Cobs have burnt
- Thread starter Nutria
- Start date
Mr.Goodtimes
Well-Known Member
Could be defective cobs, could be something with the wiring.
Take a good COB and plug it in where the one that isn’t working is and see if it works, if so, would think it would be the cob. If not check wiring.
Idk that’s where I would start.
Take a good COB and plug it in where the one that isn’t working is and see if it works, if so, would think it would be the cob. If not check wiring.
Idk that’s where I would start.
thx for your time.
I dont have any spare cob (AND I am at week 6-7 of flowering damn!).
It is a simple series wiring with wago connectors
VegasWinner
Well-Known Member
It looks like the cob fried, due to lack of thermal heat transfer, based on the diodes failed at various locations. Are the cob's loose to the heat sink or are they tight? Did you use pads or thermal grease?
edit. I also see thermal grease on both of your cob holders. If you have dirt on your cobs that would cause it to fry also. Check your cobs for no thermal grease on them that would cause failure, as well.
edit. I also see thermal grease on both of your cob holders. If you have dirt on your cobs that would cause it to fry also. Check your cobs for no thermal grease on them that would cause failure, as well.
They do seem all ok, I built a lot of PCs and I think I use enough thermal grease.
The one with the thermal pad is still ok even if it is the only one working at 1.4A
Rahz
Well-Known Member
First thing I would do is remove one of those chips and examine the paste coverage. If the paste is uneven with low mounting pressure or has an air bubble is can cause heat buildup. If not enough paste is used it can prevent full contact.
Burn pattern doesn't look location specific, but it's still a good first step. Also I'm assuming the build isn't that old, but age and quality of paste can be a factor.
Size of the heatsink of course can affect thermal performance too. Only 36 watts, but worth examining the sinks to see if they are rated for the job.
And finally, passive sinks still require some airflow especially if the are being used close to their max rating. If the exhaust in the area is low, or if the fan is set to go off at lights out and is on a separate timer it can cause thermal issues.
By appearance it looks like the sinks go too hot. I've seen failure due to bad thermal paste on a rig that had cool sinks, damage was localized to the area that had a thermal pocket, rest of the chip looked fine.
Burn pattern doesn't look location specific, but it's still a good first step. Also I'm assuming the build isn't that old, but age and quality of paste can be a factor.
Size of the heatsink of course can affect thermal performance too. Only 36 watts, but worth examining the sinks to see if they are rated for the job.
And finally, passive sinks still require some airflow especially if the are being used close to their max rating. If the exhaust in the area is low, or if the fan is set to go off at lights out and is on a separate timer it can cause thermal issues.
By appearance it looks like the sinks go too hot. I've seen failure due to bad thermal paste on a rig that had cool sinks, damage was localized to the area that had a thermal pocket, rest of the chip looked fine.
freemanjack
Well-Known Member
Parallel or series? I'm guessing parallel, in which case you probably had one cob fail pushing the circuit amps to the remaining ones, over stressing them. When using parallel wiring ensure your off load voltage is not too far over your rated voltage for your desired drive current. You can get away with excess amps in a parallel circuit but with cobs there cannot be excess amps AND volts or they will overheat.
hi
Thermal paste was new, I'll check its status when I get new cobs.
Passive heatsinks are 130mm*70(h). Exhaust on 24/24
Rahz
Well-Known Member
Not sure what to tell you. Sinks are plenty big. Pin fin sinks are usually very flat so you would need to use hardly any paste for coverage to be an issue, and air bubble from rough coverage generally produces a localized burnout. That sink/chip combo should be able to handle more current than what you're throwing at it, but might want to check the current or plug into a kill-a-watt once it's rebuilt to make sure it's running in spec. By the looks of it the entire unit got hot. Monitor tent temps first couple days to make sure the exhaust is doing a good job. It would have to get pretty hot in there for ambient temp to be the issue, but it's one avenue that can be ruled out.
DrBlaze
Well-Known Member
Yeah you'd think the plants would die before the cobs if ambient was the issue, considering that they're tested at 80c.
Rahz
Well-Known Member
Well maybe. If there's not a lot of air movement around the sinks high ambient temps can contribute to failure. A little convection will keep the plants alive while the cobs are roasting. Not saying that's what happened, just to check and make sure exhaust is up to par to rule it out.
The Dawg
Well-Known Member
Looks Like The OP Did Exactly The Same Thing As I Did Which Was Fire Up The Cob Facing Down.Seconds After I Fired Up The Unit I Smelled Smoke And Quickly Grabbed It But The Damage Was All Ready Done. No I Don't Have The Unit On Hand To Take Pics Rather I'm Using It Off Site To See If Said Lamp Is Going To Fail. The Unit In Question Is A 1812 5000K Running 285 Watts On A HLG-240-1050A. 
Randomblame
Well-Known Member
Can you post a picture of your heatsinks?
You could take the 2 damaged out and still run the rest with the same driver. This would be 2/5 less light, but only until the new COB's are there.
Ambient temp is cold at 66-68f.
I'll let you know...Could have been bad heat transfer.
Yea this is how it is working now.
Heatsink is the one from Kingbrite, pin fin heatsink like we saw a lot of times
Randomblame
Well-Known Member
Maybe the thermal grease is dirty with coarser particles. I once had a cheap, that was so grainy, that you could have grind with it. Called HY-510 or so..
What surprises me is the even distribution of the defective spots over the whole LES area on both COB's. This could also be due to faulty COB's, because at 37w and with this massive 65w heatsinks T.j should be ~60-70°C or so with a bit airmovement. But they need a lot more for frying!
What surprises me is the even distribution of the defective spots over the whole LES area on both COB's. This could also be due to faulty COB's, because at 37w and with this massive 65w heatsinks T.j should be ~60-70°C or so with a bit airmovement. But they need a lot more for frying!
Randomblame
Well-Known Member
Yepp, I would still use a good thermal grease like Arctic Silvers "Ceramique" or better and instead of a dab in the middle, I would evenly distribute it.
To securely avoid any bumps or air pockets, I would mount the COB's also with a "twisting motion" and then tighten the screws. I want to see the same amount of excess paste on all 4 sides when they are tightly screwed.
To securely avoid any bumps or air pockets, I would mount the COB's also with a "twisting motion" and then tighten the screws. I want to see the same amount of excess paste on all 4 sides when they are tightly screwed.
GBAUTO
Well-Known Member
THIS^^^^
I use thermal paste-spread a thin film over the base of the COB and place it on the sink with a twist to ensure good contact and bolt it down. Heat transfer has to be good or you'll get localized hotspots that will kill parts of the chip.