Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Direct Current - Positive and Negative Polarity

1752 views
15 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    September, 2004
  • From: Dearborn Station
  • 11,654 posts
Direct Current - Positive and Negative Polarity
Posted by richhotrain on Saturday, April 06, 2013 7:41 AM

I have several different DC power packs including a number of MRC Railpower 1370 units that I use to power my trackside signals, Tortoises, and control panel DPDTs and LEDs.

Curiously, there is no marking (+/-) to distinguish the positive pole from the negative pole.  Why is that?

Another thing that bewilders me is the different application of postive and negative polarity on my Tomar Industries signals.   On the dwarf signals, a pair of 2-leg LEDs - one red and one green, there is one white wire which is the positive (+) side of the signal.  On the search light signals, a single 3-leg red/green LED, there is one white wire which is the negative (-) side of the signal.  Why did Tomar choose to set up the white wire as the positive side on the dwarf and the white wire as the negative side on the search light?

At one time, I tried to mantain a two-wire color code for my DC power, using black for positive and white for negative.  But as I add signals to my system, the color code has become meaningless as white and black wires are connected together.

Another issue is the wiring structure of the Tortoise.  Of the eight terminals, 1 and 8 are the power terminals from the DPDT switch on the control panel.  Terminals 2, 3, and 4 are one set of power supply to signals, and terminals 5, 6, and 7 are the second set of power supply to another set of signals.  What is the difference between terminal 2, 3, and 4 (or between terminal 5, 6, and 7) ?     Does the polarity depend upon which type of signal (dwarf or search light, in my case) is being powered?

I hope this all makes sense.

Rich

  • Member since
    July, 2006
  • From: Pittsburgh, PA
  • 1,302 posts
Posted by JoeinPA on Saturday, April 06, 2013 8:02 AM

Rich:

Do your powerpaks have a built in reversing switch? If so, then the output terminals will change polarity with the switch and +/- markings would not apply.

Look at your documentation that came with the tortoises. Terminals 2,3and 4 are a SPDT switch and 5,6,and7 are a second one. They function just like a SPDT toggle switch.

Joe

  • Member since
    September, 2004
  • From: Dearborn Station
  • 11,654 posts
Posted by richhotrain on Saturday, April 06, 2013 8:12 AM

JoeinPA

Rich:

Look at your documentation that came with the tortoises. Terminals 2,3and 4 are a SPDT switch and 5,6,and7 are a second one. They function just like a SPDT toggle switch.

Joe

Joe, thanks for replying.  I have looked at the documentation, but my limited knowledge on such matters hinders my full understanding.

Currently, I use terminals 5, 6, and 7 to power my trackside signals.  I use 6 and 7 for the red and green signal wires and terminal 5 for a black wire that routes back to the DC power pack.  I get confused over whether terminal 5 is considered positive or negative.

Rich

  • Member since
    January, 2007
  • From: Eastern Shore Virginia
  • 3,123 posts
Posted by gandydancer19 on Saturday, April 06, 2013 8:14 AM

1.  I don't have the PP you are talking about but - the aux output is usually AC at a fixed voltage around 18 volts.  The track output is DC.  If you switch the reversing switch, the polarity of the track output changes polarity.  Thus it would do no good to label the polarity of the track output terminals.

2.  Tomar signals:  The most common way for individual LED's to be wired for signals is Common Anode (+).  The three lead bi polar LED is Common Cathode (-).  The Common Anode three wire LED may not have been available at the time, or maybe the signal can be specified with Common Anode wiring and you missed it in the description when you made the purchase.

3.  The color code has become meaningless because you didn't write out a color chart of what you wanted to use before you started.  Therefore you didn't remember what you did before, or were unwilling to buy the proper color wire.  In the industry, the most common colors are Black is hot, White is neutral, and Green is ground for AC.  For DC, Red is hot and Black is negative.  I believe that Red is also hot on a 220 AC circuit. 

But as I said in another post, model railroaders don't usually stick to the color codes because they tend to get whatever wire is cheaper reguardless of the color.  Thus it all gets confused in the end unless you keep a record or wire book for your layout as you are building it.

4.  One contact out of the 5-6-7 group is common to the 5-67 group. (I don't remember which one right now, but one of the ones on the end.)  One wire out of the 2-3-4 group is also common to the 2-3-4 group.  If you put the Tortoise connector on backwards, (if you use connectors as I do) the Tortoise will operate in reverse, but no electrical damage will occur to the machine or layout.  This was a very thought out design by Cirkitron. 

There is no polarity associated with the aux contacts of the Tortoise.  They are just switches.  If there is a polarity associated with them, it is due to the way that you wired them up for what you needed to do.

Elmer.

The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.

(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.

  • Member since
    December, 2001
  • 1,500 posts
Posted by Stevert on Saturday, April 06, 2013 8:15 AM

1) Because MRC didn't feel the need to mark them.  For a DC layout, it really doesn't matter.  If the train goes the "wrong" way, switch the wires around.

2) The white wire is the common.  You have one common anode signal and one common cathode signal.  The specific electronics you're using to power them determines which type you need.

3) I don't have a Tortoise manual in front of me (it explains all this, with diagrams), but one of the contacts is the "sliding" contact and the other two are the "stationary" contacts.  The "sliding" contact will connect to one or the other of the "stationary" contacts depending on the position of the Tortoise, but the two "stationary" contacts will never come in contact with each other. 

How you'd wire those depends on exactly what you want to accomplish.  If you want a single power source to power one of two loads depending on the Tortoise's position, you'd connect that source to the "sliding" contact and each of your two loads to their respective "stationary" contact.

On the other hand, if you want either a positive or negative source to a single load, you'd attach those positive and negative sources to the "stationary" contacts, and your load to the "sliding" contact.

So each set of three contacts is essentially a SPDT toggle switch.

I hope this helps.

  • Member since
    September, 2004
  • From: Dearborn Station
  • 11,654 posts
Posted by richhotrain on Saturday, April 06, 2013 8:25 AM

By the way, here is the diagram for the eight terminals on the Tortoise.

  • Member since
    January, 2007
  • From: Eastern Shore Virginia
  • 3,123 posts
Posted by gandydancer19 on Saturday, April 06, 2013 8:35 AM

If you look close at the diagram, you will see that the connector can be reversed or turned around and all the power and switch contacts still line up.  The switch commons are pins 4 and 5.  These are the movable wipers and are the same as the center contact on a SPST toggle switch.

Elmer.

The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.

(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.

  • Member since
    September, 2004
  • From: Dearborn Station
  • 11,654 posts
Posted by richhotrain on Saturday, April 06, 2013 9:01 AM

Stevert

3) I don't have a Tortoise manual in front of me (it explains all this, with diagrams), but one of the contacts is the "sliding" contact and the other two are the "stationary" contacts.  The "sliding" contact will connect to one or the other of the "stationary" contacts depending on the position of the Tortoise, but the two "stationary" contacts will never come in contact with each other. 

How you'd wire those depends on exactly what you want to accomplish.  If you want a single power source to power one of two loads depending on the Tortoise's position, you'd connect that source to the "sliding" contact and each of your two loads to their respective "stationary" contact.

On the other hand, if you want either a positive or negative source to a single load, you'd attach those positive and negative sources to the "stationary" contacts, and your load to the "sliding" contact.

Stevert, thanks, that helps a lot.

As I read your explanation, I have connected my power source to the #5 terminal, the sliding contact.  The loads, my red and green LED wire connections, are attached to the #6 and #7 terminal, the stationary contacts.

I am not sure, though, that I understand the alternative arrangement, as cited below.  Can you explain that further?

On the other hand, if you want either a positive or negative source to a single load, you'd attach those positive and negative sources to the "stationary" contacts, and your load to the "sliding" contact.

Thanks.

Rich

  • Member since
    February, 2002
  • From: Reading, PA
  • 17,228 posts
Posted by rrinker on Saturday, April 06, 2013 9:13 AM

 If you connect positieve to say #6, and negative to #7, then in one position the sliding contact #5 will connect to negative, in the other position it would connect to positive. This is what you do to power a frog, the frog needs to connect to either the left rail or the right rail depending on the way the points are lined. So one rail to #6, one rail to #7, and the frog itself to #5 (or 2 and 3, frog to 4). If it's wrong, swap the wires on 6 and 7.

 If you both sets of contacts, you have the same thing as a DPDT toggle switch 4 and 5 would be the center contacts. 3 and 7 would be one end, and 2 and 6 would be the other end, for the total of 6 terminals So you can wire the X between 3 and 6 and 2 and 7, feed power to 3 and 7, and get alternating polarity from 4 and 5. You can cascade Tortoises that way - when one throws, it changes the polarity of the next one down the line nad throws that one too. Kinda limited usefulness though, it will only work if the two need to throw opposite each other.

                     --Randy

 


Modeling the Reading Railroad in the 1950's

 

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

  • Member since
    September, 2004
  • From: Dearborn Station
  • 11,654 posts
Posted by richhotrain on Saturday, April 06, 2013 9:32 AM

Thanks, Randy, that is very interesting and very helpful.

Rich

  • Member since
    September, 2004
  • From: Dearborn Station
  • 11,654 posts
Posted by richhotrain on Saturday, April 06, 2013 9:33 AM

gandydancer19

If you look close at the diagram, you will see that the connector can be reversed or turned around and all the power and switch contacts still line up.  The switch commons are pins 4 and 5.  These are the movable wipers and are the same as the center contact on a SPST toggle switch.

ahh, yes, I see what you mean, Elmer.

Rich

  • Member since
    July, 2006
  • From: North Dakota
  • 4,771 posts
Posted by BroadwayLion on Saturday, April 06, 2013 9:47 AM

richhotrain

Curiously, there is no marking (+/-) to distinguish the positive pole from the negative pole.  Why is that?

It is not curious, for as they said, the real difference is East and West. (Not even Fwd and Rev)

Put the train on the track,  the LEFT rail in the direction of movement is (-) and the right rail is (+).

Your mileage may vary but your train will still behave properly.

ROAR

The Route of the Broadway Lion The Largest Subway Layout in North Dakota.

Here there be cats.                                LIONS with CAMERAS

  • Member since
    September, 2004
  • From: Dearborn Station
  • 11,654 posts
Posted by richhotrain on Saturday, April 06, 2013 9:57 AM

BroadwayLion

richhotrain

Curiously, there is no marking (+/-) to distinguish the positive pole from the negative pole.  Why is that?

It is not curious, for as they said, the real difference is East and West. (Not even Fwd and Rev)

Put the train on the track,  the LEFT rail in the direction of movement is (-) and the right rail is (+).

Your mileage may vary but your train will still behave properly.

ROAR

Thanks, LION.

I should have mentioned that my layout is DCC.  I only use the DC power pack to power my Tortoises and trackside signals.

Rich

  • Member since
    February, 2002
  • From: Reading, PA
  • 17,228 posts
Posted by rrinker on Saturday, April 06, 2013 9:59 AM

 Yes, the Track terminals of a DC power pack won;t be marked, because which one is + and which is - depends on which way the direction switch is set. Would be nice if they labeled the fixed DC terminals though - not everything you'd connect downstream has a diode in it to prevent damage if hooked up backwards.

Other DC power supplies are pretty much always marked. Wall wart types often have a ridge or white stripe on one of the wires, or if they come with a connector of some sort on the end, there is usually a diagram on the label showing if the center pin or the barrel of the connector is + or -. To figure it out after you cut off the connector you might not need, just remember to leave little wire on the connector side when you cut it off. The use your meter on continuity or a low ohms setting and see which side of the connector body connects to which wire.

             --Randy


Modeling the Reading Railroad in the 1950's

 

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

  • Member since
    July, 2006
  • From: North Dakota
  • 4,771 posts
Posted by BroadwayLion on Saturday, April 06, 2013 5:30 PM

richhotrain

Thanks, LION.

I should have mentioned that my layout is DCC.  I only use the DC power pack to power my Tortoises and trackside signals.

Ah... see, but it still does not matter. If the tortoise does not go the way you expected it to do, switch the wires around. When LION first built his layout he paid no attention to + or -.  Him uses a 3 wire DC system: +  Gd  -  One wire was GREEN and LION called it the GREEN WIRE. The other wire was red, and he called it the RED WIRE.

These wires pass through the control panel as a bus. LION used SPST switches. One pole was GREEN the other pole was RED. 

LION mounted the switches so that when the lever was down, the GREEN circuit was connected to the "stinger" (what the LION calls the ware between the control panel and the switch).

Switch DOWN (normal position) turn out is in the NORMAL position; switch up turnout is in the REVERSE position.

LION does not care if it is + or -, all him wants is that the turnout should be in the normal position when the control is in the normal position.

LION has GROUND wire around whole layout, so each tortoise needs only one wire to control the motor, the signals, and any extra relays if any.  When you have lots of switches you need to know how to keep your wires at bay.

ROAR

The Route of the Broadway Lion The Largest Subway Layout in North Dakota.

Here there be cats.                                LIONS with CAMERAS

  • Member since
    December, 2012
  • 163 posts
Posted by matthewd5 on Saturday, April 13, 2013 1:46 PM

If your using bipolar LEDs can't you just put them inline for the power lead going to the Tortoise?

Matthew

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!
Popular on ModelRailroader.com
Model Railroader Newsletter See all
Sign up for our FREE e-newsletter and get model railroad news in your inbox!
ADVERTISEMENT
ADVERTISEMENT

Search the Community

ADVERTISEMENT
Find us on Facebook

Loading...