Hornby R8238 DCC reverse loop control module

[stevieedge]

I would like to add sidings to my existing layout which for this purpose have shown as a single loop, i use railmaster and elink and would like to add sidings so as i can leave sidings and go round the loop in either direction generally  as shown below. can some body tell me the best way of doing this and i assume i would need something like the Hornby R8238 DCC reverse loop control module.

thanks/media/tinymce_upload/c3054fdc5e8c799653f0c8c08dda074d.jpg 

[Chrissaf]

Officially the R8238 by Hornby is obsolete, but stocks are still available on retailer shelves. Hattons are selling them at a knock down price of £12.

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Ignore the labelling on the switch. Use the 'Select' switch position if you are using the 1 amp Hornby power supply and the Elite position if you are using the 4 amp Hornby power supply.

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The triangle section of track is called a "WYE" and does indeed need a Reverse Loop Module on a DCC layout to prevent short circuits.

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Wire as per drawing below. This assumes that the sidings on the left ONLY connect to the main oval tracks via the 'WYE'. If there are any other routes back to the main layout (not shown on your drawing), these will need to be isolated via Insulated track Joiners too.

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[stevieedge]

Thats perfect and exactly what i needed to know

thanks

[stevieedge]

one more question the elink supplies the existing layout with multiple connections should i also supply the sidings from the elink but i assume with the connections reversed. ps the only route to the sidings is via the WYE

[Chrissaf]

should I also supply the sidings from the elink

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No.....you will defeat the function of the R8238 if you do. The whole point of the R8238 is that the R8238 RLM is used to MONITOR the power going into the RLM protected section and take appropriate electronic action if it detects a 'short circuit' condition. The output of the R8238 must be the ONLY power connection attached to the siding side of the layout.

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Therefore if you have implemented a DCC power BUS then that will need to be split into two. So that any BUS connections on the siding side of the layout are completely electrically separated and isolated and connect only via the R8238 RLM unit.

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[stevieedge]

ok understand now and thanks again 

[stevieedge]

Hi this is a simpliied version off my new layout could you please let me know where if what I have shown is ok and where I should put insulated joiners and R8238 connections. thanks ffor any help and advise

hi /media/tinymce_upload/eb17c79b2b2361723c7551a48311d224.jpg

[stevieedge]

hi  please could you let me know i the loop I have now designed is possible and where I should put insulated joiners and connections to a R8238. Thanks or any help and advice/media/tinymce_upload/ba7640762928ae5c5574ba4b8aad5bfb.jpg

[Chrissaf]

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[stevieedge]

good point will try to rearrange so as the loop ilonger

thanks or help

Steve

[stevieedge]

thankyou or your time and have now added a second revese loop so as can change direction both ways. can I use the same RLM or both loops, hopeully this will be my last question on this subject

 

Steve

[Chrissaf]

I need to see a sketch of your plan, before I can give an answer.

[stevieedge]

Below is sketch o layout advice would be most welcome/media/tinymce_upload/d0051399b87865c33f4297639889f2d7.jpg

[Chrissaf]

Personally, I would be more concerned about the gradients than the reverse loops. I assume that the tracks of the main loops have some on different levels.

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[stevieedge]

yes you assumed correctly and the gradients have worked out ine. I used a 90 degree crossing where I couldnt pass one track over the over. Just going to order the reverse loop module, could you confirm if I can get away with just using 1, although I will still order 2 at that price

[Chrissaf]

No, you will need two as shown.

[96RAF]

Best of luck with that box full of double scissors crossings. Slipping a decapod and a rake of 50 wagons through there could be fun.

We could do with a bit of software to analyse a layout for reverse loops same as Rocrail analyses for all possible A-B routes.

Rob

[stevieedge]

i am in process off adding current drop detectors to layout, not sure how to wire using the reverse loop as one of the blocks. Have tried to show below and have assumed that by passing the supply to the hornby RLM through the current drop feedback module this would detect a loco withing the revers loop block, would this work or is there another way

/media/tinymce_upload/7cc24b91e4620fe842e43b92462c5b3b.jpg

[Chrissaf]

No personal experience to draw upon, but the way you have drawn it, is probably the only way it has any chance of working. My main observation (from what I have previously read about current detection systems) is that they are very sensitive and can detect a few mere mA of current being drawn.

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Now take the R8238, it is an electronic device with electronic components such as resistors, capacitors, transistors and ICs. Therefore, the R8238 will be drawing a small amount of current all the time to power itself. This quiescent background current may be enough to make the current detector feedback module think that the R8238 protected block has a loco on it when there isn't.

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You will have to experiment with it and just see what happens. If your detection unit has adjustable current trigger settings, then I would advise setting the trigger current for the R8238 protected block at a higher current value.

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If you get it working, then please provide some feedback here for the benefit of others and also state what brand and model of block detection modules you are using. Since Hornby do not produce anything even slightly similar there is no problem you stating the module details.

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Note: The R8238 uses a relay for switching, therefore the relay coil will draw a reasonable amount of current when energised. Depending upon the state of the R8238 output i.e. either reversed or not reversed. Then unless it is a latching relay, the relay coil will potentially for periods of time be drawing current when no loco is on the protected section.

[stevieedge]

thanks for prompt reply, I will try but fear you may be right, will post results but have not as yet received the feedback modules

[Chrissaf]

After a bit of Googling. I found a solution, albeit an expensive one.

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The info I found concurs that the current drawn by the RLM itself can create a false occupancy trigger. The documented solution I found involves buying an additional 'current drop feedback Block Detector Unit' (BDU) dedicated purely for the R8238 protected section. Let's say for example that the BDU has four ports (as indicated on your drawing). Three of the ports are effectively abandoned and can't be used. The fourth port connects directly to the reverse loop. The BDU is then placed on the protected side of the R8238.

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The drawing below explains what I mean.

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Caveat: this solution was documented on the Internet using the Digitrax BDL168 current block detector. Your drawing shows the BDU (brand and model not known) sitting in only one leg of the DCC signal path. In theory this shouldn't make a difference as the DCC signal is bi-polar and has no polarity. It would be wise however to test the idea out using the parts you have already ordered before going to the expensive of buying more modules.

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Another reason for testing the idea first. Is not knowing how the BDU handles 'short circuit' spike currents that the R8238 needs to detect to perform its switching function. The BDU might have its own short circuit detection circuit that shuts down power to protect itself. If that happens faster than the R8238 can react, then the R8238 won't be able to see the short circuit. I would use the 'Select' switch position on the R8238 even if you have the 4 amp power supply on your Hornby controller (eLink), if only to make the R8238 more sensitive to short circuit detection.

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EDIT: Based upon your previous posts, I don't think this will be applicable to you. But for other readers. If the RLM protected section is a large one. Then it itself may have more than one 'Block' within it. If that is the case, then one or more of the three unused BDU outputs could be used for those. All that is required is that all the individual 'Blocks' that need detection reside WITHIN the R8238 protected track section when using that particular BDU.

[stevieedge]

just had a thought and would welcome your opinion.

If I cut the lenbht of track the reverse loop module is wired to (say a few inches) and have this adjacent to a turnout, could I not treat the rest of the loop as not being in the loop and have normal block detection./media/tinymce_upload/da831e4fa0c9ce4a2bb4984564e13e3b.jpg

[Chrissaf]

No you can't, because that would break the first rule of RL design. The protected reverse loop track section must be longer than your longest train (loco including attached rolling stock). If you have a protected reverse loop section that is only a few inches long, then the metal wheels of the train can easily create a situation where all three track sections are connected (electrically) together. The three track sections being the input main track, the reverse loop protected section and the output track section. This will defeat the function of the RLM. The input & output track sections will be at opposite DCC phase (polarity), thus the short circuit will be created that the RLM has absolutely no ability to control in a stable manner.

[stevieedge]

ok thanks

I thought it would have to be longer than loco but hadnt included carriages etc.

out of interest if all the carriages had plastic wheels would that have worked then

[Chrissaf]

Yes as long as the longest loco was shorter than the protected section, but fitting plastic wheels to all your non loco rolling stock would be a backwards step.

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There is a potential workaround and that is to extend the insulated gap at the ends of the protected section by physically cutting out a section of metal rail and filling the gap with some form of insulated filler to manufacture a very short piece of non conducting rail. The extended insulated gaps (four needed) needs to be just long enough such that the metal wheels of the rolling stock cannot bridge the metal rail ends. This in essence gives the same effect as having plastic wheels on the rolling stock. Make the extended insulated gap too long and you risk loco pick-up issues. There are no ready made products that you can buy for this, and would have to be custom made. This is covered in my Reverse Loop Tutorial guide I have written that I am awaiting forum Admin to publish on the forum.

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Below is a screen shot extract of the relevant document section from my forthcoming (hopefully) publication.

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Bear in mind that the concept of custom making a non conducting rail section is only a theory. How easy that would be to do in practice is unknown. The choice of insulating material needs to be carefully thought about. It needs to be non conductive, easy to work with and shape, strong enough that it doesn't break up over time and fall out and fixed in such a way as it doesn't just fall out of the gap from being hammered by wheels and vibration. My only suggestion would be to make them out of Plastruct material and glued to the top of the plastic sleeper sprue that gets revealed after cutting out the metal rail section. It would have to be a physically cut out section of metal rail within a length of track as trying to incorporate an extended insulated gap at a natural track join would IMO be too difficult to combine with an effective mechanical track join as well.

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We are only talking about an insulated gap of about 3 or 4mm. The small amount of insulating material needed has its own issues. Because the smaller the gap filler piece is, the more fragile & less robust it becomes, subject to what it is made of and method of fixing deployed.