Reverse Loop Module on a Wye

[37lover]

I have a Wye junction on my layout and originally tried unsuccessfully to wire my own changeover. But I've now taken advantage of the e-hatton prices and bought a proper Hornby R8238. I have looked on the Brian Lambert site and have a question for the  experts.

With reference to BL's Wye layout the main track goes left to right, and the Wye is vertical upwards. The input to the RLM [the DCC Feed] is taken from the main track on the right hand side. Note 1 states: where Insulated frog points are used the two IRJ's shown in the straight through track at the bottom are not needed. I'm always confused by this I have standard Hornby points, I believe these are insulated - could someone please confirm?

That aside can someone explain why are the IRJ's needed if the points have live frogs? Because I assume the RLM flips the feed(s) to the Wye branch [the vertical track] so the main track will always have the same polarity.

[37lover]

I can answer one of my own questions; Hornby points are Insulated frog.

[Fishmanoz]

Without looking at BL's, if you have a reversing loop, then by definition the polarity (or more correctly, phase) at one end of it is reversed with respect to your main track causing a short.  To stop the short, you have to isolate a section of it longer than your longest train by putting IRJs on both rails at each end.  You now power this track section with the RLM and as soon as a train starts to cross the IRJs it measures to see if a high current short exists and swaps the polarity in the isolated section to eliminate it.  If the train was entering the isolated section, then when it leaves at the other end, the polarity will again be reversed and the RLM will swap it back.

[37lover]

Fishmanoz,

Thanks for replying. I know the principles of how the RLM works but I'm just interested in why the IRJ's are needed on the particular example of a Wye when using Live Frogs. You probably need to see the sketch on BL's site. I think it's down to me not understanding how a live frog point works.

[Fishmanoz]

Sorry 37l, yes it's due to the way you wire with IRJs as part of the frog switching on electrofrog points.  Go back to Brian's DCC1 section and look at his electrofrog wiring, where the IRJs must go and why (the whole frog area changes polarity when switched so must be isolated form the rest of the layout to avoid shorts), and you'll see they are needed as shown on the Wye diagram.

 

Does that help?

[37lover]

Fishmanoz,

Tried Brian's section but not clear enough for a simpleton like myself, eventually found a explanation of how a live frog point works on an old blog called railwaybobsmodulebuildingtips that I could understand. Too cold in my garage today so fitting the RLM will have to wait.

[Chrissaf]

37L,

Just in case there is still a small amount of residual confusion regarding DCC live frog switching and the need for IRJs for use with live frogs. This web page (about half way down) has a really good animated representation of a live frog that shows colour coordinated point changes when you click the toggle switch icon next to the images. The image further below that shows the same again but this time with external frog power switches included. Again click the toggle switch icon to trigger the animation display.

.

http://www.009.cd2.com/turnouts.htm

[Fishmanoz]

These moving representations are excelllent 37L, you can find a lot more than Chris has given you, but no need.  Once you have your head around the moving one, check out Bl again and you'll understand his too.

 

But the dead simple explantation of why they are necessary in the Wye with live frog is entirely due to live frog operation, nothing to do with the reversing loop as such.  If you are using all Hornby insulated frog points, you don't even have to put the IRJs there, or give a passing thought to why if you'd prefer not to.

[37lover]

Fishmanoz & Chrissaf,

Yes,

I've looked at the animations, and read a bit more about live frog points, so I think I am now okay with how they operate. My layout uses only Hornby Insulated points so I'm okay to install the RLM without any track modifications.

 

There's no way I'm about to change my points to live frogs but if I was starting anew then I would probably use them.