10W power LED illuminating server case

Discussion in 'Computing and Networks' started by takao21203, May 4, 2012.

  1. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    Windows 2008 Server, AMD Core 2.1GHz

    10W power LED
    Diode as voltage dropper + cooling

    Switch added recently
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    No. LEDs do drop voltage, but they require a regulated current for the power supply. I suspect you are feeding this part way too many amps, in lieu of insufficient information.
     
  3. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    I have measured.

    1.08 Amps

    11.08 Volts

    Cooling fan!

    The Diode gets very hot, 140 C !!

    So it must drop voltage, like a small resistor.
     
  4. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    The LED works fine as headlight for typing computer texts, and programming source. For 5 months now.

    And makes sharp photos as well w/o flash.
     
  5. #12

    Expert

    Nov 30, 2010
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    I agree that an LED uses up some voltage. How much depending on what type of LED. But your point of conversation is not clear. Do you intend to ask a question?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    A LED like this must have heatsinking, from your description that is lacking. It will get hot, which is not its normal mod of operation. You are shortening it's lifespan quite a bit, but since the average lifespan of a LED run within spec can be 10s to 100s of thousands of hours, it can last for a while. The datasheet will have this number, look for MTF (mean time between failures). Basically it is a dice throw how long it will last without the heatsink.

    LEDs voltage drop depends somewhat on the color, and the current. A typical white LED will drop 3.6VDC, give or take a couple of 10ths. A red LED will drop between 2.0 to 2.5V.

    Yes, they drop voltage, but that is not the important spec. LEDs are current controlled devices. They are speced according to current, the voltage they drop is incidental to the specific LED. If this were a 10W white LED dropping 3.6VDC they would run on around 2.8A. Heat sinks would be absolutely critical at this wattage, or the LED would fry within minutes.

    Within any LED family there is some variation of voltage drop. It doesn't matter because the current is the critical spec.
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Judging from the resistor (or maybe the diode mentioned?) and the wiring in the lower right of the OP's photo, the LED isn't the only thing that may be hot. :D
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Don't worry, 12V led with a dropper is OK.

    But I wonder he is too shy to tell the truth.
     
  9. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    LED: 10 to 12v.
    1 Amps specification.

    At 12 volts, current seems to be too high.

    And yes it is mounted on a cooler fan assembly.

    I wanted to read opinion about the diode dropper.
    It gets hot, more than 100 degrees.
    Should I use a more powerful diode?

    Without the added wire pieces, it actually became so hot, that it unsoldered itself (lead solder).
     
  10. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    Well all I can see is I did not describe it clear enough.

    It is a small diode, no resistor here.
    The LED itself works normally, at rated current.

    And yes it's not a professional solution, too hot...

    What should be used? A big 5W resistor?
    Or a more powerful diode?
     
  11. BillO

    Well-Known Member

    Nov 24, 2008
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    As Bill said, you need a constant current supply and a heatsink.

    What is happening now is you are over heating the LED so much that it's internal resistance increases from the heat to limit the current. This is not right and the LED will eventually fail. Also, the amount of light you are gettting out of it will be a lot less than if you were doing this correctly.

    Do you have the link to a data sheet for this LE diode?
     
  12. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    Well it's beyond me what I am doing wrong (reading the replies).

    The LED is well cooled, and current is 1.08 Amps.

    What kind of circuit do I need for 12V supply?

    LED: 10-12V, 1Amps. no datasheet.

    Eventually I should mount a schottky barrier diode also on the heatsink, but that's not enough voltage drop...Don't want to use two of them only to drop voltage.

    Or a MOSFET maybe + resistor to set current/voltage? I have N-channel here as well P-channel.

    The small diode (silicon diode not LED!!!) gets too hot, and that's not right. I search for a better solution.

    I only need to drop about one volt.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    Here is part of the problem, we are being feed information in dribbles. If that is a 12V LED that does not require a resistor it is a module, and will use all of 12V. If (and I say if) this is the case then you are starving the component for power, and the reason it is getting hot is insufficient heatsinking.

    I'm not buying what I just said though. Most of the folks here understand LEDs and electronics very well, but the only way we can help is if all the information is given up front instead of piecemeal.

    So. Where did you get the LED, and what is it's part number? This is so we can look up the data sheet, and see what this part really is.

    What is the LED in line with?


    What are you needing to drop the voltage to? What is it now, and what is the current required? Ohm's Law steps in here, and is used to calculate with.


    LEDs do not drop a constant voltage. We treat them as if they do, but it varies somewhat according to current, the voltage drop in the data sheet usually assumes you are feeding it its rated current.

    There are components and circuits that will do the job correctly if you are needing to regulate a power supply. An LED was never intended to do this job, and if it works it is a kludge at best. I have nothing against kludges mind, but we can't really help if we don't have all the facts.

    As near as I can tell you are trying to solve the heat problem. That is a bit in the air also, but it is a start. There is a reason CPUs have fans on their heat sinks, it improves the cooling. It may be you have a similar situation with the LED, but I am frankly guessing at this point.

    I see several other people have taken an interest, so I will step out for now. I have written a tutorial for low power LEDs, and the basics don't change much, but with high currents some odd effects do creep in.
     
    R!f@@ likes this.
  14. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    OK thanks for your reply.

    I have drawn a schematics, and hope it is obvious to see the circuit.

    It works for the power LED, but having a diode " 140 C is not so good.
    The silicon diode, not the LED.

    I also don't want to keep a stockpile of various power resistors!

    So, how can I drop 1 volt?
     
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Try replacing the diode with a 4.7 ohm 5W resistor
    Ans if u wanna be kind to the LED, try one of the Bill's PWM circuit from his blog
     
  16. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I would try a lower value for the resistor.
    A 4.7 Ohms resistor would drop to much.
    A value between 1.5 and 2.2 Ohms would work.
    Lower values could give a to high current.

    Bertus
     
  17. BillO

    Well-Known Member

    Nov 24, 2008
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    Question, where did you get the information that it is 10V-12V @ 1A?
     
  18. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    from the vendor
     
  19. BillO

    Well-Known Member

    Nov 24, 2008
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    By vendor, do you mean the store, or do you know who actually made it? Does it have a part number on it?

    Without knowing what the device is, and its specifications, we are not going to be able to help much. Sorry:(
     
  20. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    I was thinking the specification is sufficient, as well the information I wrote.

    Voltage: about 11.08 Volts
    Current: about 1.08 Amps

    And that well makes 10 Watts.

    All these power LEDs need cooling!
    They are common I think.
    You can see the LED on the photo as well, mounted on a heat sink.

    The LED is not the problem.
    It works well as it should, light output is normal I think,
    temperature (with cooling) also is normal.

    My problem is how to drop 1 volts???

    -The diode I use gets very hot
    -I don't want to maintain a stockpile of resistors

    Any circuit that I could use, or parts that can be mounted on the heatsink as well?

    I have here some DPAK diodes, DPAK p-ch MOSFETs,
    as well ordinary IRF N-ch/P-ch MOSFETs.

    So, I need 11 volts, only have 12 volts!

    There is no datasheet, only the information I already wrote:

    10W, 10-12V, 1Amps current.

    12V is too much, current=1.8 Amps. That would shorten the lifetime, and too much light output anyway.
     
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