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Detector coil - how to determine polarity

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PED
  • Member since
    April, 2016
  • 571 posts
Detector coil - how to determine polarity
Posted by PED on Saturday, February 02, 2019 12:37 PM

I am using some small coils in a block occupancy detection circuit. Appears to work OK no matter how it is hooked up but I saw some comments elsewhere concerning polarity of the coils.

Is there a way to determine or measure the coil to identify polarity?

Paul D

N scale Washita and Santa Fe Railroad
Southern Oklahoma circa late 70's

  • Member since
    January, 2009
  • 3,678 posts
Posted by RR_Mel on Saturday, February 02, 2019 3:16 PM

I don’t think it makes any difference unless you are stacking them then + goes to – in series and + to + and – to – in parallel.  Kinda like speakers if you only have one speaker the polarity doesn’t affect the sound but more than one speaker and the correct polarity is a must.
 
 
Mel
 
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
  • Member since
    February, 2002
  • From: Reading, PA
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Posted by rrinker on Saturday, February 02, 2019 6:21 PM

 Most have an arrow printed on them. Howver, that's for DC, and what it really then indicates is that the polarity of the output will match the pinout. For DCC current detection - not going to matter.

                                       --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

PED
  • Member since
    April, 2016
  • 571 posts
Posted by PED on Saturday, February 02, 2019 7:01 PM

Randy,

Can you eloborate on the DCC angle? I have a section of dCC track that I want to treat as one block. It has multiple feeders. I want to put a coil on each feeder then connect them in parallel back to my detection board. I was advised to make sure they were all set up the same with matching polarity and the feeder wire running through the coil the same way. I don't have any problem doing that but I would like to understand more about the "why".

Paul D

N scale Washita and Santa Fe Railroad
Southern Oklahoma circa late 70's

  • Member since
    February, 2002
  • From: Reading, PA
  • 25,723 posts
Posted by rrinker on Saturday, February 02, 2019 7:23 PM

 That's not how you do it. You connect all the feeders together, then run a wire from the junction of all the feeders to the bus. On that connecting wire is where you place the transformer.

 To see why multiple sont he same line should be in the same direction, simplyfy it to 2. If they are wired opposite to one another, when the DCC signal is on the positive side, one coil will give out a positive signal. If coil 2 is wired the opposite way, it will give out a negative signal, exactly equal to the positive signal of coil 1. They cancel one naother out - the net result is nothing - liek there is no train in the block.

 But just runnign a sub-bus to connect each of the feeders together and using one tranformer on the link to the main bus is much easier, no worries about polarities or phasing, and you don;t need to buy 4 transformers where one will do.

                                    --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

PED
  • Member since
    April, 2016
  • 571 posts
Posted by PED on Saturday, February 02, 2019 8:58 PM

Randy,

Your approach is exactly what I would do if I was building from scratch but I am adding this to an existing layout and would like to avoid a lot of rewiring. Adding a few coils (in proper parallel) is a lot easier for an old guy than doing a lot of rewire work under my layout. :)

Paul D

N scale Washita and Santa Fe Railroad
Southern Oklahoma circa late 70's

  • Member since
    February, 2002
  • From: Reading, PA
  • 25,723 posts
Posted by rrinker on Saturday, February 02, 2019 9:34 PM

 Seems at least equally involved - to install the coils ont he feeder you have to cut every one, put the wire through the coil, and reattach each feeder to the bus. For all of making 4 connections you cna do it with one coil:

 1. Cut the existing bus just before the first feeder

 2. Cut the existing bus just after the last feeder

 3. Connect a new piece of bus wire between the ends of the bus.

 4. Stick a piece of bus wire through a coil, Connect one end to some point in the new jumper wire you ran, connect the other end to some point between the feeders.

Don;t forget there's the snese wires coming back from each coil to hook up as well. SO 4 sets of those to hook up if you do individual feeders.

And - if you have a decent ifead of how long a piece of wire you need to jumper the bus past these feeders, you can create that piece, and attach one end of the connector, complete witht he wire through the transformer, at the bench before ever going under the layout. Then it's just 2 cuts and 3 connections to make underneath. Seems to be this would be a lot less time under the bench than using 4 coils and cutting each feeder.

                                           --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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