Approach-lit signals

Classic Toy Trains Forum
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I have several times described a way of operating a signal, like a 153, from a control rail (a piece of insulated outside rail), most recently just last month. (http://cs.trains.com/trccs/forums/thread/1756742.aspx) I just got an idea for a way to make this into an approach-lit signal. An approach-lit signal is one that is arranged to shut off when there is no train nor engineer nearby to see it. The prototype railroads do this to reduce the drain on the batteries that they use to power the signals.

I will call the terminal of the signal that connects to both lamps C, the terminal that connects to the green lamp G, and the one for the red lamp R. Make two control rails, one a yard or two long ahead of the signal and the other for a yard or two after the signal. Connect R to your accessory voltage, or to the center rail if you prefer. Connect G to the control rail ahead of the signal. Connect C to the control rail after the signal. Connect an extra lamp between C and R. This lamp should be one that draws about twice the current of the lamps used in the signal. For a 153 (made after 1949), the signal lamps are number 53 and the number 57 is suitable for the extra lamp. You could also simply use two number 53 lamps in parallel instead of a single 57.

When the train is absent, the signal will be dark. As the train approaches, the green light comes on. As the locomotive passes the signal, the green lamp goes off and the red comes on. When the caboose has gotten far past the signal, the signal goes dark again.

Now for a further enhancement: You can do a similar trick with two signals, facing in both directions, so that the signals work the same way whether the train is coming or going. There are two things that h

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Sounds like a neat project. I’m going to have to draw it up for myself to see if I understand it though.

Thanks for sharing this,

J White

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I hope you can give it a try. If anything needs clarification, just post. I’ll be interested to hear how it works for you.

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Thanks, Bob. I was just thinking of trying to hook mine up to operate that way.

wyomingscout

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I later occurred to me that the DC supply needed for the bi-directional version could be just a 1N4001 in series with an output of a KW, VW, or ZW turned all the way up, or a V or Z set to about 20 volts. That would give half-wave DC, with an RMS voltage of about 14 volts, which would be just right for the signal. That way, you wouldn’t have to isolate the signal transformer; you could use an accessory voltage from a transformer that you might already have running trains or other accessories.

If you make more than one set of bi-directional signals, it would be good to reverse all three diodes in half of the sets, to balance the DC current drawn from the transformer.