Lighting DIY Mars to Cree Cob conversion

[Atulip]

6 will get you a bit more light and less watts. And 6 x 3070s would output more than 3x 72v 3590s, it's a nice middle ground between the 6 3590s and the 3 3590s.

 

[Ripper]

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.

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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.

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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.

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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.

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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.

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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.

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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.

I have been meaning to ask how is the spread on the new mars to cree... I am ordering my parts today....

 

[Atulip]

Much better spread. Based on the lux readings I took, the mars at 12" high had less than 1/3 the light at 12" from the center than it had at the center. And the Cree had 1/2 the light 12" than it had center.

Not perfectly accurate but close. I have 2 of these DIY conversions in my small 2.5'x2.5' tent. And I'm seeing ~800par under the lights and ~600 par at the edge. So spread is much better.

I also have a PLC cx300 and it has 90° reflectors, it's best at 18" for the same spread I'm getting at about 12" with the 115° bare cobs.

 

[Ripper]

Ordered 2 7 inch heat sinks, 2 72v cxb3590s in 4000k, 3/8's black heat shrink 3 to 1 shrink ratio, Arctic silver 5, 1/2 inch Kapton tape. I already have solder and a soldering gun.. when it all gets here I will make my own thread of how I put it all together. I want to thank @Atulip for giving such great detailed responses to my many questions. this will take my one mars hydro 300 from 4377 lumens to right at 19000 lumens... that is a big jump and my plants are going to reward me for it....

 

[dcat0921]

Ordered 2 7 inch heat sinks, 2 72v cxb3590s in 4000k, 3/8's black heat shrink, Arctic silver 5, 1/2 inch Kapton tape. I already have solder and a soldering gun.. when it all gets here I will make my own thread of how I put it all together. I want to thank @Atulip for giving such great detailed responses to my many questions. this will take my one mars hydro 300 from 4377 lumens to right at 19000 lumens... that is a big jump and my plants are going to reward me for it....

Very interested to see how this works out. Got 2 of the Mars 300 that I could possibly update.

 

[Discretepete2676]

So I assume an old mars 200x3 is able to switch to COB as well? I really need to go through this whole thread again.

 

[Ripper]

So I assume an old mars 200x3 is able to switch to COB as well? I really need to go through this whole thread again.

I would assume it is.. I will likely be doing 3 of them..

 

[Ripper]

@Atulip did you use silicon to secure your heat sinks? Any specific kind if so?

 

[Atulip]

I used GE kitchen and bath sealant, 100% silicone. Anything similar should do fine. I allowed it to dry for 24hours before continuous use, but probably unnecessary.

 

[MidMich XRM]

Hey guys, I'm thinking of looking for a cob or few for this Driver its a 20 - 38v (tested running 39v) 900ma 30w What good ones for veg or flower for extra light ?