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this bugs me / noob question`

Discussion in 'General Electronics Discussion' started by elioacm, Jul 7, 2013.

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  1. elioacm

    elioacm

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    Jul 7, 2013
    so i have a 9 voltage battery...

    how many LED that it would light.

    is this correct?.. ea: the led is 1v each, then the 9v battery would run 9 led with each one is in the same brightness..?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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  3. elioacm

    elioacm

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    Jul 7, 2013
    thanks, i read your link and watched this vid..


    my prob to that vid is how did he know the mA of the LED hes using.,.
    is it possible to use multimeter?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You read the specs for the device.

    Typically a low power LED is OK up to 20mA. Lower is OK too.

    Higher power LEDs may allow much higher currents and that is normally specified in their datasheet. Knowing Vf and the power of the LED you can usually calculate a reasonable value.
     
  5. NuLED

    NuLED

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    Jan 7, 2012
    I am not sure how practically you can measure specs for LEDs. I think it would be quite difficult and you need tools in addition to a multimeter. For example, probably an oscilloscope, so you observe how the voltages and currents behave over time across the LED.

    Generally I think you need to have the specifications. I have a bunch of LEDs that have unknown specs so I just guess at them. Now I separate the LEDs that have specs (from the package) from LEDs that I know nothing about. But as Steve said, GENERALLY you can make a guess at the most common specs.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No, a scope isn't going to help.
     
  7. BobK

    BobK

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    Jan 5, 2010
    You turn up the current slowly unitl it pops and then reduce it by a factor of 2.

    Do this with each of your LEDs, then you will have to buy new ones, and you will know their specs.


    Bob
     
  8. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    The current specifications for LEDs are governed by thermodynamics, the ability of the die to dissipate heat in a given packaging and environment.

    For an unknown LED, precise thermal measurements would be necessary to characterize it's performance and as Bob humorously suggested, destructive testing would provide the data at the end of the graph. It's only practical to do these tests for large batches (production runs) of LEDs so the LEDs sacrificed in testing are a very small percentage of the total.
     
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