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Why is This Needed?
This section captures information about the modification of trackwork to be "DCC Friendly". This isn't essential for a DCC controlled railway, but it's one of those things you don't need until something goes wrong.
With a DC controlled layout, the track is electrically broken into sections. If a train derails on a point frog, then the controller limits the maximum current at around 1A or so. If the back edge of a wheel contacts the "wrong" rail while going through a point, the the controller may remove power momentarily, or may not even notice. In either event, power loss is to one zone only and the remainder of the layout will continue uninterrupted.
With DCC, the current limit is usually set at around 5A: sufficient to power several trains. If DCC didn't allow this, it wouldn't achieve much! However, that does mean that any fault has a higher current available to flow through it: this in turn provides a higher capacity to cause heating & arcing. Consequently DCC systems usually have a much quicker shutdown. Often, a DCC booster will then wait around 0.1s before trying to reapply power; this can cause noticeable "hesitation".
The most effective way to prevent this being a problem is to stop it happening in the first place. This is achieved by changing the electrical connections within the pointwork to eliminate "back to back" shorts etc.
What Needs to Happen?
The definitive guide to this subject is in Allan Gartner's web page. That sets out the reasons, and what can be done. The specific section about points is here. My track is Peco code 55. This is covered in that site and doesn't require a lot of work.
The key changes needed are to isolate the frog from the closure (inner) rails, and to wire the closure rails to the stock (outer) rails. The frog area is then electrically separate, and needs to be fed with switched power: it will no longer collect power via the point blades. The only difference I've made is to isolate the closure rails a bit further back from the frog: this reduces the likelihood of "back to back" shorts. The quickest way to explain this is with pictures:
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Cut the two closure rails leading to the frog. I used a "Dremel" power tool with 1" diameter cutting disc. Be careful - in N gauge the disc will nearly touch the outer rails by the time it has cut to the bottom of the rail, and it will kick! |
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Add filler to the gap. I have used Araldite: it is hard when set, so hopefully will not be eroded by rolling stock. It is difficult to work with though - very stringy. |
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After the glue has set, it needs to be shaped to the contour of the rails; I simply used a scalpel. |
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Finally the bond wires need to be added. I've used 22SWG tinned copper wire, and 60%/40% tin/lead solder. Lead free solder did NOT flow well. Do the soldering very quickly (aim for a second or less) to avoid heating the plastic. Not shown here is the (essential) dropper wire to the frog. Mine simply solders to the existing frog wiring behind the point. |
Sounds fiddly? Well it is the first time - but a batch of 12 passed in no time.
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