Lighting DIY Mars to Cree Cob conversion

[Atulip]

To start, credit goes to growmau5 for the idea and just rediculous amounts of information on DIY cob leds.

https://m.youtube.com/channel/UCPSwmwj8ZLXObtBJmz-76rw

If you have any interest in DIY COB LED check him out on YouTube. There's also a 6 part series on DIY LED Basics, very informative.

So I've been researching Cobs for a month or so now, found growmau5s videos and he makes it look so easy I decided to give it a try. I have quite a few EBay Mars Hydro 300(60x5(135w)), so that's what I wanted to convert, rather than build from scratch. They're $65, give a nice box to hold everything in, 2 drivers to reuse and fan to cool everything.

Opening up the Mars was simple, some screws and we revealed the drivers.

2 x 55v-100v @ .7-.75A drivers. Perfect for 4 Cree cxb3590s 36v or 2 Cree cxb3590 72v. I opted for 72v at 3000k color(3500k is arguably the best spectrum), CB bin(best at mouser for this color). The 12v fan is shared on a driver, so one 72v cob is on that driver, and with extra available voltage on the other, I decided for 2 x 18v Cree cxa1512 6500k to add to the second driver. These will be in parallel with each other, and series with the cxb3590.

The heatsink in here is trash, my sneezes dissipate heat better than this flimsy thing. The issue inside the box becomes space. Upgrading the heatsink requires removing the glass to mount the heatsink lower down. I went with 4.85" x 7" from heatsinkusa.com, 2 of them in this mars, short enough to fit inside nicely, and much better heat management.

I used the simple method of mounting them with arctic silver 5 and kapton tape. Tapping them and using cob holders is probably the better way to go.

Once all the chips are on I got to wiring. I prefer soldering to anything else. My wall solder went out a while back and I haven't replaced it yet, so I had to use my portable butane one. A bit harder to get the temps right on it, so it's sloppy, but works.

Into the Mars case and dumped silicone everywhere. Not sure if I need to silicone off this center area or not for better airflow over the heatsink.

Only ran it for 30mins to test her out, need to let the silicone dry. I did get some lux comparisons, can't afford a par meter, lux will be fine for comparing it between my 600w HPS and another Mars 300 I have.

Mars Hydro 300 eBay model(60x5($65))(135w wall)
12" high, center 33,500 lux
12" high, 12" from center 9,500 lux
18" high, center 21,000 lux
18" high, 12" from center 7,500 lux

600w Hortilux HPS(4 month old bulb)(measurements from center of bulb, higher heights because I can't put it at 12" without torching my plants.)
18" high, center 81,500 lux
18" high, 12" from center 50,500 lux
24" high, center 55,000 lux
24" high, 12" from center 35,000 lux

New Mars to Cree(120w)
12" high, center 65,500 lux
12" high, 12" from center 31,000 lux
18" high, center 38,000 lux
18" high, 12" from center 21,000 lux

Not a perfect testing method, but it should show the efficiency of these Cree cobs. Looks like 3 of these will outperform my 600w HPS At an equal height of 18" for both. For 360w at the wall. The Mars 300 did surprisingly well, but only directly under it, the spread is garbage.

I hope this helps anyone interested in DIY cobs. If you've got a cheap led and want to upgrade, pop open the case and see what's inside.

 

[Dazed]

Excellent, thanks for this.

 

[Balarama]

Good work Atulip, you deserve some rep for this build!



I'm happy to see you also did some measurements and comparison with HPS.
The convertion puts out some impressive lumens, I'm sure it could push even more with higher bins and four cxb3590s 36V, like 3500CD or higher bin at higher cct. But the 3000CB are the best for flowering even if not the highest bin(CB is highest for 3000K model).
Anything over 4000K is more for vegetative phase or for flowering sativas.
I also have some diy leds with cxb3590 3000CB, so high 5 bro

 

[Atulip]

Thanks. Yeah looking to convert 5 more of these and outfit a 2'7x2'7 and 2'7x4'11, both my tents. Going to put this 3000k + do 5000k next for the small space and do 2 4000k and 2 3500k in the bigger tent. The meter was just a cheap eBay one, but I mainly just wanted to see how it compared.

Honestly I started researching for new LEDs when @A-Train posted a Mars 1200w Par chart showing how poorly the spread is. Hanging at 18" it's good for about a 2'2' before an HPS wins in par.

 

[Discretepete2676]

Damn I have one those 1200 too lol I just put 4 autos directly under it, and start plants on the edge lol but I have a 200x3 Mars in not using right now. ...makes me want to look into what you did with it. May I ask round about the cost for the whole conversion, minus the light you already had?

 

[Atulip]

$145 shipped for the LEDs
$80 for the heatsinks, 8 total(enough for 4 lights)($20)
$15 for arctic silver 5 and kapton tape
Had everything else(tools, solder, speaker wire, etc)

So $180 for one. About an hour's worth of work needed. Next order in, $110 for LEDs 2x CXA3590 72v CD 5000k and 18v 2700k, so like $150 in total if I buy a larger bit of arctic silver($20).

The 72v are nice that they run a little harder on these 700mA drivers, like a 36v @ 1.4A, so it saves about $100 off the cost at little efficiency sacrifice.


I'm guessing a Mars 1200 could run 8 or 9 72volt Crees, perfect amount for like a 4'x4', probably would have to stay at least 18" high for spread though if they're all in one Mars box.

 

[Discretepete2676]

$145 shipped for the LEDs
$80 for the heatsinks, 8 total(enough for 4 lights)($20)
$15 for arctic silver 5 and kapton tape
Had everything else(tools, solder, speaker wire, etc)

So $180 for one. About an hour's worth of work needed. Next order in, $110 for LEDs 2x CXA3590 72v CD 5000k and 18v 2700k, so like $150 in total if I buy a larger bit of arctic silver($20).

The 72v are nice that they run a little harder on these 700mA drivers, like a 36v @ 1.4A, so it saves about $100 off the cost at little efficiency sacrifice.


I'm guessing a Mars 1200 could run 8 or 9 72volt Crees, perfect amount for like a 4'x4', probably would have to stay at least 18" high for spread though if they're all in one Mars box.

I think of like to start with my 200x3 Mars and put that in my 2x4 tent by itself and see what it can do before I convert the big girl. Need that big girl to keep doing her thing for now while I play with her smaller cousin lol but yeah I'm looking to cover a whole even canopy of a4x4 tent with plants from corner to corner lol while marinating good light at around 18 inches. I know it's a lot to ask from one panel but I can't hang two really right now so I have to run this tent with just 1​

 

[Atulip]

Pop it open and see what those drivers are. For a 2x4 5-6 Cobs(72v @ ~.7A) would give a nice amount of light. 4 cobs would be on the low end. If that's the old mars 600, I think it has 8 drivers similar to what I had, based on someone else's mars 100x3 having 4 drivers. The old style 100x3 or 200x3 pull a good bit of watts compared to the 300 and 600 they list now(60x5, 120x5). I'd probably go for 6 x cxb3590 or cxa3590 72v. That should make up for any added height you need and still push out plenty of light.

 

[Shad3s]

Awesome stuff man, big up!

 

[Balarama]

Go for the cxb, they have almost 10% more efficency compared to cxa. Bins are also important, if you plan a veg light take the 5000 and(or) 6400 DB bin or higher if available.