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Reducing 4xAA voltage for Luxeon 1 watt driver...HELP!

Discussion in 'Electronic Components' started by CG, Nov 16, 2003.

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  1. CG

    CG Guest

    I hope someone can help me, for I know not about such things! I have
    a LEDSupply.com Micropuck driver for the Luxeon 1 watt LED "Star". I
    must run it off of four (4) NiMH "AA" cells (1800mAh) the produce
    something on the order of 5.6v (4.8v nominal).

    I have a problem. Though it will run amazingly well on this set up,
    the micropuck driver gets very hot only after a few seconds. I
    figured this would happen. My plan was to drop the voltage of the AA
    cells to the maximum operating voltage of the micropuck; 3v. However
    (and here is where my limited knowledge of such things haunts me) when
    I successfully drop the voltage to 3v by using a resistor (as tested
    on my multimeter) the LED will not illuminate. No matter how small a
    resistor I use, no light.

    I have to run the whole thing on the 4.8v, because it also runs
    another LED component that requires this.

    How can I do this? Is there another way to drop the voltage to 3
    volts so I can still run the driver/LED without overheating it? I am
    pretty sure if I continue to overdrive the driver it will fail. Any
    suggestions? And thanks in advance...

    Chris the Caver
     
  2. I have a couple of the micropucks also. They require two AA cells, or
    3VDC.
    The Luxeon star takes 350 mA or .35 A, so you need a resistor instead
    of the micropuck. Remove the micropuck completely (it may already be
    damaged by overheating). The Luxeon Star LED needs 3.2V at .35A. You
    need to drop 1.6VDC, at .35A, which requires a resistor of 4.57 ohms.
    So use a standard 4.7 ohm 1 watt resistor, or use two of the radio
    shack 10 ohm 1/2 watt resistors in parallel.
    View with courier font

    10 ohm 1/2W
    Batt + o--+--/\/\/\--------+-------o + LED
    | |
    4 AA | 10 ohm 1/2W |
    cells +--/\/\/\--------+ Luxeon Star

    Batt - o---------------------------o - LED


    I repeat, do not use the Micropuck, you will just burn it out, and it
    is _not_ needed with four AA cells.


    --
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    ###Got a Question about ELECTRONICS? Check HERE First:###
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    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  3. By the way, I forgot to mention this. Use the two 10 ohm 1/2W
    resistors that I just told you about. Put a switch on each resistor,
    so that you can switch just one resistor on, and cut the brightness in
    half and make the batteries last twice as long. The Luxeon stars are
    hungry beasts for current, and will suck your batteries dry real
    quick. So you might even consider using higher values of resistors,
    like 15 or 22 ohms, for lower current and brightness but longer
    battery life.

    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  4. Boris Mohar

    Boris Mohar Guest

    Quote form their website:

    "The LEDdynamics 2-Cell 1W MicroPuck (2009) was designed to power a single 1
    Watt Lumileds Luxeon, or strings of 5mm (T 1-3/4) LEDs (see app. note) "

    But I agree that he should be using only two cells.



    Regards,

    Boris Mohar

    Got Knock? - see:
    Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/
    Aurora, Ontario
     
  5. CG

    CG Guest

    Thank you all so much for the help. It is greatly appreciated. A few
    more points and questions:

    OK. I understand to ditch the micropuck. I will use straight
    resistors. Can you provide me with the formulae you use to arrive at
    the value? I think I understand that teh ohm you say lowers the
    vltage to within range of the Luxeon.

    I am using 4xAA because this is the main source for another LED array
    I use. It all goes on a cave helmet. I plan on using the Luxeon for
    spot illumination. Which leads me to the next question.

    How much, if at all, can the Luxeon 1 watt be "overdriven" in regards
    to voltage? Must it be 3.2 volts? If I wanted to squeeze a tad more
    light out of it, what damage will result (other than shorter overall
    life)?

    Also, as an aside, how do 1/4watt, 1/2watt and 1 watt resistors alter
    the circuit?

    So many questions! Thanks for educating me, all of you.

    CG
     
  6. CG

    CG Guest

    Thank you all so much for the help. It is greatly appreciated. A few
    more points and questions:

    OK. I understand to ditch the micropuck. I will use straight
    resistors. Can you provide me with the formulae you use to arrive at
    the value? I think I understand that teh ohm you say lowers the
    vltage to within range of the Luxeon.

    I am using 4xAA because this is the main source for another LED array
    I use. It all goes on a cave helmet. I plan on using the Luxeon for
    spot illumination. Which leads me to the next question.

    How much, if at all, can the Luxeon 1 watt be "overdriven" in regards
    to voltage? Must it be 3.2 volts? If I wanted to squeeze a tad more
    light out of it, what damage will result (other than shorter overall
    life)?

    Also, as an aside, how do 1/4watt, 1/2watt and 1 watt resistors alter
    the circuit?

    So many questions! Thanks for educating me, all of you.

    CG
     
  7. Boris Mohar

    Boris Mohar Guest

    You really need to master the Ohm's Law. It is the LAW

    http://www.grc.nasa.gov/WWW/K-12/Sample_Projects/Ohms_Law/ohmslaw.html

    http://www.ledsupply.com/techinfo.html

    You headache will be caused by the fact that the LED is not a linear device.
    In other words its resistance is not constant but is affected by how much
    current is flowing through it. The exact nature of that relationship I leave up
    you to discover.
     
  8. You take the battery voltage and subtract the voltage drop of the
    Luxeon which is about 3.2V. You get 1.6V difference. You then divide
    that by the current in amps, which is .35A. That gives the 4.57 ohms.
    Use the next highest standard value, which is 4.7 ohms. By putting
    two 10 ohms in parallel you will have the equivalent of a 5 ohm 1 watt
    resistor. The 10 ohm 1/2 watt is a common, easy to get value.
    Your problem is that the Luxeon star needs a heatsink to dissipate the
    heat. If you mount it on some aluminum, it will handle the power
    properly, without overheating. If you leave it by itself, it will get
    hot, and the life will be shortened. So that's your decision.

    Your other problem is that if you draw too much current from the
    batteries, their voltage will drop, and they will be rapidly depleted.
    So stay with the maximum rated current and you won't have problems.
    If you use a resistor of too low a power, it will burn up.

    I'm listening to 60 Minutes' Andy Rooney grousing about Windows and
    having to press START to shut it down. He said, "Well, what the hell
    else did you think I want to shut down? The bedroom window?" LOL!!

    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  9. At least he wasn't griping about old cans of paint he'll never use
    again. I quit watching "60 Minutes", because it seemed like he was
    always complaining about left over paint.
     
  10. Well, the rest of the show comes before, so you can still watch that. ;-)

    2 weeks or so ago he really got people upset when he talked about
    something. The following week, he read a lot of comments that said
    they were never going to watch 60 Minutes again. Well, they're probably
    still watching, mainly because it's an excellent news magazine with
    unbeatable stories.


    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
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