Triangular junction polarity

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UrbanHermit
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Triangular junction polarity

Postby UrbanHermit » Tue Feb 23, 2021 5:40 pm

I am contemplating adding a fiddleyard to my oval layout. For various reasons, like the need to have trains entering and leaving in either direction, the design of the layout, and its position in the room, I want access to the fiddleyard to be via a triangular junction. This, of course, raises polarity issues. I'm not that wonderful with electronics, but the solution I've come up with is shown in this diagram. The layout is DCC and the points are dead frog, manually operated.

polarity.png
polarity.png (8.52 KiB) Viewed 147 times


Questions.
Will this work, or is there something I've missed?
It does mean that the whole fiddleyard changes polarity every time points A are changed. Does this matter on DCC?
I'm assuming that the simplest way of making the polarity change is to wire the track feed for the fiddleyard section (that is, above points A in the diagram) via a DPDT switch. Or is there something better?

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Flashbang
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Re: Triangular junction polarity

Postby Flashbang » Tue Feb 23, 2021 7:01 pm

Looks OK to me. I would use an automatic reverse loop module for the fiddle yard, but using a DPDT point operated switch would also be ok and cheaper. I would not rely on anything manually operated though, as it will get forgotten!
Swapping polarity doesn't hurt as its exactly what a RLM does anyway.
All you need to ensure is that all tracks in the fiddle yard from the IRJs are only feed from the switching method. :D
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RAF96
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Re: Triangular junction polarity

Postby RAF96 » Tue Feb 23, 2021 8:17 pm

It is not exactly simple + and - polarity as DCC is a square wave bi-polar format hence we are talking matching phasing. I.e. getting the positive and negatives lumps to match as they wave. If they are contra then its the same effect as DC - a short as up meets down.
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Suzie
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Re: Triangular junction polarity

Postby Suzie » Wed Feb 24, 2021 6:56 am

Yes, what you propose will work. It will be just as easy to use a live frog point - you don't need insulated joiners on the frog rails whatever point you use.

Sometimes a manual switch will not switch fast enough and trains in the fiddleyard with sound might be reset, but you could put a couple of microswitches adjacent to the tie-bar of the point if you are operating the point manually and see how that goes.

UrbanHermit
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Re: Triangular junction polarity

Postby UrbanHermit » Wed Feb 24, 2021 10:56 am

Thank you all for your input.

The idea was to take branches off the oval's bus wires and feed them through the switch, then attach all fiddleyard droppers 'downstream' of the switch.

The switch would be right next to the points A, yes, so that hopefully it would become natural to switch the two together.

I don't do sound, so that issue won't arise.

I hadn't thought of the frog thing. The frog itself acts as the insulator, yes?
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Flashbang
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Re: Triangular junction polarity

Postby Flashbang » Wed Feb 24, 2021 10:57 am

Hi
Suzie is correct, but the last sentence of the first paragraph is true but a statement I would not make publicly, as it can very easily be picked up on by others installing Electrofrog points anywhere on their layout and then they are left wondering why their systems keep shorting out! IMO and best practice.... It is always best to add IRJs to the frog rails and then add any new rail feeds after them as needed, regardless They won't hurt being there :D

In your case only, the frog if it were an Electrofrog point is always at the correct polarity to the abutting rails as its depending on which of the the switch rails position is closed to the stock rail. :D
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Re: Triangular junction polarity

Postby Suzie » Wed Feb 24, 2021 5:11 pm

It is peculiar to reversing sections that you put the insulated joiners on the outer rails instead of the frog rails. If you look at your diagram you will see that both the rails approaching the frog are connected to the same feed (the black feed).


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