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OBRY
5th Jul 2006, 03:44 PM
The Dual-Cab set up works! (Otherwise, no one would use it. :lol: )

One powerpack controls one engine, the other powerpack controls a second engine. So with one powerpack, you can speed up, slow down, and reverse that one engine, meanwhile, the other engine keeps doing what it should according to the setting of the second powerpack.

The trick is dividing your track plan into numerous electral blocks, and keeping the engines in different blocks. As an engine move into a new block, you have to make sure that the toggle switch on your control panel or Atlas Selector is in the right position so that the powerpack is also controling the block you're entering.

There are lots of good books the explain how to do the wiring.

I hope this helps.
If you want further explanation, just ask.
OBRY

Cornreaper
5th Jul 2006, 03:53 PM
Oh, I understand the whole block concept, I'm just confused by the common rail concept, and if 2 power packs can share it. I can use DPDT toggles and have each block completely isolated from one another, but can I use SPDT's and just isolate the positive rails while wiring the common ground right into BOTH power packs? There's a big debate about this at work right now, and it's really making me want to drink!

pbender
5th Jul 2006, 04:06 PM
Common rail wiring with two cabs IS possible, but it's not exactly pretty.

Basically, the cabs have to share a common internally. When they change polarity, they change the polarity of the output from positive to negative relative to the common.

Most commercial power packs simply reverse the possitive and negative terminals when a direction change is made, so they can't be used directly for two cab common rail control.

If the cabs don't share a common, then the two throttles need to be set to run the train in a single direction. i.e. you can have independent speed control, but not independent direction control.

Paul

Cornreaper
5th Jul 2006, 04:16 PM
Looks like I gotta do it the hard way then...the "twice as much soldering" way if you will.....

Another question, what would happen if one loco manages to creep into the next block where the polarity is reversed? Is something gonna fry?

pbender
5th Jul 2006, 04:41 PM
Another question, what would happen if one loco manages to creep into the next block where the polarity is reversed? Is something gonna fry?

Possibly, you basically have a short between the two power packs in this situation. Just don't get distracted while running two trains in opposite directions on a single track.

Paul

dstuard
5th Jul 2006, 04:49 PM
The concept of "positive voltage" vs."negative voltage" is a tricky one for those not of an electrical bent (or should I say "electrically bent" <G>).

The notaion of positive and negative voltage is not absolute, but is based on the voltage of one rail RELATIVE TO THE OTHER.

You can do common rail wiring of course, with one side of each power pack connected to the common rail. The thing to watch out for is when one pack is set for "eastbound" (assume the power rail is positive compared to the common rail) while the next block is "Westboauns (the power rail would thus be negative compared to the common rail). The voltage across the gap between the two power rails would then be the SUM of the output of the two packs.

In DCC systems, common rail wiring is verboten for this reason (since DCC voltage is always full-on). Any common connection is generally at the halfway point between the two rails (so each rail swings say +6 or -6 V from the common, giving a rail-to-rail voltage of 12V -this being and alternating voltage).

All of that said, the only real cost to using "direct home" wiring instead of the common rail approach (other than a few feet of wire) is all of those Atlas Selectors, which are based on the common rail.

If you ever convert to DCC, you'll want to have direct home wiring anyway.

Doug

Cornreaper
5th Jul 2006, 06:03 PM
Ok, now I'm really confused. Check out this NMRA link.

http://www.nmra.org/beginner/extended.html

Or just read this, taken from the bottom of that page:


You now have your layout wired for dual cab control and can run two trains at a time as long as the trains are never in the same block at any given point in time. You can even run the trains in the opposite direction with no problem as long as they aren't in the same block at the same time. (NOTE: You may think that with trains running in the opposite direction would cause a short as you will have both positive and negative current running in the common rail/wire at the same time. This is not the case as all electricity returns to its own source. So the negative electrons from Cab A will not interfere with the positive electrons from Cab B as they are two separate sources.) ENJOY!!!.

So where does the truth lie exactly??? LOL, I need a beer or 10 at this point!

turbine682
5th Jul 2006, 06:09 PM
Hi,

I recently completed 2 cab, common rail, block wiring (DC, so I'm running track). I have relied on both the Atlas "How To Wire the Railroad, blah, blah" publication, and I use Atlas SELECTORS which I purchased in 1991.

COMMON RAIL: It doesn't matter which rail you select, as long as you are consistant throughout the entire railroad. Some folks will say, "it goes on the outside rail" Follow the outside rail through a crossover, and at the other side... you're on the inside rail.

How many do I need? You can't have too many. There is probably some formula for how many commons for how many feet. I THOUGHT that the power would be disrupted depending on whether a turnout was open or closed (I'm using Atas) but apparently this is not so. I have 7 commons on an 18' x 26" switching layout. Perhaps someone else is better versed on this matter.

CONTROL RAIL: This is the rail where you will put insulated joiners to establish your blocks. They will always be opposite the common rail. Again, these must be consistent throughout the RR. You MUST place an insulated joiner between crossovers.

BRIDGES, BUSES: I HIGHLY recommend the use of bridges. You can wire all of your feeds from the RR to bridges, and then wire feeds from the bridges to your control panel. Keeps things neat, easier to troubleshoot, move wires, add wires, blah, blah, blah.

LABEL EVERYTHING! Feeders, Bridge Terminals, Control Panel toggles, blah, blah.

USE COLOR CODED WIRE as much as possbile. I tried to stick with Black for Common, Green for Mainline, Red for Stubs.

TEST ONE OR TWO BLOCKS at a time - Don't wire the entire railroad and then test it. You should be able to run your entire railroad from both cabs with only 1 block installed to make sure everything is working correctly.

Crossing blocks, and other operator errors. :roll: There have been times when I crossed blocks. :hit: Engine X is running from Cab A and crosses into a block where ENGINE Y is running CAB B, etc. ,etc. You will know right away that something is not right, but I have never had any shorts, engine fries, control panel blowup, etc. You just know something is wrong (if you can see it) and you just start shutting stuff off.

I currently have 20 blocks and sometimes my hands get full running two trains. I try to keep the cabs assigned to an "upper railroad" and a "lower railroad". Depending on what I'm doing, I really have to plan especially if I'm flipping cabs / blocks because I've got trains following or meeting each other.

ANYWAY... It's a hoot, and a well planned and executed wiring job can lead to some fun and drama! :wink:

Hope this helps... excuse the long monologue

--Ed

dstuard
6th Jul 2006, 10:39 AM
So where does the truth lie exactly??? LOL, I need a beer or 10 at this point!

WARNING!!! Do not read the following until you reach the 3-beer level!

Don't look now, but there are no positive electrons (I know, I cried too when my momma told me)! Electrons are always negative, and electrical current is the flow of electrons from negative (i.e., where there are an excess of electrons) to positive (where there is a shortage of electrons) - although most folks think of current flow from positive to negative - it's easier to visualize and doesn't make much difference so long as you are consistent. It's sort of like high pressure, low pressure and wind in metorology).

All "Positive" means in a dual-cab context is that the control rail is positive with respect to the common rail (loco goes forward), while "negative" means that the control rail is negative with respect to the common rail, and the current flows in the opposite direction (loco goes in reverse).

Resume drinking.....

Doug

pbender
6th Jul 2006, 01:16 PM
Reading through Doug's comments made me realize something I had forgotten when I made my previous post (when I said you needed an internal common to make independent directional control work).

What I realized was that when the two throttles are set in the same direction, you have two batteries connected in series (and, as Doug pointed out, the measureable voltage between the two non-common rails is the sum of the voltages from the two supplies).

Similarly, when the two throttles are set in opposite directions, you end up with the two supplies connected in parallel.

This transition from a series circuit to a parallel circuit is what makes independent direction control work with a common rail, and with that kind of circuit, it doesn't matter if the common is formed internal to the supply or external to the supply.

Paul

Cornreaper
6th Jul 2006, 01:34 PM
Wow, I really have no clue about electricity! It's amazing how many different worlds this hobby delves into. All part of the learning process...

So, I guess I'm back to common-rail wiring....the general consensus now seems to be that even with common rail wiring, I can run eastbound and westbound trains at the same time with no ill-effects provided they're not in the same block.

I've also read that CR wiring is not condusive to any potential future DCC upgrade. This is just a small door layout, so I really have no interest in converting it to DCC at any time. When I chose to go the DCC route, it will be when I own a home and build a large railroad empire.

Thanks for the input, all!

Cornreaper
6th Jul 2006, 01:44 PM
OK, here is a diagram I whipped up in MS Paint. I am by no means a schematic artists, so it might be a bit messy, but I think it gets the point across nonetheless. It also includes the wiring for the remote turnouts in the staging area.

Are all my ducks in a row on this one? Sorry it's a large image, but some of those lines are only 1 pixel wide, so shrinking it might render them invisible!

http://www.uploadfile.info/uploads/f9b8a69d2e.jpg (http://www.uploadfile.info)

dstuard
6th Jul 2006, 03:41 PM
Looks good. The interesting thing is that, since you've double gapped all blocks, you could go with either common rail wiring (as you did by tying all the black feeds together), ot you could switch BOTH the red and black wires by using DPDT cab selector switches and have Direct Home wiring (remember, lots of small layouts use DCC, and Digitrax Zephyr isn't all that expensive! Ya never know! <G>).

The only other comment I would make would that you should feed turnouts from the point end and, unless you intend to use power routing turnouts, you should also have feeders on all sidings beyond the turnouts (i.e. dont trust power fed on leg "A" of a turnout to also power leg "B".

:pint: :pint: :pint:

Doug

BTW, the road (or should I say track) to my EE degree began with first Lionel train set!

turbine682
6th Jul 2006, 04:02 PM
Hi,

Sorry I can't help you regarding the wiring to your toggle switches.

Here's a thought: I counted 8 blocks. TWO (2) Atlas SELECTORS (each with 4 terminals) will allow you to control 8 blocks. They've gone up to 7.95 each according to the Atlas site; however, these will greatly simplify your wiring task. All you need to do is connect the feeder from the track block to a terminal on the selector and the selector takes care of everything else, i.e., switching that particular block between CAB A and CAB B.

Unfortunately, selectors take up control panel space and don't look nearly as clean as toggle switches. :(



I can run eastbound and westbound trains at the same time with no ill-effects provided they're not in the same block.

CORRECT :!: (one on CAB A and one on CAB B)

You can also run two trains in the same block in the same direction from ONE CAB. I do this on occasion to park two engines on the same siding. 8)

Heheheheh, you can have two trains following each other (on CAB A). Let train A pass turnout Q, then throw the turnout so train K cruises onto block G (which happens to be powered from CAB B) so hopefully you have CAB B set to the correct DIRECTION, otherwise.... :twisted:

Hope this helps, have fun!

--Ed

OBRY
6th Jul 2006, 08:23 PM
Hi again,

Nice diagram. Just a couple of comments.

While this wiring will work, most people run the wires into terminal strips rather than directly from each block to the toggle switches. This can help in any future debugging process. (See the NMRA diagram in the link you included earlier.)

I agree with dstuard that. . .


you should feed turnouts from the point end. . .

However, with Atlas turnouts, there is no need for you to. . .


also have feeders on all sidings beyond the turnouts (i.e. dont trust power fed on leg "A" of a turnout to also power leg "B".

As long as the block is a reasonable length (under 8 feet including all diverging routes) and you've got snug rail joiners and/or good sodering, one power feed is adequate.

Cheers,
OBRY

pbender
6th Jul 2006, 10:19 PM
you should feed turnouts from the point end. . .

However, with Atlas turnouts, there is no need for you to. . .


The reason for doing this is as much to avoid problems down the road as anything else.

These turnouts route power around the frog with wires that are run through the ties. Due to the small gauge of the wires, this is a relativly high resistance path. Also, those under-tie feedsfeeders seem to be prone to failure for some reason.





also have feeders on all sidings beyond the turnouts (i.e. dont trust power fed on leg "A" of a turnout to also power leg "B".

As long as the block is a reasonable length (under 8 feet including all diverging routes) and you've got snug rail joiners and/or good sodering, one power feed is adequate.


You should NEVER trust unsoldered railjoiners to carry power. Temprature variations cause the rails to contract and expand, and unsoldered railjoiners are a prime candidate for dust and grime collection. Both of these conditions can lead to intermittent open circuits over time.

Paul

Cornreaper
6th Jul 2006, 10:30 PM
Well, I think I will go with terminal blocks, and I plan on soldering every joint. I'm aiming for maximum power flow here, so I will take any advice you guys have to offer! I don't wanna be dealing with these problems in the future. I'm still stickin' with DC though!

Thanks for all the tips.