R410 Turntable. wiring.

[Kidcurry]

Hi.

I have an R410 Turntable, not motorised. I am wiring my layout to DCC. Will crank the turntable by hand. The wiring of the track on the turntable in my question.

IF, I wire one rail to + and one to - then surly when I turn the table by 180 degrees, I will get a direct short. Yes?

My outlets to the table will all be powered by a constant feed as DCC from a Busbar. I am correct that the contacts on the table at the end on the table rails will cover the power on the table. If so then the wires on currently provided on the table are not used.

I am sure this is correct but would like a confirmation.

thanks

regards

[96RAF]

In theory if the table is only powered by the contacts all should be well but in practice as the table passes the contacts a short is provoked.

Hence the table is generally powered separately and the contacts removed for DCC operation.

There are two ways to ensure correct phasing (consider this the same as DC +/- polarity in effect), use a manual DPDT switch, which really needs an indicator to show which way is which, or better still use a reverse loop module which will switch the phasing automatically.

Refer to the Reverse Loop tutorial in the sticky post at top of the DCC page for more info.

[Chrissaf]

"IF, I wire one rail to + and one to - then surly when I turn the table by 180 degrees, I will get a direct short. Yes?"

No - the TT has a 'Split Ring' that reverses the bridge rail polarity once it has passed the half way position in a full rotation.

I'm no total expert on some of these really old Hornby / Triang products, but my understanding is that the R410 is the earlier unmotorised version of the motorised R070 turntable. Looking at this R410 data-sheet, the turntable bridge contact arrangement of the R410 seems to be the same as the later R070.

R410 Turntable

Now assuming that the bridge electrical arrangements of the R410 is indeed the same as the R070 and this does seem to be supported in the above linked documentation. Then the designated 'inlet track' has a pair of rail contacts that provide power to a 'slip ring' under the bridge pivot point. The 'slip ring' then provides the power to the rotating bridge track piece.

Now this is not an issue when the R410 TT is used on a DC Analogue layout which it is designed for as the power to the bridge track is turned off, whilst the bridge track is rotating. But with DCC, the track power is live 'all the time'. This means that as soon as you start to turn the TT bridge, a short circuit is created. See the image below:

The combined minds on the forum have put together a modification plan that improves on Hornby's own suggested modification to resolve this 'short circuit' issue when using the Hornby DC Analogue turntable on a Digital DCC layout. It is documented in a 'historical thread', but unfortunately the 'historical threads' on this new forum are still awaiting their historical images to be copied over from the old forum. So the described modification method will be near impossible to follow with the supporting images missing.

However, this image below outlines at a high level what the previous thread was describing.

Basically, you add 'Insulating Rail Joiners' to each connected track piece. You then remove the 'Slip Ring' wires from the 'Inlet Track' piece and connect them directly to the DCC BUS [see images below]. Note that the 'Slip Ring' reverses the bridge rail polarities for half the 360° rotation, so it is important to get the dropper wires the right way round else a 'short circuit' is generated.

Ignore the DCC Decoder connections to the hut for the R410 TT, this drawing is for a motorised bridge R070 TT and not the manually rotated R410 version.

EDIT: If any of the TT outlet tracks on the reversed side of the TT route back onto the main layout and are not isolated sidings, then you will probably also need to add a RLM [Reverse loop Module] to the solution - see Rob's reply above. The RLM would be connected between the DCC BUS and the wires that go to the bridge rails.

EDIT: Rob posted whilst I was preparing my reply.

[Kidcurry]

Hi Chris and 96 RAF.

Thank you very much for your replies.

I understand DC wiring but did not know the "slip ring" info on the TT.

This is very helpful.

Best Regards

Steve