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DCC friendly turnouts or not

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GMD-1:
Good points Alan. I have been considering dipping my toe in Railpro by getting a TC2 & PWR-56 and a couple decoders to use with a little 4.5 x 6 'portable' layout I threw together for a local modelling show last year. Thing is I used salvaged old style shinohara turnouts. I could tolerate the occasional short as long as it does not destroy anything. Would I be right in expecting the over current protection to kick in quickly enough on such a small layout? As for the future layout, well pretty much all the main commercial turnouts are DCC friendly anyways. I will just choose the ones I like the best.

Dean:
99% of my turnouts are the old Shinohara or the Walthers/Shinohara turnouts. I think I have two Peco turnouts on my layout. The frogs are powered on them. Electrofrog?
I understand why you wouldn't want the older Shinohara turnouts with the connected points. But honestly, I have never had any problems with them. I have more problems with the copper contact that is on the bottom of the points.

G8B4Life:

--- Quote from: GMD-1 on November 23, 2016, 08:29:28 AM ---I probably should have said isolated frogs, like Microengineering's ones, rather than insulated.

--- End quote ---

Isolated is good too, in fact probably the best as they can be either dead or made to be live; it's usually up to you. Making them live to switch polarity probably doesn't have to be expensive either, if Alan gets some free doodling time one day he might be able to pen down a circuit that was discussed here a while back that should be cheap to build (remember that voltage divider network frog polarity changer Alan?).

Regarding the gap in the rails of the isolated frog variety of turnouts like Micro Engineering's, here is an idea adapted from an old issue of Railroad Model Craftsman - Fill in the gaps with little thick grey epoxy (make sure non conducting) and then neaten up with needle files etc, looks like Thermit welds after painting and no more ugly gaps.


--- Quote from: Dean on November 23, 2016, 10:14:29 PM ---99% of my turnouts are the old Shinohara or the Walthers/Shinohara turnouts.

--- End quote ---

Dean, I am glad your not having any issues with the turnouts that have both point rails the same polarity, All the planets must be lined up for you  :)  I wish I could say the same for others out there. Actually the webpage in the next paragraph explains the issue better and why they might be working well for you.

Here is another page that tells a bit on this DCC friendly term and what it means to turnouts. Some people love the guy some do not but what's on this page is good info none the less. Note, the list of turnouts is probably quite old. http://www.members.optusnet.com.au/nswmn/y_dcc_friendly_MG.htm

- Tim

GMD-1:
That is good to hear Dean. And I know what you mean about the copper contact strips. A lot of mine have broken, so I use our forum hosts manual switch machines with a DPST slide switch to do the power routing.
Another good article Tim. I only use B-B diesels on this current mini-layout, so perhaps I will be lucky like Dean. But not if it means risking frying decoders.

Richard

Alan:

--- Quote ---I could tolerate the occasional short as long as it does not destroy anything. Would I be right in expecting the over current protection to kick in quickly enough on such a small layout?

--- End quote ---

Size of the layout is not the determining factor. Total resistance is.

Shorts always do damage. The question is how much. At the very least, micro pitting of wheels and track will occur. Enough pitting at the same spot over time will be a problem especially on thin metal such as point rail taper. At the very worst, a wheel set becomes a toaster and melts truck frames and ties. On a positive note, unlike DCC, RP modules seem unaffected by shorts on the rails so module damage is unlikely.

As you know the trick is getting the breaker to sense and act fast. This requires an extremely low resistance electrical path between PWR and loco. Here is the issue... train equipment caused shorts are not zero resistance. In fact, they may not be anywhere close to zero resistance. Bus wiring is not zero resistance either. Total current flow will be determined by the sum of the two resistances. As resistance goes up current goes down. It is quite possible for the equipment short resistance and bus wiring resistance to add up to a value that causes total amperage to be less than the circuit breaker trip point. For example: RP PWR is 14.8v and trips at 4 amps. This translates to a resistance of 3.7 ohms. A 4 ohm short circuit will not trip the breaker. Instead, 55 watts of power will flow continuously. Hold a 50 watt light bulb against a plastic truck frame to see what will happen. Not good. Now imagine this situation with a poorly wired layout. Let's say small gauge wire and poor connections add 2 ohms resistance. A short circuit now has to be less than 1.7 ohms resistance to trip the breaker. It is very likely you will have shorts from time to time that have more resistance than 1.7 ohms.     

That is a long winded way to answer your question with a solid maybe. :)

You can increase the odds the breaker will protect you by using healthy size buss wire and sufficient number of track feeders i.e. make the bus resistance as close to zero as possible. There is much bantering about regarding wire gauge and number of feeders. Personally, I think it is an argument not worth having. Use 12 gauge buss wire period. Use 20-24AWG feeders 12" or less in length spaced no further than 3' apart on the track. Make sound electrical connections (solder). With this arrangement, regardless of layout size, you are guaranteed a near zero resistance path and thus the highest probability the breaker will protect your equipment.

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