Page 81 of the February 2007 Classic Toy Trains has a great diagram & explanation to do exactly this.
Use the insulated section to trigger a ~12v DC SPDT relay through a bridge rectifier. Center post of the 153 to acc. power, ground to common(center) contact of relay, NO to one bulb/post, NC to other bulb/post on 153. Vary the length of the insulated section to get the effect you want.
Here's a link to a similar topic: http://www.trains.com/trccs/forums/998337/ShowPost.aspx
I just started installing relay/rectifier combos on my layout. To save money, I purchased my parts from Mouser ( www.mouser.com ):
893-833H1CS12VDC SPDT Relay, 10A, 12VDC ($1.00 each)
821-GBU404 Bridge rectifier, 4A, 400PIV (.72 each)
Although these parts are relatively inexpensive, they require soldering wires to them (or soldering the rectifier's DC terminals directly to the relay's coil terminals). I wouldn't use them if I didn't have previous experience with soldering.
Rob, you're right, the diagram in the Feb. issue is a good reference. I noted the diagram shows the 153 center terminal (neutral) and relay common terminal (hot), but I think your way would work, too. IIRC, switching the hot side is the conventional way to do it.
leica wrote: Leica wants to know if anyone knows how to wire the Lionel 153 Block Signal with red and green bulbs so it will switch from one color to the other and back using an isolated track as the switch on 027 layouts? The pressure sensitive 153 connector won't work with a track where ballast has been used because the 027 track won'f flex sufficiently to trigger the switch. I want to use the block signals on spur lines and different combinations of the 3 posts have been tried without success. Comments and assistance will be most appreciated. Thank you.
Leica, Welcome to the forum! Hopefully the info you'll find here is better than what I'm going to give you regarding the 153 signal and an isolated rail.
Your 153 will work with an insulated rail section , but it will require a relay (12VAC) in the circuit to make it work. These relays can be purchased from (in no particular order): Burns manufacturing (see ad in CTT), scotts odds and ends (also in CTT), and my personal favorite Fuctional Devices (These relays, #RIBU1C, are found in heating and air supply houses). I'm going to try to explain the circuit, and hopefully this diagram will help as well:
I apologize for the poor image, but it was spur of the moment. Basicly, the relay's coil will attach to the center rail (or its post on the transforme), and the insulated rail. To the 153 signal, two wires will come off the relay, one from the normally open contact and one from the normally closed. The final wire will come from the non insulated outer rail. Unfortunately, I don't have a 153 in front of me, so I don't know which of the three thumbscrews attaches to which wire.
Here's how to find that out: With no train on the rails, and the transformer powered up, (with the throttle turned up) take the lead from the noninsulated rail and attach it to one of the three screws. Take one of the two wires coming from the relay and attach it to another screw. One of the light bulbs should light up, green is the one we're wanting. If the red bulb lights up, move one of the wires hooked up to the unused thumbscrew. Once you have the green bulb lit with two wires attached to the 153, unplug the transformer, and hook up the third wire (the other wire from the relay) and remember which one this wire is. Plug the transformer back in. Nothing should happen, aside from the green light relighting. Place a car (not an engine yet!)on the insulated track section. The 153 should go from green to red. If it doesn't swap the two wires that were originally hooked up (as in leave the one that I suggested to remember which one it is). Clear as mud right?
Hopefully this helps,
Forgot abut this, click on the image to enlarge it; it's not a very good drawing to begin with, but on my monitor, I can make it out after I enlarge it.
There is a way to do it that is simpler than using a relay:
The signal has three terminals, one connected to the red lamp, one to the green, and a common connected to both red and green. Connect the common to the isolated control rail. Connect the green lamp to the other outside rails. Connect the red lamp to the power supply that you will be using, whether the center rail of the track or an accessory voltage. The accessory voltage may be AC or DC, whichever is more convenient, and does not need to be in phase with the track voltage if AC. It should be a suitable voltage for the signal and should share a return with the outside rails of the track.
Finally, connect another incandescent lamp or lamps, with the same voltage rating as the signal, in parallel with the red signal lamp, that is, between the signal power supply and the control rail. This lamp or these lamps should be selected to draw somewhat more current than the red signal lamp. You can hide them under the layout; or you can use the lights of some other lighted accessory. For example, you could have a 395 floodlight tower somewhere on the layout, perhaps far from the signal, that will light up when the signal switches to red.
It works this way: When the train is not present, the red and green signal lamps are in series and powered by the signal supply voltage source. However, the red does not light noticeably because the other lamps in parallel with it reduce its voltage to almost nothing. Most of the voltage goes to the green lamp, which lights brightly. When the train comes along, it shorts out the green lamp, which is connected between the control rail and the outside rail, and applies the full voltage to the red signal lamp as well as to the other lamps in parallel with it, lighting them brightly.
I've put some numbers to it. When you use a single extra lamp of the same kind as in the signal, the green lamp should be about 82 times brighter than the red lamp when the train is absent. It's actually a little worse, because the color of the red lamp's filament shifts toward the red when it is that dim; and a red filament is easier to see inside a red lamp. When you use two additional lamps of the same type, the green lamp is about 1087 times brighter, again not considering the effect of the filament color. That should be more than enough contrast between off and on.