out the correct track polarity.  They have no stable reference track polarity to target.


1) Follow the suggested recommendation of inserting a short section of "Neutral Track” between the two reversing sections.  The section of track needs to feed from a power district that does not have any autoreversing feature.  Its polarity must remain constant.  

2) The other option is to use a special feature of the PSX-AR.  You can program one PSX-AR to be the Primary and the other PSX-AR to be the Secondary.   When the train crosses the gaps between the two reversing sections, although both autoreversers see a polarity mismatch, only the Primary PSX_AR will change its polarity.  The Secondary PSX-AR will still function as a Autoreverser but it now knows to defer to the Primary when they come into contact with each other.

Best Regards,

Mark Gurries
Electrical Engineer
DCC Website & NMRA DCC Clinics:

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