Reverse loop

[JsionyRN]

Good afternoon and HELP!!!!!!!

I have a reverse loop on my layout and have a Digitrax AR 1 fitted. I have double gapped and insulated (with Hornby insulated fish Plates) either end of the reverse loop. The locos run perfectly well untill they hit the isulated rail on the one side where upon as soon as the locos wheels run onto the rail it causes a direct short. If I move the locos manual across that point the locos function normally. I have no other issues with the rest of the layout.

Any advice gratefully received jsionyRN

[Brew Man]

I have a Block Signalling Rev 1 unit controlling mine and it works flawlessly. It sounds like yours isn't switching phase (polarity) as the train runs from one side of the IRJs to the other

[JsionyRN]

WOW thank you for your very prompt reply I will look at your suggestion

Kind regards jsionyRN

[Chrissaf]

The Digitrax AR1 has an adjustable trigger current. Last time I checked this adjustment was from 0.25 to 8 Amps. I do not know what trigger current is set as the factory default, but if it is set higher than the current available on your track, then the AR1 will not switch when it detects a short circuit. Which is basically what your post is describing that you are observing.

You need to adjust the AR1 trigger current to be no more than 60% of the current rating of your DCC controller power supply. Personally, I can see no reason to set it higher than 2 amps. The lower the trigger current is, the more reliable the switching will become. But not so low that the surge of a loco current being drawn as it enters a protected section provides a false trigger. Which is why I recommend that 2 amps be set when using a Hornby 4 amp power supply. If you are using a Hornby 1 amp power supply, then you need to set the trigger current of the AR1 to about 500mA. If you are using the Hornby 1 amp power supply, then I highly recommend that you upgrade it to the Hornby 4 amp P9300 power supply when using a RLM.

All the above is discussed in my downloadable RLM tutorial located in the 'sticky post' at the top of the Hornby DCC forum section.

[JsionyRN]

Once again thank you for the reply

My controller is a gauge master advanced prodigy 2. How would I know that the adjustment you describe is at the required optimum setting

regards jsionyRN

[Chrissaf]

The Digitrax AR1 uses a relay to switch rail phase and the instructions state that it ideally needs to see the short appearing on both rails simultaneously for reliable operation. Thus your IRJs need to be fitted parallel to each other on the track and not off-set. The relay means that you should be able to hear when the AR1 detects a short circuit and switches.

Read your AR1 manual to determine how to adjust the trip current. I suggest that you turn the trip current down to a very low current setting. I would then expect that setting to be perhaps too sensitive and cause false triggers, perhaps of a type where it thinks there is a permanent short circuit whenever any of your locos are within the protected track section and only receiving power via the AR1. This might manifest itself as an audible relay chatter. Then slowly increment the AR1 trip current up until you get reliable operation. I am defining 'reliable operation' as being when all your locos traverse through the 'reverse loop' track section without stopping, whilst the AR1 operation remains stable and you cannot hear any continuous AR1 relay chatter.

A more detailed [variation of my guidance above] 'how to' provided by Digitrax can be read on this Digitrax webpage:

KB781: AR1 Auto-Reverser Trip Current Adjustment

According to the Prodigy Advanced 2 manual the controller power supply is rated at maximum 3.5 amps. I suggest you need to set the AR1 trigger current to about 1.5 amps for reliable operation.

[Chrissaf]

The full AR1 manual for anybody who is interested can be viewed here:

AR12up2.qxd - AR1.pdf

[Fishmanoz]

For anyone else looking to set up control of a reverse loop, we know that in general, RLMs using relays to switch the phase are less reliable than RLMs doing so electronically.