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DC wiring question on a new layout

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Posted by Lastspikemike on Monday, June 14, 2021 5:26 PM

ATLANTIC CENTRAL

Again Mike, without seeing your track plan, it makes little sense, but it seems you might have figured it out.

Sheldon

 

I figured it all out last year. This year I understand better why I had to do what I figured out I had to do.

The schematic of my layout is simple to describe: two ovals connected by two turnouts facing frog to frog. The connecting track exits one oval clockwise and enters the other oval counterclockwise. Hence the East rail on one oval connects to the West rail of the other oval.

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Posted by ATLANTIC CENTRAL on Monday, June 14, 2021 10:44 AM

Again Mike, without seeing your track plan, it makes little sense, but it seems you might have figured it out.

Sheldon

    

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Posted by Lastspikemike on Monday, June 14, 2021 10:17 AM

"Wiring for DCC" explains the "home run" version of common rail. That's how I wired our DC layout (but the common rail is wired to bus bars and not DPDT) but since we are running DC only and we intend to add only a single DCC unit when we do run DCC we can delay the second part of home run: breaking the "return" common bus wires at the bus bar connections and, bingo, we have power districts. Each bus bar has a single connecting wire to its adjacent busbars. Pull that connection and wire it to the additional booster and we're good to go. Block control wires can go direct to any additional boosters anyway. Until then we can just select Cab A inputs as the DCC power source and disconnect the DC powerpacks completely while we run DCC.

Common Rail has been explained as working because the electrons leaving one powerpack "know" they have to go back to the same powerpack. That's how the circuit works. So it doesn't matter which powerpack polarity is connected to the common rail because the circuit within each powerpack is what matters. The 780 I was using was, electrically, one powerpack so the returning electrons just took the shortest available route, as they do. Nothing was left to power a locomotive connecting the two rails. Dead internal short but the "other end" of the short was across the 220 reversing switches at center off. The electrons never got to the locomotive.

Now I have connected the one throttle in the MRC 780 as Cab C not connected to the 220 at all, and the Cab B throttle is connected to the 220 and the MRC 760 is connected to the 220 as Cab A this internal circuit problem can no longer occur. Although I still match the polarity to my 220 inputs as before I now see why I did have to at that time but do not now. Oddly, this also straightens out a different polarity effect I experienced with my former setup. All three of my direction switches can now be set to operate East and West. Cool. I'm still not sure exactly how that works but it is dawning on me.

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 5:21 PM

gregc

 

 
ATLANTIC CENTRAL
???????

 

sorry, wrong wording.    the right hand screw terminal of all but the last 220 have both cab connections

 

OK, yes, no worries.

To me, this is all so much easier to simply build with toggle switches, assuming this kind of system is all you need.

And in doing so I would not use common rail in building the layout or use a common wire return.

One day I will draw some more drawings and show the advantages of not using common rail.

The OP has received my PM and we are communicating about his layout plan and wiring needs.

I will repeat, the very best DC control systems, assuming you want to control mutiple trains at once, do not use toggle switches, and do not have to tie the operator to a control panel, despite all "toggle flipping" comments I have heard in the last decade.

Sheldon

  

    

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Posted by gregc on Sunday, June 13, 2021 4:50 PM

ATLANTIC CENTRAL
???????

sorry, wrong wording.    the right hand screw terminal of all but the last 220 have both cab connections

greg - Philadelphia & Reading / Reading

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 4:32 PM

gregc

 

 
CSX Robert
"Non-reversing" does not pass both legs through to the output terminals.  Only the center position passes both legs to the output. In both of the other positions, one leg of the input is connected to common and not connected to either output terminal.

 

yes.  measured with a multimeter.  thanks

so if you center them, the last 220 doesn't see both power pack connections

 

???????

The drawing on the instructions you posted is perfectly clear. The middle position passes the power thru, bypassing the common wire connection. 

The right most Controller does see both power pack conncections but is does not pass them both thru. It creates the common wire connection and only feeds the two hot feeds (top and bottom right side terminals) from each power pack on to any #215 selectors used for block control.

And the right most Controller is used as the primary direction switch for each throttle.

I don't see what is so hard to understand here? Maybe it is just hard for people who have not built or operated a DC layout with cab control to see the end result?

Common rail or not, reverse loops need to get their power BEFORE the primary reversing switch for the rest of the non reverse loop blocks - that is the primary function of the Atlas Controller.

Second, the reverse loop block needs to be able to select which throttle will control it - the Controller does that as well.

By being able to stack them, you can have as many reverse loops as you may need.

The Selector then allows all other blocks to be connected to cab A or Cab B or turned off to isolate a loco/train.

Sheldon 

    

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Posted by gregc on Sunday, June 13, 2021 3:11 PM

CSX Robert
"Non-reversing" does not pass both legs through to the output terminals.  Only the center position passes both legs to the output. In both of the other positions, one leg of the input is connected to common and not connected to either output terminal.

yes.  measured with a multimeter.  thanks

so if you center them, the last 220 doesn't see both power pack connections

greg - Philadelphia & Reading / Reading

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Posted by CSX Robert on Sunday, June 13, 2021 3:00 PM

gregc
so there's reversing, non-reversing and pass-thru?   what's the difference between non-reversing and pass-thru

"Non-reversing" does not pass both legs through to the output terminals.  Only the center position passes both legs to the output. In both of the other positions, one leg of the input is connected to common and not connected to either output terminal.

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Posted by gregc on Sunday, June 13, 2021 2:48 PM

sheldon has said (PMs) that i like to know "why".

Lastspikemike
The 220 reversing switch has a center off but this position passes through the connection so isn't really "off".

clearly there needs to be a position when the paths between the screw terminals are isolated, before switching connections.   the  left screw terminals can't be connected to both screw terminals on the right at the same time otherwise there's a short.

but it appears the right 1/3 of the switch position is the reversing position and the left 2/3, including the center is the non-reversing position.   i was able to find a spot where there was no connection

because of this asymmetric construction, it makes sense, as Sheldon says the instructions indicate, to center the cab reversing switches in all but the rightmost 220 to indicate that they shouldn't be used to switch mainline polarity.

CSX Robert
The center position of the cab reversing switches on the 220 are "pass-through", i. e., they pass the left hand cab inputs directly through to the right hand cab outputs.  Neither of the other positions is pass-through.  They both connect one leg to common and one leg to the output and they swap which one is connected to the common versus the output.  In both non-center positions of the switch, only one leg of the input is connected to the ou

so there's reversing, non-reversing and pass-thru?   what's the difference between non-reversing and pass-thru

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 2:40 PM

Overmod

 

 
Lastspikemike
one of our group of three worked as an electrician years ago and to him white was the hot wire). 

 

OK, I'll bite on this.  In what retarded imitation version of the NEC or any other valid national code does 'white' denote 'hot' instead of neutral?

 

In part I'd like to know because I found a "professionally" wired job in Springhill where the wires mysteriously changed colors passing through a junction box.  I attributed this at the time to guild malevolence against 'outsiders' messing with electrician prerogatives (NEC's position being no colors are 'official' and you should always check before tinkering anyway) but perhaps this is some distinctive color aberration taught to apprentices?

 

OK, wires in conduits should always be white = neutral, hot or switched hots other colors based on voltage/phase.

But, in cable assemblies like ROMEX, there is no code requirement to mark white wires uses as hot legs on switch leg circuits.

If in the time I have been away from the code book this has changed, I assure you such a requirement is seldon inforced.

Open up that three way switch in your hallway, and you will find a white (or two) on the switch being used as a hot wire. 

Depending on how the whole 3-way circuit is wired, you will also find a white wire spliced to a black wire in a box somewhere in that circuit.

Same with dead end switch legs, now prohibited by the code. A single black and white cable assembly going to a switch, the neutral stopped at the light fixture.

Recent code changes require neutrals in all junction and outlet boxes. Why? To provide a neutral for home automation devices.

Sheldon

    

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 2:24 PM

CSX Robert

 

 
gregc
...any reversing switch has just to positions, if not center-off, non-reversing or "pass thru" and reversing.     ... think about it.   why would it have a pass-thru and non-reversing position?
 

 

 

The center position of the cab reversing switches on the 220 are "pass-through", i. e., they pass the left hand cab inputs directly through to the right hand cab outputs.  Neither of the other positions is pass-through.  They both connect one leg to common and one leg to the output and they swap which one is connected to the common versus the output.  In both non-center positions of the switch, only one leg of the input is connected to the output.

 

That's what I see on the diagram, but I don't have one in my hand....

Sheldon

    

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 2:23 PM

Lastspikemike

A DC primer would be handy.

I have a common rail system in that all my red wires are connected and three throttles are connected to all the red wires ( although some of the red wires are actually white because one of our group of three worked as an electrician years ago and to him white was the hot wire). 

So, I admit to becoming confused again. Since two of the three throttles are in a MRC 780 then clearly I'm not experiencing the internal short problem. We routinely have the powerpack reversing switches opposed.

My remark about train direction was a serious remark.  We have two loops and one connecting track. The "outside rail" of one loop connects to the "inside rail" of the other loop. We can't have a consistent East West or clockwise and counterclockwise. One loop is always the reverse of the other. The connecting track has neither an inside rail nor an outside rail. No left or right rail if you prefer. 

 

Once again, a drawing or picture would be helpful.

Sheldon

    

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Posted by CSX Robert on Sunday, June 13, 2021 2:21 PM

gregc
...any reversing switch has just to positions, if not center-off, non-reversing or "pass thru" and reversing.     ... think about it.   why would it have a pass-thru and non-reversing position?
 

The center position of the cab reversing switches on the 220 are "pass-through", i. e., they pass the left hand cab inputs directly through to the right hand cab outputs.  Neither of the other positions is pass-through.  They both connect one leg to common and one leg to the output and they swap which one is connected to the common versus the output.  In both non-center positions of the switch, only one leg of the input is connected to the output.

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 2:21 PM

gregc

 

 
ATLANTIC CENTRAL
I'm going by the drawing and memory, I don't have one here to test.

 

i do have one and i verified it after.

any reversing switch has just to positions, if not center-off, non-reversing or "pass thru" and reversing.     ... think about it.   why would it have a pass-thru and non-reversing position?

 

I agree, just looking at what Atlas says in both pictures and words....

Sheldon

    

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Posted by Lastspikemike on Sunday, June 13, 2021 2:18 PM

CSX Robert

 

 
Lastspikemike
The two "up down" coloured schematics seem to show the short circuit I refer to. The opposite polarities of the powerpacks connect at the Common terminal. That looks to me like a dead short. Why is it not?

 

This is confusing for many people when they first look into common rail wiring.  Take for example a single 12 volt isolated power supply.  The '+' terminal on that power supply by itself is not actually +12 volts, it is +12 volts relative to the '-' terminal of that power supply.  The voltage at any single point has to be measured relative to some reference point.  With two separate isolated power supplies there is no common reference point.  With common rail cab control wiring, you are creating a common reference point - the common rail.  The control rail can be made positive or negative relative to the common rail by switching the polarity of the cab controlling that rail.

It's kind of funny in way, many people have trouble with hooking the '+' of one power supply to the '-' of another, yet most of them have done the same thing putting batteries in a flshlight without thinking twice about it.

 

That's very helpful to me. I was working my way through the difference between potential and polarity as a way of reconciling the contradiction. 

Funnily enough the remark about electricity being magic sent me down that path. Whether you can "see" electricity is illuminating ( har, har).

Of course you can see light which is an effect of electromagnetism so is electricity in that sense. You can certainly feel potential as static electricity sets your hair on end. Lightning isn't a direct view of electricity because the visible light is an effect of the current passing through the air, not the current itself. You can see the electrons causing the light but not the electrons themselves (assuming for simplicity that lightning is a "flow" of electrons).

The effect of common rail is only "experienced" through the locomotive that closes the circuit. The puzzle is how two locomotives can run in opposite directions each connected to the same common rail. How do those electrons find their way? 

Another source explained it in layman's terms: the electrons leaving one Cab have to return to the same Cab. That makes sense as electricity is just potential until the circuit closes.

I have also confirmed that the MRC 780 is a single transformer twin throttle unit. I had deduced that from the output numbers as compared to the MRC 760 built in the same sized case. That's the reason I encountered the polarity assignmissue at the inputs to the 220.  The very useful coloured schematics posted in this thread show the points at which the blue and the red connect. When using the MRC 780 these points cross connect the single transformer outputs and the unit shorts internally. Had I understood how MRC separately protects the two separate throttles from external shorts the fact that both throttles shorted would have (should have) clued me in.  It is extremely unlikely that an external short could occur for both throttles at the same time. A single external short only cuts out the one throttle affected. The 220 "internal short" was illusory, the actual short would be inside the 780.

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Posted by Overmod on Sunday, June 13, 2021 2:12 PM

Lastspikemike
one of our group of three worked as an electrician years ago and to him white was the hot wire). 

OK, I'll bite on this.  In what retarded imitation version of the NEC or any other valid national code does 'white' denote 'hot' instead of neutral?

In part I'd like to know because I found a "professionally" wired job in Springhill where the wires mysteriously changed colors passing through a junction box.  I attributed this at the time to guild malevolence against 'outsiders' messing with electrician prerogatives (NEC's position being no colors are 'official' and you should always check before tinkering anyway) but perhaps this is some distinctive color aberration taught to apprentices?

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Posted by CSX Robert on Sunday, June 13, 2021 2:10 PM

Lastspikemike
The two "up down" coloured schematics seem to show the short circuit I refer to. The opposite polarities of the powerpacks connect at the Common terminal. That looks to me like a dead short. Why is it not?

This is confusing for many people when they first look into common rail wiring.  Take for example a single 12 volt isolated power supply.  The '+' terminal on that power supply by itself is not actually +12 volts, it is +12 volts relative to the '-' terminal of that power supply.  The voltage at any single point has to be measured relative to some reference point.  With two separate isolated power supplies there is no common reference point.  With common rail cab control wiring, you are creating a common reference point - the common rail.  The control rail can be made positive or negative relative to the common rail by switching the polarity of the cab controlling that rail.

It's kind of funny in way, many people have trouble with hooking the '+' of one power supply to the '-' of another, yet most of them have done the same thing putting batteries in a flshlight without thinking twice about it.

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Posted by Lastspikemike on Sunday, June 13, 2021 2:07 PM

The 220 reversing switch has a center off but this position passes through the connection so isn't really "off".

The grey reversing section switch and the green Cab selector switch on the. 220 both have center off.  

The Twin Switch and the Selector switch both have center off. All have center detent detectable, although the selector switches are pretty vague.

The yellow connector switches are just on/off and have a more limited range of movement.

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Posted by gregc on Sunday, June 13, 2021 1:53 PM

ATLANTIC CENTRAL
I'm going by the drawing and memory, I don't have one here to test.

i do have one and i verified it after.

any reversing switch has just to positions, if not center-off, non-reversing or "pass thru" and reversing.     ... think about it.   why would it have a pass-thru and non-reversing position?

greg - Philadelphia & Reading / Reading

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Posted by Lastspikemike on Sunday, June 13, 2021 1:53 PM

A DC primer would be handy.

I have a common rail system in that all my red wires are connected and three throttles are connected to all the red wires ( although some of the red wires are actually white because one of our group of three worked as an electrician years ago and to him white was the hot wire). 

So, I admit to becoming confused again. Since two of the three throttles are in a MRC 780 then clearly I'm not experiencing the internal short problem. We routinely have the powerpack reversing switches opposed.

My remark about train direction was a serious remark.  We have two loops and one connecting track. The "outside rail" of one loop connects to the "inside rail" of the other loop. We can't have a consistent East West or clockwise and counterclockwise. One loop is always the reverse of the other. The connecting track has neither an inside rail nor an outside rail. No left or right rail if you prefer. 

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 1:31 PM

Ablebakercharlie, I sent you a private message. With any luck the little word "message" to the right of your screen will be red and you can access my message and respond.

Sheldon

    

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 1:02 PM

tstage

 

 
ATLANTIC CENTRAL
Keep this in mind, electricity is magic, you have never seen it, you have only seen what it can do.......

 

You have if you've watched a good lightning storm...or the original Frankenstein movie.

 

I know you're just poking fun, but actually no, lightning is the ionized light produced by electricity, still not the moving electrons.

As a working electrician, I make "lightning" sparks all the time on purpose. When we want to turn off a low amperage (120v, 15/20amp) circuit we are working on, we often just short it out and trip the breaker - presto, the circuit in question is off and easy to identify in the panel.

Sheldon

    

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 12:55 PM

gregc

 

ATLANTIC CENTRAL
The cab reverse switches on the ADDITIONAL Controllers must remain in the center pass thru position on those controllers.

 

the center position (there are no detents) disconnects the ride side terminals from the input side on the left .   the left position is a pass thru, the right position reverses (verified with multimeter)

 
 
ATLANTIC CENTRAL
Only the right most Controller is used as the MAIN LINE reversing switch.

 

i agree because any other would also reverse the polarity going to the X-Y reversing switch

 

 
 

I'm going by the drawing and memory, I don't have one here to test. I sold them to a lot of people, I helped friends wire them years ago, but I never used one on my layout. I had real toggle switches, even at age 12......

They show three positions on the diagram? The instructions clearly say "center position"?

Does not matter, fact remains on intended operation as I described, all additonal Controllers to the left for additional reverse sections should have their cab reverse switches NEVER used and left in whatever position provides pass thru.

Maybe with some luck today I will find my 1957 copy of the Atlas wiring book.....

Sheldon

 

    

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 12:42 PM

Lastspikemike

I know assignment of polarity of the main powerpack is arbitrary but that's not the same thing as there not being plus and minus.

Another aspect of the way ours was wired is to have the reversing switches all set to the same direction for the same train direction.

Anyway, it appears that my particular situation related only the the internal wiring of the MRC 780 which did not show on the schematics so usefully provided in this thread.

Thanks. I believe I now understand. In effect, the MRC 780 does assign polarity but only internal to the powerpack. MRC seems not to mention this as far as I can see. 

 

The Atlas instructions clearly tell you not to use the reverse switch on the power pack - common sense might suggest putting them all in the same position, checking output polarity, and wire the whole system consistantly.

YOU just repeated in different words something I have been saying to you for months and you kept ignoring or challenging - the idea that the direction switch position should be consistant with direction of travel.

I am working on a solution of this OP, and if I have time over the coming week, maybe like my thread about trucks, I will develope a DC Primer, because it seems many who never really used DC to run their trains have very little understanding of its basic principles.

Sheldon

    

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Posted by tstage on Sunday, June 13, 2021 12:35 PM

ATLANTIC CENTRAL
Keep this in mind, electricity is magic, you have never seen it, you have only seen what it can do.......

You have if you've watched a good lightning storm...or the original Frankenstein movie.

https://tstage9.wixsite.com/nyc-modeling

Time...It marches on...without ever turning around to see if anyone is even keeping in step.

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 12:32 PM

Lastspikemike

Well. I'll be darned. Right and wrong at the same time.

Now I understand why my particular arrangement "worked funny". The MRC 760 we connected as a third Cab to run the yard (waste of a powerful throttle that was) never could play nice with the 780. Interesting sparking effects over our Peco diamond crossing and the voltage problem Mel kindly warned me about at one Electrofrog turnout, which we solved by gapping properly and making sure the blocks were always switched properly for through trains.   

When we moved the layout I connected the MRC 760 to Cab A and the second throttle of the MRC 780 to Cab B on the 220 gang. Now the 780 is performing a more usual function of running the mainline from one throttle and the yard from the other. The yard Cab doesn't need to go through the 220. The MRC 760 connects to the whole layout through a 215 selector switch which treats the entire yard as a block from the 760 operator's perspective all the Cab A yard block switches are connected through the one block switch in series with the 220. Cab B connects to all the yard blocks through that same single selector switch. 

Originally, I couldn't quite figure out the wiring I now use. I still can't figure out how to connect three Cabs to the entire layout using the 220 to control reversing sections. We used to have three reversing sections but we now realize you only need two maximum for any layout, to be able to run  any train in either direction anywhere. 

 

ALL of this is exactly why I have little use for conventional power packs, and less use for the Atlas system.....

EVERY DC layout will have a different best solution based on track plan and operational goals.

There is no GOOD "one size fits all".

I have not seen your track plan since you refuse to post drawings or pictures, I have limited understanding of your goals. So I will not presume to know what is best for you.

But I feel fairly confident that when you offer others advice on this topic, it is HIGHLY colored by you own view on what the goals are, and your own experiance meeting your goals.

Respectfully, my experiance has bit more depth, being both an electrical designer who has designed many DC systems for many layouts and having spent years behind the shop counter helping other modelers, so I don't presume to know what others need or want until I am told so.

Sheldon

    

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Posted by Lastspikemike on Sunday, June 13, 2021 12:24 PM

I know assignment of polarity of the main powerpack is arbitrary but that's not the same thing as there not being plus and minus.

Another aspect of the way ours was wired is to have the reversing switches all set to the same direction for the same train direction.

Anyway, it appears that my particular situation related only the the internal wiring of the MRC 780 which did not show on the schematics so usefully provided in this thread.

Thanks. I believe I now understand. In effect, the MRC 780 does assign polarity but only internal to the powerpack. MRC seems not to mention this as far as I can see. 

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 12:21 PM

Lastspikemike

Well, I'll check it again someday. At the moment both my view of the schematic, my testing with my multi meter and my experience wiring ganged 220 say otherwise. I wired ours up wrong and they didn't work. Wiring them correctly, not as shown by Atlas, worked. But then I was connecting a MRC 780 twin throttle powerpack to the 220's.

DC powerpacks have positive and negative output terminals or they wouldn't need a reversing switch to operate trains. Multimeters display reversed polarity, digital with a minus sign and analogue by driving the needle backwards. 

I still say that because the C terminal has to feed the reversing section terminals and that only one polarity reaches the block selector switches that it matters which way around the four input terminals on the 220 are connected to the two powerpacks. But I'm no electrical genius so I may be mistaken. 

Heck I still think all the Cabs must have the same polarity terminal connected to the common rail.....

 

As Kevin pointed out, the reverse switch on the power pack changes the polarty of the output terminals, so there is no plus or minus terminal.....

Your last statement about common rail and polarity does make it clear you are not an electrical genius and that you don't understand transformer theory or DC theory.

Hooked up as intended, and used as intended, the Atlas system works fine.

BUT you cannot use dual packs with a single internal transformer as I stated above, and you need to follow various established conventions regarding reverse sections and common rail.

Use whatever terms you want Mike, but if you want people to understand you, there may be an advantage in using already established terms and definitions......

I power my signal system, cab selector system and switch machines with a multi phase dual voltage power supply that supplies both 24vdc and 12vdc. The first thing you do to build such a system is connect the positive terminal of one DC power supply to the negitive terminal of another DC power supply...... simply magic.

Keep this in mind, electricity is magic, you have never seen it, you have only seen what it can do.......

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Posted by Lastspikemike on Sunday, June 13, 2021 12:17 PM

Well. I'll be darned. Right and wrong at the same time.

Now I understand why my particular arrangement "worked funny". The MRC 760 we connected as a third Cab to run the yard (waste of a powerful throttle that was) never could play nice with the 780. Interesting sparking effects over our Peco diamond crossing and the voltage problem Mel kindly warned me about at one Electrofrog turnout, which we solved by gapping properly and making sure the blocks were always switched properly for through trains.   

When we moved the layout I connected the MRC 760 to Cab A and the second throttle of the MRC 780 to Cab B on the 220 gang. Now the 780 is performing a more usual function of running the mainline from one throttle and the yard from the other. The yard Cab doesn't need to go through the 220. The MRC 760 connects to the whole layout through a 215 selector switch which treats the entire yard as a block from the 760 operator's perspective all the Cab A yard block switches are connected through the one block switch in series with the 220. Cab B connects to all the yard blocks through that same single selector switch. 

Originally, I couldn't quite figure out the wiring I now use. I still can't figure out how to connect three Cabs to the entire layout using the 220 to control reversing sections. We used to have three reversing sections but we now realize you only need two maximum for any layout, to be able to run  any train in either direction anywhere. 

Alyth Yard

Canada

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