1. The driver should be constant current sources. The voltage output can vary within a limited range to regulate the constant current. All diodes will have a characteristic curve in the datasheet that shows the relationship between current and voltage. Diodes do not follow V=IR, and instead of have an exponential relationship defined by the characteristic curve. For the current you want to run at, find the corresponding voltage on the characteristic curve in the cobs datasheet.
2) The efficiency for a given COB is always better when run at a lower current, but 350mA, 500ma, 700mA, 1050mA, and 1400mA are the best options for the available 91-94% efficient drivers. Pick one of those currents.
3) The datasheet explains it
4) Big. You probably will need a fan to get Tc below 70C in most setups. The baby killers are about what you need to get 20W dissipation at 47% efficiency to 35C. The 80W UFO killers will work fine without fans, but efficiency is greatly increased with a reduction of Tc from 70C.
5) Look at all the larger HLG-C driver datasheets and find how many cobs of each kind you could fit in series given it's voltage range for the current you want to run at, then pick the configuration that works best for your growing space.
Church, very good stuff. Your heat sink and hanger mounting looks very clean and professional. I noticed a Chinese vendor that sells COB lights laid out very much like yours, (Google 432w Spider COB LED by Twilight Group) I noticed it when doing more research on the 80w UFO Killer. They don't list prices or what model COBs they use (of course) but I thought it would be a good comparison for others to see how much they could save by DIY rather than buying commercial. It also has some light testing info there but if they don't list what COBs they use, I guess that doesn't help much. I asked for pricing in an email so we shall see what they are asking for them soon.
Update: Apparently this company is a sponsor on another grow forum site (420 Mag) and there are FAQs there that lists the specs of the COBs, appears they use Epistar: Pricing though is not listed.
Epistar LED
ES-CADBV45P Venus-series blue 450 45mil 700mA
ES-CABLV45P Venus-series blue 460nm 45mil 700mA
ES-SMSOPX42 UHB-PX orange 615nm 42mil 700 mA
ES-SMHRPX42 UHB-PX red 624nm 42mil 700 mA
ES-SMBRPN42C UHB-PN red 660nm 42mil 700 mA
ES-SMHFPN42B UHB-PN red 730nm 42mil 700 mA
UV and White from Epiled
Epiled
EP-U4545K-A3 45mil UV
EP-B4545V-A3 45mil White
Well, Twilight replied to my email about the Spider 432W COB, they seemed nice enough. The Spider 432W COB LED (4ea X 108W user replaceable COBs) is currently $259.50. Using Epistar COBs, they claim 17280lm, actual draw 265W, driven at 600mA. There are two spectrum ratios you can choose between.
It says the enire body acts as the heatsink, so I wonder if it is just one large square heatsink with all 4 COBs mounted to it. Also, I wonder if there is just one driver in there and they are all wired in series. I would suspect it is for keeping cost down. I don't know if the Chinese made Epister COBs and driver would be junk, or if it would perform as well as the Cree and Bridgelux. This one has lenses on it too, which looks nice and I guess if you are selling them commerically you have to consider liablity, safety due to exposed chips, etc. You could always take them off if you wanted to.
There is a spec sheet for it here:
http://www.twilightgroups.net/sitefiles/services/cms/utils.aspx?type=Download&publishmentSystemID=2&channelID=5&contentID=6
So for $260 it has a case and everything, not sure if the same money would build a much better DIY. I am still learning about electronics with LEDs, (mostly the math,lol!) on how to match up the proper driver, use one driver with 4 COBs in series, or is it better to run 4 drivers, computing mA, forward voltage, etc.
I am still confused as to determining what the wattage of a COB LED is without digging into the spec sheet for each. I know drivers use a constant current and a dynamic range of voltage based on operating temps and draw of the LED, but isn't there a quick way to know that "Cree XXXX..." is a 10 or 50 watt COB? How do you know which COB to select for the wattage you desire, eg; I want to make a 4 COB 250W HPS equivilent DIY for a small cabinet, not a 1000W? Assembly is not an issue for me.
If running them soft which COBs would be best to buy and which driver for having 4 of them in series for the same output? Is wiring in series better than parrallel with COBs or does it not matter as long as you have a big enough driver for all 4 COBs?
........................nice build church
