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Offline phyan  
#1 Posted : 19 February 2019 16:48:21(UTC)
phyan

Finland   
Joined: 14/05/2010(UTC)
Posts: 5
Location: Finland
Hi all,

A long time ago (actually, quite exactly 10 years ago) there was a discussion about preventing problems with the contact track:
https://www.marklin-user...51-Contact-track-sensing

I have read this interesting article and the studied the solution many times, but it remained unclear to me, how to really employ the Zener diode. Could someone explain this once more, please. And in a way suitable for dummies as well :) Where in the system shall you put the diode, and are there other components you need, too? A diagram would be just awsome, thanks. -M.
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Offline JohnjeanB  
#2 Posted : 19 February 2019 17:34:05(UTC)
JohnjeanB

France   
Joined: 04/02/2011(UTC)
Posts: 1,562
Location: Paris, France
Hi xx
Welcome to the forum.
This is a current-sensing schematic for DC 2 rail based on only one pair of diodes (simple rectifier diode) the third diode is not a zener but identical to the other two to drive the transistor base. So simply use the schematic for a DC layout. For AC 3 rail this schematic is not applicable but rather connect one of the -previouslyinsulated- rails to the S88 entry
Cheers
Jean
My layout videos
latest vid
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Offline Danlake  
#3 Posted : 19 February 2019 19:20:07(UTC)
Danlake

New Zealand   
Joined: 03/08/2011(UTC)
Posts: 1,546
Hi,

As I understand you are talking about the trick of installing a diode when using isolated contact track section to improve the ground return in 3 rail operation.

I haven’t found it necessary on my layout but can be advantages especially with locos with limited ground wheel return.

Dale wrote this excellent guide:

http://members.ozemail.c.../pdf/the_diode_trick.pdf

And from forum:

https://www.marklin-user...-feedback-and-diodes-etc

Best Regards
Lasse
Digital 11m2 layout / C (M&K) tracks / Era IV / CS3 60226 / Train Controller Gold 9 with 4D sound. Mainly Danish and German Locomotives.
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Offline Minok  
#4 Posted : 19 February 2019 20:43:27(UTC)
Minok

United States   
Joined: 15/10/2006(UTC)
Posts: 2,212
Location: Washington, Pacific Northwest
What he said....

There is a diode trick for the S88 sensing tracks but it is only needed to address a small subset of locos/rolling stock that have very short wheel base with limited ability to contact the two tracks...
Toys of tin and wood rule!
---
My Layout Thread on marklin-users.net: InterCity 1-3-4
My YouTube Channel: https://www.youtube.com/user/Minok1217/
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Offline phyan  
#5 Posted : 20 February 2019 09:01:57(UTC)
phyan

Finland   
Joined: 14/05/2010(UTC)
Posts: 5
Location: Finland
Thanks everybody for pointing to these information sources, it was very interesting and helpful!
- Matti
Offline rrf  
#6 Posted : 23 February 2019 14:28:30(UTC)
rrf

United States   
Joined: 15/11/2009(UTC)
Posts: 296
Location: Silver Spring, Maryland USA
Originally Posted by: Minok Go to Quoted Post
<Stuff Deleted>

There is a diode trick for the S88 sensing tracks but it is only needed to address a small subset of locos/rolling stock that have very short wheel base with limited ability to contact the two tracks...

Hello,

I am about to setup my first S88 Contact Track sections. I have quite a few of the "small subset" of loks, including four E69s. So I plan to use diodes to improve conductivity on these track sections.

Rather than mount the diodes near the S88, I would like to install them on the underside of my C-Track, in the approximate center of each the isolated section. For flexibility I am planning to solder a bit of brown wire on each end of a 1N4002 diode and then connect it to the track using 74995 spade connectors.

Does anyone foresee a problem with this?

Thanks,
Rob
Mackenrode Wende Bahn
Offline JohnjeanB  
#7 Posted : 23 February 2019 14:59:01(UTC)
JohnjeanB

France   
Joined: 04/02/2011(UTC)
Posts: 1,562
Location: Paris, France
Hi Rob
I would avoid installing components under the track if they are fixed and ballasted.
I am sure you know the cathode is to be connected to the contract track section
Cheers
Jean
My layout videos
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rrf
Offline rrf  
#8 Posted : 23 February 2019 15:09:14(UTC)
rrf

United States   
Joined: 15/11/2009(UTC)
Posts: 296
Location: Silver Spring, Maryland USA
Originally Posted by: JohnjeanB Go to Quoted Post
Hi Rob
I would avoid installing components under the track if they are fixed and ballasted.
I am sure you know the cathode is to be connected to the contract track section
Cheers
Jean

Hello Jean,

Thank you for your reply.

The track will not be ballasted or fixed. Since I tend to change my layouts regularly, I prefer to rely upon gravity and friction. As to the diode's cathode, I had a subsequent thought of color coding the wire (grey on one side and brown on the other) to make sure I don't reverse the connection. I plan to use the same for the common ground (brown) and S88 connections (grey).
Rob
Mackenrode Wende Bahn
Offline Elsleuth1  
#9 Posted : 23 February 2019 15:15:31(UTC)
Elsleuth1

United States   
Joined: 23/04/2014(UTC)
Posts: 99
I have 16 S88's and they all work perfectly without an added diode. But I am interested in specifically which cars or locos would need a diode to trigger an S88. If a car or engine doesn't trigger the S88 wouldn't the next car do the job?
Offline JohnjeanB  
#10 Posted : 23 February 2019 15:29:31(UTC)
JohnjeanB

France   
Joined: 04/02/2011(UTC)
Posts: 1,562
Location: Paris, France
Hi
As you know the S88 is very high impedence with a pull-up resistor to +5 V and cannot feed any loco so any loco with only 4 wheels of which one is a traction tire is a good candidate: Schienenbus, kittel. Robel, etc
Cheers
Jean
My layout videos
latest vid
hump yard
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Offline Elsleuth1  
#11 Posted : 23 February 2019 15:36:52(UTC)
Elsleuth1

United States   
Joined: 23/04/2014(UTC)
Posts: 99
Very interesting. So a Rail Bus would be a excellent candidate for a problem and because it has four wheels and often goes between two S88s.
Offline rrf  
#12 Posted : 23 February 2019 15:57:25(UTC)
rrf

United States   
Joined: 15/11/2009(UTC)
Posts: 296
Location: Silver Spring, Maryland USA
Originally Posted by: Elsleuth1 Go to Quoted Post
Very interesting. So a Rail Bus would be a excellent candidate for a problem and because it has four wheels and often goes between two S88s.

Hello,

I am most worried about my E69s: two axles within a couple centimeters of each other. Using the diode, in theory I reduce the chance of stalling by at least 50%.
Rob
Mackenrode Wende Bahn
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Offline PeFu  
#13 Posted : 23 February 2019 20:11:25(UTC)
PeFu

Sweden   
Joined: 30/08/2002(UTC)
Posts: 896
I use the configuration presented by LDT, see below. I asked Mr. Littfinski on why they recommend a BY251, and he responded:

”The 1N400x diodes are for a maximum of 1 Amp current. During a short circuit condition, the current trough the diode could be much higher. Therefore we recommend the BY251 for a maximum of 3 Amp current.”

BDEACAEE-7922-4177-967D-4C872E208ED3.jpeg
Inspired by Swiss railways SBB and BLS | C and K track | CS2 | TrainController Gold V9
Youtube Channel for the Andreasburg-Mattiasberg layout
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Offline rrf  
#14 Posted : 23 February 2019 21:09:22(UTC)
rrf

United States   
Joined: 15/11/2009(UTC)
Posts: 296
Location: Silver Spring, Maryland USA
Originally Posted by: PeFu Go to Quoted Post
I use the configuration presented by LDT, see below. I asked Mr. Littfinski on why they recommend a BY251, and he responded:

”The 1N400x diodes are for a maximum of 1 Amp current. During a short circuit condition, the current trough the diode could be much higher. Therefore we recommend the BY251 for a maximum of 3 Amp current.”

That makes perfect sense. Actually I have been looking thru Digikey for a suitable 3 amp rated diode. Since I am not an EE person, the BY251 code you provide made matters much easier.

Thank you!
Rob
Mackenrode Wende Bahn
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Offline kiwiAlan  
#15 Posted : 23 February 2019 22:32:22(UTC)
kiwiAlan

United Kingdom   
Joined: 23/07/2014(UTC)
Posts: 5,969
Location: ENGLAND, Didcot
Originally Posted by: rrf Go to Quoted Post
Originally Posted by: PeFu Go to Quoted Post
I use the configuration presented by LDT, see below. I asked Mr. Littfinski on why they recommend a BY251, and he responded:

”The 1N400x diodes are for a maximum of 1 Amp current. During a short circuit condition, the current trough the diode could be much higher. Therefore we recommend the BY251 for a maximum of 3 Amp current.”

That makes perfect sense. Actually I have been looking thru Digikey for a suitable 3 amp rated diode. Since I am not an EE person, the BY251 code you provide made matters much easier.

Thank you!


There is also a 3A version of the 1N400x family, but I can't remember the number off hand.

Offline rrf  
#16 Posted : 23 February 2019 22:58:26(UTC)
rrf

United States   
Joined: 15/11/2009(UTC)
Posts: 296
Location: Silver Spring, Maryland USA
Originally Posted by: kiwiAlan Go to Quoted Post

There is also a 3A version of the 1N400x family, but I can't remember the number off hand.
I ran across the various 1N400x diodes, including ones rated for 3 amps of "Rectified Current". It was the other parameter choices such as "Forward Voltage" and "Reverse Current Leakage" that complicated my choice. Having a specific component recommendation for my desired MRR application makes me feel better.
Rob
Mackenrode Wende Bahn
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