Help with wiring LED's

Discussion in 'General Information' started by MalcT, Sep 6, 2019.

  1. MalcT

    MalcT Full Member

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    Hi folks,

    After some advice please.
    I want to add some LED lighting to my inspection pit. I will be using a 12V DC Transformer as I will
    want to add additional lighting later - what size wire should I use for this, is my dropper wire which is 26x0.015 too large?

    Mods, please move thread if I've posted in wrong area.

    Thanks
    MalcT
     
  2. Keith M

    Keith M Staff Member Moderator

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    For lighting in an inspection pit, I'd be looking to use the SMD (Surface Mount Device) type of LED as they are far smaller and as they are rectangular in shape, resemble 'bulkhead' lighting fittings which would likely have been the type used in 'real life' in the steam era. Having said that, unless you are proficient with a soldering iron, they are more difficult to solder due to their small size, but the only way to get 'good at soldering' is to have a go, so don't be afraid as these SMD LED's are very cheap so knackering a few along the way is all part of the learning curve. Be aware that whatever type of LED you use, you must include a resistor in the circuit (1kohm as a starting point, depending on how bright you want) as they will go "POP" with a voltage higher than 3 volts and they are polarity conscious, so won't work if you connect them the wrong way round. The dropper wire you may find too large if you go for the SMD type, and I find that 6 core 'Burglar alarm' type cable is suitable and quite cheap (around £12 for 100 metres), it's stranded rather than solid core like telephone extension cable so will tolerate movement without breaking,- just strip out as much of each core as you need, as it goes a long way!
    Keith.
     
  3. Dr Tony

    Dr Tony Full Member

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    Alternatively if you feel you aren't up to soldering tiny wires onto things that are 1/3 the size of even the smallest common soldering iron tip, you can buy those small SMD LEDs pre-wired, usually with about 20mm of fine wire. Bit more expensive, but are a lot easier to deal with. And they come with colour coded wire to make that job easier too.
    Cheers
    Tony
     
  4. paul_l

    paul_l Staff Member Administrator

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    Hi Malc

    This may help

    upload_2019-9-6_16-27-31.png

    Depending on how many you wish to use and era I'd recommend Warm whites for steam era and Cool whites for modern era.

    As Keith said, a min of a 1K resistor per led, I have used 10 & 100K before in locos to dim the leds down, and even higher if they are to be photographed.
    The resistor drops the voltage and limits the current flowing through the diode.

    Here's a link for the full theory and calculations - Basics: Picking Resistance for LEDs

    Paul
     
  5. MalcT

    MalcT Full Member

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    Thanks for all your replies, most helpful.
    What about the size of wires to use. I have plenty of 26x0.015 dropper wire, but is that too large, would I be better using a wire with fewer strands or a solid wire ?

    Thanks Malc
     
  6. Keith M

    Keith M Staff Member Moderator

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    Best not to use solid wire even if no movement is anticipated, stranded is far better. Your choice of available wire size will likely be governed by which type of LED you eventually decide on, if it seems big and clunky then go for something smaller.
    Keith.
     

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