PLEASE HELP ME!! running a 3.6V Led

Discussion in 'Power Electronics' started by ben hughes, Sep 6, 2016.

  1. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    Hi all I'm running a High power LED but having lots of problems. the specs are:-
    Power Dissipation: 10W
    Chip: Bridgelux
    Life: 50,000h
    Forward Voltage: 2.0-3.6V
    Forward Current: 700mA

    I'm powering this with 4 x AAA's
    I only have 2 questions.
    1) how long will the LED last before it burns out if i just carry on running it straight of the 6V (4 x AAA's) this doesn't have to be exact just a rough idea.
    2) what resistor do i need to run this and still get the max light out of the LED
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi Ben,
    I don't think God is a member of AAC, maybe I could help.?

    With a 6V voltage source and say 3Vfwd for your LED, you must drop 3V at 700mA.
    That's 3v/0.7A=4R at 2.1Watt, so use at least a 5Watt resistor.
    E
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Forward current @ 700mA with 3.6V is 2.52W
    for 10W LED at 3.6V, Current = 2.78 Amps
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    AAA batteries cannot run a 10W LED for long
     
  5. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    ah i see i originally got a 2w 390mA resitor and the LED was really dim to almost out in brightness.
    so i need to have a larger watt to allow more power through and that should work :)

    can i ask if i didn't use any resistor i get a major bright light but if it's meant to last about 50,000hrs i'm thinking it would last around 2- 5000 hrs.
    you don't have to be exact but what duration of life would you possibly give it?
     
  6. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    I'm basically making a lightsaber for my son and the LED is great and i don't need it to last for days to be hounst if i can get it to last for about 6 hrs that should be enough. i hope 4 x AAA's would do this? i'm more than happy to test it though :)

    any thoughts?
     
  7. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    getting a 5w resistor is easy but what do about the Ma?
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Connect R in series with the LED and measure the current thru the LED
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If the AAAs are good quality and fresh you might get a fraction of a second :(.
    I'm rather concerned that you're using such a high power LED for a child's toy. Looking directly at it could cause permanent eye damage.
     
  10. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    your not able to look directly at the led it's in the base of the blade and the blade has a film which lights up when it's turned on. i've tested it a few times and it's had no problem with 10+ mins before i took the cables of the power points
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    How do you cool the LED?
     
  12. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    im using 3m thermal pad and then 15mm deep by 16mm wide copper rod which is just above standard for this. most makers i've looked at use 1mm pad and 10mm copper base
     
  13. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    For reference:

    http://data.energizer.com/PDFs/E91.pdf

    Expect about 1,000mAh capacity at 700mA (from 1.5V to 0.8V per cell). Probably about an hour of run time.

    But, as the batteries discharge, the LED will quickly dim long before the 0.8V/cell is reached.

    A switcher will give constant brightness through the whole battery life, but expect less than an hour.
     
  14. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    right i see thank you.

    the power supplie is going to go through a rocker switch i should have mentioned that sorry.

    i was going to use a 5 watt resistor on this to try to make sure the led wont burn out and last's longer.

    i did a test a while ago with a 3.7v 1200mah battery and the led lasted 3.5hrs so i'm hoping for better this time if i can just get it to work correctly
     
  15. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    "Switcher" != "Switch"...
     
  16. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    sorry miss read that.

    i don't mean to sound dumb but i've never heard of a switcher? is this like a resistor?
     
  17. joeyd999

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    Jun 6, 2011
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  18. ben hughes

    Thread Starter New Member

    Sep 6, 2016
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    thank you
     
  19. joeyd999

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    Jun 6, 2011
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    That's what the "like" button is for.
     
    ben hughes likes this.
  20. crutschow

    Expert

    Mar 14, 2008
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    If you could make room for AA alkalines, that would more than double the life over AAAs.
     
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