Wiring a reversing triangle

[metijg]

Firstly apologies for the terrible drawing..

 

Anyway I have been trying to wire up a DC reversing triangle with no success. In my innocence I thought that if power from a single controller was wired to the two red arrows with Insulfrog points then there should never be a conflict. The train drives from 1 to 3 under power from 1, the point is changed and drives to 2 under power from the middle, then points 1 and 2 are changed and the loco should now be able to drive back to where it started from the original power source. 

 

As I said, no luck, the controller trips instantly. Is it asking too much to have it wired to two locations that have no electrical contact? 

 

Thanks in advance for any help or advice you can give!

Cheers

Tim

[Nigelcliffe]

If you draw out all the rails, and then colour them so one rail is Red and one is Blue, you'll find somewhere on the drawing where a Red rail bumps into a Blue rail, and that's your short circuit.

 

The standard way of wiring a reversing Y is to pick one turnout (eg. #1 on your diagram) and fit four insulated joiners on its rails from the frog (the upper connections on your diagram).  Then, the top part of your Y (turnouts 2 & 3) can be powered at the top of the diagram direct to your controller.  The rails at #1 need to be wired via a reversing switch (DPDT) which can either be a manual switch, or associated with the movement of the turnout. 

 

The details of the wiring, which turnout to pick, etc.. all depend on what else is connected to the rest of the layout. 

 

 

[metijg]

Thanks for the reply Nigelcliffe, and I know this is the common wisdom and that my theory is not correct, as it doesn't work, but I still can't see why!

 

If the train travels from 1 to 3, then it is under the motive power from the bottom and the other connection is isolated by point 3. When points 2 and 3 are thrown to be aligned, then the motive power is from the top and the points isolate it from the power connection at the bottom. Once the train is the far side of points 3 and they are thrown it is isolated from the power at the top, and assuming point 1 is also moved is now receiving power from the bottom. 

 

I don't see a moment where the two power sources conflict as they are also isolated from each other by points. There would be moment when the train direction is reversed without the controller being reversed, but I don't see why that causes a problem. 

 

Thanks again..

[Sol]

Have a look at this

 

and this

https://rail.felgall.com/rlt.htm

[kevinlms]

3 minutes ago, Sol said:

Have a look at this

 

and this

https://rail.felgall.com/rlt.htm

The DPDT switch can also be linked to the points, either by such a switch connected to a point motor, or even using a switch to both throw the points & do the required switching.

 

 

A solid wire wrapped around the handle of one of these and mechanically linked to the point, does both jobs nicely.

 

https://www.jaycar.com.au/dpdt-standard-toggle-switch/p/ST0572

[Izzy]

1 hour ago, metijg said:

Thanks for the reply Nigelcliffe, and I know this is the common wisdom and that my theory is not correct, as it doesn't work, but I still can't see why!

 

If the train travels from 1 to 3, then it is under the motive power from the bottom and the other connection is isolated by point 3. When points 2 and 3 are thrown to be aligned, then the motive power is from the top and the points isolate it from the power connection at the bottom. Once the train is the far side of points 3 and they are thrown it is isolated from the power at the top, and assuming point 1 is also moved is now receiving power from the bottom. 

 

I don't see a moment where the two power sources conflict as they are also isolated from each other by points. There would be moment when the train direction is reversed without the controller being reversed, but I don't see why that causes a problem. 

 

Thanks again..

 

Unless at least one section is isolated from the others a short is always going to exist. It has nothing to do with what type of points are used, and whether the inner rails are self isolated. No three exits can be the same polarity at one and the same time.

 

As suggested draw out the individual rails in pairs. Then just colour the outer ones on the three sides. Try making them different colours - polarities - in all places. Just doesn’t work. Reversing the polarity must done somewhere, sometime.

 

Izzy

Edited July 30, 2019 by Izzy
Grammar

[metijg]

I really appreciate the replies, I understand the theory, but I still can't find the reason why the drawings below don't work. I'm being both dense and persistant, it's not an attractive combination and I apologise..!

 

Please help - I can't see a moment when the two power sources are not kept independent of each other by closed points.

Thanks!

 

 

 

 

Edited July 31, 2019 by metijg

[RobjUK]

Unless you have added extra insulated breaks, the outer rails are presumably continuous through each point?

 

eg. You have a direct link between positive at B and negative at C; all the outer rails of the triangle are permanently connected together, unless you add breaks.

 

See the diagram here:

https://dccwiki.com/images/thumb/4/47/PECO-Insulfrog-Illustration.png/800px-PECO-Insulfrog-Illustration.png

Edited July 31, 2019 by RobjUK
clarification

[john new]

Agree with RobjUk

 

Similar issue can even occur in a circle with a passing loop and siding off it. Easy to forget that the rails through pointwork which are not gapped are a pathway to either create shorts or feed power to a rail you would otherwise expect to be dead.

 

After years of building end to end layouts I made that numpties error on a basic circle layout for my grandsons, puzzled for ages, posted here on RMWeb, and was given the answer. A definite duh moment as the solution was so blindingly obvious. Power goes both ways round the circle unless you add a gap!!  Hopefully, not a mistake I will repeat.

Edited July 31, 2019 by john new
Punctuation error

[Nigelcliffe]

1 hour ago, metijg said:

I really appreciate the replies, I understand the theory, but I still can't find the reason why the drawings below don't work. I'm being both dense and persistant, it's not an attractive combination and I apologise..!

 

Please help - I can't see a moment when the two power sources are not kept independent of each other by closed points.

Thanks!

 

 

 

 

 

 

On right hand diagram, when turnout B changes the upper rail becomes "red", but it is still connected to the blue rail from A.   That is at least one short circuit location. 

 

You can wire it so the polarity sorts itself out on turnout changes (switches or relays attached to turnout movement), but you need to switch both rails at some place.  

 

 

[metijg]

Ok. It's taken me a while but I've got there..!

 

The outside rail isn't isolated and so, even when the points are switched, you have a short. Thanks!

 

Will go and buy a DPDT switch..

[metijg]

Thanks for your help. Working prototype now cluttering up the living room!

[DCB]

I would operate the changeover switch from the point at the dead end of the wye and feed it from the approach tracks, that way you can isolate a loco at the end of the wye. without a centre off DPDT.    Couple of micro switches bearing on the tie bar ends will do it or maybe have a DPDT on the panel.

Electrofrog / Live frog needs insulators along the top rail between points, but not Insulfrog / Dead frog

 

Edited August 30, 2019 by DavidCBroad

[Grovenor]

David, I suggest you check the switch wiring, especially for when the point is set straight.

[DCB]

On 27/08/2019 at 13:21, Grovenor said:

David, I suggest you check the switch wiring, especially for when the point is set straight.

Yep wires the wrong way round.   

Now changed.   Also plan for 2 X microswitches, mine cost 20p each from China, ideal for DC, probably not for DCC.

The loco can be reversed by changing the point without touching the controller if you are in lazy mode.

[Grovenor]

Still the wrong way round!

[John ks]

2 hours ago, Grovenor said:

Still the wrong way round!

Is this how they should be?

 

 

John

[Grovenor]

Yes.

[newbryford]

17 hours ago, DavidCBroad said:

Yep wires the wrong way round.   

Now changed.   Also plan for 2 X microswitches, mine cost 20p each from China, ideal for DC, probably not for DCC.

 

 

 

 

Why do you consider them unsuitable for DCC?

 

For a triangle - it is the same wiring for DC and DCC (although you do have the option of an auto reverser for DCC )

[DCB]

2 hours ago, newbryford said:

 

Why do you consider them unsuitable for DCC?

 

For a triangle - it is the same wiring for DC and DCC (although you do have the option of an auto reverser for DCC )

I would expect them to shrivel up and die at the first hint of a short on typical DCC amperage.  They are tiny and cost 10p each including postage, I would be thinking 3 amp for DCC

 

See John KS drawing.

[Sol]

David, I guess is depends on the current capacity of the microswitch - on my DCC layout, a short circuit is reduced to about 1.75Amps and is cleared within 10 seconds. And even on my DC layouts - still kept to about 1.75A as each of my DC supplies per cab were 2Amp units.

[WIMorrison]

7 hours ago, DavidCBroad said:

I would expect them to shrivel up and die at the first hint of a short on typical DCC amperage.  They are tiny and cost 10p each including postage, I would be thinking 3 amp for DCC

 

See John KS drawing.

 

A motor used on a DCC system is still a DC motor and doesn't draw any additional current. The DCC chip uses milliamps, LEDs (also present on DC) also take milliamps (~5-10mA per LED), and sound draws milliamps when operating - though there can be a current inrush when initially switched on.

 

In short, a DCC loco is not drawing much more current than a DC loco and most certainly not at the level your suggest and a switch that operates for DC will operate for DCC.

[DCB]

3 hours ago, WIMorrison said:

 

A motor used on a DCC system is still a DC motor and doesn't draw any additional current. The DCC chip uses milliamps, LEDs (also present on DC) also take milliamps (~5-10mA per LED), and sound draws milliamps when operating - though there can be a current inrush when initially switched on.

 

In short, a DCC loco is not drawing much more current than a DC loco and most certainly not at the level your suggest and a switch that operates for DC will operate for DCC.

The ones I use are 99p for 10 including P+P from Hong Kong.    Rated at 1 amp at 125 volts AC  The problem is if the point C is set wrong and against an approaching loco there will be a short circuit as the leading wheels and trailing wheels on the same side which have pickups will be at opposite polarities. If everything is 100% the overload will ping instantly, but a bit of dirty track or dirty pickup and the partial short may take rather longer to register during which time the microswitch may well prove to be the weakest link.  I have ruined the plunger pickups on many many Airfix 14XX tanks through running in to a wrongly set point.   Personally I would use the ordinary larger microswitch rated at around 7 amps at £1 each inc P+P from Hong Kong if designing for DCC or stick a 1 amp polyswitch in the feed wire if using the small ones.

[Dunsignalling]

4 hours ago, WIMorrison said:

 

A motor used on a DCC system is still a DC motor and doesn't draw any additional current. The DCC chip uses milliamps, LEDs (also present on DC) also take milliamps (~5-10mA per LED), and sound draws milliamps when operating - though there can be a current inrush when initially switched on.

 

In short, a DCC loco is not drawing much more current than a DC loco and most certainly not at the level your suggest and a switch that operates for DC will operate for DCC.

 

You are correct that, under normal no-fault-present running conditions, those are the maxima that should pass through these microswitches.

 

However, what happens under normal conditions isn't the same as what can happen under short circuit conditions external to the loco. 

 

If a short circuit occurs on the layout, whilst the protection built-in to the DCC controller should trip everything out in a fraction of a second, until it does, it may attempt to dump its entire potential output (often 5 amps or more). Depending where the short is, that could pass through one or both microswitches and. In those circumstances, I'd consider cheap "allegedly" 1 amp rated components to be vulnerable.

 

John