Questions for the DIY CXA COB experts

First of all, thank you Supra and Cap’n Morgan. You guys are winning the internet with your DIY CXA threaqds and Cree flowering threads. Been following a long time, and just terrific stuff. Thank you for your time and effort on these projects.

I am a noob to wiring/electronic assembly/diy lighting. I have followed the threads, but have some questions that I am still unclear on. So any input form anyone would be greatly appreciated.

1) What do you all think is best, ideal/molex cxa holders or just thermal adhesive? I like the idea of the holders because I do not have to solder. But following Cap’n Morgan has made me realized it’s more involved than I thought (I don’t wanna buy a drill press!). OTOH, it’s only 2 places to solder per cob, how hard could it be. OTOOH, I would have to ditch the heatsink if the cob died. OTOOOH, the heatsink is the cheapest part. OTOOOOH, it also takes the most labor to make flat, and I would like to avoid doing more sanding than necessary. Whaddya all think?
2) What about COBs as side lighting? Would using CPU heatsinks in an application where they are not facing “down” (as in most applications here) but to the “side” interfere with heat dissipation?

3) What do you use to connect the driver to the power cord? Just wirenuts, or…..? Capn Morgan mentioned needing fuses. Why are fuses necessary and what kind does one need?

4) Any reference to a good wiring schematics or video? I am a noob basically to wiring. I am specifically wondering how you connect a single power cord to multiple dirvers. Just take the positive from the cord and link it to all the positives from the driver (and same with the negative)?

5) If I were to design a passive COB, how much surface space would I need to dissipate 55 W or so?

Thanks all.

Alright Mr Bangalot,I'll throw you a few of my ideas on things. The holders are just a option that I chose for two reasons,I've done a bit of soldering and welding but not much with electronics or small wire connections like the COB and I liked the idea of being able to change COB's if one dies or I want to upgrade. Flattening the cooler maybe took a half hour each so not that big of a deal but a work out if you sit and do a few all at once and a must if you use a holder with a ceramic COB. Tapping that small of a thread is best with a drill press to keep things lined up,if you start the tap crooked you won't be able to tap it deep enough without it binding or braking,if you can figure another way to keep your drill and tap lined up with some sort of guide. If a cooler has a fan, orientation shouldn't matter. I bought some extension cords from home depot for like $1.50 and gave each driver it's own cord. I'm driving my COB at 1.4 amps and the COB can max at 2.8 amps so I put a 2 amp auto fuse between the COB and driver on the positive side for overload safety. Wire colors can vary from one company to another but would be documented.

Hey Billly. As you have probably seen I use high conductivity thermal paste and strap the COB down with kapton tape. It is not the best looking solution but it gets the job done and you get a better thermal transfer than you would with thermal adhesive. Soldering with 63/57 lead solder is very easy, but I can see the appeal of a no-solder approach as well.

I think COBs for side lighting would work great and there is no problem with running the CPU coolers sideways.

Very important warning for beginners regarding AC power wiring, this part of the build has to be treated with the utmost care and respect because 120V will easily jump through your skin and there is a ton of current backing it up. Another danger is the possibility of sparks or heat creating a fire hazard so it is critical to make sure wires are not damaged, connections are secure, and no conductors exposed anywhere in the circuit. I have been shocked dozens of times because I grew up messing around with greenhouse wiring (idiotic things kids do...). So getting shocked doesnt mean you drop dead, but if the conditions are right it is possible. You can increase your personal safety by adding a GFCI outlet to this circuit. I zorked myself just last month because I was working on a wire that I thought I had unplugged, and of course no GFCI.

For power cords I did the same thing as Capn, extension cords from Walmart. I cut the female end off, stripped the wires and used crimp slide connectors to connect to the driver. Then I cover the connections with heatshrink tubing. I use slide connectors because I am constantly swapping components, but you could use crimp on butt connectors for a more permanent and secure connection. Mr Flux suggested WAGO connectors which are cheap on eBay and would allow you to power several drivers with one cord. You are correct, they connect in parallel. Most drivers are fused on the AC side but I like to add a fuse on the DC side to try and protect the LED in the case of a short or driver fault.

For passive heatsinking, I recommend 100cm²/W (dissipation watts).

Good luck!

Great answers so far.

You could consider using a 2 part thermal adhesive mixed with 1:1:1 with a thermal paste. I haven't tried it myself but apparently it is much easier to remove. I would personally use a non conductive paste (think artic alumina instead of artic silver). Also, you have to solder the Cobs before you mount them or the heatsink will just draw all the heat away from the pad and you won't get a clean long lasting solder joint. Not to scare you, but the cobs are much smaller in person and you should practice soldering on other electronics before moving to the cobs of you don't have much experience. Don't forget the flux, too

Regarding the AC side, I personally wouldn't trust anything but soldered and double heat shrunk connectors with strain relief unless it was mounted inside an isolated project box. No wire nuts for me...

Be sure to post your progress!

Awesome, thank you guys. Pretty much filled in most of the gaps in my understanding of this.

Supra when you say "For passive heatsinking, I recommend 100cm²/W (dissipation watts)." Do you mean total surface area (i.e. the "front" or "face" of the heatsink + the surface area of the fins) or just the surface area of the "front." Cuz, goddam, either way, that's a lot of surface area of one watt. Oh well.

Those Wago connectors look like the shit. Too bad I don't need 50 of them, lol.

I have been zapped by 220V (exposed/worn 220v wires and mop water - no bueno!), so bring it!

Given all the above advice, I think holders are the way to go for me

Homer, I mean Cap'n, are you just going to use these individually or integrate them into a fixture of some sort? Dude on here the other day with the cxa light bars, looked pretty bad ass. Seems like a lot of possibilities as to making fixtures.

One last question(ish) - how far apart would you space the cobs for optimal spread if using 4 cxa 3070 or 3590? Gaius' thread had them on a 3 X 1 board, looks like his spread was pretty good, but wondering if there was some unwritten rule or best practice for this.

Again thanks all

I'm using mine individually so that I can adjust them to the plants easily,just manipulate the chains to move up and down or tilt them.

It's hard to give a one-size-fits-all answer. I'll throw some thoughts out there. If none of these apply then you might want to do different.

The idea of using a holder appealed to me immediately. Gluing the COB's down irreversibly was something that did not appeal to me at all.

I didn't have huge chunks of aluminum heatsink like Supra, and I didn't want to buy. I had several CPU heatsinks laying around, so decided to put them to use. I wanted to be able to abandon the CPU coolers with minimal fuss in case I found a sack full of large aluminum heatsinks along the side of the road.

I've got a basic drill press. I can borrow drills and taps from work. I've drilled/tapped stuff since I was a teenager so it's not intimidating. I've soldered stuff since I was a kid too, but didn't like the idea of buying COB's and immediately doing dangerous things to them.

AFAIK Molex doesn't make holders for the CXA 30's or 35's yet so Ideal seemed to be the best choice.

I didn't mess with sanding any of the CPU heatsinks I've used.

You could use a hand drill to make the holes, but using a press is so much better. The holes are perpendicular and straight, not sideways and wallered out.

The tapping part was easy by hand. A little tap wrench is the best way to go but I did OK with a small needle-nosed Vise-Grip. With a small tap like that, you have to be very gentle, and you have to make an effort to keep the tap straight as you begin to cut thread. Especially the first 3/8" or so. Use a tapping fluid, like Rapid-Tap. If you feel the tap starting to resist, stop and turn backwards a half-turn to clear the chips. And make sure you don't run the tap all the way to the bottom of the hole. If you torque the tap and it's on the bottom, it will break.

If you decide to go with a holder, and you're not familiar with drilling/tapping, I'd suggest getting the right drill bit and tap, and practicing on a scrap piece of aluminum. Hit up a buddy who works with metal, ask a metal shop for a piece of scrap, whatever. Then place a piece of wood under your aluminum and clamp that to a bench and practice. After you've done a half dozen your confidence level will be much higher. I'd venture to say that a guy could practice for an hour or so with a hand drill and get to a level of high proficiency without a drill press.

I wouldn't worry too much about optimal spread. Just come up with some sort of framework above the plants that allows you to move them around. It'll be pretty obvious as you go along. IMO giving yourself some method to tweak things left or right is more helpful than bolting them to some pattern that you picked up off the web.

Nice setup Capn!

Yes I was referring to total surface area. This is an example of 110cm²/W passive cooling. It gives a great spread in the canopy and as capn and Mel have pointed out, adjustability is helpful.


I have found that when I add a fan I can add watts and still run cooler, so I have been converting to active cooling. More complex system but those heatsinks are expensive so might as well put them to good use.

SupraSPL said:

Nice setup Capn!

Yes I was referring to total surface area. This is an example of 110cm²/W passive cooling. It gives a great spread in the canopy and as capn and Mel have pointed out, adjustability is helpful.
View attachment 3138852 View attachment 3138853 View attachment 3138854

I have found that when I add a fan I can add watts and still run cooler, so I have been converting to active cooling. More complex system but those heatsinks are expensive so might as well put them to good use.
View attachment 3138872 View attachment 3138875

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Inside my mind .....

here is a question, im not sure how you would regulate amperage output but.. ever consider a computer power supply to power the LED COBs?

ive seen in other fourms of people asking the same question but powering only a few 1w and 3w LED lights. being that the power consumption of these COBs is about 45W i could see a power supply being a good source for these lights, the only problem i see is going about how to regulate the amperage. maybe a resistor could be added? this is only an idea and maybe something someone could use if they couldn't find a driver or needed to power a large set of lights. being that a 500w power supply is 40 bucks. it might be something to consider

HolyGhost23 said:

here is a question, im not sure how you would regulate amperage output but.. ever consider a computer power supply to power the LED COBs?

ive seen in other fourms of people asking the same question but powering only a few 1w and 3w LED lights. being that the power consumption of these COBs is about 45W i could see a power supply being a good source for these lights, the only problem i see is going about how to regulate the amperage. maybe a resistor could be added? this is only an idea and maybe something someone could use if they couldn't find a driver or needed to power a large set of lights. being that a 500w power supply is 40 bucks. it might be something to consider

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Not going to work , These cobs run on about 38 volts. PSU,s for computers have 12 volt rail 5 volt rail and a 3.3 volt rail. Nothing even close to 38 volts. You want to use LED drivers or a constant current power supply rated to run LEDS.

HolyGhost23 said:

here is a question, im not sure how you would regulate amperage output but.. ever consider a computer power supply to power the LED COBs?

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If you want the PSU to work, you would use a dc to dc step-up converter....probably a good idea for higher current.

You can look on Ebay for cheap versions, just watch for specs...

The basic principle is converting the original DC into AC, then step this AC up to the desired value by a transformer, finally rectify it to get the necessary DC voltage.

http://www.edaboard.com/thread85462.html

One of the most important pros of this principle is we can use the AC with the frequency higher than the mains, upto hundreds thousand hertz, so we can use the smaller transformer, smaller filtering capacitors and inductors, thus get the smaller and lighter DC-DC converters. In the other hand, we can stabilize the output voltage easily.

Depending the power you need, or how important your project is, so you can design by yourself the simple circuit with 2 transistors and a transformer, or use a 555 timer as astable multivibrator with the power amplifier on transistors, or design a more complicated DC boost converter, or use the dedicated ICs for this purpose such as popular MC34063

But...Supra gave their opinion on the efficiency of such a setup and currently, they tend not to be as efficient as direct constant current drivers.

Things change and there are some other ways down a converter path that may yield more efficiency, is that the road you will take? Or harder answer than you were looking for ?

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PC PSU + buck +chinese COB = What's the point. Get a 315W CMH you'll get much better results and the bulb will probably last longer than the LEDs

overthinkingismything said:

PC PSU + buck +chinese COB = What's the point. Get a 315W CHM you'll get much better results and the bulb will probably last longer than the LEDs

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what are you referring to?

nvm holy shit thats old skool....the point....is to get bud? and if you can do it with crap laying around why not?

The inefficiencies of running a PC PSU, plus the buck driver needed to convert the VCD, plus the inherent lower radiometric efficiency of chinese COBs, coupled with the cost of heatsinks and fans, make a Ceramic Metal Halide (CMH) a much better option, especially around the 300 watt, and 300$ range.

Philips driver, 110 to 220 converter, socket, some wire, bare vert bulb (250$) will destroy any DIY LED designed around the criteria which you have been querying about.

Sorry to hijack Billy.

EDIT: What Vf are the chinese COBs? Bucks need +3V on the DC line as a general rule.

HolyGhost23 said:

what are you referring to?

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okay.. say you didnt need to factor the cost of power.. the cost of a psu or heatsinks and fans?..and instead of a Chinese cob go with a cree.. and what about just getting a general use 40V 1.5 amp converter? i know they make them for oilfield control boxes

i guess we are referring to the same thing.. what you call a buck.. that i can buy for 97 cents.....ohh ill factor that cost in for sure

There are so many factors involved in optimizing a light source for a given situation. I'm sure many people would chime in if you created a thread giving us insight into your specific environment and needs. Great folks on these forums.

so i have it down to this idea and its simply that....what i need to get a COB to turn on and run is
psu.. okay got one one those
heatsink and fans/ same place as the psu.
random wire molex connectors soldering bits and what not.. check
weller soldering gun.. yep
cree cob chips..nope 30 to 40 bucks..okay
40v 1.5amo buck at 150mhz.. 97. cents

cost to build (including random nonsense fees) 45.97??

or would i need more to get it to run?.... im not putting in the cost of the frame and shit but you get the point
.

The buck is not going to help you. That is for taking a higher then 40 volt source voltage down to 40 volts. You guys are also forgetting that you need to limit the power going to a COB. if you hook a 50 watt COB up to 38 volts 400 watts it will use all 400 of those watts. Now look at the resistor idea to regulate the power. 1 watt resistors not too pricey 50 watt resistors start at 5 bucks a piece for the shitty ones a quality one will cost you about 20 bucks. Now if you take a 400 watt psu 40 bucks your going to be lucky if it is 80% efficient go to a boost converter to get to 38 volts which is another converter that runs about 80% to 85% then go to some resistors that will fuck the efficiency up even more. Basically you going to build something so inefficient that over the lifetime of the light your going to spend hundreds of more dollars in power then what your going to save on buying proper LED drivers. So i would quit fucking around and spend a few bucks now and get the proper Shit to power your COBS...http://www.ebay.com/itm/160927171811?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Hello, I've been following this thread and others dealing with the 3590 chip and would like to ask something, but maybe it's the wrong thread... Looks like a couple subthreads are already open, but if not, please give me a hint and/or shift it to the proper thread...

Anyway, great info here and it's amazing what effort some people (like supra) put in to help others! Thank you

So I already ordered

http://www.leds.de/High-Power-LEDs/Chip-On-Board-LEDs/Cree-CXA3590-warmweiss.html
http://www.ebay.de/itm/Orginal-HP-CPU-Kuhler-fur-d530-USDT-Vollkupfer-326170-001-/201467426837?hash=item2ee864f815:g:Ji4AAOSwsFpWSFnE
http://www.voelkner.de/products/825692/Mean-Well-LED-Treiber-Schaltnetzteil-LPC-150-1400.html

because I'm in germany, and I'm pretty sure that it should work at or around a good efficiency. Only later I saw the dimmable hgl-series, oh well.

Now I've come across this video http://freevideos.diyhq.net/video/8WjYmuUcvXo/LED-Tutorial-Light-a-100W-LED-from-12V-Simple-Cheap.html that uses something like this
which made me wonder if the whole thing could have been much cheaper (of course the actual power supply is needed in his case). But probably also less efficient and more insecure due to less quality of the led and also the power supply? if a similar 100w-setup could cost maybe 40$ instead of 120, would it also mean a noticeable efficiency in real terms, i.e. g/w? Or are these threads here like the search for the holy grail of efficiency, no matter what the cost?

EDIT: this seems to be explained here https://www.rollitup.org/t/your-cxa3590-mission-should-you-choose-to-accept-it.827693/page-6 as too inefficient.

I'm basically asking because I already plan to replace or at least reinforce my old fluroescent lamps with a panel of xm-l2's.

And I've seen power supply's being used with 300 or 500 or 700 ma on leds that seem to need more like 1400 ma to get to about half or 2/3 of their max wattage, like the cxa3590. That would mean at 700 this one could only get about 50w maybe? And that would mean that i would need to buy 3 cxa3590 to have the same wattage like one 3590 @ 150w, which would of course be much less efficient. But cost-wise it should be less $$/w, right?

Please excuse my ignorance, I've soldered a lot of audio gear from scratch already, but never actually understood the whole electrical thing. The main thing I'm confused by is how the 3590 "chooses" to use either 72v at ~1200ma or rather 36v at ~2400, as specified in its data sheet... Does it take whatever voltage it gets and then you can adjust the current? Or since the current is fixed in my case, it should just take whatever voltage it can get.. :s

And do I assume correctly that the cxa3590 would break if one would put in maybe 20v at 5 amps?