LED lamps drawing 1 amp at 12V

Discussion in 'General Electronics Chat' started by spinnaker, Jan 6, 2013.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    I ordered a few of these

    http://dx.com/p/gu5-3-3-5w-6500k-420-lumen-60-led-white-light-bulb-12v-131888


    from Dela Extreme. I hooked them to my homemade LM317 power supply (it has no current limitation). I connected an amp meter and measured over 1 amp.

    I assumed these bulbs had their own current regulation but they are advertised at 3.5W

    At 3.5W I should only be drawing less than 300 ma correct?

    Am I correct to assume they don't have current regulation?
     
  2. thatoneguy

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    It looks like it is a plug in replacement for incandescent bulbs in RVs, so I would assume there is some sort of limitation on them. Since dx is a mainstream outlet, I doubt they'd sell something that requires an external circuit without notifying the purchaser (though they may not state expected lifetime...) For that number of discrete LEDs, the fixture would either need a boost current regulator, or several strings with current limiting at 12V.

    What is the estimated difficulty of dis-assembly? Looks like a plastic welded (ultrasonic vibration until plastic melts together) enclosure, but it may be clips holding the front on which you can open with a "case tool" (mini pry-bars for phone and notebook teardown).

    --ETA: 60 LEDs @ 20mA each comes out to 1.2A, in worse case wiring.
     
  3. spinnaker

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    Impossible to take apart without damaging them.

    Why are they drawing so freaking much? I had planned to use 2 or 3 of them to replace my current sign light project but at over 1amp that battery won't last very long.

    My current light takes about 500ma but is not very bright and is getting older. I already had to replace several leds so I guess the rest on on their way out.

    I was considering replacing it with one of these.

    http://www.ledwholesalers.com/store/index.php?act=viewProd&productId=780

    There are small but supposed to be very bright. I saw a review where they consume .8 amps at 13V. That is almost double of what I have but I was wondering if I might be able to use PWM to limit the consumption further.

    I still want to know why these current lights draw so much. Also what us strange about these lights is there is no polarity marking whatsoever on the terminals. I took a chance and hooked them up. The first time backward but it did not seem to damage the light.
     
  4. spinnaker

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    Wow these lights are really bright but also get really warm.
     
  5. thatoneguy

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    What is the application? Backlight for a sign, or general illumination?

    The second one you linked looks well built, and the 800 lumen output is about equivalent to a 60W Incandescent bulb.

    Just an idea to "black box" test it: If you have the dx 12V bulb and a regulated power supply, you could see if the brightness goes down with voltage, if so, it probably has some sort of passive limiting. If they stay at full brightness down to 10V or so, it probably has a boost or buck converter in it with regulated current output.
     
  6. spinnaker

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  7. spinnaker

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    Brightness does see,m to change with voltage. Even when I vary a volt or so.
     
  8. tubeguy

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    There probably was a typo in the specs to begin with... (that never happens)

    Lowering the voltage shouldn't hurt.
     
  9. spinnaker

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    What specs?

    I still would like to know why they are drawing 1 amp. There are only 80 LEDs. I have a light with 120 leds and it only draws 400 ma.
     
  10. thatoneguy

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    The "Worst Case" scenario.

    Input goes through a bridge rectifier, then each LED has it's own current limiting resistor on the board that holds them all.

    I would only be mildly surprised by something like that from a no-name product, they tend to minimize the parts count as much as possible, so they'd try to put at least 2 LEDs on each resistor.

    I think the only way you'll get an answer is with a dremel tool and a sacrificial lamp (Only $6). Then post pictures here, and a review on the dx site.
     
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  11. spinnaker

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    So you are saying that each led has it's own current limiting resistor so the whole thing might consume an amp?

    Why would they advertise 3.5W? (Yeah I know cheap Chinese junk :) ) I emailed the manufacturer. They are Sencart. I might wait to hear from them before I sacrifice one.
     
  12. thatoneguy

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    3.5W could be the sum of all the mW values of each LED (light output), neglecting any power loss from input polarity and current limiting methods.
     
  13. spinnaker

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    Maybe I should just order these?

    http://dx.com/p/3w-160-180lm-6300-7000k-led-white-light-bulbs-20-piece-pack-133093

    That way I know what I am dealing with.

    I could put 3 in series. That would only be 650ma. A little closer to what I am currently drawing.

    Or maybe even move up to the 3W that is only another 50ma or so.

    http://dx.com/p/3w-2850-3050k-160-180lm-led-warm-white-light-bulbs-10-piece-pack-146854

    I already have a 700ma (adjustable) current regulator.

    I like the idea of putting 3 in series because I can spread them out. Take a look at my light housing on my link in the projects form and you can see why I would want to spread them. The housing is about 10-12 inches across.

    What do you think?
     
  14. thatoneguy

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    3 of the 3W would give you the equivalent 600-ish lumen output, but you could spread it out more through diffusers.

    If you have a way to dissipate the heat (The photo shows the 3W LEDs as surface mount, not mounted to a sink like CREE LEDs can be ordered with), that would probably be the best looking and more efficient method of lighting a sign compared to the spotlight type at top of page, depending on distance.
     
    Last edited: Jan 6, 2013
  15. Audioguru

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    Dec 20, 2007
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    Are you going to buy a CHEAP LED light that has 60 CHEAP LEDs that does not have a manufacturer's name and does not have a datasheet??

    All traffic lights in my city use high quality name-brand LEDs and most have some burnt-out LEDs after a few years.

    The light with 60 LEDs might have 20 or 30 of them still working after a few days if you are lucky.
    The one with a single 10W LED is expensive but it looks like high quality.
     
  16. spinnaker

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    I'm leaning toward these:

    http://dx.com/p/3w-160-180lm-6300-7000k-led-white-light-bulbs-20-piece-pack-133093

    I would only need 3 leds. I get plenty so if some go they can be replaced.

    P.S. I already have the housing and it is much larger than the one above.
     
  17. spinnaker

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    I was thinking of getting these for heat sinks.

    http://www.ebay.com/itm/50pcs-20mm-...100?pt=LH_DefaultDomain_0&hash=item20ccf6164c

    I have seen those LEDs soldered to those.

    Here is one mounted.

    http://www.ebay.com/itm/New-5pcs-1W...253?pt=LH_DefaultDomain_0&hash=item416fc60775

    Looks like the same leds I am looking at or close no?


    I was going to attach them to those 1x1 aluminum tubing so that would give me more cooling.

    Thanks for the tip on the diffusers.

    Is this something like I would need?

    http://dx.com/p/23-36mm-optics-light-diffusers-for-cree-emitters-glass-5-pack-1920

    How do I figure out what type (angle)? The light is about 6 feet from the sign and the sign is about 12'4'.
     
  18. thatoneguy

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    at 12 feet, the diffusers will soften the light, making it slightly dimmer, but more even.

    The field of view is hit and miss with the cheap LEDs, I'd order 6 LEDs, heat sinks, and diffusers to ensure you have enough for even coverage if it is that far away. Some are extremely wide angle, which would be bad, as you'd need a focus/reflector on the LED as well.
     
  19. spinnaker

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    You get like 20 leds in the pack so that is not an issue.

    The current housing has a reflector that covers the outside edges of the housing.

    Maybe add something like these?

    http://dx.com/p/plastic-led-reflectors-10-pack-66786?rt=1&p=2&m=2&r=3&k=1&t=1&s=66472&u=66786
     
  20. thatoneguy

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    Check and see how it looks with just diffusers, if it is to spread out, you may need to add the reflectors, I wouldn't get them all at once unless you have future Power LED projects in mind.
     
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