LGB Reverse loop kit

Airbuspilot

Airbuspilot

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There are 4 reverse loops on the G scale DCC layout I am working on, three setup by someone who is no longer around and one by myself. The three existing loops have a sensor track around 20 cm long, I have rewired all of them as the cables were looking sad. The fourth loop came from a new box where I discovered (for the first time) sensor track of about 3 cm and used this in the last loop.

I have been told the longer sensor track is required as some longer locos with two bogies have problems when they cross over. In reality I have found different problems between each of the three existing sensors, small locos work well on some and stop on others while the long locos stop on some sensors and in one case shorts the sensor. So far it seems the LGB track length of 3 cm works but this is on a fairly steep gradient which some locos are having a problem climbing, I don't have reliable information to warrant my picking up and modifying the track on the other three loops.

Does anyone have experience of the LGB Reverse Loop sensors? I assume the short lengths are made this way for a reason and I will probably need to modify them all but I don't want to make changes until I know what I am doing.

I made a simple phase sensor to test the track phase, looking at the sensor track it seems to switch phase continuously, I cannot find a circuit diagram and I'm not sure why it does this?

Robin
 
Airbuspilot said:
There are 4 reverse loops on the G scale DCC layout I am working on, three setup by someone who is no longer around and one by myself. The three existing loops have a sensor track around 20 cm long, I have rewired all of them as the cables were looking sad. The fourth loop came from a new box where I discovered (for the first time) sensor track of about 3 cm and used this in the last loop.

I have been told the longer sensor track is required as some longer locos with two bogies have problems when they cross over. In reality I have found different problems between each of the three existing sensors, small locos work well on some and stop on others while the long locos stop on some sensors and in one case shorts the sensor. So far it seems the LGB track length of 3 cm works but this is on a fairly steep gradient which some locos are having a problem climbing, I don't have reliable information to warrant my picking up and modifying the track on the other three loops.

Does anyone have experience of the LGB Reverse Loop sensors? I assume the short lengths are made this way for a reason and I will probably need to modify them all but I don't want to make changes until I know what I am doing.

I made a simple phase sensor to test the track phase, looking at the sensor track it seems to switch phase continuously, I cannot find a circuit diagram and I'm not sure why it does this?

Robin
Click to expand...
I have done a vid on creating the use of these, on a triangle but the principle hold good. One thing to note, yes long locomotives can cause problems but so can even longer trains with all metal wheels that are not necesarry linked electrically.
 
Thanks John, I did see your Video some time ago. I will replace one of the "old" sensors with a 3 cm section of track and see what happens.

In principle as long as the mid section is longer than the longest train there should be no change of phase on the mid section of track until the compete train is in that section. The reverser unit doesn't care which direction the train is entering and switches the mid section of track correctly regardless of entry direction.

My phase detector shows a steady signal before and after switching but for some reason the sensor track switches phase rapidly and continuously, I don't understand why. Possibly with a longer loco sitting on a long sensor track the decoder sees a rapidly changing phase and gets confused, with a short sensor the decoder picks up the steady supply from the mid section very quickly and doesn't see the sensor track long enough to cause it a problem.

Hi Paul - my sensor works with AC only hence phase not polarity.

Robin
 
Hi Robin,

Are you sure you've got the sensor tracks wired properly? I would not trust your "phase detector". You need to physically verify each wire connection is correct. The manual for the LGB reverse loop module can be found on their website. It shows how the module needs to be wired for a standard reverse-loop installation. This thread should be somewhat helpful too: https://www.gscalecentral.net/threads/wiring-plan-for-my-wye-section.317900/#post-655581. Something is not right with your wiring if a loco (or wagon with metal wheels) shorts out your system when crossing the sensors. Also, you need to make sure each sensor segment is insulated on both ends and the sensors are kept reasonably clean. I recommend you install the diodes on the sensor wires as shown in the LGB manual too.

But to answer you original question, in my experience, the length of the sensor segments don't matter. (Although 20 cm is excessive!) The sensor segments just need to be shorter than the distance between power pickups on your shortest wheelbase loco. The sensor segments are not powered (except through a traversing loco's wheels). A loco's power pickups must be able to bridge the sensor segments or it will stall. Two of the three sensor pairs on my RR's wye are the 25mm segments that came with the reverser. The third is a LGB 42 41 mm track makeup piece that has had all its rail joiners replaced with insulating joiners. My LGB reverser has functioned flawlessly for over five years now. I run locos sized from a LGB Santa handcart to the RhB Ge 6/6 IIs.

Edit added: Here is the LGB manual https://static.maerklin.de/damcontent/4c/95/4c95ca844b982d9b2087d5c74d229f1f1612248264.pdf

2nd edit to correct LGB 10040 make-up section length: 41, not 42 mm
 
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Airbuspilot said:
In principle as long as the mid section is longer than the longest train there should be no change of phase on the mid section of track until the compete train is in that section. The reverser unit doesn't care which direction the train is entering and switches the mid section of track correctly regardless of entry direction.
Click to expand...
Your first sentence above is close but not quite correct - "will" needs to replace "should". In a LGB/Massoth standard reverse loop installation using sensors the "mid section" entry sensors will switch, if necessary, the "phase" of the mid section to match that of the track that the train is exiting. The mid section will retain that phase until the train comes to the exit boundary sensors. The mid section phase is then switched to match the phase of the track the train will be entering. This is why the mid section needs to be longer than the train. If it isn't, the train could cause a short between the mid section's incoming and outgoing tracks.

Robin, I'm being rather picky here and do apologize if it offends as that is certainly not my intent.
 
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For what it's worth I use two Massoth (presumably similar to LGB) reverse loop modules on my layout. I use the short (3 cm ish) insulated sensor rails that come with them. Per Phil S's experience mine just work. I would ensure that the area of track around the sensor rail is laid nice and level.
 
Thanks Phil and James

The set up-is correct with the sensors insulated correctly, I am reasonably certain the wiring is as per the manual (I have 4 of them), each loop was wired on the bench and checked by a colleague however I will certainly recheck. Three of the four are level but we are still working on no 4 so its something we will have to look at.

My phase detector was only designed to look for stupid wiring errors and to test continuity so its very basic, you are correct in saying its not necessarily reliable in this situation. You say the sensor is not powered under normal conditions, that makes more sense I will check next opportunity, in this case my detector is effectively seeing an earth which would account for the indication.

It seems strange that some locos work perfectly while others stall and one makes a short. Of the 4 loops the new one, which I made from scratch, seems to work but I can't duplicate the problematic locos as the gradient is a bit too steep.

So, plan B, re-make all the sensors to be LGB standard lengths and re-check the wiring. At what point do I get to play trains??

I welcome picky answers and I will certainly ask for many more as I get my head around all this stuff. :(

Thanks again

Robin
 
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