LED Wiring help for a moron?

Discussion in 'Replica Props' started by Birdie, Dec 6, 2011.

  1. Birdie

    Birdie Master Member RPF PREMIUM MEMBER

    Trophy Points:
    2,660
    Okay, I'm trying to wire up a simple 5 led chain for a PKD custom. I put the circuit to gether and apply power. Nothing. Check all the polarities, can't find a fault.

    So I unsoldered everything, tested all the bulbs and they are fine. It seems I just can't get more than two bulbs to light at a time, like so:

    Two bulbs
    [​IMG]

    Yay!

    Single third bulb
    [​IMG]

    Yay!

    All three
    [​IMG]

    Zippo. Boo!

    I've tried substituting different bulbs, same result. As soon as I try adding a third bulb, nothing. What the hell am I doing wrong, this is driving me nutso :confused??
     
  2. C0mmand3rC0dy

    C0mmand3rC0dy Sr Member

    Trophy Points:
    1,046
    keysersoze30 likes this.
  3. ReproMan

    ReproMan Well-Known Member

    Trophy Points:
    567
    my guess not enough power from supply for 3 leds

    Connecting LEDs in series
    LEDs in series If you wish to have several LEDs on at the same time it may be possible to connect them in series. This prolongs battery life by lighting several LEDs with the same current as just one LED.

    All the LEDs connected in series pass the same current so it is best if they are all the same type. The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor. To work out a value for the resistor you must add up all the LED voltages and use this for VL.

    Example calculations:
    A red, a yellow and a green LED in series need a supply voltage of at least 3 × 2V + 2V = 8V, so a 9V battery would be ideal.
    VL = 2V + 2V + 2V = 6V (the three LED voltages added up).
    If the supply voltage VS is 9V and the current I must be 15mA = 0.015A,
    Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 / 0.015 = 200ohm,
    so choose R = 220ohm (the nearest standard value which is greater).
     
  4. Birdie

    Birdie Master Member RPF PREMIUM MEMBER

    Trophy Points:
    2,660
    Good page, but just seems to be telling me I'm doing it right....very weird :confused


     
  5. ReproMan

    ReproMan Well-Known Member

    Trophy Points:
    567
  6. Birdie

    Birdie Master Member RPF PREMIUM MEMBER

    Trophy Points:
    2,660
    Yup, seems to be a power issue. Just hooked up a new 9v battery and it seems to be doing the job :)

    Guess I'm doomed to suck a electronics :$


     
  7. ReproMan

    ReproMan Well-Known Member

    Trophy Points:
    567
    im not too great with electronics either. i'd rather re-purpose l.e.d. circuits out of crappy toys to put in props lol, but im learning so i can try some of the sci-fi rifles
     
  8. CousinDave

    CousinDave Member

    Trophy Points:
    191
    Check the specs on the forward voltage for your LED's.....(ie. voltage drop across LED's required to turn it on) Usually about 2 volts per LED.

    - If wired in series, the current across LEDs is same as source but voltage is divided.
    - If wired in parallel, the voltage across LEDs is same as source but current is divided.
     
  9. Purple Dagger

    Purple Dagger Active Member

    Trophy Points:
    332
    LED Series Resistor Calculator

    This ones close to the one I used to get my Jawa eyes going about a week ago, deleted the bookmark already:unsure. It calculates in all the variables, just enter the fields for a good clean circuit.
     

Share This Page