Mark Gurries on DCC Friendly
Maybe I can help from a technical standpoint.
First the term DCC Friendly.
All switches are DCC Friendly if properly used, in gauge and matching wheel sets are also in gauge. In other words, everything follows the NMRA Standards. The only issue is to not attempt to run a engine that is to big for the given turnout you are going through.
The reality is:
1) Seldom do people check the wheels and track to see if they are in gauge.
2) Many of us cannot help but want to run that big loco through that two small switch anyway!! Run that Big Boy though the #4 switch!
3) DCC power is much less forgiving of shorts than plain old DC power.
The same short that a DC powerpack can care less about and simply forgive is NOT so forgiven with a DCC system. In other words all those electrical flaws in your track that you never knew about under DC suddenly become noticeable under DCC.
So regardless of best intentions, switch manufacture must update the track design to minimize the potential for shorts if they are going to be successful in sales in the long run. Hence this term "DCC friendly"
has become to mean a track switch that has been changed or improved electrically compared to the previous version to meet the new reality of the situation. The challenge of course is to come up with a good looking switch and integrate all the new internal "wiring" at the same time.
With that said, let get into the details
There are three electrical aspects to a switch
1) Point rail polarity.
2) Frog polarity.
The Power Routing feature turns out to be very much interrelated to the above due to practical issues.
POINT RAIL POLARITY
Point rail polarity is about the polarity of the point rail that is in the OPEN position. Naturally the point rail that is closed MUST take on the polarity of the stock rail it touches.
Power routing turnouts will electrically short both point rails together so they both pick up the polarity of the point rail that is closed. This also means the closer rails, frog and diverging rails can all be shorted together. Commercial Power Routing switches are made by
Shinohara Code 100, 70, 55
MicroEngineering Old style.
Walthers old style code 83
Here is the problem with power routing turnouts. If the turnout is relatively sharp (#6 or less) and the locomotive you're using has a long wheel base (2-10-2 for example), often the engine will short out on the point rails when taking the diverging route.
Why? If you draw a straight line which represents the driver length and tire width of the one side of the drivers (wheel base) and try to fit the line into the gap created by the open point rail side, you will see that at some point any one of the drivers will be FORCED to come into contact with the back side of the open point rail as it passes
Since the open point rail polarity is the same as the opposite closed point rail, the contact of the driver creates a strong short circuit.
The key is how wide is the gap between the backside of the open point rail and the stock rail. The wider the gap gets, the point rails look un-prototypical in terms of spacing distance to each other but prevents the short circuit. The narrower it gets, the better cosmetic look, but shorts will become possible even on shorter wheel base length engines.
Blind drivers may or may not help much here. Often the open point rail sticks up a bit in the air above the rail height allowing the blind driver to come into contact. OR the blind driver will actually roll over the open point rail and create contact.
To become more DCC friendly, many manufactures have eliminated the power routing feature and re-introduced the same switch using the more traditional non-power routing configuration where the point rails are insulated from each other and are ALWAYS the same polarity as the stock rail the come into contact with. Now that same long wheel base locomotive driver can come into electrical contact with the open point rail with no consequence.
This has NOTHING to do with being DCC friendly...period. The question is about smooth engine movement through the frog of the switch. Frog can come in 3 variations.
1) Insulated "Plastic" Frog
Since the frog represents the electrical shorting of opposite rails, the frog is forced to be designed in such a way as to prevent the short.The simplest solution is to make the frog electrically dead or "insulated frog". Unfortunately this is what creates the stall problem and the longer the frog gets, the worse the problem gets. Long wheel
base or engine with lots of pickup wheels need not worry, but trying to get the 0-4-0 through will make you mad! However from a power point of view, there are no shorts of any kind at any time. Not a perfect solution but the easiest and cheapest to make. The companies that make this style are:
Bachmann old style (toy train)
Atlas Snap track.
Almost all brass track
2) Power Routed metal Frog
With power routing switches, this whole frog power issue goes away. The entire frog and rails leading to and away are all electrically tied together since the wheel that must go through the frog is controlled by the point rail position. In other words both mechanical switch position and electrical polarity needs are one in the same. The problem of course is the point rails as discussed before. So one problem is traded for another. Again not a perfect solution.
Shinohara Code 100, 70, 55
MicroEngineering Old style
Walthers old style code 83
3) Insulated metal Frog
If you could insulated the rails on both sides leading to the frog from the frog but keep the frog metal, then you would have a insulated "METAL" frog. If you leave the frog alone, the switch will not perform any better than the Insulated "Plastic" Frog. But if you can somehow get the point rail position to activate an electrical switch which chooses which stock rail the frog shall get power from, then the frog is "alive" and no engines will stall. Combine this feature with the no DCC issues with the point rails shorts. The downside is that no one has been able to integrate the electrical switch into the track switch which simply means the installer is left to figure out how to power the frog.
Fortunately there are solutions provided by many Switch machines manufactures that have electrical contacts that can be used to power the frog. So this to is not a perfect solution, but it does get ride of the biggest problem or point rail shorts and ALLOWS one the ability to solve the dead frog problem at the same time. The companies that make this style are:
Walthers Code 83
MicroEngineering new style
Atlas Code 83
It should be said that Atlas switches, with the exception of SNAP TRACK SWITCHES, have always been the type 3 above with the code 100 product line. Specifically the Atlas "custom line". It should also be noted that some manufacture make is easy to solder a wire to the metal frog compared to others. So may find it to difficult and thus despite the metal frog, is forced to leave it in insulated mode.
Opinion: The unfortunate side of Atlas code 100 was that there were better cosmetic looking switches offered by other companies. In many ways, if Atlas had designed its code 100 custom line like it did the code 83 line, it would have owned the market till code 83 became so popular. Actually I happy that did not happen since code 100
Translates to a very rare 155 Lb rail size. The wave of popularity and quick conversion to Code 83 by manufactures has given us the chance to address almost all of the track switch shortcomings. Win Win!
Power Supply & Battery Charger Applications Engineer/Manager
Model Railroad Club and NMRA DCC presentations are at:
Audio Enthusiast (Love SAE equipment)