LED lighting for station building

[ellocoloco]

Hi all,

 

I know this subject (or similar) has been on the forum recently I cannot find it!!!

 

I am building a station building and considering using 3mm LEDs for lighting. Of the selections on Ebay, would it 3v or 12v required? I would be using 6/10 LEDs  - design not finalised yet - and power would be taken from a fixed voltage 12v supply, probably the side of an HM Duette. Also do I need a resister wired in, if so what spec,and should they be wired in series or parallel?

 

Any help or directions to previous post would be appreciated.....

 

Thanks in advance.

 

 

[Rog RJ]

If the leds are 12volt then they will have a resistor built in and can therefore be connected directly to a 12volt supply.

3 volt LEDs will need a resistor to be fitted in series with each one.

 

I don't recommend using the 12volt supply from the Duette as it is not regulated  Far better to use a separate regulated power supply.

[Chrissaf]

Also do I need a resister wired in, if so what spec,and should they be wired in series or parallel?

.

Definitely wire the resistor in series with the LED......if you did wire the resistor in parallel across the LED, the LED would not be protected and burn out. As a rule of thumb, 1,000 Ohms (1K0) is the most common value. Any generic resistor with that value will do. Typically 5% tolerance (or better, if you have deeper pockets). 1/4W power rating. Although, 1/8W is perfectly acceptable too. The LEDs are better off being wired in parallel with each LED having its own dedicated resistor. Like Rog above, I would use a regulated DC supply dedicated for the task.

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https://www.hornby.com/uk-en/forum/installing-lighting/

 

 

[ellocoloco]

Thanks to both of you - the link was what I had seen before but could find again............

 

One more thing, does the resistor connect to the Anode (long leg)??

[Chrissaf]

Technically it doesn't matter what side of the LED the resistor connects to. My personal choice is to standardise where ever possible to connect to the LED anode (positive leg). The reason being, that some time later if you need to diagnose a fault. You then know that the resistor is on the positive side of the LED, as you can't see the long positive anode LED leg as it has probably been trimmed off as part of the installation.

[ellocoloco]

Thanks Chrissaf, 

 

I'll pop to ebay for some shopping.................

 

(Got 'Taken' (series) on in the background and the Trans-Siberian Express was definately not filmed on location.........)

[The son of Triangman]

I second what has been said.  Use a 12V regulated supply. A resistor will be needed in series with the LED/s unless it/they have a built in resistor like some of the 12V ones.

I would go for a 2K(2000 Ohms) 0.25 Watt resistor with a 5% tolerance to get a realistic lighting level.  You could use a bog standard 1K(1000 Ohms) resistor but the LED will be very bright.  

[ellocoloco]

@Margate-Richmond

 

Thanks for the point about higher resistance and bright LEDs - I had intended darkened windows for that very reason.

[2e0dtoeric]

As a suggestion - if you use an old (or a modern toy) controller, with reversable direction, if you wire some of your LED's one way around, and some the other, then by 'changing directions' you can create different lighting patterns in the buildings without any extra wires.

A blocking diode for each set might be an idea, to reduce the reverse volts applied to the 'off' leds. (Chrissaf or Flash-Bang?)

[Chrissaf]

A blocking diode for each set might be an idea, to reduce the reverse volts applied to the 'off' leds. (Chrissaf or Flash-Bang?)

.

Not needed in that particular scenario. If the LEDs are wired directly in parallel but the opposite way round, then the LED that lights up produces a fixed forward bias voltage across it which inherently protects the LED that is unlit. Probably a bit clearer to understand on the following image.

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As you can see Eric, the 'reverse bias' voltage across the 'unlit' LED can never exceed the 'forward bias' voltage of its adjacent neighbour. In this case, about 3 volts for a white LED. The 'unlit' LED never sees the full reverse polarity 12-15 volts supply voltage across it, because the 'lit' LED is drawing current and generating a voltage drop across the resistor. In this example 9 to 12 volts.

.

The LEDs can share the resistor because only one LED is using the resistor at a time.

[ellocoloco]

@Chrissaf & Ericm0hff

 

Thanks for the additional info...

 

I think I'll try and keep it simple. I'm already thinking I have chosen too complex a prototype for what will be my first scratch built structure. The LEDs and resisitors should arrive at the start of next week so I should get a picture of progress posted in the near future.............maybe!

[2e0dtoeric]

Couldn't see the wood for the trees!  😎

[ellocoloco]

One more question guys..........

 

What type of wire would be suitable for the 3mm LEDs and resistors? 

 

Thanks

 

[Chrissaf]

Whatever wire you want to use that is appropriate. If the LED is going to be fitted in a completely hidden location then it doesn't matter if the connecting wires are thicker as they won't be visible. In such a case I use 7/0.2mm wires as they are thin and flexible enough to make installation easy, but thick enough to not give issues with soldering and heat induced insulation shrinkage, and robust enough to not break when liable to accidental tugging in an exposed under baseboard position.

.

If the LED is going to be in a more exposed visible location where connecting wires will be visible, then you would want the wires to be as thin and unobtrusive as possible. If you look at ready made LED products such as street and platform lights, the connecting wires are more than likely less than 0.7mm diameter and maybe even hair thin 'enamelled' insulated wires. Working with this type of wire for home made products has its own challenges, particularly working with enamelled wires where the enamel removal can be problematic and delicate wires easily broken through rough handling.

.

A typical LED with a 1,000 ohm resistor on 12 volts is only going to draw 0.01 amps or 0.005 Amps with a 2,000 ohm resistor. These very low current levels just do not need thicker wires.

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Many of my LED home made projects use what they call 'strapping or wrap wire'. This wire is typically about 0.5mm diameter but unlike 'enamelled' wire has more traditional PVC insulation which is easier to work with. More readily found online in Electronic Component retailers. Search 'www.rapidonline.com' for "wrap wire" as one example.

[96RAF]

For a power ‘bus’ consider using self adhesive copper tape along the street, then solder your individual building led groups to this.

Another method is to run a bus which has 2-pin sockets at each building position and each building has a plug to allow easy removal for whatever purpose. I did this with my platforms which were lighted.

For wire I use what is sold as equipment wire. Mine is all in a box on the high seas so I can’t look at a reel for the spec.

[Chrissaf]

The 7/0.2mm wire I mentioned would fall into the 'Equipment Wire' labelled variety, but 'Equipment Wire' can be thicker or thinner. In general, the 'Equipment Wire' term is typically used to denote a single insulated wire rather than a cable containing multiple separate wires within it.

.

And as Rob added a comment about a power Bus. I focused my reply on the wiring that made the initial connection to the LEDs. As Rob quite rightly says. These thinner wires would be considered as droppers for connection to a main 12 volt power distribution system located under the base board, which could take many different forms.

[ellocoloco]

Thanks to the both of you.

 

Time to continue building - resistors and LEDs have arrived and main structure is assembled. Its probably overkill - 5mm ply frame fronted by 2mm card and scaled from Google earth and street view.

 

Will stick up a picture when its presentable.........

[ellocoloco]

One more question...

 

On completing the wiring of eight LEDs inside my station, I have decided that they are a little bright.....!

 

I have wired a 5K linear potentiometer onto the positive side of the circuit which successfully brings the light levels down to a more reasonable illumination level. 

 

Is this likely to have a detrimental effect on life expectancy of the 3V LEDs with 1K resistors I have used in the set up??

[Chrissaf]

Not at all.....actually it will be the opposite and improve life expectancy.

[96RAF]

I had my old layout lights fed by the 12vDC controlled output of a spare analogue controller, thus I could dim them as required. The 15vAC Aux output from the same controller fed my points CDU.

[ellocoloco]

@Chrissaf & RAF96

 

Thanks once again guys.

 

I feel I might finish the model in the next month and then get some pictures up..............maybe!

[Chrissaf]

Just be aware that the 5K Linear potentiometer will be passing the combined current of all eight LEDs. So do make sure that the power rating (Wattage) of the potentiometer is sufficient to handle the potential heat dissipation. It is difficult to give a precise wattage value as the power dissipation will be dynamic in nature subject to how much dimming is applied, the number of LEDs (i.e if expanded later to more than 8) connected and the voltage of the supply. But a rough guesstimate based upon a 12 volt supply and eight LEDs in total, is that a potentiometer with a 0.5W power rating will be more than adequate.

[Jimbo1707820979]

@ ellocoloco

Looking forward to seeing your railway station. I hope it is a replica of Canfranc !? 😛 (in view of your location).

[ColinB]

This is probably too late. What I use is short "stick on" LED strips off a popular auction site. The cheapest ones come from China. They come with the resistor wired in and just a black and red wire. They use SMD LED's so they small but bright. I think they will take 9 to 15 volts input. I also used them in carriages. In resin buildings I found I had to paint the insides matt black to stop the light shining through the resin. If you are not into wring they are the easiest option.

[atom3624]

Canfranc would be interesting - loved the documentary recently aired.

 

Big, straight station, side goods yard, then straight into a tunnel ...

 

Al.