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DIY COB lighting

Discussion in 'Growing Areas' started by ezluckyfreee, Sep 21, 2018.

  1. ezluckyfreee

    ezluckyfreee New Member

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    Hi everyone,

    so I've been looking through the very helpful blog post here by Naoki:DIY Chip-on-board (COB) LEDs

    On DIY COBs, and I'd love to try putting a couple together as they are way cheaper than my current lights. The biggest problem for me is drilling the holes into the heatsink to attach the COB to it.

    My question is: do we have to drill holes? Would it work to just epoxy them or something similar?

    Thanks!
     
  2. carl

    carl Active Member

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    I'm not sure epoxy is the answer, you want an adhesive that's thermally conductive, and somewhat flexible, as you're going to get differential expansion between COB and heatsink. The one I built used a COB that had an adhesive-backed substrate.

    Anyway, aluminum is not hard to drill. I have a cheap-a harbor freight drill press ($70), and used that, but a hand-held drill would work just as well. Using a little light oil when you drill, kerosene works, as would say 3-in-1 oil, will help the drill run cooler.
     
  3. naoki

    naoki Well-Known Member

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    There are some thermal epoxy. But I haven't used them. Generally, the epoxy wasn't as a good heat conductor as the thermal paste. I have forgotten the details, but I remember that Cree wasn't recommending thermal glue for COB (I might be wrong). But we run them at a much lower current than the nominal current, so thermal epoxy might be good enough.

    I haven't checked the price recently, but I'm pretty sure Bridgelux Vero is better deal than Cree now.

    What kind of area are you trying to cover (grow area and height from the plant) and what kind of plants are you growing? The strip types (Bridgelux EB-strip Gen 2, Samsung F series etc) might be easier and better. For example, with EB, some people runs it without any heat sink. So all you have to do is connect them to the driver, and hang them some place. Or you can glue them to aluminum C-channels like this : Samsung Linear LED module H-series Gen. 3
    I used H-series, but I think F-series is a better deal now.
     
  4. ezluckyfreee

    ezluckyfreee New Member

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    I'm trying to light up a 36"x36"x18" exo-terra.

    I don't really plan to grow any low-light plants in there, and I'd like to be able to grow high-light stuff close to the top of the tank and med-light elsewhere.

    Ah thanks. I saw your post on the Phillips LED strips but I guess that's a couple years old!. The plan was to do two 50W COBs hanging at the top, and a single strip down the corners of the tank facing towards the mounted plants (beside the doors if that helps the visualization). What do you think?

    I currently have a 50gal fish tank, lit with a 65W board from Horticultural Lighting Group (which is great quality but was very expensive compared to this DIY stuff). I can grow very high-light stuff right under it so I will probably keep this setup as well.
     
  5. naoki

    naoki Well-Known Member

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    If you are going with some decent COBs, I think 2x 50W COBs on the exo-terra will be at a rather high-end. I was using 36"(W)x12"(D)x24"(H) for Cattleya, and they grew well with 2x CXA3070, driven at 25W each. I'm guessing that the PAR efficacy of this older COB is probably similar to your set-up with Horticultural Lighting Group. 55 gallon tank is a bit bigger than mine, so I think with 65W, they were getting similar intensity.

    If I were you, I would probably go with 2' Bridgelux EB strip Gen 2, and use 4-5 of them. As you mentioned, it would be good if you can use some of them on the side wall to get more even illumination (e.g. 3 strips on the top and 1ea on the doors attached vertically). With 700mA, each strip is 13.6W. These give a bit more light per watt, so it will be quite a bit more than your 65W light.
     
  6. ezluckyfreee

    ezluckyfreee New Member

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    First, thanks so much for your help! Navigating this stuff is not easy.

    5 of those bridgelux strips will cost me CAD $75, whereas two of the bridgelux vero (like BXRC-40G4000-C-73-SE) are only ~CAD $ 27
    . Although I would have to get heatsinks for COBs, but that only adds $20. Seems safer to me to err on the side of too much than too little light, cause I can always drive them at a lower wattage, right? Will they be too intense near the top of the exo-terra you think?

    My girlfriend's father has a drill press he can lend me, so drilling the heat sinks is no longer an issue. I have an automatic watering loop setup, and I've been toying with the idea of using the outgoing water as a liquid cooling thing, have you ever tried that?
     
  7. naoki

    naoki Well-Known Member

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    If you are going with dimmable constant current driver, then you can dim (i.e reduce the current). But if you are going to dim dramatically (<50% of the normal current), then the driver efficiency (AC -> DC conversion) is reduced. Now with the lower current, efficiency of LED (electricity -> light) is increased. It depends on the driver, but in general, with dramatic dimming, the overall efficiency goes down.

    Since you mentioned 50W each, I assumed that you were thinking of Vero 29. But Vero 18 SE is about 40W at their nominal current. When they calculate the nominal current (to balance the initial cost and efficiency), they probably assume that they are used much shorter duration per day than grow lights. So in general, for us (12h/day or so), it is better to drive them softer than their nominal current. But if your electricity is cheap, you can drive harder (or at the nominal current). With 2x Vero 18-C, I would probably use the cheap non-dimmable LPC-60-1400 with 2 Vero 18 connected parallely (each get 700mA, so around 25W each) since we pay >20 cents /kWh. But with cheaper electricity, LPC-100-1050 gives the approx. nominal current (1050mA) and you'll get 40W each, which is probably a good amount. You need to connect Vero 18 in serial in this case. Dimmable drivers are a bit more expensive. The cheapest dimmable is probably Meanwell LPF series.

    In one of my enclosures, I wanted to put LEDs inside of the enclosure instead of going through acrylic ceiling (to reduce light loss). If I put the COB inside, it overheats (for a relatively cool growing orchids). So I thought that I would use water cooling to pump out the heat. I got materials (heat blocks, a water pump, and a radiator + fan) with CXB3070. But before I assemble the system, I discovered Samsung H-series. So I didn't try water cooling. H-series is more efficient than COBs, so it doesn't overheat the enclosure. For 3'(W)x2'x2' enclosure, I have 2x 2' of H-series (40W) + 2' XF-3535L (22W). It is fairly tight enclosure, but it raise the temperature only slightly. If you do, you should implement some thermal protection in case the pump dies.

    The linear modules are a bit more expensive than COBs as you mentioned. But I recently prefer the simplicity of the linear modules. With active cooling of COBs, it is better to use thermal protection (e.g. I mentioned it in here LED Driver). CPU fans are pretty reliable, but my thermal protection did kick in when one of the fan failed. You can do passive cooling of COB, but the heatsinks can be quite a bit more expensive. With linear modules, we don't have to worry about those issue, and it is super simple to assemble (and a bit higher efficiency).
     
  8. ezluckyfreee

    ezluckyfreee New Member

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    Alright so I think I have my lighting setup planned out. I chose linear modules, as you made some good points with the ease of use.

    6x
    Bridgelux BXEB-L0560Z-40E2000-C-B3

    1x
    Mean Well Enterprises LPC-100-1400

    This is about 15,000 lumens and it'll cost about $105 CAD.

    The plan is then to have two parallel sets of three linear modules in series.

    Since each linear module uses a nominal drive current of 700mA, this should drive both sets at the nominal current. Each module has a vF of 19.5, therefore a vF of ~60 for each set of three, and this power supply has a voltage range of 36-72V, so that is fine.

    I guess the one thing I am unsure about, is that this power supply puts out 100W, but the "typical power" of each linear module is 13.6W. In total that is only 81W, so will I have to overdrive them if i wanna use this supply?

    Perhaps I should choose a different supply and drive them under the nominal current?

    There is the
    LPC-60-1750 in stock at the vendor I want to order from (arrow.com, they are cheaper for Canadians it seems). It is cheaper and I could get around the different current supply by doing three parallel sets of two each, but this would underdrive them by a lot.


    Thank you!!




     
    Last edited: Sep 25, 2018
  9. naoki

    naoki Well-Known Member

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    I think that your combination will work well (with quite a lot of light).

    LPC-100 series is rated up to 100W, but you are right, you'll be using around 80W. This is not over-driving. The driver still supplies 1400mA = 700mA ea (remember this is a constant current driver?). So the LED modules are at the nominal current. The driver efficiency (AC/DC conversion) is slightly lower since it is using 80W instead of 100W (the driver is most efficient at the maximum wattage). But I wouldn't worry about it. The Meanwell data sheet doesn't provide the information about the load vs efficiency. They do give this kind of info for some other dimmable drivers. Base on these other info, I think you'll be still getting a decent AC/DC conversion efficiency at the 80% load. For the cheaper drivers, LPC-100 is probably the best match for your situation. There is dimmable LPF-90D-42 (2.15A, 25.3-42V), but it is usually $15-20 more expensive than LPC.

    But you might want to consider LPC-100-2100, 3 parallel sets of two each. This will give the same amount of light (700mA each). Below, I included the reason why I would prefer 2100mA version over 1400mA version.

    In general, a single serial circuit would protect the light best (e.g., HLG-80H-C700, which can do 700mA with 117V=19.5*6). If one module completely fails, other modules will not receive the electricity, and all of them get turned off (so the other modules are protected). The driver shutdown in this case. I should note that a complete failure of the entire module is unlikely. Within each module (same of COB), there are multiple parallel circuits. So if one LED dies, only a small portion of the module gets turned off. The only time a module completely fail might be when the wire connected to the module get disconnected. However, the single serial loop is problematic because you have to use a high voltage driver (more dangerous for human).

    If you were to consider the (unlikely) complete failure of a module in parallel circuit, with 2x parallel, the current would double in the module which didn't fail. So it would receive 1400mA. But if you have 3x parallel, failure of one module causes that the other 2 modules to receive 1050mA. EB should be ok in either case, but the later scenario is more gentle to the modules.

    So I would wire like this:
    Code:
         / LED1 \    / LED4 \
    + ---- LED2 ------ LED5 ----   -
         \ LED3 /    \ LED6 /
    
    This is safer than:
    Code:
         / LED1 ------ LED4 \
    + ---- LED2 ------ LED5 ----   -
         \ LED3 ------ LED6 /
    
    When LED1 dies, with the former, only LED2 and 3 receives the extra current. But with the later, LED2,3,5,6 receives the extra current.

    LPC-60-1750 can't be used. It is rated for 9-34V. Serial connection of two requires 19.5 * 2 = 39V.
     
    Last edited: Sep 25, 2018
  10. ezluckyfreee

    ezluckyfreee New Member

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    Ah ok, thanks so much! I understand now.

    LPC-100-2100 isn't carried by arrow.com unfortunately, so I'll go with the setup I specified.
     
    naoki likes this.