Reverse Loop Module

[Flinny]

Hi,

    I can see that this subject has been touched on before but I am new to dcc and can not get mine to work without cutting out. The train passes over the first set of isolating connectors but stops at the second giving an overload on the controller which can be immediately reset.

This happens both clockwise and anti clockwise.

I have tried many combinations of wiring and even bought another RLM.

Does the point need to have spring the clips fitted?

Please help or I will have to take up bowling

[Chrissaf]

How long is your protected track section?

How long is your longest train?

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The train (loco including all attached rolling stock with metal wheels) must be allowed to fully enter the protected track section to clear the first set of isolating connectors BEFORE it tries to traverse the exit isolating connectors. Your issue description fits in with the RLM protected section being too short.

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If the protected track is LONGER than your trains, then you will need to post some drawings showing your layout design (so that a more effective evaluation of your issue can be assessed) that includes:

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where the Insulating Rail Joiners are located?

where the RLM connections are made?

where the main DCC power connection is made?

where is the point you have mentioned relative to the RLM protected section?

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Note: To post images, use the Black & White hill & moon icon between the tree and the smiley icons in the reply text tool box. Images will be held back for Admin approval during normal UK office weekday hours and won't appear straight away.

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EDIT: Please also answer these additional questions:

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Is the RLM the Hornby R8238, if not what brand & model is it?

If it is the R8238, what switch position are you using 'Select or Elite'?

What power supply current rating does your layout use, the 1 Amp or 4 Amp supply?

 

 

[Flinny]

/media/tinymce_upload/b116a500c3942cb1bb18c61453f4951c.jpg

[Chrissaf]

Thank you for the drawing I requested.

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At first glance, I can't see anything obvious that would cause your issue. The length of the reverse loop section doesn't look to be the issue.

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The only thing not on the drawing that just needs to be confirmed and that is, what side of the R8238 connects to the main track section. With the 'Select / Elite' selection switch positioned at the bottom of the R8238, the left hand terminals on the R8238 should go to the main track section and the R8238 terminals on the right hand side should go to the protected loop.

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Do you get the same short circuit issue arising if you hand push a wagon (with metal wheels) over the Insulated Rail Joiner transitions?

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If you do, then there is something possibly wrong with the way you have the RLM and track wired or configured (however see note further below). If you don't get a short, then that would indicate something is wrong with the loco and/or its decoder.

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Just checking, but I take it the loco DOES have a DCC decoder fitted?

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In answer to your other previous question. Now that I can see you layout schematic, the point should have the R8232 point clips fitted.

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Note: If the R8238 and track are all wired and configured correctly and there is no fault with the loco and/or decoder, then the 'short' you are seeing is probably because the R8238 is failing to switch at the correct trigger current, and the Select is responding faster to the short circuit condition before the R8238 has switched. The 'Select / Elite' switch position on the R8238 defines the trigger current that is required to cause the R8238 to switch. The 'Select' position is a trigger current of about 0.8 Amps and the 'Elite' position is about 3 Amps. There have been a few comments on the forum in the past that the R8238 exhibits unreliable switching when using the Hornby 1 Amp power supply. Others have fixed the issue by upgrading their power supply to the Hornby 4 Amp power supply (P9300) which is the official Hornby upgrade power supply for the Select controller. But that is a drastic step to take without doing further tests to prove the power supply as the cause of this issue.

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Since this is your second R8238 unit, then that would seem to infer that the R8238 is not directly at fault, it may be that the 1 Amp power supply is invoking its short circuit protection at too low a current. i.e less than the 0.8 Amp trigger current of the R8238. Thus the power is being shut down before the R8238 can react. This is just a plausible theory that tries to fit in with your observations.

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One final consideration.

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How are you creating the Isolation gaps in the rails. BOTH rails need to have isolation gaps, not just one rail.

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Hornby produce two Isolation track products, the R616 which only gaps ONE rail and the R618 which gaps BOTH rails. See images below. The usually adopted option to create the isolation gaps is to use Hornby R920 Insulated Rail Joiners.

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The R616 was originally produced by Hornby for use with DC Analogue layouts to provide manually switched isolation and isn't suitable for use with a R8238 RLM.

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/media/tinymce_upload/11fbb5913acd3cada32d3a1d56fbfb03.jpg

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The R618 (below) is the double gap version of the R616 above and IS suitable for use with a R8238 RLM.

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/media/tinymce_upload/218d9a6a35b9b1b0d31de4f25386356e.jpg

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For a RLM to work correctly, the protected track section MUST be TOTALLY isolated from the rest of the layout. That means a total of FOUR rail gaps are required (two each end of the protected section).

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You have used up your initial 2 posts in 24 hours (introduced to combat auto-bot spammers). You will be able to post again tomorrow, with the limit being lifted shortly afterwards.

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Just for information. I would advise you not to use the White Arrow in Blue Box button to make a reply. Firstly this is not a 'Reply to this post' button. Secondly, because of my posted images any reply you make using the blue button will be held back for Admin approval. It is much better to ignore the blue button and just write any reply you want to make in the reply text box at the very bottom of the page.

 

[Rog RJ]

How close to the points are the IRJs?  Is the loco clearing the point before it begins to enter the RLM section and vice versa.

[Fishmanoz]

A question and a comment.  Rog, why does the point position matter?  It’s all the same phase/polarity so I would have thought being on the point and the isolated section entry at the same time wouldn’t be a problem. 

 

And the comment is the length of the isolated section - the possible problem with such a length is that you have the potential in operation for a train to be entering/leaving the section at the same time as another train is entering/leaving.  This would cause the RLM to go berserk trying to reverse the phase in two directions at the same time so is a no-no.  Much better to shorten the section to minimize the chance of this, as long as you leave it longer than the longest train.

[Rog RJ]

A question and a comment.  Rog, why does the point position matter?  It’s all the same phase/polarity so I would have thought being on the point and the isolated section entry at the same time wouldn’t be a problem. 

 

Just wondering if there could be some sort of fault with the point causing an interaction.  When I'm fault finding I like to eliminate as many possibilities as I can.

[Flinny]

Hi,

Two of my trains are from a DCC set and the other one I have fitted a decoder to and all run fine. I originally used isolating fishplates and now it is a R618 double isolating track and insulating fishplates at the other end of loop. The connections to the RLM are correct.

I am thinking that maybe I need a 4amp supply

[Chrissaf]

Given all the questions and answers given to date, that would be my conclusion too.

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Just to note, there are users on here using the Hornby 1 Amp supply with the R8238 without any apparent issue, but that does not account for a rogue 1 Amp supply being out of its design specification with regard to protection current trigger levels.

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If you do get the 4 Amp supply and that proves to resolve your issue, please do come back and update this thread with that info as it helps others in the future with similar issues.

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Just from a RLM design point of view. I don't have an issue with the protected section in your design being 22ft long. In fact, having the track isolation gaps fairly close to the point in your loop is beneficial as the point can only be in one switched route at a time. This effectively eliminates the chance of having a train entering and leaving the protected section at the same instant in time. Because to do so, both trains would have to be traversing the point simultaneously, which is a physical impossibility.

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PS - if you do get the 4 Amp supply, I would still use the R8238 with the switch in the Select (low current) position. This will make sure that the R8238 is more sensitive to short circuits than the power supply system.

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Just as an aside, I would just like to thank you for the detail that you have given in answering the questions as asked...ALL the questions. So many times we ask clarification questions and the poster fails to answer less than half of them. The questions are invariably asked for a reason, they help us to help the poster. We are then left to second guess and make assumptions about what the poster is experiencing and why. Crucial clues are then missed.

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Although that said, you didn't answer my question about the hand pushed wagon with metal wheels. But not to worry....

[Flinny]

As my set is in the attic and it is a hot day I did not venture up with a truck but when it is cooler I will

[Flinny]

I have tried a truck with metal wheels and the RLM performs correctly

[Chrissaf]

The only difference between using the truck and the loco is that the truck isn't drawing any current of its own through the R8238 RLM.

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So as the truck bridges the rail gaps, the current rise through the the R8238 will be far more sudden (i.e.more detectable) because the current is going from zero to the maximum supported by the power supply.

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Whereas the loco (lets us assume is drawing about 300mA) is reducing the amount of surge current that the R8238 will see for the purpose of detecting the short, because the detection starting point is already nearly half the current output available from the 1 Amp supply.

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Only a theory, but It may be that the more extreme surge of current generated by the passive truck is allowing the R8238 to do its job more effectively and trigger before the Select power supply reacts to the short.

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Given every question, answer and diagnostic test documented so far, It is looking more in favour of the Select power supply being the source of the problem. I can't guarantee to you that replacing the 1 Amp supply with a 4 Amp one will cure your issue, but the evidence so far does seem to point to that as being the only logical conclusion.

[96RAF]

My take on the matter...

Look at the ‘mechanics’ of the overload protection between the power supply units and you can see why the sensitivity switch is provided on the RLM.

 

The 1-amp supply protects against shorts by dropping its output voltage until the attached control unit drops out (in the design case this is the Select or eLink controller showing an error and cutting track power) hence the characteristics of the short will change with this voltage drop and in our reverse loop scenario the RLM will have to react to this falling flow of voltage and current, hence the switch is set to allow the RLM to react before the voltage and current start to drop so far as to cut track power via the controller.

 

In the case of the 4-amp supply overload protection is provided by the attached unit (design case Select or Elite or eLink) tripping out track power and flagging an error, so in our case the RLM does not have to be so quite so quick off the mark in its reaction as the characteristics of the ‘short’ are more stable.

 

Given the RLM polarity reversal is by way of mechanical relays within the unit it works better with a 4-amp supply and the less sensitive Elite setting. A pirely solid state device would probably auto-select if indeed detection sensitivity was an issue.

 

Rob

[Flinny]

I thought I had already sent this message but it does not seem to br there. Anyway a 4amp transformer has fixed the problem so thanks for everybody's help

[RDS]

Glad you sorted it out and thanks for letting us know.

I guess that the upgrade to a 4A supply could be the immediate answer for this problem in future.