Multiple DC power packs

[Joe Satnik]

Dear All,

Just a warning:

If two power packs are connected, and the voltage levels are different or opposite polarity from one another, significant damage can occur to either or both power packs. 

If you try to run multiple DC power packs on your layout (i.e., multiple "throttles" or "cabs")

you run the risk of connecting one power pack to another, either through

1.) a mis-wire, or

2.) "bad block switch selections" and a wheel rolling (connecting) across a gap between blocks, or

3.) "bad block switch selections" and 2 trucks on a loco (or other rolling stock with 2 truck electrical pickup) straddling a gap between blocks.

If you are wired properly using the correct electrical (block) switches, you would be prevented from connecting one power pack to another on an empty layout. 

This type of wiring (block, multi-throttle, multi-cab) is shown in many different books, including "The Complete Atlas Wiring Book" (Atlas book #12).

Hope this helps. 

Sincerely,

Joe Satnik

[phillyreading]

Also along with what Joe S. mentions, the old Lionel ZW does this, with two or more positve side outputs from the same transformer the voltage doubles; example 16 volts can become 32 volts. This depends how your transformer is wired.

Don't think you need to worry about this with DCC.

I am not sure how H.O. multiple output transformers work, but would like to advise not to hook-up two outputs to the same set of rails, unless you have current protection devices in the circuit.

Lee F.

[Desertdweller]

All you have to do is divide the track into isolated blocks by gapping one rail only.  Make sure all your gaps are in the same rail.

The ungapped rail is the "common rail".  It can be wired directly to the same polarity terminal of all the power packs.  You need to determine the polarity of the track terminals on the power packs and wire them together with a jumper wire.

Each powerpack is then wired to the isolated secions in the other (gapped) rail, by routing the power from the remaining DC terminal through a DPDT switch, or, in the case of more than two powerpacks, through a rotary switch with multiple poles.  An Atlas Selector can be used to obtain four DPDT switches on a single panel.  This is explained in the wiring book mentioned in the previous post.

If this is done, it will be impossible to connect more than one powerpack to the same section of track simultaneously.

Reversing sections (reverse loops, wyes) are a little more complex.

This system has an advantage in that if the power throttles are turned off, no power reaches the track.

Les

[WTierce1]

All you have to do is divide the track into isolated blocks by gapping one rail only.  Make sure all your gaps are in the same rail.

The ungapped rail is the "common rail".  It can be wired directly to the same polarity terminal of all the power packs.  You need to determine the polarity of the track terminals on the power packs and wire them together with a jumper wire.

Each powerpack is then wired to the isolated secions in the other (gapped) rail, by routing the power from the remaining DC terminal through a DPDT switch, or, in the case of more than two powerpacks, through a rotary switch with multiple poles.  An Atlas Selector can be used to obtain four DPDT switches on a single panel.  This is explained in the wiring book mentioned in the previous post.

If this is done, it will be impossible to connect more than one powerpack to the same section of track simultaneously.

Reversing sections (reverse loops, wyes) are a little more complex.

This system has an advantage in that if the power throttles are turned off, no power reaches the track.

Les

Actually that won't work because then you can't reverse the trains separately, they will both have to be running in the same direction to keep the polarity the same in both track sections. If one rail is connected and not insulated, then you will have a short if you reverse one train and not the other.

[poliss]

If using two controllers they should have seperate transformers as shown on Brian Lambert's website.
http://www.brian-lambert.co.uk/Electrical.htm
You must never connect two seperately powered DCC controllers to the layout. Boosters should be used. See the DCC section on the same website. http://www.brian-lambert.co.uk/

[richg]

Our club used four throttle's and fourteen blocks, common rail, for many years. The layout also had a master reverse switch. We had homemade throttles that used the 2N3055 transistor and all had circuit breakers.
The only issue we was, Who has my train? We also had a dispatcher at the control panel switching blocks for operators and sometimes was gabbing. Operators had to ask for the next block and sometimes forgot to.
I made and installed single target lights at different blocks and sidings using red/green LED's which made it easier to ID your block. You got a red if your throttle was not selected for the next block.
We are only boys playing with toys.

We switxhed to DCC early 2000.

Rich

[Desertdweller]

wtierce,

One of us must be missing something.  I would refer you to the publication mentioned in the original post.

I've been using this system to run trains since 1968.

Les

[jward]

All you have to do is divide the track into isolated blocks by gapping one rail only.  Make sure all your gaps are in the same rail.

The ungapped rail is the "common rail".  It can be wired directly to the same polarity terminal of all the power packs.  You need to determine the polarity of the track terminals on the power packs and wire them together with a jumper wire.

Each powerpack is then wired to the isolated secions in the other (gapped) rail, by routing the power from the remaining DC terminal through a DPDT switch, or, in the case of more than two powerpacks, through a rotary switch with multiple poles.  An Atlas Selector can be used to obtain four DPDT switches on a single panel.  This is explained in the wiring book mentioned in the previous post.

If this is done, it will be impossible to connect more than one powerpack to the same section of track simultaneously.

Reversing sections (reverse loops, wyes) are a little more complex.

This system has an advantage in that if the power throttles are turned off, no power reaches the track.

Les

Actually that won't work because then you can't reverse the trains separately, they will both have to be running in the same direction to keep the polarity the same in both track sections. If one rail is connected and not insulated, then you will have a short if you reverse one train and not the other.

wtierce,

that is so not true. common rail wiring has been the standard for dc wiring for at least 50 years. the two controllers will operate independently of one another regardless of polarity. reversing one controller does not short out the other. remember, they are each connected to different blocks, not the same section of track.

[M1FredQ]

someone mentioned ZW

when I hooked up my "old" ZW everything was fine except I can't get any of the trains

to whistle, horn or sounds.

Any suggestions

I went back to using the CW-80 so we can have rail sounds

[Desertdweller]

wtierce,

I tried to reason why an ungapped common rail could serve as half a circuit when the other (gapped) rails were of differing polarity.  It didn't make sense to me, either.

So I went downstairs to my model railroad to test it out.  With locos in two different blocks, I connected each one to different power throttles and set them to run in opposite directions.  Each one ran in the direction selected.  This works with both throttles in use at the same time.

My railroad also uses a double-track main line.  Sometimes I enjoy running trains on both loops at the same time in opposite directions.  Both main mines use a common rail for half of the circuit, ungapped.

Logic would tell me the common rail would have to be carrying current of opposite polarity at the same time, and for all I know, it does.  I can't tell you why it works, because I don't know.  But it does work.

Les

[jward]

the explanation is simple:
the common rail is being used as a common return. the rail may be carrying current of opposite polarities, in theory. in reality, since there is no connection between the power supplies other than the common rail, they won't short out. a locomotive completes the circuit between the rails, and the circuit it completes is only connected to one controller. if you have a locomotive accidentally straddle the block boundary between two power packs, then it completes the circuit to both. if they are of differing polarities, the locomotive will often "dance" back and forth. it will also cause a short circuit in this situation. but if it is within the block, it will only take power from the controller connected to that block.

this concept is also often used in computer and electronic applications which require both a positive and negative power supply.

[Desertdweller]

Thanks, Jeffery.

So it is possible for the common rail to be carrying both positive and negative charges at the same time, to complete two circuits that are isolated on the other side?

I can think of no other explanation for why this works.  But there is no question that it does work.

In my simplistic mind, I always envision a stream of moving electrons, like water in a pipe.  The analogy breaks down when the "water" has to flow in opposite directions at the same time.

So a mutimeter, with one lead attached to the common rail and one to the gapped rail, would always show the common rail to be opposite of whatever polarity was applied to the gapped rail.  If you had two multimeters, and attached them as bridges between the common rail and two gapped sections powered with opposite polarity of each other at the same time, one multimeter would show the common rail to be positive while the other, at the same time, would show the common rail to be negative.

I get it!  Ain't nature grand?

Les

[jward]

you pretty much have it. and because this works so well, wiring a layout for dc uses only half as much wire as it otherwise would.

[Joe Satnik]

Les,

Currents are additive in the single common return wire.     

If Power Pack 1 is running a loco forward in Block A, its current goes through the loco and back through the common rail, through the common wire, and back to the other side of of Power Pack 1.  Power Pack 1's outbound current is the same as its return current.

Same with Power Pack 2 and Block B.  Separate isolated path going out, shared common rail and single common wire coming back in, with the current eventually coming back to the other side of Power Pack 2. 

Again, currents add in the single common wire.

I guess the "magic" is that each power supply takes back from the single common wire exactly the number of electrons it sent out....though the wire would contain a mixture of electrons from both power supplies...

So, if both locos are drawing one-half amp (0.5A), the common wire current would be one amp (1.0A), as currents are additive. 

Now, reverse the direction of one of the locos.   The current in that block is now backwards, or opposite polarity, or -0.5A, or negative one-half amp, or minus one-half amp. 

The currents are still additive.  0.5A + -0.5A = 0 amps, so no current is flowing through the common wire back to the power supplies.   

Mystery..Both power supplies are putting out 0.5A, though one in the opposite direction, and both locos are using (drawing) 0.5A, though one in the opposite direction.  Current requires a complete, unbroken circuit (from the word "circle") to flow, though there is zero flow back through the single common wire...... (Hint 1, there is still current flow through part of the common rail and the common connection between the supplies)

Sketch out the circuit(s) to solve the mystery...

Jim Banner, you're good at drawing.....

Hope this helps.

Sincerely,

Joe Satnik



   

[Desertdweller]

Thanks, Joe.

I spent 18 years in Minnesota.  And started model railroading (and actual railroading) there.

Les