Thank you, fellows, all of you - there is a lot of information and thinking here to digest. This is one exchange I need to print out rather than rely on finding it again.
Dave Nelson
Due to the possibility of momentary shorts at the insufficiently-insulated frog, a lot of so-called, "DCC friendly," commercial turnouts - aren't.
Here's a description of a truly DCC friendly turnout - with one caveat:
The caveat - it is the engineer's responsibility to stop short of the clearance point if a turnout to be crossed in the trailing-point direction is not aligned for the branch his train is on. Signals may, or may not, be provided to inform personnel of the position of switch points.
If the above sounds like a description of my hand-laid specialwork, I'm sure that's only a coincidence...
Chuck (Modeling Central Japan in September, 1964 - with bulletproof track electricals)
Fred - thanks for the best explanation of the issue ever given!
dknelson Can someone provide a brief description of the factors that make a turnout more or less DCC ready? I just saw an add for a new line of Micro Engineering turnouts that are said to be DCC compatible. It suggests this feature was not present in their prior product, but does not go into how they differ from prior Micro Engineering products to warrant this claim. I assume it all relates to a need to avoid even the briefest of short circuits because of the faster acting circuit breakers (where DC can and does bull its way through a brief short circuit).
Can someone provide a brief description of the factors that make a turnout more or less DCC ready? I just saw an add for a new line of Micro Engineering turnouts that are said to be DCC compatible. It suggests this feature was not present in their prior product, but does not go into how they differ from prior Micro Engineering products to warrant this claim.
I assume it all relates to a need to avoid even the briefest of short circuits because of the faster acting circuit breakers (where DC can and does bull its way through a brief short circuit).
The other impact of using DCC instead of DC is that a short circuit in DCC shuts down the entire power district - entire layout if only one power district - where a short circuit in DC only affects the specific block and the throttle selected for that block. With a short circuit in DC, the rest of the layout still works normally.
Good turnout wiring works better in both DC and DCC. Back in April 1963 - long before DCC was a gleam in anybody's eye - Jack Work was proposing what is now called "DCC-friendly" turnout wiring in the pages of Model Railroader. My handlaid turnouts built in the '70s used "DCC-friendly" wiring.
But because a short at a turnout doesn't shut down the entire layout in DC as it does in DCC, turnout manufacturers used inferior wiring schemes as a trade-off to enhance the mechanical strength and reliability of their turnouts. Linking the points together with a metal strip, and not gapping the closure rails near the frog does make the frog area and throwbars mechanically stronger. The cost is occasional temporary short circuits when a wheel back brushes against the open point. And the gap between open point and stock rail has to be wider than otherwise necessary to minimize this type of short circuit.
Where do classic old Shinoharas and Atlas customlines come out in this debate -- I thought there was a comparison article in MR this but darned if I can find it.
Classic Shinohara and ME turnouts are classic power routing turnouts with the frog and both points forming a single electrical unit that switches polarity when the points are thrown. Both are susceptible to the wheel back brush shorts at the open points - especially if the wheels are not in gauge. That said, folks who use classic Shinohara turnouts and converted to DCC reported problems with less than 20% of their turnouts. And those were generally fixed by making sure the open point gap was wide enough, and that the wheels were properly gauged. That means less than 10% of the classic Shinohara needed surgery to make them work with DCC.
Atlas Custom-Line went a different route when they were developed for beginners and train set folks looking to step up in the late '50s and early '60s. The Custom-Line turnouts feature an insulated, dead frog and points that are tied to the stock rails, not to each other. This made wiring simple for those who struggled to learn the gapping rules of power routing turnouts.
The older code 100 Custom-Line #6s did have rails of opposite polarity in very close proximity at the diverging end of the frog. Occasionally, wide wheels or slightly mis-gauged wheels could contact both rails simultaneously, causing a temporary short circuit. Peco code 100 and code 75 Insulfrogs have the same problem, which is a direct result of trying to minimize the length of the dead frog. Nail polish is the temporary solution.
As a supplement to that question, between the Peco electrofrog and Peco insulfrog turnouts, I have been under the impression that it is the Insulfrog that is the more DCC friendly of the two. But I am not sure why this is so if the frog is correctly wired, or maybe I am misreading the Peco instruction booklet. And I have visited layouts with electrofrog that are indeed DCC. I write this as someone (see first two sentences of this posting, above) who in a distracted moment has unintentionally purchased both insulfrog and electrofrog Pecos. And as a still further complication, assuming Insulfrog is the more DCC friendly of the two, does that mean it is the more DC unfriendly of the two? Dave Nelson
As a supplement to that question, between the Peco electrofrog and Peco insulfrog turnouts, I have been under the impression that it is the Insulfrog that is the more DCC friendly of the two. But I am not sure why this is so if the frog is correctly wired, or maybe I am misreading the Peco instruction booklet. And I have visited layouts with electrofrog that are indeed DCC. I write this as someone (see first two sentences of this posting, above) who in a distracted moment has unintentionally purchased both insulfrog and electrofrog Pecos.
And as a still further complication, assuming Insulfrog is the more DCC friendly of the two, does that mean it is the more DC unfriendly of the two?
Live vs dead frogs - neither one in and of itself is more DCC friendly than the other, though the pervailing (wrong) perception is that dead frogs are more DCC friendly.
Live frogs require an electrical contact to switch polarity of the frog when the turnout is thrown. Live frogs require a feeder to the frog from the polarity contact. And live frogs require knowledge of power routing gapping requirements for the diverging side of the frog if the frog is not isolated. Because turnouts were not sold with switch machines and polarity contacts, most manufacturers (except Atlas and Insulfrog) used the points to do the polarity switching of the frog which takes us back to the problems at the points discussed earlier. Newer Shinohara and ME turnouts, in addition to tying the points to the stock rails and not to each other, isolate the frog and provide a way to tie a feeder from the contact to the frog.
Dead frog turnouts, while requiring less and simpler wiring, have dead spots that cause lights to flicker and small wheelbase locomotives to stall. Higher # dead frogs, as discussed, try to minimize the length of the dead area by bringing the rails of opposite polarity fairly close together at both ends of the frog area.
The best on-line guide to turnout wiring I have seen is at http://www.proto87.com/turnout-wiring-for-DCC.html.
Peco Insulfrog and Electrofrog turnouts have internal wiring options that can (if the option is exercised) make them slightly different from Atlas or classic power routing, respectively. Not owning any Peco turnouts, I can't say authoritatively what those options are and how they work. I do know there is a lot of (mis) information floating around about wiring Pecos that assumes an option is exercised or not. I would look for Peco or other authoratative information on how to wire their turnouts.
yours in wiring
Fred W
See http://www.proto87.com/making-rtr-turnouts-dcc-friendly.html
You'll notice that on the unmodifies turnout the frog is not isolated. More importantly, you'll also notice that there are two metal straps that join the two point rails which get removed during the modification. With the metal straps in place on the turnout in the picture, the straight stock rail and the two point rails will have the same polarity, while the curved stock rail will have the opposite polarity.
Assuming an engine will take the curved route, a problem may occur when the back of a wheel on the curved stock rail contacts the point rail at the same time. A short will then occur, tripping the command station (or other fast acting) breaker.
Some of the nay-sayers will claim that this cannot occur when all the wheels are in gage, but I have found that some of my 6-axle diesels will cause a trip. I believe that this is due to the attack angle as the diesel truck enters the turnout, primarily from the frog end.
My club just recently purchased some of the new Shinohara code 100 #6 turnouts, and these appear to be partially DCC friendly. They still have the metal strap at the ends of the points, but the metal strap at the closure rails has been replaced with two rail-joiner type connections.
Additional information can be found at http://www.wiringfordcc.com/switches_walthers_old.htm
Regards
Dave,
I am with you - I never really understood where the problem lies. I have been using turnouts with insulated frogs on various DCC layouts without any additional wiring than a set of feeders for each track, spur or siding and I never had any problems with engines stalling or short circuits. All I did is to check my wiring with a volt meter and to ensure my track is in gauge and clean.
DCC friendly does not me DC unfriendly and a Peco Electrofrog can be also used with DCC, proper wiring assumed.
IMHO, it finally boils down to the questions of how many pick-ups your locos have and whether they can "bridge" the dead frog properly.
Mea culpa, mea maxima culpa. My brain seems to be shrinking at an accelerating rate. I guess -- heck, I'm sure -- there have been magazine articles and forum postings on this issue but I cannot seem to find them readily.