Turntable wiring

[crosbystills]

I have recently modified my hornby turntable ready to add a decoder. I followed the instructions from Hornby and so far everything is ok. (no decoder yet) So I now have a turntable with no direct electrical connection from the turntable rails to the turnout rails. In my case there is only one of these. That section of rail is now wired to the main bus. I am puzzled as to why whichever end of the turntable rails is opposite the turnout there is never a short as the locomotive is transitting onto the new section of rail?

Any clues would be welcome.

[Chrissaf]

I am puzzled as to why whichever end of the turntable rails is opposite the turnout there is never a short as the locomotive is transitting onto the new section of rail? Any clues would be welcome.

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Because the TT has a 'split-ring' that reverses the polarity of the bridge rails when it rotates through 360°. You have been very lucky in your selection of which outlet track you have chosen to use and you have not wired it in reverse when you connected it to the main DCC bus.

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Too late now, but the Hornby method of stripping out the bridge rail contacts is not the best DCC modification method to use. If you had asked about 'how to modify the R070' first, you would have been directed to the threads below that provide a different modification methodology. The 2nd link shows a diagram that explains the bridge track rail split-ring reversal in more detail.

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R070 Turn Table DCC Modification

http://www.hornby.com/uk-en/forum/r070-hornby-turn-table-to-dcc-including-images/?p=1

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R070 DCC Conversion – my version with a detailed drawing

https://www.hornby.com/uk-en/forum/post/view/topic_id/27722/?p=2

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I am not suggesting that you reverse your modifications in favour of the method above, I am just providing the links above for information.

[Seacommander]

If you look at Hornby service sheet 178 you will see a part number M1321 which is an ingeniously simple piece of printed circuitry that switches polarity of the bridge track as it revolves to ensure that there are no polarity conflicts between the bridge and outlet tracks.

[crosbystills]

Thanks to all. I thought there must be something internally in the turntable that switched polarity but hornby as usual, do not provide details. Yes I have 'Got Lucky' and it suits. This is my last layout (third) getting on a bit now. Now have RailMaster but early days yet. Layout is U shaped 7' x 12' x 14' three levels 24 points. Currently trying to source 2mm MDF for backscenes.

Thanks again to you all.

[Chrissaf]

As you have RailMaster, then this link may be of interest to you.

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http://www.hornby.com/uk-en/forum/r070-turntable-configuration-in-railmaster/?p=1

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