There is one huge advantage relay devices like the AR1 and PM42 have over the others (besdes that the PM42 can report state to Loconet) - thsoe relays have effectively NO voltage drop. Even the best MOSFETS like used on the PSX4 and PSX-AR (assuming they DO use the best) do not have a zero resitence when ‘on’ and those cause a little voltage drop. If you build your own computers at all, you may have seen motherboards advertised as using “Low RDS MOSFETS” - This is the resistence, drain to source (don;t worry, you don;t have to undertsand all that) - basically, this is the resistence you will measure between the terminals that the power flows through. It’s never 0. It can;t be zero (unless someone invents the ideal semiconductor). Just like long runs of bus wire, or on a larger scale, the resistor in series with your LED headlighs, the more resistence, the larger the voltage drop (also proportional to current). Relays don’t have this problem.
As far as reversers (and frog power, for that matter), I will have PLENTY of “old fashioned” relays on my layout - to set frog polarity and also automatically flip reverse loops when the turnouts change position. Rather than wait for a short and then fix it, my plan is to avoid shorts altogether. Sure it’s a bit more complex than hooking up 1 wire from a Frog Juicer to the frog, but a short is a fault. The idea is to avoid faults.
I suspect that you are referring to reverse loops. But, at least some of us have one or more reverse loops on our layouts including the OP who has two reverse loops. I have 5 reversing sections on my layout. Nothing wrong with reverse loops, certainly not the equivalent of the plague.
As far as reversers like the AR1 and the PSX-AR are concerned, they don’t work on DC layouts anyhow, so they only matter to DCC users in the first place. The AR1 works just fine in the right environment, and Harold nicely solved his problem with a simple turn of the TTC adjustment screw. Once you start to add some solid state electronics like a PSX circuit breaker to your layout, however, only then does the AR1 show its age.
As far as powering the frog, you can get by quite nicely with an unpowered frog in most cases. I do. I have over 60 turnouts on my layout, and none of the frogs are powered. No problemo!
No, avoid auto-reversers. Since with DCC you can change the phase under the moving train at any time, you can use a relay to change it when you line the switch, BEFORE the train hits the gaps. This applies to any loop that is at least as long as the train that will be running over it - line switch, train enters, any time after the last car clears the switch but before the loco hits the switch, you line it the other way, and this also flips the loop track phase. No short ever occurs. Works for a wye as well. ANd yes, even a turntable - that fancy NYRS PTC III turntable controller has an option to drive a relay to reverse the bridge polarity when it turns more than 180 degrees. So you get instant flip instead of the dead zone of split rail, so sound doesn’t cut off, and there’s no short to be corrected by an autoreverser.
Yes, it’s slightly more complicated to set up (depending on things such as what sort of switch machines you use - the servo drivers I use already HAVE a connection to drive a relay, and there are others that even shut off frog power while the servo is moving and then applies correct polarity only after it reaches the end of throw, so you don’t have to worry about “DCC friendly”), but there is never any chance of hesitation and no issues with high inrush reset.
I think that zstripe was referring to reverse loops when he mentioned ‘avoiding them like the plague’, per an earlier post in which he remarked, “I have a large DC layout…but I avoid reversing sections like the plague. I just can’t see creating a short on purpose. I would rather redesign my track plan.”
You can use a DPDT relay (your choice of coil voltage) and cross wire like a reversing DPDT toggle switch!
I used a DPDT toggle sw for a few years on my current layout to control the polarity of my huge Reverse loop staging until I rebuilt the layout to use a differeny type of staging tracks.
I had the toggle sw at the end of the Reverse Loop and would have the Toggle handle set that it would point into the Loop or out of the Loop when flipped to show direction of the Train and thus track polarity!
Each time a train went into the Reverse Loop staging I would just flip the toggle to set the polarity for the next train coming out of the Reverse Loop Staging!
I could have easily replaced the Toggle Sw with a Relay and using a Caboose Ground Throw w/Electrical Contacts - to auto throw the Track Polarity.
One doesn’t have to have the ELECTRONIC Auto Throw Auto Reversers as good old Mechanical Relays lasted for years in the good old days!
I wondered if Randy was referring to a DPDT. I have used that approach in the past to manually switch my reversing section(s) before moving to an auto-reverser mechanism.
I appreciate your making that distinction between a manual DPDT toggle switch and an automated DPDT relay.
A couple of additional comments from the OP - First, I realized I needed another way to turn trains and the solution was a second reverse loop. I finished it up yesterday and it going to add so much to the ability to run trains and to keep my interest. In addition, it is going to finally allow me to create a little place called Elmer’s Crossing in memory of my dad.
Second comment is this - I remember, and not too fondly, the days of an Altas Controller that only worked when I was very profane, or of the days of block wiring when it seemed as if I was forever throwing toggle switches. if I read the posts correctly, maybe components like the Digitrax AR1 have been the next step in the evolution of reverse loop controls and the new all electronic components are the next generation.
For me, it was once again a matter of cost and then simply not having the knowledge to do it any other way. When someone starts talking about PSX’s and MOSFETS, my eyes just glaze over because I don’t have the understanding. As I said in an earlier post, I wish there was a print resource for guys like me who aren’t familiar with the intricacies of electronics - one that started with the basics and went from there. I have found places on the internet but even some of those assume too much.
For a revers loop, of course you need a DPDT relay. It gets wired just like a DPDT toggle, with the X wiring. The coil is triggered by switch machine contacts. The reason for a relay is that most switch machine contacts aren’t rated for the full load of a train. For a frog, it’s fine, there can not possibly be more than one loco or lighted car on a frog at any given time so there never can be that much current flowing through said contacts. For the entire power to a complete reversing section - there could be multiple unit locos plus lighted cars, easily exceeding the rating of the switch machine. Plus most have 2 sets of SPDT, or in other words, one DPDT, which means if you use all the contacts for the loop you have none left for signals or frog power.
As for the eyes glossing over, I did say youc ould ignore the terms and just go on with what I explained they mean. No model railroad book will explain any of this. Even basic electricty, model railroad boosk tell you how but do not explain theory. The palce to go would be to find a book on basic electricity. A PSX is just a name of a device, like the AR1 is the Digitrax device, the PSX is Tony’s product. A MOSFET - well, it will take a lot more tha a basic electricty course to understand what a MOSFET is and how it works. Suffice to say, they are commonly used as high current solid state switches. Which is what I thought I got across in my explanation. Unlike physical contacts, such as a relay or switch, a semiconductor device will have some measurable resistence between its electronic ‘contacts’ and resistence is what causes voltage drops. No need to dig further. To inderstand the DETAILS of how one works and what all the parameters are, would require a course in solid state electronics. There’s no ‘cheat sheet’. Explaining what MOSFET stands for - Metal Oxide Semiconductor Field Effect Transistor - I’m sure makes even LESS sense. Again, the ‘cheat sheet’ as best as can be is that it is a sw
Well then, I’m afraid that they have baffled you with BS, or at least with more information than you needed. The PSX or AR devices are what I would call black box items. That is, you only need to have a minimum of knowledge to get them to do what you want. In the most basic case there are two wires going in from your power bus, and two wires coming out to the loop. If you managed to get the rest of your layout wired for DCC, I think you will have no trouble figuring out how to make the connections. You don’t really need to know what happens inside the device.
There are no relays, contacts, or toggles to contend with. And if there is really some small power loss associated with the device, I don’t think you will notice.
On a DCC layout with a reversing section (loop), a short occurs but an auto-reverser like an AR1 or a PSX-AR reacts quickly to reverse the polarity and end the short before any harm is done.
It happens so quickly that the momentary short isn’t even noticeable.
What’s wrong with that?
What’s with the obsession to prevent a short from occurring in the first place?
Rememebr the DC days? There was never a short, you flipped the toggle BEFORE a short happened. Only more recently did anyone figure out that if you can build a circuit to ract fast enough, you can wait for the short and then fix it. It conflicts with my engineering background that says a short is a fault. Every time.
Plus, I control my reverse loop with a $3 relay and I don’t need a $14.95 AR1 or even more expensive PSX-AR. I’m also cheap. I haven’t checked for mass quantities from eBay seller in China like for other electronic components, but I suspect I can probably get relays with sufficient current capacity for even less than that.
No doubt the ‘black box’ of an autoreverser is easier to understand, if treated as a black box, anyway. 4 wires to hook up, done. Relay needs the crossed wiring plus the 4 wires, plus connections to the coil via the switch machine contacts, and a power supply (no big deal since my layou will have an accessory power bus around it to tap off for lights, switch machines, UP5 panel power, etc.). Zero adjustments, and the train will always roll smoothly across the gaps, jut like moving from one piece of mainline track to another, no chance of even the slightest hesitation or stutter or break in sound.
From an engineering standpoint, the idea is to design a system so there are no faults.
Fault recovery is second level, a backup as it were, for a fault creeping in regardless of attempts to prevent them.
Not that it’s on the same scale, but, theoretically, if you short a wall outlet in your house, your house won;t burn down because there is a circuit breaker that trips and cuts off the power. It’s there in case soemthign you plug in shorts out. Ideally, you never want to have the short in the first place.
It does follow through with the rest of my layout building - the booster has a circuit breaker, and I do have downstream circuit breakers. But I srive to make my trackwork as buleltproof as possible, so nothing ever deraisl adn NEEDS that circuit breaker to act. SO far that’s worked out pretty well, when I can shove cars through the trackwork at warp speed and they all stay on the rails, I know it’s going to be pretty good for runnign at proper speed, and that’s proven out across the two layouts I’ve built since going DCC. I expect my next one to be no different, even though it is going to be by far the largest layout I’ve ever built, AND i will be using a track brand that I have personally never used before. But with slow, careful work and making sure all straights are straight and not all kinked, and all curves flow smoothly with easements, and the roadbed nice and even withou humps to put vertical kinks in the track, and grade transitions made very gently and smoothly, I expect nothing less than the same high reliability I’ve gotten from my previous layouts.
I guess I am just picky. I’m not very good at scenery, but dang it, my track and electrical work is as bulletproof as I can make it. There may be no pretty scenes for the trains to run through, but run they do. With my usual slow rate of construction, I may dabble in some of my own control circuits for this stuff, but it’s hard to justify other than for satisfying a cur
With the use of DCC I would think that using automatic reversers like the AR1 or PSX-AR would be the only way to go. using a DPDT reverses the polarity on the main line while the AR units reverse just the reversing section.