Points and decoders

[Gazah]

Evening all, 

this is may seem a silly question and has probably already been asked and answered also.

if I have two points and two point motors can I wire/programme them to use only one socket on the hornby decoder, so that loco is travelling on line A to change to line B I can open both sets of points at the same time.

hope this makes sense to all

 

G

[Fishmanoz]

Yes it makes sense and yes you can.

 

Such points are usually referred to as a crossover.

[Gazah]

Yes it makes sense and yes you can.

 

Such points are usually referred to as a crossover.

Hi Fish 

thanks for the response so would this be done via RM or just simply wire both points into one output socket?

[idlemarvel]

Both.  To make it work electromechanically you wire them both to the same accessory decoder socket.  To make RM reflect the fact that the points are interlocked you give them the same accessory decoder port number, so if you click one they both switch.

[Fishmanoz]

Great teamwork idle.  I wish they were all this simple.

[Graskie]

Parallel wiring from one point motor to the other would save a bit of wire compared to feeding both directly from the same accessory decoder outputs, wouldn't it? I think that's what I would do with my crossovers, having always done that with my old DC system, with an uncontrolled AC output.

[Flashbang]

Actually parallel wiring isn't such a good idea even though it uses less wire.

Reason is the first motors coil will 'grab' most of the pulse of power leaving little power to be forwarded to the second motor.

Therefore its always better to run three totally separate wires back to the source (Acc. decoder or passing contact lever) from each motor and at the same time try to keep all the wires to roughly the same length. 

[St1ngr4y]

Actually parallel wiring isn't such a good idea even though it uses less wire.

Reason is the first motors coil will 'grab' most of the pulse of power leaving little power to be forwarded to the second motor.

Therefore its always better to run three totally separate wires back to the source (Acc. decoder or passing contact lever) from each motor and at the same time try to keep all the wires to roughly the same length. 

I thought that WAS parallel wiring?

Ray

[Michael_A]

Actually parallel wiring isn't such a good idea even though it uses less wire.

Reason is the first motors coil will 'grab' most of the pulse of power leaving little power to be forwarded to the second motor.

Therefore its always better to run three totally separate wires back to the source (Acc. decoder or passing contact lever) from each motor and at the same time try to keep all the wires to roughly the same length. 

I thought that WAS parallel wiring?

Ray

I think this is only an issue if the length of wire to the second or even third point motor produces too much volage drop. If the wring is heavy enough and the distances between point motors are not too great, it should be possible to 'daisy chain' the parallel wiring, if necessary.

[RDS]

 

I thought that WAS parallel wiring?

Ray

I agree - I think what Graskie has described is actually 'series' wiring.

[Flashbang]

 

I thought that WAS parallel wiring?

Ray

I agree - I think what Graskie has described is actually 'series' wiring.

Perhaps my original reply/answer wasn't clear enough?

Both are Parallel wiring e.g. The coils of each motor are connected across the supply in Parallel, they are NOT in series with it.  I.e. From decoder or lever switch to first motor then linking onto second motor or by running seperate wires back to the decoder or switch to each motor. Both are connecting the motors coils in Parallel. 

Best is always to take indivual wires back to the source or switch etc. linking from one to the next is often asking for problems to occur!

[37lover]

 

I thought that WAS parallel wiring?

Ray

I agree - I think what Graskie has described is actually 'series' wiring.

Perhaps my original reply/answer wasn't clear enough?

Both are Parallel wiring e.g. The coils of each motor are connected across the supply in Parallel, they are NOT in series with it.  I.e. From decoder or lever switch to first motor then linking onto second motor or by running seperate wires back to the decoder or switch to each motor. Both are connecting the motors coils in Parallel. 

Best is always to take indivual wires back to the source or switch etc. linking from one to the next is often asking for problems to occur!

When I first read this I too thought one was series and the other parallel but once I'd sketched it you can see that Flashbang is of course correct and both are indeed parallel. However, I'm not convinced that if I have say 70cm of wire to my first point motor that then running a further 30cm on to the next point will result in the first "grabbing" all the power. The only way to safeguard that situation would be to make sure the nearest motor of the crossover pair was separately connected with wires/cables of equal length to those used on the further motor! Flashbang am I interpreting that correctly?

[Fishmanoz]

Interesting conversation with some interesting interpretations of circuit theory.  At least it might appear that way.

 

In theory, it is simply not possible for one of a number of identical connections to "grab" all of the power, and also in theory, none of them are "first" anyway.  However, this is possible in practice if the wire gauge is too light and there is a significant resistance/voltage drop along it.  Then more current will flow in the lower resistance connection closer to the decoder and less in the higher resistance one further away.  This is not one grabbing the power over the other, but it is Ohm's Law in operation.

 

Let's put in some more practicality though.  We are talking about a crossover here so the points are adjacent to each other. The chances of getting a significantly different resistance between the two only of them is most unlikely. So wire them in parallel as convenient and it will work fine.

 

Now I know you all knew that, even if some of the wording was a little unclear.  So please don't think me condescending, I was just clearing up the words.

[Graskie]

Fantastic! So I was right for a change? I used to wire my crossover points that way and had no problems. I had a CDU to boost things, but that is already built into Accessory decoders anyway, so is not needed now.

[96RAF]

I have one cross over that has both an underfloor solenoid motor and a newer surface mounted motor link-wired and they both throw fine, but there again I only use the acc decoder to pulse a relay which fires a great big CDU charge down the analogue wires.

[WildSwan]

I have one cross over that has both an underfloor solenoid motor and a newer surface mounted motor link-wired and they both throw fine, but there again I only use the acc decoder to pulse a relay which fires a great big CDU charge down the analogue wires.

I'm very interested in this reply. If I understand correctly you are using DCC to control (perhaps latching?) relays and in turn using the relays to fire the points from a CDU.

 

Can you elaborate why you have done this - I assume you are getting more reliable point throws?

 

Mark