Help please - wiring a loop


T

TheZeke

New Member
I'm trying to figure out how to wire this loop. I have used the internal SPDT switches built into the Tortoise switch motor to handle the polarity of the dead-end that goes up to the right but I cannot, for the life of me, figure out how to power the frog properly depending on which direction the turnout is switched. [edit: I've used one SPDT on each tortoise to power the frogs on all other turnouts but there's only two SPDT switches on a tortoise so I can't reverse the polarity for the loop *and* power the frog on this particular one.]

Illustration:
Loop.jpg


Currently this is a DC layout. I've labeled the polarity for discussion on the image above. The most northerly rail is + in this case. The continuous interior bend eventually goes over the red rails and then eventually comes back around and is connected to the red rails. Effectively it is a basic figure 8 shape but bent into an L. There is a turnout that is out of frame to the left that brings locos in off the main line into the blue area.

As I said I already have the polarity of the blue track to the right of the blue turnout reversing depending on the direction of the turnout (when it's thrown the polarity changes properly to match the connecting rails).

The frog however does not match and I cannot connect the frog to both of course since that'd be a short. I tried connecting two diodes up how I thought they should work but that did not work. It shorted. Maybe I am misunderstanding what diodes do or maybe I overheated them while desoldering them to get them off something else and one or both of them are damaged. I don't have anymore though to play with right now.

In the schematic below the blue turnout is switched to go straight through (not thrown). The north spur rail polarity is the same as the north rail on the main line.
North-is-North.png


In the schematic below the opposite is true. The turnout is thrown (RH) up to the most northerly turnout onto the main line. The north spur rail polarity is the opposite of the north mainline rail.
North-Bus-goes-South.png


This all works fine, as I said. But the big question... How do I power the frog on this bottom blue turnout?

When the turnout is thrown the frog should be powered from the north bus. Can I accomplish this with some creative use of diodes? or something?

Thanks for reading!
 
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I've read your description a few times now, but I do not understand to which turnout the tortoise that is controlling the reversing section is attached. Is that the last one in the yellow that connects the blue and red? Why does the yellow section end there instead of going all the way down to the turnout in the blue at the bottom right? Or is it that blue colored turnout that has the reverser associated with it such that it reverses the power under it?

If it is just a mater of needing another set of SPDT contacts how about hooking up a relay to trip. simultaneously with the tortoise contacts.
 
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Hi Iron Horseman,

Thanks for reading my issue. The turnout I'm having issues with is the very bottom most turnout in blue that connects the spur that goes up to a dead-end on the right. The blue section has two turnouts, its the one near the middle of the photo. The one on the left is fine.

I hadn't considered relays though - that's an excellent idea. I wonder if I could use a solid state solution instead though like a couple of transistors or even an IC with transistors built in. Wish I had a proper breadboard to test stuff like that on. Maybe I'll just find some relays though like you suggested.

Thanks!
 
Why do you need to power the frogs? You running locos with only 1 wheel set to pick up power? Its hard to say without seeing the entire track, but if you have a polarity missmatch, then you need a autoreverser. Im pretty sure changing the polarity of the frog will not help. One thing i had to learn by myself(the hard way) when i was building my layout. (allso dcc) If you are using power routing turnouts, shinahara in my case, then you can have shorts by feeding power from the divergent section of track. I had a three way switch within one of my reverse loops that kept giving my shorts.
 
If I understand the situation correctly, then you do not need to switch the frog. The frog has to match the inside rail of whichever leg to which the turnout is set. You have both legs of the turnout powered, but of opposite polarity, correct? That would mean that the inside rail of the two legs should match, so the frog just needs to be common with them and does not need to be switched.
 
It would be far easier for us to analyze your problem if we could see a smaller-sized diagram that includes all of the layout. We don't really need to see both rails, just so we can determine where the reversing loop actually occurs. Generally, reversing loops require two double-pole, double-throw (DPDT) toggle (or slide) switches, one being the reversing switch for the entire layout (usually on your controller), and the other dedicated to a portion of the reversing loop. Such a reversing switch has to be wired in a certain way, which I can't show by illustration but will try to explain:

a b c
: : : The dc leads from the power pack can be connected to either a and d or b & e
d e f or c & f. For example, if you connect the power input to a & d, then the output to the track should be connected to b & e. Then you need jumper wires connected from a to f and from d to c. Throwing the toggle from one side to the other will reverse the output polarity to the track. This could be done using a properly wired relay, but it would have to be a latching relay (one that stays to one side or the other without the coils being constantly powered). Depending on the relay, the powering current may have to be MOMENTARY, so you might need a momentary pushbutton to keep from burning out the coils. The Atlas Snap Relays could be used for this purpose, but, as I said, since it is a twin-coil setup, like the Atlas Switch Machines without the throwbar, the coils must only be energized momentarily.

If you can show a diagram of the entire layout, or at least the part that separates from the main, we can probably tell you where to gap the tracks and where to feed wires.
 
I ended up going with a relay as someone suggested (thank you). The local radio shack (in Canada they are called The Source now because of some trademark dispute) but they only had an automotive relay but that's fine.

I had to isolate the frog here because the south rail and north rail coming into the frog are the opposite polarity. That's kinda the hole crux of the issue and why I'm changing the polarity of the frog. The relay is hooked in paralel to the tortoise motor terminals. When I change the polarity on the tortoise the relay either closes one way or clicks over and closes the other way (SPDT, frog is on the center contact, + or - on the other two contacts). This powers the frog nicely. I could have used the switches internal to the tortoise if I didn't need to also power the track with a switching polarity depending on the turnout being thrown or not. There's a click sound when I switch the switch but it's masked by the tortoise motor sound anyway so it matters not.

Anyway, it all worked out this way when I got some cleaner power. The half rectified 18VAC --> 12VDC I was using was too dirty for the relay and made it literally buzzzzz. It already made the tortoise hum quietly so once I got a symetric +12VDC and -12VDC bus from two power adapters (found some 12VDC regulated 500mA ones at the same store) it was golden. Works nicely and everything is quiet again. I'll be putting some LED signals near on the turnouts (maybe scratch built tiny things on poles if I can) when I get the rest of my SPDT switches (they are on order from led-switch.com) and then I'll finish my control board next.

:-D

Thanks for the power ideas and the relay ideas.
 
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