Diy cob light build help!! Input needed please!

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Death-StoNeD

New Member
Alright so here we go first diy cob build...

So im going to hook up 5 parallel strings of 2 parallel cobs each on a cpu heatsink+fan using a single power supply(36v 11A) 5step up buck converters(one on each string for the leds) and one step down to run the 10 fans.

List of equipment
10 CXA2530 5000k 3800lm ( 37v 800ma but will be run at 750ma)
10 heatsinks + fans
5 step-up ( 250w 10a (8.5 to 48v in) (12 to 50v out))
1 step-down (36v to 12v)
6 electrical boxes (for buck converters)
1 36v 0-11A power supply(400w)
power distribution block
Thermal paste
25ft 18gauge tew wire
Small metal bars to screw heatsink to

So the cobs can take 1600ma max and need 37v at 800ma so i will run 5 strings of 2 at 1500ma using a stepup so if a cob goes out the other one wont burn.
So if my math is right 10x750ma is 7.5a X 36v(270w) + 10 x (12v x ~120ma) (15w) my overall power would be about 285W.

So power supply to distribution block will give me 6x 36v (5 with step up cc/cv and one with step down cc/cv)
Then i will have 6 matching negatives paralleled to the same block going back to power supply.

But for some reason this all sounds way too simple... am I missing something? Do I need some sort of a resistor or would the step-up unit include that? Do I need something between my -36v and -12v before they all go back to the power supply?
 
nfhiggs

nfhiggs

Well-Known Member
Death-StoNeD said:
Alright so here we go first diy cob build...

So im going to hook up 5 parallel strings of 2 parallel cobs each on a cpu heatsink+fan using a single power supply(36v 11A) 5step up buck converters(one on each string for the leds) and one step down to run the 10 fans.

List of equipment
10 CXA2530 5000k 3800lm ( 37v 800ma but will be run at 750ma)
10 heatsinks + fans
5 step-up ( 250w 10a (8.5 to 48v in) (12 to 50v out))
1 step-down (36v to 12v)
6 electrical boxes (for buck converters)
1 36v 0-11A power supply(400w)
power distribution block
Thermal paste
25ft 18gauge tew wire
Small metal bars to screw heatsink to

So the cobs can take 1600ma max and need 37v at 800ma so i will run 5 strings of 2 at 1500ma using a stepup so if a cob goes out the other one wont burn.
So if my math is right 10x750ma is 7.5a X 36v(270w) + 10 x (12v x ~120ma) (15w) my overall power would be about 285W.

So power supply to distribution block will give me 6x 36v (5 with step up cc/cv and one with step down cc/cv)
Then i will have 6 matching negatives paralleled to the same block going back to power supply.

But for some reason this all sounds way too simple... am I missing something? Do I need some sort of a resistor or would the step-up unit include that? Do I need something between my -36v and -12v before they all go back to the power supply?
Click to expand...
Forget the step-up converters - you're making this too complicated, and those little boost converters are quite unreliable. The 36V power supply will have a voltage adjustment to set your voltage to get 750 mA through each COB. Just wire your 10 COBs in parallel and make sure you have adequate cooling for each one. You can use a 1 ohm 5 watt resistor in series with each COB for additional current limiting if you want, but I've found they work fine with or without. If you want an easy way to monitor the current through each cob, you can put a 0.1 ohm, 1/2 W resistor in series, and the voltage drop on the resistor will equal the amps divided by ten. Just adjust your power supply voltage until you get 7.5 mV across your current sense resistor.
 
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Death-StoNeD

New Member
Hi thanks for the reply! The power supply does not seem to have any adjustments... cant post links but amazon.ca/gp/aw/d/B075K5N1MB/ref=oh_aui_i_sh_post_o0_img?ie=UTF8&psc=1
 
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1212ham

Well-Known Member
These supplies normally have a voltage adjustment. I have the same unit, there is a voltage trim pot just to the left of the terminal strip. Put them all in parallel as nfhiggs suggested and uses use any old 12v wall transformer to run the fans. Then consider better cobs, or strips, or boards.
 
Last edited:
nfhiggs

nfhiggs

Well-Known Member
Death-StoNeD said:
Hi thanks for the reply! The power supply does not seem to have any adjustments... cant post links but amazon.ca/gp/aw/d/B075K5N1MB/ref=oh_aui_i_sh_post_o0_img?ie=UTF8&psc=1
Click to expand...
Yes, there is. Its a small adjustment right next to the little green power light.
 
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