How to make a simple block for two trains on one track

just happened to stumble on this article while looking for wiring diagrams last night.

http://www.thortrains.net/manual9.htm

I think this page describes what you're talking about.

Cheers,

USNRol

USNRol - Thanks, thats sort of what im looking for. However, I want to avoid using 153C contactors. I have a few of these and don't like adjusting them. Also, some train cars are lighter than others so a 153C contactor wont be very reliable. Is there a relay at radio shack that does the same thing a 153C contactor does? What are the specs of this relay I saw a bunch at radio shack but didnt know which one simulates a 153C contactor. Anybody know? While at radio shack I didnt understand pole and throw.

The "pole"-"throw" terminology really comes from switches.  Imagine a knife switch.  The knife is pivoted on the base and can be thrown to either direction to connect with one or the other of the other terminals on the switch.  That is a single-pole-double-throw switch.  Leave out one of those outer two terminals and you have a single-pole-single-throw switch.  Take any single-pole switch and connect it mechanically to another similar switch, so that one handle operates both, and you have a double-pole-whatever switch.

The proper terminology for a relay is different; but the switch terminology is better known and can do the job if the contact arrangement is not very complicated.

To duplicate a 153C, you need single-pole-double-throw contacts.  It wouldn't hurt of course to get double-pole-double-throw and not use one half.

The relay coil should be coordinated with the power supply you have.  If you have 24 volts AC, use a 24-volt AC relay.  If you have 12-volts DC, use a coil specified for that.  (24-volts AC is used in HVAC controls.  You can get transformers and cheap relays from an HVAC distributor.)

Connect one side of your power supply, whatever it is, to the outside rails.  Isolate one outside rail to create a control rail in the region where you want the relay to operate.  For block signals, I guess that would be the entire block.  Connect the relay coil between the isolated rail and the other side of the power supply (the side not connected to the outside rails).  If you are using AC, you will be advised by everybody and his brother to "phase" your transformer.  You don't have to.

Just the way lionelsoni says. Also TM Books new DVD building a layout explains it to. CTT I think had a article over a year ago about doing blocks with just insulated tracks but the trains need to be very close in speed to operate with out running into each other. Another thing I would suggest is to use a trasformer with enough wattage to run two trains. I've got a 1033 pretty warm running two trains on the same track.

To simulate a 153C contactor, you would use a Single Pole Double Throw (SPDT) relay operated by a 12VAC coil and with a contact amp rating higher than the highest anticipated amperage through the track.  RadioShack doesn't offer a standard relay like this.  Other suppliers do, but 12VAC relays tend to be expensive.

The alternative is to get a 12VDC relay and use a rectifier at the coil to change the transformer AC to DC.

Here's an example of a relay: http://www.radioshack.com/product/index.jsp?productId=2062482&cp=&origkw=275-248&kw=275-248&parentPage=search

The rectifier should be rated to handle the current load of the relay coil (usually a lot less than 1 Amp) and have a PIV (Peak Inverse Voltage) rating of at least 50.  Here's an example of a rectifier: http://www.radioshack.com/product/index.jsp?productId=2062582&cp

The "+" and "-" terminals of the rectifier are connected to the relay coil terminals.  The "~" terminals are connected to the transformer 12V (fixed) terminal and to the insulated outside track rail.

A SPDT relay would have 5 terminals.  Two terminals would be for the coil.  The remaining three terminals often are labeled "C" (Common), "NC" (Normally Closed), and "NO" (Normally Open").  On a 153C contactor, terminal 3 is "C", terminal 1 is "NC", and terminal 2 is "NO".  The weight of a train activates the contactor, just as a coil activates a relay.  You can use the information already provided for the 153C contactor to use the relay as a substitute.

The shortest block needs to be longer than the longest train.  The number of blocks would be at least one more than the number of trains. 

As you can see, wiring for automatic blocks is anything but simple!

You do not need to use an AC relay.  Nor, if you use DC relays, do you necessary have to put a rectifier on each one.  You can either use a suitable DC supply separate from your transformer or create your own DC supply from an isolated train transformer and a single bridge rectifier.  What is not practical is to create a DC supply of any great size from an accessory output of the same transformer that is running the trains, since the resulting supply will not have a return in common with the track transformer.

I think that the blocks do not necessarily have to be shorter than the trains.  If the relay is simply unpowering or reducing the voltage in the block that the train has come from (in a safe way), the only problem with a short block is that lighted cars at the end of the train (like a caboose) will go dark.