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LED Question

  1. Nov 21, 2006 #1
    Hey guys,

    I have a question regarding connecting up 6 * 3mm/5mm super bright mcd Led's in parallel (since they would all have the same forward voltage when wired this way), using a supply voltage of 3V but not sure whether is should be 2*1.5V AAA or 2 * 1.5V AA batteries.

    The reason i put these in red is because im not sure which of the LEd's(3mm or 5mm) would last longer with the either of the power supplied (AAA or AA)? Its obvious that the 5mm would consume more power but just thought ill ask to clear my question.

    Any help would be appreciated thanks:cool:

    Jake
     
  2. jcsd
  3. Nov 21, 2006 #2

    berkeman

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    Staff: Mentor

    What is the amp-hour rating of alkaline AA batteries versus AAA batteries?
     
  4. Nov 22, 2006 #3
    The problem is not just Amp-Hour to Amps Drawn.
    You start with the current draw of the circuit and datasheets for the batteries you intend to use.
    The battery datasheets will have a set of curves showing life against discharge currents as a ratio of the ideal discharge current "C"
    Different battery chemistries are better for different loads. People often put expensive high energy batteries in clocks thinking they will last longer, but clocks have very low current draw more suited to the budget batteries that run dry in 30 seconds of use in a radio.
    Saying that, if you are using batteries of the same chemistry and manufacturer "AA" will always out last "AAA".

    P.S. Another way of getting brighter looking LEDs is to use less LEDS but pulse them over their rated input. So long as the average power follows the derating curve in the data sheets you can drive LEDs much harder and hence brighter than constant illumination using less average power.
     
  5. Nov 22, 2006 #4
    I have no idea but i would like to know:grumpy:

    Hey Panda,
    Thanks for replying,
    The idea is to use 6 * 3mm/5mm super bright LEDs to put on my guitar pickups in place of the actual pickup. you see that there are 6 magnetic nuts one for each string. Im removing those and putting LED's there. So i was wondering if its better to use 3mm or 5mm LED's? Also what batteries to use assuming that each LED consumes 20ma? :cool:
     
  6. Nov 22, 2006 #5

    NoTime

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    I'm thinking your guitar won't work any more, if you do that.

    The size 3 or 5 would depend on how big the screw holes are. Pick the one that fits best.

    You can look up the power for different size battries.
    Sometimes its printed on the battry itself.
     
  7. Nov 23, 2006 #6
    Hey NoTime,

    I completely know what im doing, the guitar wont work for that particular pickup only which i hardly use to out it goes and in comes the LED's. I have picked 5mm as the screw holes are 5mm themselves.
    Here are the specs:

    White LED 17000mcd 5mm
    SPECIFICATIONS:
    SOURCE MATERIAL:InGaN
    EMITTING COLOUR:White
    LENS TYPE:WATER CLEAR
    LUMINOUS INTENSITY-MCD:15000 TYPICAL17000MAX
    REVERSE VOLTAGE:5.0 V
    DC FORWARD VOLTAGE:3.3V TYPICAL/3.5V MAX
    DC FORWARD CURRENT:20mA
    VIEWING ANGLE:15 degrees
    LEAD SOLDERING TEMP:260oC for 5 seconds

    Im planning to use 6 of these LED's in parallel using a voltage supply of 2AAA 1.5 V batteries. Will this be enough voltage to light up these LED's fully and roughly how long will it take till these batteries die out??

    Thanks
    Jake
     
  8. Nov 24, 2006 #7

    NoTime

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    2 * 1.5v = 3v
    That is less than the required 3.3v to 3.5v.
     
  9. Nov 26, 2006 #8
    Wont it still work though, although not to its full capacity??:uhh:
     
  10. Nov 26, 2006 #9

    berkeman

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    Staff: Mentor

    Not in the general case. If you are below the forward voltage, you generally don't get any light out.
     
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