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How to power one or two of these clusters

Discussion in 'LEDs and Optoelectronics' started by Lol999, Mar 3, 2019.

  1. Lol999

    Lol999

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    Feb 16, 2017
    Hi, not had to worry about electrical stuff for a while but digging out an unfinished project I have come across a couple of led applications I have to finish.
    I bought a couple of these:
    https://www.joom.com/en/products/5ae6dcd88b2c3701f94ecfcc

    and am curious as to what sort of psu and circuit would be necessary to have a switching system for either one or both clusters to be lit at once?

    any help would be much appreciated thanks.
     
  2. Bluejets

    Bluejets

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    714
    Oct 5, 2014
    Appears they connect directly to 12v dc.
    At 8w a piece you would need around 1.5A (or more) supply capability to drive 2 units in parallel.
     
  3. Lol999

    Lol999

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    Feb 16, 2017
    cheers, would it be too much current if just feeding one cluster?
     
  4. Alec_t

    Alec_t

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    Jul 7, 2015
    One cluster would draw less current than two. so the 1.5A supply would be perfectly happy.
     
    Martaine2005 likes this.
  5. Lol999

    Lol999

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    Feb 16, 2017
    cheers, much appreciated :)
     
  6. dave9

    dave9

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    Mar 5, 2017
    You may have some trouble getting those to the correct drive current. I have not used this particular product but it looks like many where they did an extremely poor/lazy/cheap job of it, just threw 4 LEDs in series, and paralleled several series of 4.

    They're thinking that at 12.0V each LED will drop about 3V each which may work, but they intend it for automotive which gets up to 14.4V and it may burn up at that voltage, unless they have done something not evident (one picture has a surface mount component that I assume is a resistor but it looks more like an inductor or capacitor) which allows it to run at the right drive current limit at 14.4V but then would run way under spec at 12.0V, and most of the pictures don't have that component.

    It would be easier to suggest "Just don't use this", because it's not set up well for equal current sharing even with a current regulating driver, but then if you use a voltage regulating driver instead, it becomes a science experiment where measurements, and fine tuning with more parts may be needed.

    You asked "what sort of PSU" but you did not tell us if it will be mains powered. If doing mains powered and I had a terrible itch to use some of those COB modules because I already had them and was bored, I would try one of these "20W 6-10X2(3)W AC85-277V 50/60Hz DC 18-35V 600mA 6-10pcs 3W and 1pcs 20" with the two COB modules wired in series:

    https://www.ebay.com/itm/High-Power...tant-Current-COB-Chip-LED-Driver/122480543106
     
  7. Bluejets

    Bluejets

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    Oct 5, 2014
    At $3 I'd just suck it and see do-to-speak.
     
  8. dave9

    dave9

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    Mar 5, 2017
    ^ Yeah I know the cost is trivial, but say you want something that works more than a few hundred hours, you're investing time and materials (for a housing & heatsinking, soldering PSU wires to two COBs is the least of the time spent to do it right).

    It could be better to just throw them away now and design around different LEDs, but regardless, I'd want some current margin if trying a voltage regulated 12V, at least 2A rating and that's not much cheaper (if any) than a current regulating LED driver. The one I linked was only $6 delivered, and if it turns out that these COB modules are failure prone junk, the LED driver can be reused with good quality LEDs instead, in single series for proper current regulation.

    For example you could get one of the other ~ $6 drivers at the link I posted, like the "20W 3-6X3W AC85-277V 50/60Hz DC 12-20V 900mA" and power the following $4, 5 pack of Cree XT-E in series to produce more light with less power, more reliably, with easier heatsinking. I assume Lol999 knows that the 8W COB modules need heatsinking added, more of it too, than 5 of these will at the same light output:

    https://www.fasttech.com/product/2058900-cree-xt-e-450lm-4500-5000k-led-emitter-5-pack
     
  9. Lol999

    Lol999

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    Feb 16, 2017
    hmm this is looking like a no-go with the modules I have bought but that's not a problem.
    I'm making a steampunk lamp for someone and I would like it if possible to run off a wall wart so the need for PAT testing is obviated (I live in the UK).
    If someone could suggest some components to make this assembly then it would be much appreciated.
    FWIW the housing for these components is a large metal food mincer - good heat sink?
     
  10. Lol999

    Lol999

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    Feb 16, 2017
  11. dave9

    dave9

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    Mar 5, 2017
    I haven't built any lights with those integrated COBs, but I do have a cheap work light with one. Unfortunately I haven't ran it for long enough to know if it's going to have good lifespan. It is 12W, and came with a heatsink, but the whole thing got so hot that I upgraded the heatsink. It still gets quite hot, if the COB does fail then I"ll put in a lower wattage replacement.

    As far as not needing one on a COB, you're pretty much limited to 2W. They don't give you extra metal to get that done, assume one way or another you're going to heatsink it. In some cases even 2W may be better off with one.

    When I write heatsink, it doesn't have to be a traditional one. If you have an aluminum plate or chassis you're mounting it to with grease as the interface that may work, just a matter of sufficient thickness behind the COB, surface area, and airflow.

    When DIY, sometimes it's easier to start out with the enclosure/heatsink/etc or budget if you don't have materials, then decide how many watts it can handle.

    Keep in mind that one with a mains powered driver integrated onto it, requires more care in ensuring good/safe electrical isolation so it isn't dangerous to random unaware people/pets/etc.
     
  12. Lol999

    Lol999

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    Feb 16, 2017
    cheers mate. the cob will be attached to a large metal food mincer, weight about 5-8lb and have air clearance around it.
    I've ordered some thermal adhesive to affix a cob to the vertical surface it is intended for.
    I assume the earth point on the cob is a matter of attaching an earth wire with a suitable circular crimp and a nut and bolt?
    Seeing as it will be mains powered I will have to have it PAT tested anyway so that will highlight any earthing problems etc.
     
  13. dave9

    dave9

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    Mar 5, 2017
    There is no earth point on the COB (not necessarily at least, but the one you linked looks like it has markings for one, you could if you wanted to as you described), but it would be best to earth ground any exposed metal portion of the chassis, especially if the metal it is heatsunk to is electrically conductive to it. The same mounting fastener might be able to do both the COB and chassis.

    I might also look into insulating washers on fasteners if the traces on the COB are right up against the mounting points.

    A food mincer seems a strange place to put one? The mechanical aspects of attaching, heatsinking, aiming/reflecting the light is probably going to be the larger part of the project.

    Everyone has their own reference to what "large" is but I wouldn't think a personal sized mincer would need that many watts worth of LEDs, assuming the area has other ambient lighting too.
     
    Last edited: Mar 11, 2019
  14. Lol999

    Lol999

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    Feb 16, 2017
  15. dave9

    dave9

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    Mar 5, 2017
    Although the LED page you linked has 3 different LEDs on it, all seem to have a series of LED dies internally at 300mA current, and the linked driver page also has multiple models, but all at 300mA current, so yes it appears the driver should be suitable if you pick the one with a corresponding output voltage range to the COB you chose.
     
  16. Lol999

    Lol999

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    Feb 16, 2017
    many thanks!
     
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