Diamond crossing polarity switching

[Andy1963]

Hi, Can I use DPDT relay's triggered by point motor switches to switch the polarity on my diamond crossings? I've seen lots written on the subject of diamond crossings, with people suggesting either DPDT switches or auto reverse modules, but I've never seen an answer about using relay's although I've seen comments about magnetic fields.

[Suzie]

Hi,? ? Can I use DPDT relay's triggered by point motor switches to switch the polarity on my diamond crossings?? ? I've seen lots written on the subject of diamond crossings, with people suggesting either DPDT switches or auto reverse modules, but I've never seen an answer about using relay's although I've seen comments about magnetic fields.

 

If you have a point adjacent to your crossing it can be used to switch to polarity of the frogs on your diamond. It is an easy matter to connect a PL15 or similar switch to the point to switch the frog polarities and a relay will not be required.

 

 

If you are using a solenoid point motor you can use a latching relay with it's two coils connected in parallel with the point motor coils instead of the PL15 switch. Alternatively an ordinary relay will do if you are using slow-motion tortoise type point motors - but these will probably have sufficient switching built in.

 

 

 

 

 

[RFS]

If your crossings are Insulfrog then no switching is required at all. However, these can cause problems with DCC (momentary shorts) and Electrofrog crossings are a much better option. I had endless problems with a code 75 Insulfrog short crossing on DCC.

 

A DCC Concepts Masterswitch Plus is a good solution: it can be used the operate the point motor and it has 4 SPDT switches built in, and a 5th one for an LED.

[sse]

If you have a point adjacent to your crossing it can be used to switch to polarity of the frogs on your diamond. It is an easy matter to connect a PL15 or similar switch to the point to switch the frog polarities and a relay will not be required.

 

 

If you are using a solenoid point motor you can use a latching relay with it's two coils connected in parallel with the point motor coils instead of the PL15 switch. Alternatively an ordinary relay will do if you are using slow-motion tortoise type point motors - but these will probably have sufficient switching built in.

 

Hi I'm looking at using a Seep PM1 for point switching - can I use this to switch the adjacent diamond? Plan to use DCC.

 

Thanks

[Grovenor]

For a point with adjacent diamond as in a double junction, you will need two sets of changeover contacts, if the PM1 has that then OK. If it only has one set then use the PM1 to operate a DPDT relay.

Regards

Keith

[Guest Moria]

not a cheapest option, but for the diamond crossing on my layout, I isolated all exit roads on all 4 tracks and wired the two sharp frogs to an auto-reverse module and fed the outside rails normally. Kind of fit and forget with no problems so far.

 

Regards

 

Graham

[RFS]

The PM1 has only one changeover switch built-in and you will need two switches. Including the controlling point there are 3 frogs that need switching although 2 are always the same polarity. A Peco PL10E mounted below the baseboard fitted with a PL15 twin microswitch would be the simplest option.

 

I made the mistake of using an Insulfrog diamond crossing (Peco code 75) and kept getting momentary shorts because the rail gaps are insufficient. I have since isolated all 4 rails and fed the outside rails normally. The 2 diamond frogs + the points frog are switched by a DCC Concepts Masterswitch plus which has 4 SPDT switches and which controls the point.

[sse]

The PM1 has only one changeover switch built-in and you will need two switches. Including the controlling point there are 3 frogs that need switching although 2 are always the same polarity. A Peco PL10E mounted below the baseboard fitted with a PL15 twin microswitch would be the simplest option.

 

I made the mistake of using an Insulfrog diamond crossing (Peco code 75) and kept getting momentary shorts because the rail gaps are insufficient. I have since isolated all 4 rails and fed the outside rails normally. The 2 diamond frogs + the points frog are switched by a DCC Concepts Masterswitch plus which has 4 SPDT switches and which controls the point.

 

Thanks, I think from this I have two options:

- masterswitch plus to switch the (Seep) point motor and the all three frogs (point and two on the diamond)

- Peco motor and microswitch on the bottom of it, does the same thing

 

I assume I still need a CDU to switch the motors?

 

Mine will be a double track junction so do you switch the point on the non-diamond line too?

 

Thanks

SSE

[Grovenor]

Mine will be a double track junction so do you switch the point on the non-diamond line too?

 

A double junction has three possible positions, both left, facing point to the left and trailing point to the right, and both right. (assuming left hand running). You can control this with a three position switch or with two seperate switches and a bit of interlocking, or with 3 pushbuttons. You need to lock out the situation where the facing point is set right and the trailing point left giving two conflicting routes over the diamond allowing collisions and shorts as the diamond frogs can only be the correct polarity for one route.

I would switch the diamond polarity with the facing point leaving the training point just to switch its own frog.

 

The three position switch, or 3 push buttons is the simplest for control but requires a traditional panel. If you want to operate your points by DCC then you need to set up the interlocking in the PC if using one or between decoder and points. The Masterswitch plus would be OK for the latter and includes a CDU, if you need one its a good buy.

Regards

Keith

[Suzie]

Thanks, I think from this I have two options:

- masterswitch plus to switch the (Seep) point motor and the all three frogs (point and two on the diamond)

- Peco motor and microswitch on the bottom of it, does the same thing

 

Additionally you have the option of connecting a latching relay (which has two coils) in parallel with the PL1. This has the advantage of not requiring DC power supply to the relay - it changes when the point changes. Available from Maplin part No N38AW.

 

 

 

 

 

 

[sse]

Additionally you have the option of connecting a latching relay (which has two coils) in parallel with the PL1. This has the advantage of not requiring DC power supply to the relay - it changes when the point changes. Available from Maplin part No N38AW.

 

Thanks for all your replies and help, I got a couple of masterswitch plus units for the two diamond junctions I have planned.

 

There was me thinking DCC had two wires...............

 

SSE

[amdaley]

Thanks for all your replies and help, I got a couple of masterswitch plus units for the two diamond junctions I have planned.

 

There was me thinking DCC had two wires...............

 

SSE

 

As Dutch_Master has said Dc & Dcc wiring are the same 2 wires but no matter what you use a short will always be a short,its just in DCC it's a bit more noticeable.The most important thing to remember is to follow proper wiring practice,strong bus wires & plenty of drops from the tracks & you will be fine.I have the same situation as you have,I have the MasterSwitches but haven't got round to fitting them yet as I am building my layout at present.I hear these MasterSwitches are wonderful things. The important thing about point switching with solenoids is you must have the power.The auxiliary power from the back of a controller doesn't just seem to be enough.Let us know how you get on.

[RFS]

A point to bear in mind with the DCC Concepts Masterswitch Plus is that it does not retain SPDT positioning when you power it off. Therefore, when you power up at the start of a new operating session, you need to operate it at least once to get the SPDT contacts in sync with the point status.

[amdaley]

A point to bear in mind with the DCC Concepts Masterswitches is that they do not retain positioning when you power them off. Therefore, when you power up at the start of a new operating session, you need to operate them once to get the SPDT contacts in sync with the point status.

 

What position would they be at when you power up for a session ?

[RFS]

Let's say the default position is the straight road: if you power up and the points are also set to the straight road then there's no problem. But if the points are set to the diverging road at start-up then the frog(s) will have the wrong polarity as the switch will have reverted to the default. Hence you need to change the points at least once on start-up to get them in sync.

[sse]

Thanks all, hope you'll all be checking the forum over the Christmas break!

 

I have ordered a couple of the masterswitches for the diamonds, plus I've ordered Seep motors and a CDU for the "normal" points. In terms of power I understand I can run a separate power "bus" at 16-20v AC or so for the points. I don't intend to power or switch the points from the DCC controller (Dynamis to start with) so I'll get a suitable transformer - I think someone said laptop power supplies are good for this.

 

A diagram would be incredibly helpful (understand there's good documentation with the masterswitches too) - much appreciated.

 

SSE

[Andy1963]

Thanks for all the responses to my initial question. The diagram from Dutch_Master is great, I think this is the solution I was looking for but I have one more question. I am using Peco point motors with PL13 switches to set route markers on my control panel. Can I therefore power the relay in your diagram from the same switch or should I use the self latching relay's described above by Suzie to set the diamond polarity from the initial point change?

[RFS]

As this is DCC then the polarity of the frog on point SW 101 will always need the same polarity as the RH diamond frog in the diagram, so only two switches will be needed, assuming both frogs are in the same power district. On my layout I have made the isolation gap on road E a good 2 feet away from the frog: this means if route A-C is set, a train travelling from E-D should stop short of the diamond and avoid a potentially damaging collision.

[Grovenor]

As this is DCC then the polarity of the frog on point SW 101 will always need the same polarity as the RH diamond frog in the diagram, so only two switches will be needed. On my layout I have made the isolation gap on road E a good 2 feet away from the frog: this means if route A-C is set, a train travelling from E-D should stop short of the diamond and avoid a potentially damaging collision.

Indeed we got this far way back in the topic, and the drawing has reverted back to a DC solution. You don't need a 'diamond relay' unless your point motor has less than two contact sets, if you do need the relay it should operate in conjunction with point SW 101. The Masterswitch does provide for that.

Keith

[sse]

As this is DCC then the polarity of the frog on point SW 101 will always need the same polarity as the RH diamond frog in the diagram, so only two switches will be needed, assuming both frogs are in the same power district. On my layout I have made the isolation gap on road E a good 2 feet away from the frog: this means if route A-C is set, a train travelling from E-D should stop short of the diamond and avoid a potentially damaging collision.

 

I was thinking of doing this to provide protection, but how do you leave the lower rail (below the E) unpowered unless the switch is set for "black"? I assume in the current diagram you'd get a short when the first wheel went over the join....

 

DM - Thanks for the diagrams BTW!

 

SSE

[Grovenor]

Forget postcards, since your protection is intended for approaching trains on converging routes the tracks that need the dead sections are E and F, not C and E.(Assuming Left Hand running). So your second switch on 103 needs to connect to these two lines. Making the dead section equal to the longest train is very restrictive. The signals approaching on those two lines will be closer than that and you need to run up to the signal. Such dead sections should only cover the overlap distance from signal to junction. Generally on our models we don't have room for prototypical 200 m overlaps in such places, often the prototype didn't either and the overlaps would include the points but with only one train allowed to approach at a time.

Regards

Keith

[RFS]

Forget postcards, since your protection is intended for approaching trains on converging routes the tracks that need the dead sections are E and F, not C and E.(Assuming Left Hand running). So your second switch on 103 needs to connect to these two lines. Making the dead section equal to the longest train is very restrictive. The signals approaching on those two lines will be closer than that and you need to run up to the signal. Such dead sections should only cover the overlap distance from signal to junction. Generally on our models we don't have room for prototypical 200 m overlaps in such places, often the prototype didn't either and the overlaps would include the points but with only one train allowed to approach at a time.

Regards

Keith

 

The point on switch SW 103 is no different than any other normal point, ie you need to provide a dead section in front of the frog to stop an approaching train from running onto it and derailing when the road is set against it. It's not possible in all positions but I have about 12-18 inches where that's possible - usually enough to stop without a derailment. The dead section doesn't need to hold the complete train - just enough for the loco. In fact, the section isn't dead: polarity either side of the rail gap is different so as soon as it's bridged a short circuit will occur stopping the train. If you have trains with the loco at the rear then you need some form of pickup on the leading vehicle (eg lighting) to protect it. My new 4CEP is protected in this way due to the lighting pickups.

 

The problem with the double junction is that it's not just a derailment that can occur: a train running E->D can collide with one running A->C even though the points at SW 103 are set correctly. Hence the rail gap on track E needs to be further away from the junction to provide some protection for this.

[RFS]

OK - so I mixed up dead section with an extended isolation point next to the frog. But your diagram would be clearer if you showed the extra isolation gaps on rails E and F to show that section is electrically separate, and dead when the road is switched the other way.

 

But dead sections cause a number of issues.

 

1) They need to be long enough to not only hold your longest train but also provide a stopping distance to overcome the momentum the train may have if the power unit is at the rear.

2) If the loco is at the front, it will stop a long way from the junction, which might be undesirable.

3) If you have a double header, the first loco will lose power on entering the section but the second won't and could end up spinning its wheels, especially if it's a multiple unit with a power car at each end.

4) I understand the problem with lighted coaches but they won't always provide power continuously. Hornby Pullmans, for example, pick up from the LH side of one bogie and the RH side of the other, so the dead section is only breached if the bogie on that rail spans the gap. The loco could stop and the momentum carry the Pullman bogie over the gap starting the engine again briefly. I can understand the problem if all the coaches have pickups and are electrically connected, such as the Bachmann 4CEP.

 

My view is that if you cannot provide sufficient length of dead section then you should instead simply allow the frog isolation gap to be longer. This way the first loco (or lighted coach) will trigger a DCC short circuit if it does a SPAD, and this will also stop any other train approaching the junction. That's how mine is configured and it works well - no collisions yet!