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Introducing CobKits.com - specializing in DIY and Citizen COBs

Discussion in 'LED and other Lighting' started by CobKits, Aug 2, 2016.

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  1.  
    Lost Green

    Lost Green New Member

    You're the man!

    Seriously though, you are a wealth of knowledge. Reading through your threads has been a huge help. You have ensured one more loyal customer.

    Hope the surgery goes well/did go well.
     
  2.  
    nxsov180db

    nxsov180db Well-Known Member

    False
     
  3.  
    CobKits

    CobKits Well-Known Member Rollitup Advertiser

    i put it off till 11/20 (week of thanksgiving)

    so just a heads up (will repost then)- no shipping on 11/20 or 21, maybe 22 , no 23 (thanksgiving), yes shipping fri. 24th
     
  4.  
    GrowLightResearch

    GrowLightResearch Member

    The OP posted the electrical characteristics where the forward voltage was 35V

    The voltage of a buck LED driver is a function of the LED's Vf. Not requiring any adjustment (aka auto adjust). It's a simple way to explain it to a novice.

    WRONG!! None of the chips will be running at their individual forward voltages as by the nature of physics the voltage at each chip will be the same when wired in parallel. They WILL run at their independent Vf when wired in series.

    The is no GOOD way to wire CoBs in parallel driven with an HLG. If you do not believe me wire some in parallel and measure the current going through each CoB.

    When wired in parallel the forward voltage must be the same because all the anodes and cathode are connected together at the same potential which means they cannot operate at their individual forward voltages. Wouldn't common sense say that is not a good thing to do?

    I just ran a test on two CoBs. At 600 mA the measured Vf were 33.4V and 34.2V powered by a HLG-60H. At 1200mA wired in parallel the currents were 768mA and 463mA respectively and the forward voltage 34.9V (higher than either of the individual Vf).

    Substantially??? Really? HLG-600 93-96% at 100% load and max voltage. HLG-240 93.5%. But what I was saying it is better to match the load to the driver rather than just pick a driver capacity willy nilly. It is best to maximize the forward voltage and have the string of LEDs just under the driver's max voltage for the best efficiency.

    As an electrical Engineer I worked on designing military grade switching power supplies beginning in 1978. It is you that does not fully understand how to properly wire CoBs.

    The key there is "with adequate cooling". As you increase the current over the test current the efficiency will drop 30% between 1200mA and 2400mA, the forward voltage will rise (increasing wattage) and due to mediocre thermal resistance, the temperature will rise further diminishing efficiency. Sure you can run them at 2.5 amp, but you will need substantial (i.e. costly) thermal management and efficiency will be significantly diminished. It is best design practice to design a passive heatsink then add a fan. this way when the fan fails you will not damage the CoB. You cannot do economical passive cooling at 2.5 amps.

    The case temperature of these CoBs will run about 100°C at 700mA with minimal thermal management. The max operating case temperature of these CoBs is 105°C.
     
  5.  
    GrowLightResearch

    GrowLightResearch Member

    WRONG!
     
  6.  
    nxsov180db

    nxsov180db Well-Known Member

    Correct, wrong is another word for false.
     
    key4 likes this.
  7.  
    nxsov180db

    nxsov180db Well-Known Member

    Still wrong. I run what most people would consider a decent size grow op, I have well over 100 COB Led's all wired parallel and I didn't just start yesterday. Why are you even here?
     
  8.  
    CobKits

    CobKits Well-Known Member Rollitup Advertiser

    sure thing "VegasWinner". sorry i dont have time to pick thru all your points one by one. ill let the thousands of cobs in hundreds of rigs out there running in parallel speak for themselves.

    to address one point: 96% is indeed substantially more efficient than 93.5%, esp when it can be achieved for pennies a watt and people are tripping over themselves to get incremental efficiency with cob and cooling selection and current reduction
     
    key4 likes this.
  9.  
    CobKits

    CobKits Well-Known Member Rollitup Advertiser

    10" center to center at 60W sounds fine you could prob go 12"

    depends on width of coverage and if there are cobs in the other direction
     
  10.  
    Dave455

    Dave455 Well-Known Member

    Any Black Friday pre sales ? hee
     
  11.  
    CobKits

    CobKits Well-Known Member Rollitup Advertiser

    we'll see!
     
  12.  
    Humanrob

    Humanrob Well-Known Member

    I hope cobkits.com comes back online soon...

    Screen Shot 2017-11-10 at 8.28.23 AM.png
     
  13.  
    GrowLightResearch

    GrowLightResearch Member

    Yes you can wire them in parallel and they will light up. The problem is the current flowing in each CoB will be significantly different. If you do not care about not having any uniformity and having hot spots, continue to wire them in parallel.

    Each CoB has a slightly different forward voltage. When wired in parallel they will all have the same voltage because they are all connected to each other. It's simple DC fundamentals being violated.

    I'm just saying wiring them in parallel is wrong. If you think you know more than me, ignore this.
     
  14.  
    Humanrob

    Humanrob Well-Known Member


    How much variation do you think there is between COBs (you say "significantly different")? They are built to a spec with certain tolerances, I'm wondering if its 2%, 5%, 10% +/- is the normal variation from one to the next?

    For my lights, so far I have one in parallel (only two COBs connected to the driver) and all the others are in series, but I was thinking about building another in parallel. Honestly, if they are off by less than 5% I'm OK with that.

    Also, in your second sentence you say, "When wired in parallel they will all have the same voltage because they are all connected to each other." Did you mean to say "in series"? Otherwise, I'm confused.
     
  15.  
    nxsov180db

    nxsov180db Well-Known Member

    Significantly different? I doubt it. I am sure it would be possible for 2 cobs to receive significantly different current if one or both of them are out of spec by a good amount. I wire each set of 8 COBs parellel and connect them to a HLG-320H-36A and I get uniform par readings under each COB.
     
  16.  
    TD816

    TD816 New Member

    Hows it going everyone, new member and just placed and order with cobkits last night. Man theres alot of info through out these 156 pages and its best to smoke after reading I've figured out haha.

    Just wanted to say thanks to Cobkits for providing a great service at great prices.

    Looking forward to growing with these 5 citi 1212's just need a driver for them. Would a Mean Well HLG-240H-C1400A be enough to run them or should i be looking at a different driver?
     
  17.  
    CobKits

    CobKits Well-Known Member Rollitup Advertiser

    he is misinformed and doesnt understand these systems, at all
    yes there are current variations between cobs, no its not enough to cause hotspots. there are also flux and voltage variations when cobs are run in constant current in series, same deal

    "growlightresearch" appears to be another in a long line of trolls which is why hes in this thread and not out there making his own thread about the "dangers" of parallel wiring
     
    Last edited: Nov 10, 2017
    key4 and nfhiggs like this.
  18.  
    CobKits

    CobKits Well-Known Member Rollitup Advertiser

    wordpress plugin gone wild

    update: is back up
     
    Last edited: Nov 10, 2017
    pop22 and Humanrob like this.
  19.  
    BuddyColas

    BuddyColas Well-Known Member

    I was not agreeing with growlightresearch. He's a legend in his own mind. Just saying I've had good success running both series and parallel cobs. Much respect to your patience in answering 150 pages of questions...with many repeats, and for your detailed tests and comparisons! Thanks.
     
    pop22 likes this.
  20.  
    Humanrob

    Humanrob Well-Known Member

    . :)


    @CobKits -- do you know when you are going to get more 1818 3000k 90 CRI cobs in?
     

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