Wiring turntables for DCC

8610 Views 11 Replies 8 Participants Last post by ahammond, Jan 23, 2008

markw

Discussion Starter · Jan 19, 2008

Hi Peeps

I have a mate who will shortly be wiring his layout. It will be a small shed layout that will have a peco motorised turntable. He will be using DCC for points but manual control of the turntable via a simple switched DC motor.

I have advised him on wiring of the points and main trackwork for DCC but i'm not sure what needs to be done to wire the turntable.

I'd be most grateful if somebody could advise please.

Thanks

Mark

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neil_s_wood

· #2 · Jan 19, 2008

How does the motor work? Does it keep moving while your fingers on the button? Or does it move to the next offramp?

I did a thread on this a few months ago in view of controlling a Fleischmann turntable with a lokpilot decoder through ECoS and came to the conclusion that it was pointless as all it would do is the same as the dial that cam with the turntable. It seemed a lot of extra work for little gain.

There is a thread on the ESU ECoS forum which tells you how to use a Lokilot decoder to control the turntable. It involves diodes and the such but this may be the go. Sorry I can't remember exactly where on the forum it was.

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Makemineadouble

· #3 · Jan 19, 2008

As far as I can recall (it's years) the Peco turntable does not need an auto reversing unit, it has a copper slip ring inside of it, that only supplies power to the unit when it lines up. The worst that can happen if you try it is I save you the cost of an auto reversing unit. Not all turntables require this, the Hornby one for all it's short comings and lack of appearance is highly DCC friendly and does not require an auto reversing unit either. You can use any old poor specification decoder to control a turntable if it's motorised, and the nice thing you can have total control over it's speed. Just pre program it with CV1 before installation.

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Petal

· #4 · Jan 20, 2008

The Hornby turntable is not very DCC friendly in it's "out of the box" state.

If you have live tracks on both sides of the turntable, as soon as the bridge rails rotate so that opposite polarity bridge rails line up with the fixed rails a short circuit occurs.

There are a number of ways of overcoming this problem and an auto reverse unit is one method. Another method (as shown on the Hornby site) is to remove the contacts from the ends of the bridge rails.

The turntable motor is very simple to convert to DCC operation and the functions of the decoder can be used for lighting.

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Makemineadouble

· #5 · Jan 20, 2008

QUOTE The Hornby turntable is not very DCC friendly in it's "out of the box" state.

just a few minutes work with a soldering iron

what so unfriendly about that.

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ahammond

· #6 · Jan 21, 2008 (Edited by Moderator)

I am in the middle of converting and motorising a Peco N gauge turntable to DCC operation. I am using the standard motorising kit and driving it as a normal locomotive from the controller with a cheap TCS decoder hooked up to the drive motor and the address twenty two. The track on the turntable is fed from a DPDT switch, with centre off, to enable manual reversing of the current flow as the turntable completes a one eighty degree turn. The main problem that I am having with the conversion at the moment is the shaft on the drive gearbox slipping when under load. I am hoping to investigate and rectify that this week when I have more time.

Along with this I am converting the turntable to an over girder type. This has proven to be an awful lot simpler than I expected. The girders are provided by a Peco 00 gauge bridge suitably butchered. The original turntable wheels from the kit have been cut from the under girders, which are relegated to the spares box, and glued directly to the original deck along with I section Plastruct girder lengths. The central steps and hand rails have are courtesy of some model boat gangways which look exactly right or will hopefully will when glued in place after the motorising is sorted. Other than that it is built as per the instructions.

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Sol

· #7 · Jan 21, 2008

The Hornby turntable gives no problems with either DC or DCC, the principles are the same - just because one is DC & the other AC, the table automatically reverses table track power & only feeds power to the tracks it faces. Tracks that radiate out from the table to store locos gets their power only when the table is facing them.

They are not like Heljan or Fleischmann which gets power from the centre pivot & a continuous pickup - these do need a reversing switch or auto-reverse decoder.

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SPROGman

· #8 · Jan 21, 2008

QUOTE (ahammond @ 21 Jan 2008, 08:06) <{POST_SNAPBACK}>I am in the middle of converting and motorising a Peco N gauge turntable to DCC operation. I am using the standard motorising kit and driving it as a normal locomotive from the controller with a cheap TCS decoder hooked up to the drive motor and the address twenty two. The track on the turntable is fed from a DPDT switch, with centre off, to enable manual reversing of the current flow as the turntable completes a one eighty degree turn. The main problem that I am having with the conversion at the moment is the shaft on the drive gearbox slipping when under load. I am hoping to investigate and rectify that this week when I have more time.
The Peco N gauge terminal reverses the polarity automatically as it rotates. There's no need for a manual switch. Just make sure the breaks in the commutator ring are well out of alignment with the entry/exit tracks so that the reversal takes place at the correct point.

Andrew

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ahammond

· #9 · Jan 21, 2008

I am not that well versed as far as electrics go and stand to be corrected. But whilst I would agree with you as far as DC current is concerned I am quite certain that for AC operation with DCC then the polarity to the turntable tracks has to switched if it is rotated 180 degrees. Otherwise you would end up with a positive feed rail on the table facing a negative feed rail on the track that you are lining up with.

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SPROGman

· #10 · Jan 21, 2008

QUOTE (ahammond @ 21 Jan 2008, 12:43) <{POST_SNAPBACK}>I am not that well versed as far as electrics go and stand to be corrected. But whilst I would agree with you as far as DC current is concerned I am quite certain that for AC operation with DCC then the polarity to the turntable tracks has to switched if it is rotated 180 degrees. Otherwise you would end up with a positive feed rail on the table facing a negative feed rail on the track that you are lining up with.
It makes no difference whether you use AC (DCC) or DC. The two sprung plungers pickups on the deck pick up power from the two halves of the split ring in the well. Each 180 degrees the polarity of the deck is changed as each pickup moves from making contact with one half of the ring to the other. Think of it as a rotary double pole changeover switch.

The disadvantage of this arrangement is that there will be a momentary loss of power to the deck as it turns, which may upset sound decoders.

Andrew

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Free_at _last

· #11 · Jan 21, 2008 (Edited by Moderator)

QUOTE (Sol @ 21 Jan 2008, 09:44) <{POST_SNAPBACK}>They are not like Heljan or Fleischmann which gets power from the centre pivot & a continuous pickup - these do need a reversing switch or auto-reverse decoder.

My bridge on my Heljan turntable picks the track supply up from a split ring

I have not tested it on dcc yet to see if the gap is big enough to cause a short or not.

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ahammond

· #12 · Jan 23, 2008

You were right Sprogman the table does reverse polarity automatically. Which has saved me a bit of wiring. I have got it up and running but it will take quite a bit of fine tuning to get it working smoothly. The problem is that the deck rocks fore and aft preventing vertical alignment with the exit/entry rails. I thought that I had sorted this when fixing it to the table but it now looks as if I will need to put some form of shimming under each end. The only other thing is that it is noisy. Forward is not too bad, but reverse is pretty horrible to listen to even after copious oiling.

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