# dcc polarity



## sid (Mar 26, 2018)

ive searched till im sick of searching . how do you check polarity in dcc. i know them wires got to be on the right track rail or theres a short or something. but i can not find a way to check polarity. now dc is easy ... but dcc i give up other than taking my track apart and reversing every dang connection one at a time and checking there has got to be a better way. frustrated again sid. 
i had a problem with my X crossing and have figgered that out by switching the wire blue one where the white one was ect. but im not gunna do this with my whole lay out thats a pain.


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## MichaelE (Mar 7, 2018)

AC does not have polarity.

Just be consistent with what wire goes to what rail and keep them the same everywhere.


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## DonR (Oct 18, 2012)

Sid

There have been others who feel your pain.

DCC is a modified AC thus it has phases which
which some think of as polarity. I know the reason for
your question but since AC means Alternating
Current, the Polarity reverses
per the specified cycle (60 Hertz). Your multimeter
would simply show voltage no matter which way
you use the probes.

The best way to avoid DCC short circuits is to
use color coded bus wire and track drops as a beginning step.
Never connect a Red drop to a Black bus.

If you have a complex layout you would be
advised to draw your layout using Red for the
Right rail and black for the left rail. (or any other
2 colors you choose) Any time
in your drawing when you see a Red touching
a Black rail, you have a short circuit.

There are two parallel main tracks in a double
crossover. The right rail of each should
be connected to the 'Red' bus wire, the
left of both to the 'black'. In this situation when the points
are thrown there is no short.

However, in many layouts the modeller uses
a double crossover to connect both 'sides' of
an oval which enables a train to be turned
around and go the other way on the layout.
In this situation the Right rail of the 'East' track is
Red, but the Right rail of the 'West' track is black.
When the points are thrown this causes a short circuit and requires that you establish isolated sections with reverse
loop controllers. 

Follow these simple rules and you won't 
have electrical problems.

Don


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## wvgca (Jan 21, 2013)

feed it DC to check polarity, then switch to DCC when you are done, it will all work except the reversers


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## sid (Mar 26, 2018)

i figgered it out by painting a car white on one side then blue on the other ( i read that some place ) any way thats how i got the wire connected so far so good. the kato track worked as is but when you throw the turn outs they must be thrown together or it shorts is what i have found. one on one end and the other end . it really didnt short just no power . ive put feeders every where untill i ran out of them i need three more. so far i really like dcc i can play with two trains at the same time with one controller pretty cool. i quess my biggest problem is me not paying attention to what wires are on what rails. i do know that when i switch the blue wire to where the white wire was it dont work no more , so there is some kinda polarity there. i understand how ac works and with ac it dont matter what wire goes where (except the ground ) and it works . but im not finding that with dcc . thank you guys for the help. 
WVGCA i didnt even think about using dc to test the rails and wires . hahahaha ill have to remember that. i forget a lot of stuff. thanks for the reminder. i need to put things in a book and catalog it all. or a file on my computer. heres a pick of my temp layout till i can get some pink foam board. give me time to play and sort out the wire stuff ect.


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## fcwilt (Sep 27, 2013)

Hi,

I created simple tester for this sort of thing.

Two LEDs, (one RED, one GREEN), one resistor for each.

Wired up in parallel with two leads with alligator clips on the ends.

When connected one way to a DC source the RED LED illuminates. 

Reverse the connection the GREEN LED illuminates.

On DCC the both illuminate.

When connected to two rails that should be the same DCC polarity the LEDs should not illuminate.

If they do the the rails are of opposite polarity.

Frederick


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## sid (Mar 26, 2018)

fcwilt said:


> Hi,
> 
> I created simple tester for this sort of thing.
> 
> ...


HI ya i saw that some place i was reading .if i remember correctly it was a small box with two leds and three wires. i need to find it again . i think i remember how to make it . some place i read that you can do this with leds to make a signal of some sort to tell witch way the train is going some thing like that. im pretty green to all this train stuff , but i am learning .


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## mesenteria (Oct 29, 2015)

I don't use electronics except to meter the rails when they are powered to see IF they are powered with the correct voltage range.

When I am wiring a layout, I use the logic "inside rail/outside rail." No matter where you are on the layout where tracks run connected to the main line, your rails are closest to the edge (outside) of the layout, or they are closest to the center of the layout (inside). Then, I pick one colour of feeder and bus wires and remember that they always go to the 'outside' rail. This works very well...or at least, it has worked reliably for me.

Naturally, where they double back as they do in a reversing loop, you must gap and use either a DPDT or a reversing mechanism. But, that gap makes the logic sound up to the gap.


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## fcwilt (Sep 27, 2013)

sid said:


> HI ya i saw that some place i was reading .if i remember correctly it was a small box with two leds and three wires. i need to find it again . i think i remember how to make it . some place i read that you can do this with leds to make a signal of some sort to tell witch way the train is going some thing like that. im pretty green to all this train stuff , but i am learning .


If you like I can provide the simple schematic which will make clear what my words did not.

Frederick


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## sid (Mar 26, 2018)

fcwilt said:


> If you like I can provide the simple schematic which will make clear what my words did not.
> 
> Frederick


Thank you sure if you like. i found it again . you got me curious as to where i found it so i went searching. hahahaha ive got about 16 leds with wire attached someplace around here , ive lost one of my kato right hand turn outs too. how i dont know but its MIA . i suffer from CRS syndrome


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## Lemonhawk (Sep 24, 2013)

You can make the tester with a single 2 lead Red/Green LED also.


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## fcwilt (Sep 27, 2013)

sid said:


> Thank you sure if you like. i found it again . you got me curious as to where i found it so i went searching. hahahaha ive got about 16 leds with wire attached someplace around here , ive lost one of my kato right hand turn outs too. how i dont know but its MIA . i suffer from CRS syndrome


Here you go.

The values of each resistor will depend on the LEDs you use, the nominal voltage you expect to use the device on and the desired LED brightness.

Frederick


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## fcwilt (Sep 27, 2013)

Lemonhawk said:


> You can make the tester with a single 2 lead Red/Green LED also.


I tried that but found using separate LEDs made it easier to view from a distance which I found I was doing on a number of occasions.

Frederick


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## gregc (Apr 25, 2015)

sid said:


> how do you check polarity in dcc? I know the wires got to be on the right track rail or there's a short or something. but i cannot find a way to check polarity.


you can certainly check the polarity of unpowered rails by measuring with an ohm-meter with the supply disconnected. 0 ohms means that the rails are connected and will be the same polarity.

you can determine the polarity of powered rails by measuring the voltage between them with an AC volt-meter. There should be no voltage between rails connected to the same supply terminal -- the same polarity.


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## sid (Mar 26, 2018)

Thanks guys ill make one of these . and thanks for the ohms reminder as well . i for get so much stuff.if you dont use it all the time i tend to forget. used to do electrical stuff back in my 20's but been out of that for 30 years.


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