L.E.D. datasheet: I need help with this.

Discussion in 'General Electronics Chat' started by Mixednutt, Jun 19, 2010.

  1. Mixednutt

    Thread Starter New Member

    Jun 16, 2010
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    Hi there. Mind helping me with some newbie stuff? I'm working on a 56 led wall wart project, and I found these great flat wide angle leds here:
    http://cgi.ebay.com/100-x-5mm-White...aultDomain_0&hash=item3cab9cb642#ht_500wt_696

    Here's the deal. The datasheet this seller offers seems to me, with my lack of experience, to suck. I can't figure out how many mA's or Volts these things need to run. Can someone help me figure out what my min's and max's for a sustained current should be?

    Here's the datasheet so you don't have to browse ebay:

    Specifications: Size: 5mm Lens Color: Clear Reverse Current (uA): <=30 Life Rating: 100,000 Hours Viewing Angle: 120~140 Degrees Absolute Maximum Ratings (Ta=25°C) Max Power Dissipation: 80mw Max Continuous Forward Current: 24mA Max Peak Forward Current: 75mA Reverse Voltage: 5~6V Lead Soldering Temperature: 240°C (<5Sec) Operating Temperature Range: -25°C ~ +85°C Preservative Temperature Range: -30°C ~ +100°C
     
  2. bertus

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    Apr 5, 2008
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  3. Mixednutt

    Thread Starter New Member

    Jun 16, 2010
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    OI just wanted to confirm with people who are smarter than me that these leds should work at 3V and 20mA/LED. I know these things need to be precise, and I'm poor so I don't want to destroy these 56 leds, or buy a wall wart with the wrong numbers. Will 3V 20mA/LED work? I guess I need some clarification on the amps. The datasheet says 24mA Max, so I should be able to get away with 20mA/LED and still be safe, right?

    Also, thanks for that link. I learned a lot. Ill read it some more to see if I can bolster my confidence.
     
    Last edited: Jun 19, 2010
  4. Mixednutt

    Thread Starter New Member

    Jun 16, 2010
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    This stuff is a lot of fun, but there sure are a lot of ins and outs. So far it looks like I will be using a 6V 580mA wall wart to power a series/parallel circuit. I have the circuit hooked up with 2 series circuits each with 28 leds wired in parallel, for a total of 56 leds. I might try to get some more volts and toss in a couple of resistors, but since I'm using a wall wart I don't need to worry about battery voltage drops.
     
  5. Mixednutt

    Thread Starter New Member

    Jun 16, 2010
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    Ok, so in reading about voltage drop, it looks like I might need a 100V wall wart, and since that seems like an unlikely product, I might have to rethink this wiring scheme.
     
  6. sceadwian

    New Member

    Jun 1, 2009
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    You should have bought more, I bought a pack of 100 for a few bucks off e-bay and put enough in series and anti-parallel that it would run directly off of 120V AC. Worked great. I didn't leave it plugged in for long because I guess that many LED's in series need some paralleld resistance to ballance the voltage, but for the few minutes I had it plugged in it provided plenty of light, the only thing that sucked was the flicker, it was run off straight AC no DC with filter caps so the flicker was pretty nasty.

    12 volts is a good voltage to run an LED string off, you run three LEDs in series with a resistor to drop the last few volts and provide current limiting. Then you run as many of those three strings + resistor combination as you have LEDs for.

    A spare ATX power supply could power hundreds of such paralleled strings easily.
     
  7. sceadwian

    New Member

    Jun 1, 2009
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    That's hardly a data sheet, it doesn't even list the forward voltage.

    Lets do some basic assumptions, 3.1 volts per LED dropped at 20ma of current draw. 3 LEDS is 9.3v's, that's 2.7 volts left to drop with a resistor, or the one closest to 135 ohms that you can find. Aim for a slightly higher resistance than the calculated one and the string will last longer.

    The reason I suggest an ATX power supply is because they're incredibly easy to use, and they're fully regulated, they're also dirt cheap if you don't have one floating around your basement. The one I have sitting on my desk that I grabbed from an old PC to use as a bench supply would run around 600 strings like that. Save up for some more LEDs =)
     
  8. bertus

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  9. Mixednutt

    Thread Starter New Member

    Jun 16, 2010
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    Sceadwian, thank you for the advice! I agree with you, that IS hardly a datasheet. In fact, the difficulties that I've been having with this wiring can all be traced back to this poor datasheet. You know, I think I've learned that buying electronic components off of ebay is rather a 'crap-shoot'. I can't tell you how many wall-warts I found that advertised Amps and Volts which, when multiplied, did not equal anywhere near the Watts. Am I missing something, or are these people posting auctions with false info? I'm a newb. Anyway...

    I haven't bought anything yet. I want to make a complete shopping list before I order my first materials. This being said, I might just have to find a different auction with better datasheets.

    Real quick question, just a thought, if I bought the LED's first, and wanted to test them myself for min and max forward Voltage, min and max Amperage, and Vf, A: would this be possible, and B: what tools would I need?
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    You dont have to use auctions.

    Try reputable companies. You may pay 2 cents more per LED but they are worth it.

    If you get 100 of the 'ebay' far east LEDs and lit them all up, you will be HARD PRESSED to find 2 that are the same brightness. And a few minutes later, you will only have 82 left that have not burned out.
     
  11. Mixednutt

    Thread Starter New Member

    Jun 16, 2010
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    Retched, thanks for the info. I'm shopping around for a new source of LED's right now. Any suggestions for where to look? I'd prefer to order them off the web.
     
  12. wdkh68

    New Member

    Jan 12, 2010
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    You can buy these same LED's at this address for HALF the cost and free shipping with good delivery! http://stores.ebay.com/bestshop2008hk plus a lot more choice! I have bought hundreds of their leds and I am very satisfied
     
  13. sceadwian

    New Member

    Jun 1, 2009
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    retched I disagree, if you can shop well on e-bay and know what you're buying you can get really good deals, a lot of the stuff you can buy there is direct from people that work at plants over there that are making a buck cutting out all the middle men, but e-bay is saturated with a lot of rip offs and bait and switch items as well, you have to mind your buyers and do your research.
     
  14. retched

    AAC Fanatic!

    Dec 5, 2009
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    If your buying brand named or reputable merchandise, then yes. But if you get the 100 no-name far-east LED packs for $3. I stick by my statement.

    I also said, you dont HAVE to use auctions.

    Many people seem to think that ebay is the ONLY place to get electronic components.
    I was also trying to convey that you get what you pay for.

    And if you want to give your money to someone who:
    Which to me means "thief".

    There is a huge difference between the quality of QUALITY leds and BULK leds.

    If you care about your product, and you dont want to throw the dice HOPING that the product is going to be consistent, thats up to the penny pinchers.

    If Im putting my name on and time into something, I dont want to find out after I have it all together that I have been duped and my leds start popping like corn.

    I helped a friend make a 500 led wall. eBay specials.

    Same supplier. got king brights 4 orders of 100. SAME AUCTION the 5th order showed up generics. KINKBRIGHT on the package.

    So, he dumped all 5 bags into a tray and we got to work. 500 smd resistors soldered to the anode leads. 1000+ holes drilled. 1000s of inches of adhesive copper foil tape...ugg.

    We didnt have the board lit for 30 seconds before the first led blew.

    a few ACTUALLY POP. crazy.

    It was painfully obvious just by color and brightness alone which ones were which.

    18 of the LEDs failed. all the generic ones. There was a little bump on the flat side of the lens of the generic ones. So, we ended up ordering another 100 from digikey. Paid 2 more dollars after shipping.

    replaced all 100 of the fakes.

    Now there was a difference between each batch of the Kingbrights, but they were pretty well uniform throughout the batches.

    If you are breadboarding and just inspecting which pin is high or low on a uC or IC, then they are fine. But, they should not be used on anything you want to keep or show.

    So, you can find people who have 100% great reference, and have bought from them before, but eventually greed takes over and they replace their stock with cheaper stock because orders keep rolling in.

    knikbright...geesh.
     
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