Peco LK55 Turntable, DCC & Auto Reverser Module

[Mike Parkes]

Simple solution to that unless modelling a prototype location is that a rail served military based existed nearby and the turntable was upgraded in WWII to cater for larger locomotives.

Did this actually occur in the UK? AFAIK the limit was 70' on the rail network

Juat throw in it was future proofing, bit like any new motorway bridge has to higher than existing ones so if lorry sizes increase its one less bridge that will need raising.

[centenary]

The sole problems I have had with this TT:
the turntable pit flexes under load while rotating if heavyweight models (Heljan 2-8-0, Loco drive 9F, metal bodied pacifics, center moter twin bogie traction,etc.) are on it. A support beam underneath to take the load at the pivot point fixed this,

May I ask how the support beam was constructed and fixed to the bottom of the TT well?

Was this effectively 'U' shaped under the pivot point of the well and attached to the board underside or, just a couple of strips of plastic to form a couple of chords that bridge the 3 well sections together?

Thanks!

[Bigmet]

This was 'tailored' to specifically prevent a regular flex of the pit on one diameter which I was concerned would fatigue the mouldings to failure in time. Some 3mm ply pieces glued on to the pit underside to stiffen it along the flexing diameter, and to act as contact pads for the supporting beam on the same diameter, which is a length of salvaged aluminium extrusion* (attached directly to the layout frame made from the same ally extrusions) with a hemispherical cut out to clear the pivot.

*The aluminium was the framing of the ugliest 1960s secondary double glazing I have ever seen, which had apparently 'seen off' a number of potential purchasers of the property it was installed in over the months before we saw it. All I could see was useful structure construction material; but I didn't mention that in my negotiation for a better price on the basis that it hadn't sold in a fast moving market...

[centenary]

Another question on this turntable, please.

According to the destructions(!), when wired for DC, there are 2 areas, roughly 10 o'clock and diagonally opposite at 4 o'clock, where there will be no power when the turntable bridge is in these location, therefore do not position any entry \ exit roads there.

Presumably, this is due to the way the split ring is orientated under the TT bridge?

Do these 'dead sections' apply when wired for DCC as well?

There are no other comments in the instructions except 'the TT will be elctrically disconnected when the ends of the bridge are in the 10 & 4 o'clock positions.' Neither is there any comment about how to orientate the well / bridge (on DC) to make sure the isolation happens at these two positions!

[Flashbang]

The Peco TT uses a split ring with an isolated gap between the two halves and two sprung loaded plungers wipe on the split ring and provide track power to the rotating bridges rails. As the TT rotates the plunges have to pass over the split section. This "split" is a little wider than the surface of the plungers and therefore as the TT rotates the plungers pass over a dead section and all power is lost to the TT rails.
DC this hardly matters, DCC the same, but where sound is used then the sound will usually be cut off until the plungers reconnect again when the sound fitted loco will often have to go through its start up proceedure. The use of Stay Alive units may overcome this on DCC!

[centenary]

The Peco TT uses a split ring with an isolated gap between the two halves and two sprung loaded plungers wipe on the split ring and provide track power to the rotating bridges rails. As the TT rotates the plunges have to pass over the split section. This "split" is a little wider than the surface of the plungers and therefore as the TT rotates the plungers pass over a dead section and all power is lost to the TT rails.
DC this hardly matters, DCC the same, but where sound is used then the sound will usually be cut off until the plungers reconnect again when the sound fitted loco will often have to go through its start up proceedure. The use of Stay Alive units may overcome this on DCC!

Thanks for this!

Apologies if this is a dumb question, how do I orientate the turntable \ well to ensure the dead spots on the TT are not where I want to position entry and exit tracks?!

[Flashbang]

You can see the two gaps in the semi circular rings So its easy to mark where they are on the top of the TT in pencil and align as required.

[centenary]

You can see the two gaps in the semi circular rings So its easy to mark where they are on the top of the TT in pencil and align as required.

Thanks again for this tip!

[Free_at_last]

With the gaps at 11 o'clock and 5 o'clock positions the deck will be dead at 9 and 3 o'clock.

[centenary]

Apologies for asking what may seem obvious questions about this TT and thanks for all the comments and advice so far.

Another question: I acknowledge the comments about this being a split ring TT and an auto reverser not being necessary for DCC operation. But, is that still true for when needing to turn a loco through 180 degrees and where the TT bridge crosses the split rings contacts?

The split ring wires and hence the rails on the TT would be connected to my standard of black to back, red to front. When the turntable rotates through 180 degrees, black will now be to front and red to the back on the TT rails.

When the loco leaves the TT, the normal track will still be black to back, red to front. As the wheels breach this, surely that will result in a short and need an auto reverser?

[Free_at_last]

Apologies for asking what may seem obvious questions about this TT and thanks for all the comments and advice so far.

Another question: I acknowledge the comments about this being a split ring TT and an auto reverser not being necessary for DCC operation. But, is that still true for when needing to turn a loco through 180 degrees and where the TT bridge crosses the split rings contacts?

The split ring wires and hence the rails on the TT would be connected to my standard of black to back, red to front. When the turntable rotates through 180 degrees, black will now be to front and red to the back on the TT rails.

When the loco leaves the TT, the normal track will still be black to back, red to front. As the wheels breach this, surely that will result in a short and need an auto reverser?

No, the polarity on the deck will stay right whatever way around it is. That's what the split ring is for.

[centenary]

No, the polarity on the deck will stay right whatever way around it is. That's what the split ring is for.

Thank you for your comment, it is appreciated. I understand DCC doesnt have the same 'polarity' issues as DC but do not really see the TT turning through 180 degrees to be different from a reversing loop when black to back and red to front become black to front, red to back when the loop re joins itself?

If I may, when set up, the TT deck will be black wire to the back, red to the front, the same as the entry and exit track.

However, when the TT is rotated through 180 degrees and it rotates and crosses the split in the ring, the DCC will now be black to the front, red to the back. This will be the opposite of the entry and exit track. Thus, when the loco now leaves the TT shouldnt this cause a short without an auto reverser?

The Peco instructions which seem to be written for DC operation suggests switching polarity on the entry and exit track when crossing the split in the ring ie + on the back, - on the front on one side of the ring and 180 degrees opposed - on the back and + on the front.

I dont propose wiring like this. All my TT entry and exit tracks will be black to back, red to front.

I appreciate DCC is a type of alternating current and in theory positive and negative will alternate on the same rail. This still leaves me uncertain that when the loco crosses from the TT onto an entry or exit track, there isnt a short created just like there would be on a reversing loop if there was no auto reverser.

[Free_at_last]

However, when the TT is rotated through 180 degrees and it rotates and crosses the split in the ring, the DCC will now be black to the front, red to the back. This will be the opposite of the entry and exit track. Thus, when the loco now leaves the TT shouldn't this cause a short without an auto reverser?

When the deck rotates and crosses the split ring the polarity of the deck rails will change meaning black will still be at the back and red at the front.
DC or DCC makes no difference.

[centenary]

However, when the TT is rotated through 180 degrees and it rotates and crosses the split in the ring, the DCC will now be black to the front, red to the back. This will be the opposite of the entry and exit track. Thus, when the loco now leaves the TT shouldn't this cause a short without an auto reverser?

When the deck rotates and crosses the split ring the polarity of the deck rails will change meaning black will still be at the back and red at the front.
DC or DCC makes no difference.

Thanks again for the clarification.

I realise my misunderstanding. The power is supplied to the ring, which remains constant due to being fixed in the well. The rails take up the power via the contacts from the ring so the 'polarity' on the rails changes. D'oh!