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At the request of dropkicker, new to both Large Scale and this forum who runs on-board battery power, I've developed a universal block detection system that will work with any system (ac or dc, track power, dcc, on-board battery, live steam, etc.), and with any engine or railcar with metal wheels.  I put this in the Public Forum because it is universal and not specific to any one type of power.

The system is extremely simple and can be contructed for well under $5 per block with the most expensive part being the insulated rail joiners. The system uses cheap and simple, four (or more) pole double throw (4pdt) relays that can be of any value so long as you match them to a power source. The power source can be a simple wall wart. The system is based on my prior development of the Tortise Bump Accident Sentinal System (Bump A.S.S.), but is greatly simplified. The only parts necessary are the insulators, the relays, and their power source.

The detectors consist of short sections of rail sandwiched between track insulators (AristoCraft, LGB, Split Jaw, or what have you).  If you really want to do this on the cheap you could simply cut your existing track and install a small insulator on either side, so long as the center section of track is held in alignment. The rail is only long enough to fit in the gap between the two insulators pressed together, so any power loss to a wheel (for track power or DCC) is VERY short (less than half of a turn-out frog). This rail has a feed to a 4pdt relay that is matched in voltage to your power source. When any metal wheel crosses the gap, it sends a pulse to the relay.

It is important to note here that for those who don't run track power, it is not important to power up all of your track, so you don't need to worry about continuity.  You only need to apply power to the small piece of track in which the detector is located so that the engine/railcar wheel completes the circuit to pulse the relay. 

The relay "self latches." The relay will unlatch when the train crosses the next detector, regardless of which direction it is headed. Three of the relays' poles are involved in this operation. The fourth pole (or more) is/are available to operate anything your heart desires (e.g., lights, accessories, other relays, etc.).

This is the system is its simplest form. A switch can be added to the negative side to reset each or all the relays simultaneously is desired. It is expandable to as many blocks/relays as desired, so long as you follow the wiring scheme.

It is readily adaptable and detectors simply wired in parallel can be placed to either side, just inside of an electrical block so it can be activated as the train enters the block from either side. (However, if a train straddles detectors in two adjoining blocks, the relays will pulse. This can be overcome by leaving a big enough space between detectors to keep trains from stradling them, or changing the detectors to reed switches and equipping the engines with magnets.)

I buy 6 volt 4pdt relays surplus for $0.60/each in lots of 10 ($1/each in smaller quantities). This is the cheapest detection system you're likely to come across!  Additionally, these contacts will switch 5 amps and I use them to switch MU trains with no problems.


For another 50 cents, you can go 6 vac.


Need more poles?  You can get 6pdt for $1.50 at Brigar Electronics, but these operate at 20 volts (16 vdc would be fine though).

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