Wiring a Turntable for DCC

 
  disasterrisk Station Master

I seek advice on the need or otherwise for a reverse loop unit  to operate an "Antons Trains" 90ft NSWGR turntable manufactured by CIL Distributors of Castle Hill NSW. With my general wiring the approach rails to the turntable are  left rail "black" right rail "red", this convention would apply to the rails on the turntable and to the rails leading into the engine shed.  When the engine is reversed onto the turntable and the table turned through 180 degrees, the left rail is then red and the right rail black, and I assume which will cause a short when the engine is driven off to proceed onto the main layout.
The instructions with the turntable say
"Attach the 6 core cable colour coded and marked to the terminals " Now connect track power to the two terminals , so marked. This will energise the bridge. "Connect 16 volt AC power to the terminals marked AC"  Select the direction turntable switch and press the red button the bridge will start turning, release the button , the bridge will turn till the next index exit and lock and stop. Power is then off to the motor. Power is on to the track at all times. Track power will reverse polarity when 180 degrees turn on the bridge is made"
From these directions I assume that a reverse loop unit is not required to be connected to the turntable

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  Booly Junior Train Controller

What you will need is a tam valley frog juicer
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Good  luck with getting the turntable to operate reliable, ive got one of the antons 75ft tables and it's not very reliable.  Im not the only one to have this complaint.
  c3526blue Deputy Commissioner

Location: in the cuckoos nest
The description in the instructions is slightly ambiguous and not clear in its context.   The last sentence can be taken to mean different things.

Although I do not have experience with this turntable the instructions may indicate that the contacts supplying power to the bridge rails have a break, rather than being continuous for the full 360 degrees.   This interpretation appears to be similar to that of the Walthers 933-2849 turntable.  See 09330000002849.pdf which has a photo of this contact area on page 4.

In this case the polarity does not remain constant as the turntable passes through 180 degrees.  There are likely to be breaks on opposite sides of the turntable circular contacts.  If you can lift the bridge from its base the breaks in the contact strips will be readily apparent, and will be located about 180 degrees apart.  The bridge rails will have no power as the bridge contacts pass over this dead area.  Once past the dead area the bridge rails will be of a polarity consistent with the starting polarity.

One problem with this arrangement is that the loco chip will shut down as it passes over the dead section.  I don't know what effect a stay alive will have in this situation.

A frog juicer or auto reversing component is not necessary or advisable in this situation.  

If however the turntable has continuous contact strips (such as a vertical RCA plug) the bridge rails will have a constant polarity which will cause a short after a 180 degrees turn as a loco leaves the turntable and contacts an approach track.  

In this situation a frog juicer or auto reversing component is very desirable for the circuit supplying power to the bridge deck.  The only alternative is a manual (and risky) reversing switch.

You can check the table rail polarity in situ using a simple multimeter or voltmeter on DC but not DCC.  Check it at various locations throughout the 360 degrees rotation.  Temporarily supply DC from a battery or simple low voltage transformer with a DC output.

Happy turning,

John
  The railway dog Train Controller

Location: Adelaide Hills
What 3526 said.
My Antons turntable has breaks in the contact strips so the polarity is always correct. There's an arc of several degrees where there's no power to the turntable rails before they pick up again. I suppose there'd be pickup problems if you wanted to take a track off the table at this precise point. When the table's in that arc & not picking up there is of course no sound, but  steam locos using the table are usually just making a slight hissing noise & the momentary absence isn't all that apparent. Diesels would be more obvious but we don't care about them do we. At the speed my table rotates there's a gap of several seconds without power & sound. I don't know what effect a stay alive would have either.
  disasterrisk Station Master

What you will need is a tam valley frog juicer
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.tamvalleydepot.com/products/dccfrogjuicers.html&ved=2ahUKEwiLmsyWkYzvAhX0zTgGHTgcAXgQFjAAegQIAxAD&usg=AOvVaw0JgQm9v2Ve9z01FG2z6JM7
Good  luck with getting the turntable to operate reliable, ive got one of the antons 75ft tables and it's not very reliable.  Im not the only one to have this complaint.
Booly
Thank you for the comment and for the warning of potential unreliable operations.
  disasterrisk Station Master

The description in the instructions is slightly ambiguous and not clear in its context.   The last sentence can be taken to mean different things.

Although I do not have experience with this turntable the instructions may indicate that the contacts supplying power to the bridge rails have a break, rather than being continuous for the full 360 degrees.   This interpretation appears to be similar to that of the Walthers 933-2849 turntable.  See 09330000002849.pdf which has a photo of this contact area on page 4.

In this case the polarity does not remain constant as the turntable passes through 180 degrees.  There are likely to be breaks on opposite sides of the turntable circular contacts.  If you can lift the bridge from its base the breaks in the contact strips will be readily apparent, and will be located about 180 degrees apart.  The bridge rails will have no power as the bridge contacts pass over this dead area.  Once past the dead area the bridge rails will be of a polarity consistent with the starting polarity.

One problem with this arrangement is that the loco chip will shut down as it passes over the dead section.  I don't know what effect a stay alive will have in this situation.

A frog juicer or auto reversing component is not necessary or advisable in this situation.  

If however the turntable has continuous contact strips (such as a vertical RCA plug) the bridge rails will have a constant polarity which will cause a short after a 180 degrees turn as a loco leaves the turntable and contacts an approach track.  

In this situation a frog juicer or auto reversing component is very desirable for the circuit supplying power to the bridge deck.  The only alternative is a manual (and risky) reversing switch.

You can check the table rail polarity in situ using a simple multimeter or voltmeter on DC but not DCC.  Check it at various locations throughout the 360 degrees rotation.  Temporarily supply DC from a battery or simple low voltage transformer with a DC output.

Happy turning,

John
c3526blue
Thank you for the comment. Sorry my description of the problem was confusing.
  disasterrisk Station Master

What 3526 said.
My Antons turntable has breaks in the contact strips so the polarity is always correct. There's an arc of several degrees where there's no power to the turntable rails before they pick up again. I suppose there'd be pickup problems if you wanted to take a track off the table at this precise point. When the table's in that arc & not picking up there is of course no sound, but  steam locos using the table are usually just making a slight hissing noise & the momentary absence isn't all that apparent. Diesels would be more obvious but we don't care about them do we. At the speed my table rotates there's a gap of several seconds without power & sound. I don't know what effect a stay alive would have either.
The railway dog
Thanks for the comments. I will look closely at my unit to see if there are breaks.
  Marco407 Beginner

I set up a Fleischmann Turntable with a mate and because the layout is digital an automatic DCC reversing module was hooked up between the turntable bridge and the main line. All the turntable entry/exits are wired directly to and in synch with the main line power supply. Using this arrangement the turntable bridge is automatically switched to match which ever entry/exit track is being used. One thing to note is that the contacts between the bridge and entry/exit tracks must not be used in this digital configuration as the bridge is powered solely from the DCC auto reverser. They have been removed by cutting them off. Check it out here


https://www.youtube.com/watch?v=E7WMBZvLM6A
  NSW3802 Junior Train Controller

I set up a Fleischmann Turntable with a mate and because the layout is digital an automatic DCC reversing module was hooked up between the turntable bridge and the main line. All the turntable entry/exits are wired directly to and in synch with the main line power supply. Using this arrangement the turntable bridge is automatically switched to match which ever entry/exit track is being used. One thing to note is that the contacts between the bridge and entry/exit tracks must not be used in this digital configuration as the bridge is powered solely from the DCC auto reverser. They have been removed by cutting them off. Check it out here


https://www.youtube.com/watch?v=E7WMBZvLM6A
Marco407
If you want an inexpensive turntable that is easy to wire then the Peco one is very good. Just connect two wires to the approach track and it is ready to use. There are motorising kits available for it if required. No need for DCC reversers.

Suits most Australian large locomotives except the NSW 60 class.

Les.

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