LED driver 4-7 x1w problem

Discussion in 'General Electronics Chat' started by martik777, Sep 2, 2015.

  1. martik777

    Thread Starter New Member

    Feb 16, 2013
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    I have a 4-7 x 1w led CC driver but it does not work right. When I test 5 1W led's, 4 are bright and 1 is dim and it burns out the middle led. I tested the voltage without any load and it is 32VDC. The 1W LED's I am using are 3.2V, so 32V seems way too high. Is a no-load voltage test valid with a CC driver?
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    post the real specs or part number of the CC driver?
    I suspect its an Ebay Chinese cheap junk model and failures are VERY common with them.

    What is its rated output current?
    What is its rated output voltage range?
    What is the rated current for the LEDs?
    Are you wiring them in series or parallel?
     
    Last edited: Sep 2, 2015
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    If you could post the circuit, test circuit and model numbers of the LEDs. You will get answers that are more accurate.
     
  4. MikeML

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    Oct 2, 2009
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    No. It should be putting out a constant-current, so here is how I would test it:

    Connect a 10Ω 2W resistor in place of the LEDs. Since it is a 1W/LED driver, it should be putting out I = P/Vf = 1/3.2 = 0.312A.

    0.312A thru 10Ω is E= IR = 0.312*10 = 3.12V.

    A second test with a 100Ω resistor would prove that it is delivering the right current near its max. output voltage: E=IR = 0.312*100 = 31.2V. The resistor would have a power rating of P=IE = 0.312*31.2 = 10W. If you don't have a 10W 100Ω resistor, you can immerse a 100Ω 1W resistor in motor oil for a quick test.

    If one of the LEDs went bad, it is either because you bought crappy Chinese LEDs, or you forgot to put them on a heatsink. Heatsinks are required under 1W LEDs.
     
    Last edited: Sep 2, 2015
  5. AnalogKid

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    Aug 1, 2013
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    No manufacturer
    No part number
    No schematic
    No idea.

    ak
     
  6. martik777

    Thread Starter New Member

    Feb 16, 2013
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    Here are the parts: LED's are in series

    http://www.ebay.com/itm/12142366387...49&var=420360538808&ssPageName=STRK:MEBIDX:IT

    http://www.ebay.com/itm/50pcs-Brand...1-Watt-/191217602967?var=&hash=item2c85751197

    I did not include a link in my OP, since I was just asking a generic question:
    " Is a no-load voltage test valid with a CC driver?"

    Thanks for your detailed reply Mikeml - I'll try that test.

    BTW, I have used these LED's and drivers to light my entire shop (8 work stations) for 5 years, and to date, I have had ONE failed LED bead and zero driver failures.
     
  7. MikeML

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  8. AnalogKid

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    Depends on what you want to know. With no load, a CC output will rise to its maximum output voltage, called its compliance. In your application, his can tell you the max number of LEDs you can have in a string. Alternatively, a short circuit current measurement will tell you the CC setting. It takes both numbers to fully characterize a CC output.

    ak
     
  9. martik777

    Thread Starter New Member

    Feb 16, 2013
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    I use aluminum discs or HDD platters led1.jpg led2.jpg
     
    Last edited: Sep 2, 2015
  10. martik777

    Thread Starter New Member

    Feb 16, 2013
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  11. martik777

    Thread Starter New Member

    Feb 16, 2013
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    I think they were mis-labeled. The driver works with over 5 LED's, voltage is correct (Ledcount x ~3.2) and current is 300ma

    "With no load, a CC output will rise to its maximum output voltage"

    If this is true then the max LED's would be 10 since I measured 32v w/o load. This would make them 6-10 drivers.

    Thanks for the help!
     
  12. AnalogKid

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    Check the datasheet. It might have a different opinion of its max output voltage under load.

    ak
     
  13. mcgyvr

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    Oct 15, 2009
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    Output voltage is stated as 12-25VDC
    So as long as your LED forward voltage range is greater than 12VDC and less than 25 VDC it should regulate the current properly.

    I would also check to make sure you don't have a short to the heatsink. sometimes that happens when soldering to those pads.
     
  14. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    As for the led driver, It should be able to drive 4 (4X3.2 = 12.8) to 7 (7X3.4 = 23.8) of your leds.
    As for the leds, do you use heat conductive compound between the leds and the plate?
    Also what is the temperature of the disk after some time?
    Power leds must be cooled to have a long life time.

    Bertus
     
  15. martik777

    Thread Starter New Member

    Feb 16, 2013
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    It was specified to drive 4-7 LEDs but as I said in my OP, it does not work with 5 or less, 6 is the minimum it will work with.

    I have tried both thermal compound (ie: cpu thermal paste) and epoxy. No significant diff in temps, both were approx 95F after 20 mins, measured on the surface of the HS within 1/8" from the LED. Some of these LED's have been on for 4-5 years 12+ hrs/day
     
    Last edited: Sep 3, 2015
  16. Denesius

    Member

    Feb 5, 2014
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    I don't see an answer to your original question: a CC power supply without a load with increase its output voltage in order to reach the expected current. And there's the rub: cheap power supplies will ramp up until they burn themselves out; good ones will reach a voltage limit and hold it there. If your power supply has a voltage rating (ie- 32volts) it means it will ramp up to 32v to try and push the rated current. If it succeeds, fine, if not (because there's no load there), see first sentence
     
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