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DC track power issue at points.


barney121e
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Because i saw the trackplan and someone's use of switches the plan below suggests where the switches should go (the yellow circles). These are operated by switches, which is where the cab control comes in. I know there are different types of switches, any ideas what switch type i would need? 

sectionplanswitches.jpg

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4 hours ago, barney121e said:

Because i saw the trackplan and someone's use of switches the plan below suggests where the switches should go (the yellow circles). These are operated by switches, which is where the cab control comes in. I know there are different types of switches, any ideas what switch type i would need? 

sectionplanswitches.jpg

 

Cab control is where each SECTION has a switch to enable it to be connected to one (of two or more Controllers.  Sometimes this is combined with COMMON RETURN , where one wire from the track section goes to a BUS BAR which is connected to all the controllers and the other is connected via the selector switch to a controller.  Its quite easy to connect up to 11 CONTROLLERS  to a layout using 12 way rotary switches , and there is no limit to the number of SECTIONS.   Unfortunately the drawing above has an error which would stop trains using the lower loop, the Orange feed needs to be moved clockwise, beyond the points to the lower loop.  I would take out thee sections which have little use, The lower  right hand section on a siding is a liability in that a loco can be left against the buffers taking power with the points against it.  I would put a simple isolator so the end of the siding can only be powered up when the points are set for the siding.

 

Screenshot (163).png

Edited by DCB
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Smokebox gave you the answer here,

On 12/04/2022 at 22:10, smokebox said:

Guessing that the class 42 picks up power from one rail on the front bogie and from the other rail on the rear bogie, therefore stalling when the loco is straddling the two different power suplies.

Fitting metal fishplates avoids the problem by joining the two power supplies together. But leaves you open to other and potentially worse problems. As others have said it will be much better in the long run to replace the insulated fishplates and use cab control. There is plenty of guidance on the web as already mentioned.

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14 hours ago, barney121e said:

any ideas what switch type i would need? 

 

Simplest method is to use what's called DPDT (double-pole-double-throw) which are designated on-off-on - this will allow 2 controllers to be used. Then wire each controller to the outer connections, and connect the middle connections to each section of track. Then when the switch is in either of the 'on' positions only one of the controllers will power that particular section of track.

Edited by Graham108
Wrong info
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On 12/04/2022 at 14:10, smokebox said:

Guessing that the class 42 picks up power from one rail on the front bogie and from the other rail on the rear bogie, therefore stalling when the loco is straddling the two different power suplies.

 

Yes, and using metal joiners in the middle of the crossover solves that problem. There's nothing wrong with using metal joiners there. The concern might be that the two controllers are connected back to back but there's nothing wrong with that either. The worst thing that will happen is, if they are set in opposite directions, they will overload just as if their outputs were short-circuited.

 

When the points are returned to straight through the controllers are completely isolated from each other.

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BTW, you can also solve the problem by using one metal joiner and one plastic joiner. That will tie the controllers to a common reference when the crossover is in use and it will ensure that there is always a return path for the current flowing from either controller regardless of which one is powering the loco.

 

You can get the same result with two plastic joiners if you connect one of the output connections on both controllers together. It does not matter which of the two connections you use. You can think of that connection as a sort of ground or earth point (but do not connect it to mains earth!) If you measure voltages from the other connection on the controllers relative to that common connection they will be either positive or negative depending on the controller's direction setting.

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Here's a diagram that might explain things better than my word picture 😀

Crossover.jpg.aabd578a1b851f6d2e939c6e5bbf9bc2.jpg

The loco is represented by a badly drawn filament light bulb. The straight lines are the rails.

 

In the top diagram if the loco happens to pick up power from one controller on one side and the other controller on the other side there is no complete circuit. It's actually quite common for that to happen even with six-coupled steam locomotives and guaranteed to happen with some diesels as described by Smokebox above.

 

Without a complete circuit to return current to the controller there can be no current flowing through the motor so it will stop turning.

 

The lower diagram has an additional common wire between the two controllers. If you follow the circuits you'll see that there is always a complete circuit through the motor regardless of which controller (or even both) is supplying the current.

 

 

 

Edited by AndyID
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On 13/04/2022 at 05:08, kevinlms said:

That crossover should ALWAYS have 2 insulated joiners there.

If you ever want to have 2 controllers, to control 2 trains, you risk a short under some conditions. 

Better to solve the problem, before you go further. 

 

 

No. The insulated joiners are causing the problem and even two insulated joiners cannot prevent the controllers opposing  each other. Even cab-control does not eliminate that possibility. In some situations, but not all situations, it's necessary to insulate both rails to isolate live fogs. Apart from that the only time it's essential to insulate both rails is at the ends of a reversing loop.

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Cab control wiring looks like this, switches are DPDT (double pole double throw), centre-off, circuits/sections must be separated with IRJs on both rails at section joints.  You can use a common return, but I think this complicates things (including understanding).

DPDT2.jpg.ff7ce0310278d0c23bfd6da338221eda.jpg

 

 

 

Edited by Chimer
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31 minutes ago, Chimer said:

Cab control wiring looks like this, switches are DPDT (double pole double throw), centre-off, circuits/sections must be separated with IRJs on both rails at section joints.  You can use a common return, but I think this complicates things (including understanding).

 

 

 

 

Why both rails? I only have IRJ's on one rail and I don't have any problem

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56 minutes ago, Graham108 said:

Why both rails? I only have IRJ's on one rail and I don't have any problem

 

To separate the sections completely, as I don't like common return.

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Whilst I understand the concept of multiple sections and controllers run as cab-control, a relatively simple layout like this doesn't really need this complication unless multiple trains are envisaged to be run simultaneously.  The self isolation of points basically allows trains to be parked in sidings with one train running on the main part of the layout at a time.

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2 hours ago, Chimer said:

 

To separate the sections completely, as I don't like common return.

 

As you alluded to earlier, common return requires a little more understanding.

If I was helping somebody else to wire a layout, how do I know that they won't sell it or change controllers at a later date to a pair running off the same winding?

If it used common return, this will cause a problem. Anybody aware of common return wouldn't "activate" the problem in the first place.

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4 hours ago, Pete the Elaner said:

 

Anybody aware of common return wouldn't "activate" the problem in the first place.

 

 Common return prevents the problem from happening in the first place 😀

 

(It's also much simpler and has higher reliability. I'd try to explain why but I'm pretty sure I'd be flogging a dead horse.)

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6 hours ago, Jeff Smith said:

Whilst I understand the concept of multiple sections and controllers run as cab-control, a relatively simple layout like this doesn't really need this complication unless multiple trains are envisaged to be run simultaneously.  The self isolation of points basically allows trains to be parked in sidings with one train running on the main part of the layout at a time.

 

The OP is using two controllers, so presumably does run trains simultaneously on the two circuits.  His issue is shifting a train from one to the other, which is always (imho) better done with both circuits temporarily switched to the same controller.

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A short attempt to demystify common-return.

 

 

ComRet1.jpg.260f926975553af6fa55675b6f9ec909.jpg

 

 

ComRet2.jpg.8271cd9a74f5c23e8272c12d675f3a86.jpg

 

 

I doubt if anyone has a problem with A.  B includes a common but I don't think it would bother anyone. C is similar but the currents are flowing in opposite directions but as they don't need to flow on the common connection it should not be a problem. In D the currents do follow a common path and I think that's the bit that can be confusing. E and F might seem even more confusing but in reality there really isn't any difference between B, C, D, E and F.

 

The trick is to not "overthink" it. The electrons sort it out all by themselves.

 

 

 

 

 

 

 

 

Edited by AndyID
enlarged pics
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15 minutes ago, Chimer said:

 

The OP is using two controllers, so presumably does run trains simultaneously on the two circuits.  His issue is shifting a train from one to the other, which is always (imho) better done with both circuits temporarily switched to the same controller.

 

Yes, that's probably the best way to do it but the wiring would be a lot less complicated using common-return 😀

(Please see above.)

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14 hours ago, AndyID said:

 

 Common return prevents the problem from happening in the first place 😀

 

(It's also much simpler and has higher reliability. I'd try to explain why but I'm pretty sure I'd be flogging a dead horse.)

 

You are not flogging a dead horse, you are assuming that others with less understanding than you will understand what you have done.

I would not have an issue using common return on my own layout because I understand it.

 

If you were helping somebody else, could you trust them to understand the need to keep each controller fed from a separate winding & ensure they stuck to this? Probably not because if they understood it, they wouldn't be needing your help or advice in the first place. This is why I view it as a potential problem.

 

The same applies to advising people on the internet: If they understood common return well enough to implement it, would they be asking what some consider simple questions about how to split their layout into blocks for power supply?

 

Also, a layout split into too many sections can easily be connected below the baseboard & one split for discrete return can easily be connected for common return.

The reverse is not true: if there are too few power breaks at track level, separating them at a later date involves lifting track.

I have seen it argued that cutting the rail is sufficient to split a section into 2 but after spending time recently dealing with a raised rail 1 side of such a cut, I would disagree that this is as good as using an insulated rail joiner.

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8 hours ago, Pete the Elaner said:


You are not flogging a dead horse, you are assuming that others with less understanding than you will understand what you have done. 

 

I don't know how you know what anyone might be assuming but yes, many people do seem to find it difficult to get their head around common-return. That's why I went to the trouble of posting the diagrams. Do you think they are unhelpful?

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4 minutes ago, AndyID said:

 

I don't know how you know what anyone might be assuming but yes, many people do seem to find it difficult to get their head around common-return. That's why I went to the trouble of posting the diagrams. Do you think they are unhelpful?

 

I understand them, but I also understand how & why common return works so that makes me a poor choice to judge if they explain the principle to somebody who doesn't understand them.

I think of it as -12, 0 & +12v, or 0, +12 & +24v. I am sure that makes perfect sense to you, but others may be alarmed if they see 24v or -12v when they only expect 0-12.

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7 minutes ago, WIMorrison said:

What happens to common return when people are using wallwart or SMPS rather than the old, somewhat outdated and inefficient transformers?

 

No problem at all. They have isolating transformers.

 

The old concern about running multiple controllers off the same transformer secondary is a bit of a red herring. Anyone who us actually doing that these days should know they can't use common return.

 

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If I was to be brutally honest I would say that anyone reading this thread wouldn’t know what common return actually is, let alone whether it is a good thing, a bad thing or how to implement it using either a traditional transformer or an up-to-date SMPS.

 

I suggest it would be of great benefit if this was explained, with diagrams, to remove doubt and potential problems for those less experienced than some of the posters in this thread.

 

 

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I don't know why we are discussing power supplies as the OP has confirmed his controller is a Gaugemaster Q which has 4 separate windings on the transformer for the 4 controls.

 

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