Buzzing, flickering DIY cob fixture

(4) 3000 K Cree CXB3590,
HLG-320H-C2100B
2' x 4' space

I have been slowly turning my lights up in flower and at about 240 watts it started flickering and making a buzzing noise. Its a 320 watt driver. I did notice the flickering a few times when I first put the fixture together.

I removed all the cobs and cleaned everything up. Checked wires were secure after reassembling everything. Plugged it in and now I can get up to about 260 watts before flickering and buzzing. The symptoms aren't as severe either.

Last bit of info. When I removed 2 cobs there were perfect black silhouettes of the Ideal holder. These 2 cobs, apparently, overheated and scorched the aluminum black when I had them on a previous fixture. I'm assuming black is bad and I will add some more fans. Are these 2 cobs creating a problem? How do I check?

I have a multi meter but I'm unsure of how to diagnose this problem. Thanks for the help. Been a frustrating day.

That happened when I had a loose connection to my PWM. Check the connection to your potentiometer

What are you using as a thermal interface material?

Post a pic of the wiring too.

Therrion said:

That happened when I had a loose connection to my PWM. Check the connection to your potentiometer

Click to expand...

Ya, it could be the dimmer. Not sure its a PWM though? This is what is on there.
https://www.rapidled.com/cased-potentiometer-with-knob/

coreywebster said:

What are you using as a thermal interface material?

Post a pic of the wiring too.

Click to expand...

I'm using thermal paste.

My wires are all messy because I just took it down. Probably going to mount the driver on the fixture after this. Also added a fan to blow across the top of the heatsinks.

A pulse width modulator for dimming.
https://www.rapidled.com/coralux-storm-led-controller-with-10v-analog-converter/

You get the occasional shitty driver, even with Mean Well.

I think I'm going to remove the potentiometer tomorrow and see if that fixes it. Will update.

ANC said:

You get the occasional shitty driver, even with Mean Well.

Click to expand...

I removed the dimmer but no luck. I'm going to get into contact with Mean Well. Not sure how thats going to go. Guessing I'm going to have to buy a new driver while I'm shipping the other off...sucks.

I could move some drivers and cobs around and buy a couple more cobs to increase my flower space. I kinda think 2100ma is too much. If I switched to a 1750ma and moved my lights closer would I be getting similar results?

I just replaced a Cree cob. When removed, the heatsink was scorched just as you explained. The cob was damaged/cracked. Check your chip. Driver could be fine, the chip may be on its way out.

Our PSU to the active cooling took a shit one day, luckily my buddies weren't any good at soldering so the wires desoldered themselves... I think we only lost like 2 COBs that day. out of over 40

CoB_nUt said:

I just replaced a Cree cob. When removed, the heatsink was scorched just as you explained. The cob was damaged/cracked. Check your chip. Driver could be fine, the chip may be on its way out.

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Hmmm. I didn't inspect them carefully but when I was cleaning them I initially thought there was a crack in one. I dismissed it as an imperfection in the ceramic. *sigh*

I checked the voltage across each COB using a multimeter and I bypassed the one that looked the oddest (was hard getting my probes in the Ideal Holder). Working great now. I'll order two more cobs to replace the damaged ones. Thanks!

Anyone have any fan suggestions for this style of heat sink that will mount on the top?

Teag said:

Hmmm. I didn't inspect them carefully but when I was cleaning them I initially thought there was a crack in one. I dismissed it as an imperfection in the ceramic. *sigh*

I checked the voltage across each COB using a multimeter and I bypassed the one that looked the oddest (was hard getting my probes in the Ideal Holder). Working great now. I'll order two more cobs to replace the damaged ones. Thanks!

Click to expand...

Yea, any imperfection or black dots on the cob surface= done deal. Next time, use 3 port wagos if you have them and some scrap wire with the multi meter when checking. Makes it a lot easier.

I have a 4 cob fixture with the same driver. It isn't too much for my space. Pushes the cobs at about 75 watts each.

Teag said:

Anyone have any fan suggestions for this style of heat sink that will mount on the top?

Click to expand...

I have bigger splayed heatsinks for the cob bars that have the 320-2100 driver on it. Airflow from my tent fans keeps them righteous.

I'm not sure what how much heat those sinks are rated for,but I have some similar smaller pin heatsinks but they are on 185-1400 drivers About 50 watts each and are in the same tent as the 320-2100 cob bar. Fans keeps them righteous as well. It's an 12 " oscillating fan and a couple of tent pole clip on fans.
So, airflow over the heatsinks should suffice,unless you're pushing the sinks limits.

CoB_nUt said:

I have bigger splayed heatsinks for the cob bars that have the 320-2100 driver on it. Airflow from my tent fans keeps them righteous.

I'm not sure what how much heat those sinks are rated for,but I have some similar smaller pin heatsinks but they are on 185-1400 drivers About 50 watts each and are in the same tent as the 320-2100 cob bar. Fans keeps them righteous as well. It's an 12 " oscillating fan and a couple of tent pole clip on fans.
So, airflow over the heatsinks should suffice,unless you're pushing the sinks limits.

Click to expand...

Rapid Led had some cheap fans and fan speed controllers. Going to go with those and work out how to mount them when they get here. A friend has a 3d printer that might work out for this. I'm thinking of press fitting the printed part onto the pins and into the holes on the fan...maybe.

I installed the 2 new cobs today. Still have a buzzing noise with 4 cobs at max power. The voltage at max power on the 2 new cobs was 34 and the 2 slightly older cobs were 34.8. When very slowly turning up the dimmer I was able to get a max of about 35.3 volts before the buzzing/flickering started.
At the AC side I measured 300 watts and 118 volts at max power.

Not sure what the issue is (driver?) or how to proceed from here. Guess I'm going to hang it up as is to get my lights back on and keep it dimmed below full power.

I measured the voltage and amps across the driver. Got 152V and 2.1 amps. Which is what its rated for. I also checked the volts from the Ideal Holders to the ground wire and never got anything more than 20 mV.

Any ideas what the problem is / what to check next?