Hi,

I have a 6 block system in basic DC. There are 2 controllers so 2 people can run trains either concurrently or individually.
There is a single 12V DC power source that needs to power up to 2 locos and 6 bipolar 3.5V LEDs.

My electrical theory is limited... Would somebody mind taking a look and letting me know if this will work? I've attempted to calculate how much resistance I'll need for the LEDs (there may be any number of LEDs powered from 0 to 6). But I'm unsure if my calculations have provided enough power to run locos and LEDs together...

Help in laymans terms much appreciated!

Download full size diagram

I've noticed an obvious flaw - for some reason I had overlooked both controllers could send power. So I've got negatives from both controllers hitting an LED concurrently ....
Perhaps provide power to the controllers separately?

Okay, first things first, separate controllers 'always' need separate supplies. There are instances where one supply can run more than one controller, but it's unlikely anyone will ever have such an instance. Hence, your second drawing is better than the first.

You don't want to limit the current into your DC controller, so having calculated the resistance for your LEDs seemingly correctly, I would suggest running them at somewhat less than 20mA and consider a series resistor in the order of 560 ohms or more. In addition to this, aside from some very specific circumstances, every LED should have its own resistor, you're using tricolour LEDs, so I would use two, one on each cathode, because I like to be elegant and tweak brightness individually, hence you may find you use different values for different colours. The other acceptable thing may be to use one resistor connected right at the LED anode.

I would use your switches to drive a relay to switch between the track controllers, one side of the switch powering the relay, the other side of the switch deciding which LED is lit, and yes, I would power all the LEDs from their own supply (as in one supply for all the LEDs). If you don't want to go with relays, then I would suggest a four pole switch, giving the LEDs a separate set of switch contacts, isolated from your track wiring.

And this is really neither here nor there, but just a minor thing on your drawing, as neat and logical as you have it, you sort of have the LEDs coloured incorrectly. When looking at the switches, especially toggle switches it's important to remember that the contacts on the base of the switch end up back to front. As drawn, when the switch is pointing toward the yellow you will have the blue LED lit and v.v.

Hi,

.

My electrical theory is limited... Would somebody mind taking a look and letting me know if this will work? I've attempted to calculate how much resistance I'll need for the LEDs (there may be any number of LEDs powered from 0 to 6). But I'm unsure if my calculations have provided enough power to run locos and LEDs together...

Help in laymans terms much appreciated!

you have hit the next step in layout design. we don't use track power for control panel displays.

you need to start using relays with a separate power supply for power.

basic terms

1/ you use a DPDT relay ( just like the switch) to switch track power from the controllers

2/ the switch will control the coil of the relay with one set of contacts

3/ the switch's second set of contacts will be used for the led's ( you will need a resistor for the led

3/ a separate power supply will power the relays and the led's via the switch.  

just test the above before you build it.

When looking at the switches, especially toggle switches it's important to remember that the contacts on the base of the switch end up back to front.

I always thought this too, until I ran into some that didn't... Work of the devil.

I suspected (and dreaded) someone would say "relay" ...
I appreciate the advice and would certainly prefer to follow best practice.

I wonder, could I wire it up as per the diagram - but without the LEDs - just to get trains running (for my boys who are wondering why nothing is changing), then add the LED component later???

As you have drawn your track plan, there is no need for the reversing switch for section B3 as it is not a true reversing loop.

All you do is swap polarity to the rails. For example, The outer rail on the blue block is + the outer rail of the yellow block will be -

You can do it without relays if you are particularly allergic to them. You just need to use switches with more contacts. Relays are definitely the best way to go, but if the goal is purely simplicity then you can do without them.

I like the idea of the controller LEDs, but that said, you could just paint each side of the switch a matching colour to the controller. Use the switch to point between yellow and blue rather than using an LED to display it could be an option.

When looking at the switches, especially toggle switches it's important to remember that the contacts on the base of the switch end up back to front.

I always thought this too, until I ran into some that didn't... Work of the devil.

Yeah, like the odd case when you can use a common source for controllers, and have to use a common resistor for LEDs there is always the exception that proves the rule. Toggle switch contacts are likely to have an exception proving the rule too.

Keeping things simple is certainly strong on my agenda.
A mate made a good point today - what happens when the loco direction is reversed...

How about this, no relays or additional switches but the LEDs are powered before power reaching the controllers (with individual resistors). Shown only 2 blocks for simplicity. If this checks out I'll draw it up neatly.

I suspected (and dreaded) someone would say "relay" ...
I appreciate the advice and would certainly prefer to follow best practice.

I wonder, could I wire it up as per the diagram - but without the LEDs - just to get trains running (for my boys who are wondering why nothing is changing), then add the LED component later???

+1 on planning on the LEDs in a future 'phase 2' .

You've only got a handful of switches so old school approaches will work just fine.  You can always put a big "1" and "2" on each controller and then have "1" and "2" on each side of each DPDT.

Also - why do you need a separate green and pink sections in the connection between the yellow and blue loops?  Seems a little inconvenient to have to flip two switches to cross over?

How about this, no relays or additional switches but the LEDs are powered before power reaching the controllers (with individual resistors). Shown only 2 blocks for simplicity. If this checks out I'll draw it up neatly.

you will have problems with the two power supplies ( mostly if you switch mode types ). just use a single power supply for common rail setup.

a for the led's they will not change colour. fix - common +ve method required if you just using the switch  re the negative leads of the led go to the switch. common of the switch goes to -ve ( using a single power supply)

best option is to get a book - how to wire your layout.  

I suspected (and dreaded) someone would say "relay" ...  

a relay the best option depending on your layout and control box. there are limits to switch's and wires before you have to make the change over  ie 4PDT do take up space and can cost a bit. ( looks like you may hit the limit by using DPDT switch's and changing to a common rail setup ) but it's your choice.

Hi,

having a look an http://www.altronics.com.au/p/z0885-red-green-bi-colour-5mm-led/   you can use the design with a changed setup for the LED's .

you will be using track power the led's will change brightness with the voltage.

the changes =  the led anodes ( +ve) will connect to the track wires of the switch ( red to one side green to the other ) the common cathode ( -ve ) via a resistor will connect to the power supply negative ( not the controller negative as it will not fully work ).

design note - the above works as a method for showing direction it will not show which controller your using.  


note - if you use 2 standard led's and a resistor in a bi direction circuit you just connect across the track wires for direction .

I am going to stick my boof head in here and ask why use this type of switching unless its for cost instead of the system that puts Voltage into the track and each 'locomotive' has a circuit board internally mounted and coded to respond to the controller allowing each 'locomotive' to move independently of each other over anywhere on the layout without the need for 'blocks'?
The method I am thinking of isnt totally perfect but when you consider the time, cost and energy needed to run wire and connect it up makes it worth considering.

I am going to stick my boof head in here and ask why use this type of switching unless its for cost instead of the system that puts Voltage into the track and each 'locomotive' has a circuit board internally mounted and coded to respond to the controller allowing each 'locomotive' to move independently of each other over anywhere on the layout without the need for 'blocks'?
The method I am thinking of isnt totally perfect but when you consider the time, cost and energy needed to run wire and connect it up makes it worth considering.

beginner vs skilled person. a dc layout is fine we all start with one. setting one up with blocks is a good idea. DCC is high cost item to play with if you don't have the basic understanding of wiring up a layout

Yes, the decision to go DC was intentional - to learn and keep costs down. Originally there were to be only 2 independent blocks. If I had anticipated increasing this to 6 blocks DCC may have been more viable.

Returning to the matter at hand, the revised sketch (on pink paper) has power reaching the LEDs before it reaches the controllers. I assumed this would mitigate the issue of variable power reaching the LEDs.

you will have problems with the two power supplies ( mostly if you switch mode types ). just use a single power supply for common rail setup.

No, that advice is totally wrong. You NEVER use 1 power supply with Common Return.

Returning to the matter at hand, the revised sketch (on pink paper) has power reaching the LEDs before it reaches the controllers. I assumed this would mitigate the issue of variable power reaching the LEDs.

may wish to test with a battery and check the diagram.

edit correction - you may have a better parts suppler but you need to check if you have a common '+'ve or '-'ve led.

you will have problems with the two power supplies ( mostly if you switch mode types ). just use a single power supply for common rail setup.

No, that advice is totally wrong. You NEVER use 1 power supply with Common Return.

Kevin is correct, and incidentally, the type of power supply whether it be switching, linear or cold fusion makes no difference to the argument. Almost never common supply to multiple controllers, certainly not with a common anything else.

I've never used common return for traction power. I do use it for signals and points. I've always wired my tracks with separate wires for both polarities, using double pole switches if necessary. Apart from saving a bit of wire, what is the advantage? Figure-8 flex and multi position, double pole switches are not vastly more expensive than the single pole variety. And doesn't DCC hate common return? You can also use a single power supply since all cab blocks are isolated, although I don't given the power requirements.

Is it just a hangover from car wiring, where the chassis is the common return? Even the railways don't use that, both wires are kept separate. Which is why diesels are always quoted as failing with "ground relays" - the relay goes off when it detects a short from either wire to the chassis frame of the loco.

you will have problems with the two power supplies ( mostly if you switch mode types ). just use a single power supply for common rail setup.
No, that advice is totally wrong. You NEVER use 1 power supply with Common Return.
Kevin is correct, and incidentally, the type of power supply whether it be switching, linear or cold fusion makes no difference to the argument. Almost never common supply to multiple controllers, certainly not with a common anything else.

ok  fix the problem the pink sheet. I only posted to drop a single 12 volt power supply to make the job easy.

but the pink sheet does have the controllers wired up as a common rail layout.

note = there are two controllers on every diagram

I've never used common return for traction power. I do use it for signals and points. I've always wired my tracks with separate wires for both polarities, using double pole switches if necessary. Apart from saving a bit of wire, what is the advantage? Figure-8 flex and multi position, double pole switches are not vastly more expensive than the single pole variety. And doesn't DCC hate common return? You can also use a single power supply since all cab blocks are isolated, although I don't given the power requirements.

Is it just a hangover from car wiring, where the chassis is the common return? Even the railways don't use that, both wires are kept separate. Which is why diesels are always quoted as failing with "ground relays" - the relay goes off when it detects a short from either wire to the chassis frame of the loco.

(sorry wandering of track a little) I cannot remember why we did it those many years ago.But In the very early days of MMRS when I was just starting out a PMG (Telstra?) tech was pretty senior in that Club. He provided heaps of scrap wire, relays and PMG "type" intelligence and dominated the layout wiring at MMRS.
First thing we were all taught was to use two transformers and a common return. One transformer pumped out power to the +ve side and a second identical and matched transformer supplied the -ve side. We bought masonite boards painted grey pre drilled for a circle of brass cheese head screws. To these we measured various links of jug element replacement wire, straightened in places to attach to the backs of the cheese heads via washers and two nuts each. A nice handle, center shaft with wiper was loosely fitted to a middle bearing. The off position was unconnected to the jug element and resistance changed as the wipers moved across two cheese heads at a time
Today I would not go that way, but 50 years ago almost everybody used the "Allan Dowel" (?) wiring system, single strand pmg wire ( and all its problems) as well. ugh!!  I still see old layouts still using it, but would love to be reminded of why we used it in the first place? Was it a legacy of three rail systems?
Rod Young

Remember back then (late 50's~early 60's) Tri-ang Transformers (cant remember what Hornby had) put out a 12V DC regulated circuit for Locomotive control and a 16V AC power to switch the Points solenoid.
The DC circuit was regulated by a flat strip of Nicrome steel wire over a Mica board and a wiper blade swept over it to give you power to the 'Locomotive'.

You could add a 'controller' to the AC circuit to convert it to DC and allow you to run another locomotive but it didnt output much current.
From what I remember reading in Hobby books (UK Model Railways and US Model Railroader) was to use another separate transformer to power any signal lights and operate points solenoid.
I have the feeling it was in this context they made use of a 'Common Return' partly to reduce the need for additional wire.
For many years I had a layout/wiring diagram book written by a well known US Railway Modeler whose name I have now forgotten, dammit.
Ignore that, the writers name was Linn Westcott and I have just found out that EVERY issue of this magazine (Model Railroader) from 1934 is available Online.

Hello Gombul,

OK, this post has taken me from lurking to posting.  I've been messing around with electronics for about 40 years so I thought I'd lend a bit of a hand.

I agree that you should have separate power supplies for each controller because there is a potential for things to get a bit smokey if you don't.

What I would do, however, is use 4 pole switches if they'll fit in.  3 pole switches would be fine but they don't seem to be so readily available.  An example is one that Altronics stock, catalogue number S1385.

I would use two poles for the block switching just like your second post, except without the LEDs and the resistors you have drawn.  Then I would use a third pole on the switches for the LEDs.

You only need to use one of the power supplies for the LEDs, which won't draw enough current to be a problem.

I drew up a quick diagram just for the LEDs but I don't have anywhere to host it, so you will have to try to decipher a text version.  Assuming the LEDs are "common anode", connect the common lead through a 720 ohm resistor to the positive of the power supply.  Connect the middle terminal of the switch to the negative of the SAME power suppy and then connect each of the other LED leads to the outer terminals on the switch.

Repeat for each switch.

Hope this makes sense.