Points on Track-powered Layouts – the basics
A quick review of the basics, on track-powered layouts, each rail is connected to the power source. One rail is positive (+), the other negative (–). Locomotives pickup power from one track, run it through the motor and out to the other track to create a circuit (DCC is a little more complicated but functions on the same principle). If the two rails touch in an unintentional way (e.g. a metal bar connects both) you create a short circuit.
This makes points interesting because as shown in the diagram below. The bottom rail needs to cross over the blue rail in order to let the wheels move around to the switched track. If the whole thing was metal, we’d cause a short. In the example above, LGB get around this by making the frog (the place where the two rails meet) plastic. Plastic doesn’t conduct electricity so there is no short.
But if there is no power on the front, how does the locomotive keep moving when moving over this point? Essentially, the loco will have multiple pickups. This will beat least 2wheels on each rail and often at least 1 skate. While the first wheel is on the insulated frog, power is still drawn from the other wheel and the skate. As they move over the plastic frog, the front wheel is now back in contact with the rail. Great! Everything works.
It does – until the curves of the point get longer. With wider radius curves, the frog has to be longer; and if it’s plastic this means more area that is not conducting electricity. There are a few ways you could address this:
- Only run locomotives with a longer or more electrical contracts (such as more wheels or more spaced out wheels
- Add a powerbuffer so the loco can continue to move for a short time even without track power
- Power the frog based on the direction of the switch
This article, covers the third item.
TrainLine 45 R3 Points
I purchased both a left and right-handed from Modell-Land.de. The curve matches an LGB R3 curve with the straight being 450mm (1.5 lengths of the standard LGB straight). They match the LGB R3 points.
The points don’t come with attached fishplates (connectors) as you may be used to with LGB. However, they do include x3 railclamps (which I actually prefer). Underneath, screwed brass bars connect the different rails to minimise the risk of electrical connectivity issues. The other interesting thing with this point is the frog is metal and can be electrified.
Extending the from the diagram at the start of the article, the image below shows the frog marked in orange. If wired properly, if the point is set straight on, it can be set to the polarity of red (–). When the point changes to diverse (right) it can be set to blue (+).
Wiring the frog
The initial explanation below is valid for both DC and DCC layouts. I’ll highlight anything that is specific to DCC (my choice of power).
In order to have this work, you’ll need:
- LGB 12010 – Switch Motor
- LGB 12070 – Supplementary Switch (or LGB 102030 which is the older version but functions the same)
The LGB 12010 is used to change the train’s direction between the straight and divergent tracks. The LGB 12070 plugs into the LGB 12010 switch motor and essentially gives you two switches that change based on the direction of the points – perfect for our usecase.
The diagram below from The World of LGB visualises how the switches work
We’re only going to use one of the switches (the left on). We’re going to run a wire from the frog to the second input (from the left). Then we run power from each rail the first rail to the first contact and the second rail to the third contact. This means, as the points change direction – we also change the polarity of the frog. The diagram of this is below:
So how does this look in practice? The picture below shows the setup. At the left of the image you’ll see black wires running from the rails to the supplementary switch and then the middle wire that runs on the underside of the point (directly under the sleepers of the right rail) to the frog. I used all black to help the wiring blend in. The TrainLine45 R3 Point comes with a soldering tab that can be screwed into the frog making attachment easy.
The yellow/white wires run to an MD Electronics VKW Switch Decoder, this lets me change the points from a handheld control. However, the points can be switched manually or using analogue connections and the guide above is still valid.
It is important to note this setup does risk introducing a short. If a loco arrives from the curve (on the right) heading towards to the left and the track direction is set to straight – the frogs polarity will be wrong. I’ll get around this by using reed track contacts to automatically switch the direction based on a train approaching. This is something that can be achieved a reasonably simple way with both analogue and DCC. It’s something I’ll write up in the future.
