Model Train Forum banner

1 - 20 of 235 Posts

·
Registered
Joined
·
169 Posts
Discussion Starter #1
Hi there,

I hope this is in the right forum. I am building/have built a 6' x 4' (1800mm x 1200mm) layout. At the moment it is connected to DC for testing purposes - inclines, curves, etc., - which is now almost complete except for tunnels scenery and other bits & pieces. I have a Digitrax DCS50 ready to go when I have completed my control panel - signals, points (as we call them here in Australia), and scenery lighting - to run DCC.
Now I need some help/advice. I have attached a jpg of my layout along with text to explain the volt readings at the track joints with circled numbers.

At the moment the running direction is anti-clockwise, but by using the crossovers at PM 5 - PM 8, direction can be reversed. This part of the layout is my dilemma as the polarity reverses on that section when going from straight running, through the crossovers to the other tracks. What do I now have to do to correct this "imbalance"? I do have some knowledge of DC, albeit 55 - 60 years ago when I was an apprentice electrician, (the brain cells aren't as good now as back then!) but am trying to come to grips with DCC. Once the crossovers are used I can institute reverse running, then back to normal. Also note in the layout jpg, there is a long station platform where points PM 2 to PM4 are located. The platform ends just past the temporary power supply location. This platform is the common starting point.

What I would like to know - and I think this is correct - I need at least one auto-reversing unit at the crossover. Also where and how many droppers do I need to connect to the DCC Bus? Also do I need insulated rail joiners anywhere - (hopefully not!!). :)

Sorry for such a long post, but I want to get moving on sorting out the electricals before doing the scenery and tunnels. (Upper tunnel on left end of layout at the points.) Only the first part of the left hand end of the crossovers are in the tunnel.
 

Attachments

·
Registered
Joined
·
2,953 Posts
You don't say if the crossover is a self contained unit or made from four turnouts. No matter, you won't need any auto reversing units, but you will need insulated joiners at points 1, 2, 3 & 4. Sorry I've just seen its made from sectional track. And also on the straight sections between PM 6 & 7 and PM 5 & 8 plus one at 5. As for power feeds these would need to be at PMs 5, 6, 7, 8 & PM3 at the bottom. This should be enough to supply the whole layout. That's how I see it unless I've gone wrong somewhere!
You will also need an insulated joiner at R600 near PM4.
 

·
Registered
Joined
·
169 Posts
Discussion Starter #3
Thanks Cycleops.

Would I require insulated joiners on both rails, or just one? Or better still, - if it's not too much trouble - would you be able to copy the attachment and mark the position of the joiners and send via PM? Also I thought of adding feed droppers at all the points where I have "+" & "-" marked. Would that be "overkill"?

At my age - 70's - I have forgotten a lot of my electrical theory, as I have been retired for about 15 years. :( Therefore that is why I have posted this thread.

Thanks again for your reply.
 

·
Registered
Joined
·
2,953 Posts
No problem, I'll try to copy it and make some notes on the plan and pm you. I've had another look at it and your power feeds are all fine, except you have a few too many.
 

·
Registered
Joined
·
169 Posts
Discussion Starter #5
Ok, thanks Cycleops.

Just cross out the power feeds I don't need. :) They were where I measured the polarity and voltage on the joints. I assume the insulated joiners will prevent any shorts - if there are any? :)

Those polarity and voltages: note on the 3 tracks on the left, 2 are "+" & "-" and 1 is "-" & "+".
 

·
Registered
Joined
·
1,018 Posts
Since you have already discovered the polarity conflicts causing your shorts, you will need auto reversers or manual DPDT switches to avoid the shorts while running trains. The insulated joiners will prevent the shorts on the powered static track, but when the trains cross them, the short is made again.
 

·
Registered
Joined
·
5,242 Posts
If your layout is working fine with DC, it will work just fine with DCC.
A short is a short. If no short in DC you won't have any with DCC.
I don't think you can have too many feeders. I hope to have feeders
to each piece of track on my new layout. It might be overkill, but won't hurt a thing.
 

·
Registered
Joined
·
169 Posts
Discussion Starter #8
Thanks Mopac for your reply.

If you refer to the 2 attachments in my original post, you will see in the second attachment where I state the main voltmeter drops from 15.9V to 4V indicating a short.
 

·
Registered
Joined
·
5,242 Posts
I must admit I did not look at the 2nd one. Volts all looked good on first and
I made my post. Maybe I am missing something but I don't know how you
could take measurements with a short. My DC transformer's circuit breaker
would blow with a short and shut off. Yes you have a voltage drop but I don't
know if it is a short. Looking at the diagram of your layout I don't see a short.
I don't claim to be an expert though.
 

·
Registered
Joined
·
8,458 Posts
We had a very similar reverse loop problem to this on another layout
a few weeks ago involving a double crossover.

I drew out your layout using red for 'left' rail and black for 'right'.
You should do the same. It would guide your track drop wiring.

The designers of a double crossover assumed it would connect
two parallel 'mainline' tracks. Thus it is internally connected
electrically to that end. Thus when a double crossover is
involved in a reverse loop situation all 4 tracks it is connected
to must be left rail RED right rail BLACK.

Thus when you connect your tracks in the 'parallel' manner
I suggest, the track design then creates TWO different sections that
would need to be isolated and use a reverse loop controller.

#1 would be from the PM4 lower right turnout up into the 'figure 8'.
It would require insulated joiners between that turnout and
the track and again a 'trains length' within the 'eight'.

#2 would be from the PM2 lower left turnout up to the exit from the
'figure 8'. It would require insulated joiners to the left of
the lower left turnout and a 'trains length' toward the
eight exit.

I use the term trains length because if you have lighted passenger
cars you want them to be clear of the insulated joint when the
loco is crossing the next one else you would have a short again.

This would require two reverse loop controllers. I have seen Digitrax
AR-1's on Amazon for around 30.00 each.

The reverse loop controllers would take power from your main DCC buss.
The output of each would go to the isolated section associated with
it. They are fully automatic, usually placed under the table and once
installed you never bother with them again.

A short primer on how they work. When the loco wheels span
the insulated joiners a short circuit is created. The RL controller
senses that and very quickly reverses phase (polarity) of the isolated
section to match the main. The loco continues without pause and
when it spans the 'exit' insulated joiners another short is detected
by the controller and it again reverses the phase and the loco
continues on it way. Obviously this will work with DCC only else
the loco would reverse as polarity changed.

The crossing in the 'figure 8' would not require any
special insulated joiners or wiring. Track A current
does not connect to the rails of track B crossing it.

The slight voltage variations you are show are not of concern.
If they were greater you may want to increase the number of
track drops, or solder joints.

On this layout I would have drops adjacent to the double crossover
in both tracks and also the main at the bottom. The isolated sections
would get their power thru the RL controller. It should get it's power
from the main buss.

Don
 

·
Registered
Joined
·
500 Posts
This is one way to do the reverse-track-section (denoted in red). The thick-red-lines denote double-isolation-gaps. The bottom two double-isolation-gaps could be move back on their reverse-track-sections to suit your purposes. This all assumes that I have not misunderstood your layout.
Bob
 

Attachments

·
Registered
Joined
·
8,458 Posts
Bob

I know you are pretty sbarp on these situations, but,
are you saying that the ONE isolated 'reverse loop' section is
the entire track shown in RED on your drawing?

Pretty long isolated section.
Wouldn't that be open to more than one loco entering it
from any of the various turnouts? That could be quite an
electrical short. It is usually recommend that an isolated
section be no longer than the longest passenger train with
lighted cabooses, with only the two ends as open to entry.

Don
 

·
Registered
Joined
·
169 Posts
Discussion Starter #13
Thanks for all your replies. I'm starting to get a bit overwhelmed now. :confused:

Remember, I am testing with DC, but the finished article will be DCC. :) So I realise that obviously I may be a bit off with those volt readings. As I said in reply to Cycleops, I have been retired from the electrical industry for 15 - 20 years, and the old brain cells aren't what they used to be. :p

All I want to do is get things running properly and start on the scenery, etc. I eventually will suspend the layout from the ceiling of the garage, by ropes/wire and pulleys connected to a hand operated boat winch. "She who knows best" is pushing for this to happen. I want to get my car back in the garage to keep her's company. It's been on its lonesome for about 6 months now!!

In response to Mopac's reply, my DC controller is one I built myself from a kit. Using an input transformer of 240V AC to secondary of 6/9/12/15V then thru a bridge rectifier from the 12V AC for the DC, using the 15V AC for accessories.

Thanks again guys.
 

·
Registered
Joined
·
500 Posts
Don,
but,are you saying that the ONE isolated 'reverse loop' section is
the entire track shown in RED on your drawing?
Yes!

Pretty long isolated section.
Wouldn't that be open to more than one loco entering it
from any of the various turnouts? That could be quite an
electrical short. It is usually recommend that an isolated
section be no longer than the longest passenger train with
lighted cabooses, with only the two ends as open to entry.
In my understanding this is always a problem (except for simple one-turnout-reverse-loop). The user (OP) is really the only one that can decide what suits his needs. I would have trouble controlling more than train-unit at a time on this layout, so I suggest the referenced solution. The “reverse-track-section” could be made into two reverse-track-sections by adding another double-isolation-gap” at the double-crossover. I also previously suggested the following to the OP, “”The bottom two double-isolation-gaps could be move back on their reverse-track-sections to suit your purposes.”, thus shortening the “reverse-track-section”.
Bob
 

·
Registered
Joined
·
169 Posts
Discussion Starter #15
Don,

In my understanding this is always a problem (except for simple one-turnout-reverse-loop). The user (OP) is really the only one that can decide what suits his needs. I would have trouble controlling more than train-unit at a time on this layout, so I suggest the referenced solution. The “reverse-track-section” could be made into two reverse-track-sections by adding another double-isolation-gap” at the double-crossover. I also previously suggested the following to the OP, “”The bottom two double-isolation-gaps could be move back on their reverse-track-sections to suit your purposes.”, thus shortening the “reverse-track-section”.
Bob
Now you've got me more confused than when I started. :confused::confused::confused:
 

·
Registered
Joined
·
169 Posts
Discussion Starter #16
Don,

In my understanding this is always a problem (except for simple one-turnout-reverse-loop). The user (OP) is really the only one that can decide what suits his needs. I would have trouble controlling more than train-unit at a time on this layout, so I suggest the referenced solution. The “reverse-track-section” could be made into two reverse-track-sections by adding another double-isolation-gap” at the double-crossover. I also previously suggested the following to the OP, “”The bottom two double-isolation-gaps could be move back on their reverse-track-sections to suit your purposes.”, thus shortening the “reverse-track-section”.
Bob
Now you've got me more confused than when I started. :confused::confused::confused:

All I want to do, (and my grandson), is start at the bottom, round the outer track, straight through at the top - through points, oops sorry turnouts :p then down the middle track through PM 1 & PM 3, then to the left at PM 4, through the X crossing then straight through PM 6 & PM 7 to the X crossing again down to lower tunnel, through PM 2, Then PM 3 and straight through PM 4 to PM 5, then through the crossover to PM 6, round the figure 8, back to PM 4, through PM 3 and PM 2 and to terminate at the original start. I will probably form another route using PM 8 & PM 7.
 

·
Registered
Joined
·
8,458 Posts
We understand that you wanted a continuous running layout
with some interesting routing. But you have a 'reverse loop'
situation that must be electrically correct or you will have
a short circuit.

I can understand your confusion when you read the discussion
of Bob and me. We both have a solution to your electrical
problem, either would work, but you will have to decide which
would work better for you.

Since you have had electrical experience you should have no
problem understanding the circuits. Think of the rails
as a 2 wire pair; that is the way the function.

Again, I suggest you
draw your layout Starting from the double crossover. Use
Red for one rail, and black for the other. You will then see
where a short circuit exists when a turnout is thrown.

It won't matter whether you test with DC or DCC. The short
will be there unless something is done.

But again to Bob, it seems to me that this layout would lend itself
well for more than one train running at the same time. It will
be DCC per the OP and thus both locos would be fully under
control of the operator. For that reason, I still prefer my
solution.

Don
 

·
Registered
Joined
·
924 Posts
The letter"r"helps denote thecolor code and polarityof wires of main buss.

DonR, I don't want to be a nit picker here, but I believe, you may have your color combinations
reversed. I think the NMRA recommended practices calls for the Right rail to be Red in color.
And the Left rail to be black in color. That is due to the layout started out most likely with dc
voltage. And was later converted to DCC. The color code for dc voltage is red =(+) and
black=(-). An easy way to remember this is with the letters that make up the word with an "r"
where the letter "r" can stand for right, and also the color red. That is how I keep the color code correct. Regard's,tr1
 

·
Registered
Joined
·
169 Posts
Discussion Starter #19
NMRA recommended practices calls for the Right rail to be Red in color.
And the Left rail to be black in color.
I looked on the NMRA web site and after a bit of digging, I discovered that is correct.

Again, I suggest you
draw your layout Starting from the double crossover. Use
Red for one rail, and black for the other.
I'm about to do that tonight. I will attach to a later post.

Thanks
 

·
Registered
Joined
·
8,458 Posts
DonR, I don't want to be a nit picker here, but I believe, you may have your color combinations
reversed. I think the NMRA recommended practices calls for the Right rail to be Red in color.
And the Left rail to be black in color. That is due to the layout started out most likely with dc
voltage. And was later converted to DCC. The color code for dc voltage is red =(+) and
black=(-). An easy way to remember this is with the letters that make up the word with an "r"
where the letter "r" can stand for right, and also the color red. That is how I keep the color code correct. Regard's,tr1
I just was not thinking of the NMRA, I most certainly defer to their
standards. The important thing tho is drawing out the rails as if they
were electrical wires. That always shows up the problems.

Don
 
1 - 20 of 235 Posts
Top