With a polarity reversing switch (forward-reverse), the same wire isn’t always negative.
I found out a long time ago, when I was using common rail on a layout with a common rail connected throughout, that there was no way I could have two trains running in oppisite directions on the same track, even with separate power packs, because they short each other out.
I switched to dual rial block control and can now run two trains in opposite directions on the same track with two separate packs, using DPDT switches to control the blocks.
In common rail, one rail is intact all the way through. The other rail is gapped with power being supplied through a SPST switch. Try running two trains (DC) at the same time in oppisite directions on this track. It can’t be done, unless the motor leads of one locomotive have been reversed. This is the reason why reversing loops require DPDT switches. When positive comes in contact with negative, you get a short.
If common rail is a mistake, then I have been happily mistaken for over half a century.
The straight DC control system I’m currently using is a common rail adaptation of Ed Ravenscroft’s MZL scheme. Using common rail allows me to reduce the track power wiring at the panel by approximately 45%, not to mention the savings in (electrical) switches with half as many poles. Over the years, just the latter has freed up enough money to buy several brass locomotives.
The key is, there is no direct connection between locomotive power supplies downstream of the 120VAC house power connection until the controlled-voltage DC passes through the DPDT reversing switch at the locomotive controller. With even the least amount of care, no train will ever bridge a gap with a 24VDC differential. They only occur where two zones meet, on the connecting track halfway between ‘towns,’ and there are 24V warning bulbs masquerading as house lights at those points.
One thing which common rail allows is that detection blocks don’t have to correspond with control sections, either in length or in location of boundaries. I do gap the common rail, both for detection and to ease troubleshooting. If I ever go to DCC (which is less likely than a change of the scale I model) the gaps are there, so sorting out power districts won’t be a problem for whoever buys my final layout from my estate.
One thing that bears mention, no matter whether you run DC or DCC, or how you wire the tracks on your layout. Document everything! Not only will that simplify troubleshooting, but it sure beats trying to remember just how the old track was powered when making changes to something that has been operating for years.
Chuck
Hi there. Have you been taking circuit design lessons from Charles Eugene Doane? Neither of you seems to know how this stuff works. Chuckie thinks that you can use a diode to increase voltage and you’ve obviously gotten “common” wiring incorrect. My last layout had a small yard, a passing siding and a long looping run. While a train was on the long loop, another was going back and forth arranging itself and then waiting for the other to pass on the siding. So you’re telling me that the switching I was doing never happened? I imagined it all? I suppose next you’ll send around an email like chuckie did asking for someone to shoot me.
My next layout will be wired “common” for THREE train operation! [}:)] I’ll be sure to have the fire department ready when I plug it in.[soapbox]
As Jeffery hinted, I hope you’re not planning any reverse loops or turning wyes. In them there is no such thing as a common rail, it would be called a short.
What are you calling the “same track”? There is no way this is possible with DC power regardless of how it is fed. The only way one can run two (or more) trains on the same track in opposite directions is to use some sort of command control system like DCC.
Yes, I believe how the common rail method works is common knowledge, is widely used, and the people responding to this post obviously understand it.
The rest of this just makes no sense. Either the terminology for what is being described is imprecise, incomplete, or it is just wrong. If what is meant by a “single track” is a loop of track with common wire blocks in it, then this is just wrong. If it didn’t work as is claimed and there is a “short” between the two power packs then it was done incorrectly. And on a bigger level if the common wire system didn’t work then why would there be three decades of books and articals written about it and why does this thread even exis
You bring up the exception but that is only in the “common rail”. But that doesn’t mean a “common wire” system cannot be used to control it. Once again, as many have been saying, people have been using common wire control systems for layouts with wyes, reversing loops, and turntables for decades. This is not rocket science.
[quote user=“TomDiehl”]
As Jeffery hinted, I hope you’re not planning any reverse loops or turning wyes. In them there is no such thing as a common rail, it would be called a
Are you sure about that? I’ve read a few threads where they talked about Mars and aliens and I even made a reference to a model rocketeer using DCC.
I am somewhat confused here. Are you saying that with DC common rail wiring you cannot have 2 engines in adjacent blocks running in different directions unless you gap both rails? If that is what you are saying then you are mistaken. I have been using common rail for over 15 years on my layouts. You have to remember one thing; positive to negative only causes a short if the circuit is complete. Batteries do not short out when + to – occurs because the other side of the circuit is connected to a load, not each other. This is how every thing from a flashlight to an EV / Hybrid battery pack is wired. It’s called a series circuit.
On the subject of interrupting both sides of the circuit, it’s really is a waste of time. Home and Automotive wiring does not break both sides of the circuits. Neither should you. The more circuits
Thanks for being professional to Jeff. I was being a meanie. Sleeping on the in-laws sofa has made me unhappy.
Ha, he, ha, ha, [alien]ha, ha…[alien][swg][(-D][:-^]
The major limitation to double gaps and dpdt switches to select cabs is that you’re limited to 2 cabs. I run 2 mainline cabs, 1 hostler cab and a depot switcher cab on my (common rail) RR in my psgr depot and in normal operation I commonly am cutting power off of one end of a track while the depot switcher is tying onto the opposite end, an inbound train is arriving on another track and a departing train is starting to pull on a third track. No smoke, no sparks!
Another factor to consider is that common rail uses slightly more than half of the amount of wire that double gapped systems use. If you’re operating medium is a 4X8 this isn’t all that important but if you’re talking abbout a large RR (I have almost 2000’ of track) and you think that’s not a factor you haven’t been pricing no.12 braided wire lately.
Hey, guys! When I’m not trying to figure out how to do the impossible with common rail wiring, I write science fiction. If anyone thinks rocket science is complex, try checking out subnuclear particle physics.
Reverse loops and wyes are special cases, no matter whether the operating system is DC or DCC. I will say that a single DPDT toggle switch is almost certainly less expensive than an electronic instantaneous DCC autoreverse circuit.
As for how many cabs (locomotive controllers) can be operated with common rail, my EOT module could, theoretically, have as many as six connected. As a practical matter, it would be all but impossible to operate more than three without tripping over each other - the module is only 16" by 96". (There are advantages to operating in HOj, one of them being that my freight cars are about as long as N scale 50 footers. My teakettle tank locos aren’t giants, either.)
Chuck.
Yeah but saying, “It’s not Psi / J science”, doesn’t have the same ring to it, nor mean anything to the general population (Assuming one buys into the quark model. Sorry my sub-atomic particle physics knowledge is 20 years old.).