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DCC newbie - planning stage questions


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I'm planning a layout 4mm scale about 16 feet long, 2 feet wide, single branch line into a terminus and goods yard, fiddle yard at the other end. It has 8 turnouts and a couple of signals for which I am thinking servos/Arduino or Cobalt for the turnouts.

 

1)  Do I need both a power bus and accessory bus, or will one bus do?

2)  I have read the bus wires should be twisted or separated by a wide margin - if twisted how tight and if separate how far apart? Does this apply to both busses (if I have two)?

3)  If the bus wires are twisted, how best to attach droppers?

4)  I have an NCE power cab starter already so answers above should be compatible with this

 

 

Thanks in advance

 

David

 

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I can't answer about the NCE Power Cab, but hopefully can still help...

 

1) I'd consider separate buses if possible, as it is easy to wire them to the same controller for now and separate them in future if you wish. I use a Gaugemaster Prodigy Advance 2 and managed to pick up a Hornby booster when Hattons were selling them off. So, I have two buses, track powered through the booster (as it had a higher rating than the Prodigy) and accessories direct from the Prodigy. The biggest advantage is when I have a train hit the points when they are set incorrectly, there is still power to the accessories to change the points even though the track power has been killed.

 

2) For the track bus, had some old twin & earth cable that was a single solid core. I've strung out two lengths of that along the board, to form the two bus wires and then just solder droppers to that. The bus wires are taught and are at opposite side of the board, so there is no chance of them accidentally shorting. My only accessories are points controlled by MERG boards, so for the accessory bus I just run wires between each of the boards - no twisting or anything. 

 

 

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3 minutes ago, MartynJPearson said:

 

1)  The biggest advantage is when I have a train hit the points when they are set incorrectly, there is still power to the accessories to change the points even though the track power has been killed.

 

 

 

This is the reason people use separate buses. You don't need separate boosters if you are within your system's limitations (which for PowerCab is about 1.8A), but a cut-out on the track bus only will cut this off when you drive a train into some incorrect points, leaving the accessory bus live to change the point.

 

There is nothing unusual (quirky) about the PowerCab. You can display the current draw instead of the time to see how much is being drawn.  I doubt you'll need a booster for the layout you've described.

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57 minutes ago, MartynJPearson said:

My only accessories are points controlled by MERG boards, so for the accessory bus I just run wires between each of the boards - no twisting or anything.

 

I was told the twisting helped eliminate spurious signals, nothing to do with shorting. I was concerned that if the bus wires are twisted, soldering droppers could get difficult.  And I have looked at the MERG boards and I do like the idea of an 'analog' panel controlling dcc signals and points.

 

Edited by rynd2it
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I must be a rebel, my layout is an expanded/adapted version of Bredon using Trix-C track about 10’ X 4.5’ with eighteen powered points eight sidings one and a half circuits all powered and controlled by the ECoS base station via one connection to the track, runs great.

 

I didn’t want the impossible task (for me now) of clambering under the baseboards with wiring and soldering, so opted for the easy route. I have made the provision of the baseboard being in three sections, each one of these will have a connection from the track to the controller eventually if and when I move, but for now it works.

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32 minutes ago, rynd2it said:

I was told the twisting helped eliminate spurious signals, nothing to do with shorting. I was concerned that if the bus wires are twisted, soldering droppers could get difficult.  And I have looked at the MERG boards and I do like the idea of an 'analog' panel controlling dcc signals and points.

 

 

Certainly with the size of my layout (round the wall in a 12' x 10' room) I've never had any issues with spurious signals; anything unexpected happening has always been down to user error! For longer runs, maybe a twisted pair for longer runs to link boards connecting to terminal blocks to which droppers can be routed? (Thinking out loud there, as I haven't done this in practice)

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1 hour ago, Pete the Elaner said:

 

This is the reason people use separate buses. You don't need separate boosters if you are within your system's limitations (which for PowerCab is about 1.8A), but a cut-out on the track bus only will cut this off when you drive a train into some incorrect points, leaving the accessory bus live to change the point.

 

There is nothing unusual (quirky) about the PowerCab. You can display the current draw instead of the time to see how much is being drawn.  I doubt you'll need a booster for the layout you've described.

Taking both bus feeds from one controller/booster negates the benefit of having a seperate bus in the first place, a short circuit on either bus will cause the single controller/booster to trip out, cutting power to both busses.

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17 minutes ago, MartynJPearson said:

 

Certainly with the size of my layout (round the wall in a 12' x 10' room) I've never had any issues with spurious signals; anything unexpected happening has always been down to user error! For longer runs, maybe a twisted pair for longer runs to link boards connecting to terminal blocks to which droppers can be routed? (Thinking out loud there, as I haven't done this in practice)

 

There was a long discussion on the Cobalt forum about the point motors losing their dcc addressing as a result of spurious signals and the twisting of the power bus was recommended plus having other wires cross the power bus at 90 degrees.  Hence my questions above.

 

 

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2 hours ago, rynd2it said:

1)  Do I need both a power bus and accessory bus, or will one bus do?

One will do but as explained, two are better.

2 hours ago, rynd2it said:

2)  I have read the bus wires should be twisted or separated by a wide margin - if twisted how tight and if separate how far apart? Does this apply to both busses (if I have two)?

Never found that necessary and cannot really understand the rational given the close proximity and lack of twist in Cat5 network cables which carry complex signals without problem.

2 hours ago, rynd2it said:

3)  If the bus wires are twisted, how best to attach droppers?

I run the bus to terminal blocks and take groups of droppers from those.

2 hours ago, rynd2it said:

4)  I have an NCE power cab starter already so answers above should be compatible with this

Sorry - Cannot help with that.

2 hours ago, rynd2it said:

servos/Arduino or Cobalt for the turnouts.

ESU Servo Pilots work very well and are simple to use if you go the servo route.

2 hours ago, rynd2it said:

 

 

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9 minutes ago, JimFin said:

One will do but as explained, two are better.

Never found that necessary and cannot really understand the rational given the close proximity and lack of twist in Cat5 network cables which carry complex signals without problem.

I run the bus to terminal blocks and take groups of droppers from those.

Sorry - Cannot help with that.

ESU Servo Pilots work very well and are simple to use if you go the servo route.

 

Thanks for all that, I'll look at the ESU servo pilots although I have used Arduino before for signals.

 

The DCC Concepts guys were absolutely adamant that twisting the bus wires would solve the Cobalt lost addresses problems - it's on their forum. But I'd never seen it anywhere else hence my raising it here

 

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3 hours ago, rynd2it said:

2)  I have read the bus wires should be twisted or separated by a wide margin - if twisted how tight and if separate how far apart? Does this apply to both busses (if I have two)?

 

Separating the DCC bus wires by a wide margin is the worst possible thing to do, with respect to radiating interference. All you are doing is creating a large loop aerial.

 

Perhaps you, or the writer, were confused with keeping the DCC bus separate from other wiring? The high current and fast transients in the bus wires could couple into other wiring systems.

 

The two bus wires should be kept close together. If you use twin conductor cable, such as speaker wire then twisting adds very little for DCC.

 

If you use individual conductors (e.g. stripped from mains cable is popular) then twisting is a convenient and easy way to keep them together, but don't get anal about the number of twists per foot, etc. Twisting them tightly just makes it more difficult to break in to make connections

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1 hour ago, DaveArkley said:

Taking both bus feeds from one controller/booster negates the benefit of having a seperate bus in the first place, a short circuit on either bus will cause the single controller/booster to trip out, cutting power to both busses.

 

I think you mis-understood me.

 

You don't need separate boosters if you are within your system's limitations (which for PowerCab is about 1.8A), but a cut-out on the track bus only will cut this off when you drive a train into some incorrect points, leaving the accessory bus live to change the point.

 

Cut-out = overload circuit breaker, not a short circuit. This reacts more quickly than the booster's protection to shut off only the track.

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They say a picture is worth a thousand words so have a look here.

 

This is the underside of Danemouth  and shows the wiring - note the three switches!

 

Since these photos were taken the frog juicers have been removed and the Cobalt point motors now switch frog polarity.

 

Dave

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  • 1 month later...
  • RMweb Gold

[shameless plug]

 

if you like me like the idea of powering everything from the DCC bus (track or accessory) then my little PCB might be of interest

 

 

No need for a separate DC power supply for your lighting, accessory decoders etc etc

 

[/shameless plug]

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10 minutes ago, Oldddudders said:

"One output full rectified and smoothed DCC" was a phrase I didn't quite understand. 

 

It's not regulated, so just rectified by a bridge rectifier and smoothed with a 1000uF capacitor. if the DCC booster voltage varies, so will the output voltage. 

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On 11/05/2020 at 12:21, rynd2it said:

 

3)  If the bus wires are twisted, how best to attach droppers?

 

 

 

A neat solution could be these:

 

https://www.brimal.co.uk/power-distribution-board-18-way-screw-terminal-connection.html#product_tabs_applications

 

 

 

Best


Scott.

Edited by scottystitch
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