Help wiring Lionel Mainline Dwarf Signal

[lmsjim]

I am trying to figure out a way to connect my Lionel Mainline Dwarf signals so they will work with insulated/isolated track. I am using FasTrack but I don't that really enters into it. I have successfully got my block and semaphores to work but the dwarf has four wires instead of 3. The best I have been able to come up with is have the signal green when the siding is not occupied and switch to red when a train enters. The problem is I cannot figure out a way to get the green to turn off when this happens.

Any help would be appreciated.

Thanks
Jim

[Roger Bielen]

Jim - if they are anything like the MTH dwarfs I have to indicat throw of switches a relay may be necessary. Try going to the Lionel web site (www.lionel.com) and see if they have anything.

[lmsjim]

Hi Roger,
I should have pointed out that it was already determined by me and Lionel that you cannot use these signals with the new FasTrack switches. So I cannot tie them to the throw of the switch. That was my first option. Also I am not interest in timer delays or SPDT toggle switches even though the toggle may end up being my only option.

Thanks for your thoughts
Jim

[lionelsoni]

Wire the two lamps in series. Connect the red end of the series string to the supply, whether the track center rail or a separate accessory voltage. Connect the green end of the series string to ground, that is, the non-isolated outside rail. Connect the midpoint of the series string to the isolated outside rail. Get an additional lamp and wire it across the red lamp. Hide it somewhere where it can't be seen or cover it with shrink tubing. This extra lamp should be suitable for the voltage you are using and preferably draw rather more current than the signal lamps. If necessary, add multiple smaller lamps in parallel until the red signal stays off when the track is unoccupied.

The way this works is that, when the track is unoccupied, current flows through both lamps; but the extra lamp shunts most of the current around the red one, turning it off and presenting a low resistance to the green lamp, which lights brightly. When the track is occupied, the train shorts out the green lamp, turning it off and presenting the full voltage to the red lamp, which lights regardless of being shunted by the extra lamp.

You could use a resistor in place of the extra lamp, but it doesn't work nearly as well. The lamp's resistance drops substantially with reduced voltage, making it a much more effective shunt. A resistor low enough in resistance to keep the red lamp dimmed out will draw much more current when the red lamp is lit, because its resistance does not increase with voltage.

[lmsjim]

Bob,
You are a genius!! It worked. I admit I had my doubts but I did exactly what you said. I did use a 24 volt bulb I got from Radio Shack and mounted it under the table so you cannot even see it.

I am in your debt. By the way I am a long time graduate of UT back in 1967.

Thanks again
Jim

[lionelsoni]

You're welcome! Thanks for letting me know it worked for you.

I got my MSEE at UT in 1967.

[lmsjim]

mine was in Geology. I guess we are both dating ourselves.

Jim

[Anonymous]

Just started to get back into three rail stuff after being into ho gauge for the last 40 yrs. What's the difference between isolating the the third rail or one of the outside rails when you are building a siding or spur or a dead end. felix

[lionelsoni]

You would isolate the center rail in order to be able to switch off the power to the spur. You would isolate one of the outside rails to operate a signal or accessory, as Jim is doing. The isolated outside rail acts as an electrical switch, open when there is no train on it, closed (connected to the other outside rail) when a train is there. The ability to do this is one of the principal advantages of 3-rail track and a feature shared with prototype railroads. Two-rail modelers can't do it because they are using both of their rails for power, something that prototype railroads never do, as far as I know.

Of course, you very well might isolate both the center rail and an outside rail on the same piece of track, for the two different purposes.