DIY COB lighting

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.

 

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.

 

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.

 

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).

 

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.

 

Hi there, I wanted to chip in my 2 cents on this one.

Currently I’ve got a 36x36x18 enclosure like you. I spent a decent amount of time looking into lighting. I ended up going with this light from Amazon. It’s got a Cree COB, meanwell dimmable ballast/driver. It’s full spectrum so the colour is great. I didn’t want s purple blue light even if it was “better” for the plants.

Anyhow it’s 200 watts...2 x 100 watt Cree cob leds. I wanted the spread of two lights over a larger width tank. Plus this unit is dimmable so that’s even better. The plants are doing great. I’ve got jewel orchids at the bottom of the tank, and high high light loving plants at the top. I’m around 500-700 Fc at the bottom and at the top I’m running around 30,000 lux . A little high on the light for the jewels but they’re managing. I know I gave two different light measurements...I know that jewel orchids upper end is 500 fc and the other high light twig epiphytes require around 30,000 lux so hence the different measurements.

Anyhow, the light is turned down to about 65% or so. It’s well built it awesome replaceable top shelf components , and if I ever wanted to it could be re purposed easily or repaired easily with normal easy to buy parts.

They do sell a single cob unit, but it is not dimmable. And I opted for dimming , better light spread.

Also I mounted the light at a slight angle. So that the back “wall” of the enclosure would be getting the most light. An attempt to create multiple zones for different light requirements. I may add some “shade cloth” to help shade the jewel orchids a bit at the bottom but they’re all doing well, just growing a little short and squat currently

All the plants LOVE this light. Flowering and growing beautifully. Bit of an adjustment from growing with florescent lighting.

Here’s the light I got , a link on amazon. Yes it’s pricy but it’s worth it and extremely well built. I’ve worked with leds and meanwell products before, but I just wanted to get the job of lighting done and continue to work on other aspects of the setup. I don’t regret it one bit.

https://www.amazon.ca/Intensity-Spe...words=CF+Grow&qid=1557545365&s=gateway&sr=8-1