resistors and led lights

dave45train Nov 21, 2011

  1. dave45train

    dave45train TrainBoard Member

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    Hi everyone,
    I have a new question and looking for some help. My dual pack contoler puts out 12 dc and 15 v ac power.
    I am looking for is some advice on what size resistors go with what size led lights. I want to set up lights on a few of my buildings and street lamps. However with somany sizes and styles out there I am not sure where to start. Does anyone have any suggestions or charts or past experience that has worked.

    Thanks
    Dave
     
  2. PW&NJ

    PW&NJ TrainBoard Member

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  3. dave45train

    dave45train TrainBoard Member

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    Thanks I will check it out.
     
  4. Harris Creek Central

    Harris Creek Central New Member

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    Basic LED's are in the 1 1/2 to 3 volt range. This is why it is not recommended to test an LED without using a resistor. If you have a power supply that has a controlled voltage set the voltage to no more than 1 1/2 volts and you could then test the LED without a resistor. If you are testing with say a 9 volt battery I would start with perhaps a 1K resistor, and work down to perhaps a 640 ohm resistor.
     
  5. dave45train

    dave45train TrainBoard Member

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    I checked out the website. It was a great help thank you. Now I just have to figure out between series and parralell conections. If I read the site corectly a series is connecting all the anodes + together then to the resistor then to the + power side of the power back and connect all the cathodes - together with the - neg side of the power supply. Is this correct. Because parellal splits the ressitor between the 2 leds and is not correct.

    Thanks
     
  6. Harris Creek Central

    Harris Creek Central New Member

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    Series takes an anode from one Led to the Cathode on the next Led. Parallel joins all cathodes to the Plus side and anode to the Minus side.

    Lay two wires down side by side. solder all Anode legs to one wire and all cathode to the opposite. You now have a strip in parallel. Hope this helps.
     
  7. dave45train

    dave45train TrainBoard Member

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    I see. Thanks. So when I get done hooking up the leds connecting one anode to the next cathode I will end up with 1 anodeleft to hook up to the correct resistor and then the + of my power supply and one cathode left to hook up to the - power supply. Now this makes sense to me not the way I described it. Thanks for the help.
     
  8. RBrodzinsky

    RBrodzinsky November 18, 2022 Staff Member TrainBoard Supporter In Memoriam

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    Just remember, when doing in series, to ADD the voltages of each LED in series (for total voltage drop).

    If doing in parallel, don't count on a single resistor. Always have a dedicated resistor for each LED.
     
  9. dave45train

    dave45train TrainBoard Member

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    Yeah, i dont want to blow up the lights on the first try. thanks.

    I found a formula from the website that PW&NJ railroad sent me. it was R=(Vs-VL) / I where R is the size resitor i need.
     
  10. Artieiii

    Artieiii TrainBoard Member

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  11. lexon

    lexon TrainBoard Member

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    Take your time and read though all the links. It appears you have little electronic experience. More info below.
    I have found that inverted cone LED's emit light 360 degerees and are quite nice for inside lighting. LIght bulbs can give a beter possibility for dimming though.

    http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm

    Rich
     
  12. Alan C.

    Alan C. TrainBoard Member

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    Most of the led's used are 3-5 volts and have a max amp of around 15 milliamps a good starting point is to use a 800ohm resistor and go up from there. I'm a cut and try person My rule of thumb is just make it bright enough to get the effect you want, but remember the brighter you make it the shorter the life of the LED or the Bulb
     
  13. dave45train

    dave45train TrainBoard Member

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    Use this formula when calculating the resisitor you need.
    I found a formula from the website that PW&NJ railroad sent me. it was R=(Vs-VL) / I , where R is the size resitor (ohms)you need. Vs is the total supply voltage, VL is the Light voltage (either LED or Incandesant) and I is the Amps of the bulb
    (##Ma / 1000) as a decimal [ie 20Ma = .02 amps (I)]

    Hope this helps.
     
  14. Alan C.

    Alan C. TrainBoard Member

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    The first place to look is on that back of the pack of LED's and get the max current rating. MY rule of thumb is just light them up bright enough to get the effect you want and keep the current rateing about 50% of what is max on the back of the LED package. I usually start out with a 1000ohm resistor in series and go up or down in value from there. Take Care Alan C.
     
  15. SinCity

    SinCity TrainBoard Member

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    If you are reusing the lightboard LED for a DCC install, what value resistor should be used? Or just reuse existing resistor?
     
  16. TwinDad

    TwinDad TrainBoard Member

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    Cathode == negative
    Anode == positive.
     
  17. BarstowRick

    BarstowRick TrainBoard Supporter

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    Dave, what are you working with? Name of unit, link, and if working with Led's reconsider what I advised you on a recent p.m.
     

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