Double latching relays for reversing loops

[Dani]

I was searching a cheap solution to control reversing loops, and finally I found it using double latching relays. Just for 4€ you can control reversing loops in DCC.

Latching relays are those that keep the position without power supply. You can change the position of the relay just sending a pulse. Double latching means that you can control the relay with two signals and you don't need to invert the polarity to change the position.

Many people will not find it useful unless you have Uhlenbrock modules or any kind of detection modules capable to send commands to the accessories modules. If your detection modules are not able to do it, the only possible solution with relays is to control the reversing loop with a PC software.

In my case, I did a detection section before entering the reversing loop and other at the end inside the loop. Each detection causes to activate an output connected to the relay and switches the polarity. That's something that you can configure in the Uhlenbrock detection modules through the Loconet.

If someone is interested, here you have all the information and specifications.



Cheers,

Dani.

[KenS]

This is a great idea. I think it's a lot better than waiting for a short to happen and then "fixing" it, which is the usual technique used by "reversing section" controls for DCC.  I'd still want a circuit breaker on the track just to turn things off if a mistake occurs (although you can probably count on the one in the command station for that, a local one that's only sensing draw from one train is preferable for maximum reliability of detection).  I don't have any reversing sections today, but I'm going to keep this idea in mind for future use.

One thing for anyone looking to do this to be aware of is that the V23079 is a family of devices that comes in both non-latching (monostable) and latching (bistable, available in both one and two coil models).  From the text I believe you're using a bistable two-coil version, although the picture on your website has the part number (V23079-A5001-A201) appears to be a monostable model (although the "A5" part isn't listed it's the "001" after it that shows type and coil voltage). 

It also comes in a variety of coil voltages, and this has to be matched to the control voltage you're using.  The 5V model shown is probably going to work with a lot of logic, but if the "pulse" is at track voltage you'd need to use a 12V model (which would be safe over the full range of track voltages allowed by DCC, but wouldn't work with a 5V pulse). And the picture on the original site you link to appears to be using 12V as the coil voltage from the diagram there.  Depending on the manufacturer, a 5V coil might work at 12V, but Axiom rates theirs to a maximum of 10.9V. More is likely to shorten the lifespan of the relay, or just burn it out.

BTW, the relay should work fine in any scale.  The data sheet says it's good to handle voltages of hundreds of volts on the switched contacts, far more than even G scale track would use.

[stevenh]

This is a great idea as long as your detection can handle trains with the ends powered, or motor cars half-way through the consist.
It means that you instantly have to ensure your detection points are all relative to your longest train... If the end car just includes accessories and not motors then you'd be fine... but I'd love to see an XPY/IC powered trailer car start pulling in the wrong direction... Of course, this is with DC.

I haven't actually seen latching relays before... had heard of them, but didn't realise how they actually functioned. Thanks for this article!

[The_Ghan]

The latching relay is also an excellent tool for turning sections of track on and off.  For example: sidings, spurs, ladders, etc.  This is something you might want to do if you've fitted in-car lighting to your EMUs and want to be able to turn the lighting off when an EMU is in a siding.  It can work out a lot cheaper than installing function decoders to all of your rolling stock, depending on the ratio of sidings to EMU cars.

Cheers

The_Ghan