Built my first COB setup - Safety question with COB's wired in parallel.

Heat sinks being used: 6 - CUTTER-HS14080P
COB's being used: 6 - CLU048-1818 80CRT
Drivers being used: 2 - Meanwell HLG-185H-48A
No Fans, wanted passive cooling.

I have 3 of the cobs wired in parallel to each driver.

I am running the drivers at around 60% output power each (around 150 watts per set of 3) - around 300 watts total when all 6 are on.

After like 3 hours being on the heat sinks max out temp wise at around 110 degrees F each with no additional cooling, ambient room temp is around 73 F.

I went as far as wiring up a DS18B20 temp probe to each heat sink, I have a raspberry pi monitoring the temps to each and figured I would just have it turn off the LED's if temps go over a certain # indicating some type of issue. (like 120 degrees F for example) My thought was, if one or more of the cobs in the sets of 3 go out the remaining current draw will go up, and the heat sink temps will rise.

So the question, is running them in parallel a big deal from a safety perspective? My understanding even if I was running one single CLU048-1818 with the HS14080P heat sink with the Meanwell HLG-185H-48A driver at 100% power output, I would be OK, its not going to start a fire.. I would just be pushing the heat sink to its max. (in the event that 2 cob's out of 3 failed and was left with 1 operating off the driver) And that would be if I was running output on the driver at 100%, which at the moment I am not.. am only at like 60%.

Also the 110 degree F on each heat sink, is that high or low? I still have to do a test to see what the heat sinks temps rise to when I run the drivers with 100% power out.

Thanks for any information.

Just as a matter of interest, what was the total cost of the build please?

It was around 430.00 USD including all of the reflectors/holderers without shipping cost.

if youre concerned turn the voltage screw down to limit the amount of current that can flow in the event you drop a cob. this would be a good video to do -"tuning" the 185H-48A.

samsung42 said:

My understanding even if I was running one single CLU048-1818 with the HS14080P heat sink with the Meanwell HLG-185H-48A driver at 100% power output, I would be OK,

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it cant do it. driver would top out on 53.5 voltage around 2200 mA

CobKits said:

it cant do it. driver would top out on 53.5 voltage around 2200 mA

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Thanks for the reply.

Listed on the product description for the CLU-1818 on cobkits.com it says:

CLU-1818 is a nominal 50V COB which can operate up to 4.14A max (approximately 250W)

I don't plan on running 1 of these cob's at the full current, the max current on the HLG-185H-48 is 3.9A based on the spec sheet I am looking at.

So that lead me to believe if worse case I had two COB's go out, and there was one remaining cob on that driver it would be running pretty darn hot, but it would not blow it right away. (The heat sink is only capable of dissipating passively up to 100 watts, so in that configuration it would not last that long - the reason I have temp probes that will shut the light down if any of the heat sinks go over a certain threshold)

Can you please explain how my logic is wrong, what am I not getting here? Thanks

the drivers run out to about 4.25A max per the test report and my own testing case tem pis well within meanwells 70C limit at this point

your logic is sound but even with both pots turned up it cant feed a single 1818 cob 4A due to voltage range which will limit it to a max of 2.2. you could easily turn max voltage down to 53 or 52V

CobKits said:

the drivers run out to about 4.25A max per the test report and my own testing case tem pis well within meanwells 70C limit at this point

your logic is sound but even with both pots turned up it cant feed a single 1818 cob 4A due to voltage range which will limit it to a max of 2.2. you could easily turn max voltage down to 53 or 52V

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OK thanks, I am running them by default at 60% dimmed down, so if 2 go out, the 1 remaining cob will get 60% of the output of the driver. I always thought I had some headroom though if I wanted more some more power I could turn it up. My 6 1818's with the 2 HLG-185H-48's at like 60% run around 300 watts.

So what exactly would happen if I had the HLG-185H-48 set to 100% output, and I connected 1 1818 to it?

Thanks

Actually just did a test, with 3 CLU-1818 on the HLG-185H-48 connected in parallel Vo adjusted to like 144 watts the measured voltage was 50.1 volts adjusted to max it was using 241 watts its was measured at 51.5 volts. (Io was at max during both tests)

with 2 CLU-1818's in parallel Vo adusted to max it was like 53 volts same wattage used around 241 (Io was at max)

With 1 CLU-1818 connected, with Vo adjusted to max it was only using 142 watts. (Io was at max) - I forgot to measure voltage.

So I think that confirms (which I was not expecting) if I run these in parallel, and one goes out, there is no danger, if 2 goes out, there is definitely no danger even if I am running at MAX Vo, and MAX Io because it will actually go down in wattage. 142 vs 240 when 2 or more.

Is what I am seeing to be expected? I know enough about electricity to get around, I am just trying to make sure I am not creating a fire hazard.

samsung42 said:

With 1 CLU-1818 connected, with Vo adjusted to max it was only using 142 watts. (Io was at max) - I forgot to measure voltage.

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53.5 +/-

samsung42 said:

So I think that confirms (which I was not expecting) if I run these in parallel, and one goes out, there is no danger,

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well i mean 142W on that heatsink might kill your cob in short order, but beyond that i wouldnt expect it to start a fire

Actually I must not be thinking clear today. 142 watt is double at 100% then when running 3 (80 watts each) So yeah your right it will kill it at some point.. I am going to have my Raspberry pi checking the temps on the heatsinks every few minutes, so if I loose one or 2 cobs it should shut all of them down before any damage is done. Each heatsink is rated up to 100 watts passive, so if I was down to only 1 if it ran like that long enough to raise the heatsink temps past 120 F for example I would have the relay turn off lights till I could check it. I hope there would not be much damage if it was only a couple of minutes running at that wattage.

And of course the above is assuming I am running 100% output, I hope to get by on like 60% output. I think when I set it to 60% output, when running on one COB, I think it was around 60-80 Watts. So I should have no issues I guess in that case.

heres a real simple test you can do on any heatsink
-look at datasheet and determine % of voltage droop that will occur at mfrs rated Tj vs ambient 25C*
-fire up cob and measure cold voltage quickly
-let cob run and observe voltage. it will drop and hopefully level off.
-if it levels off calculate voltage % drop and compare vs allowable on datasheet*
-if it unstable it will keep dropping voltage and eventually dim. you'l usually see this when you have a chip with bad thermal paste contact etc.

*the reason i say figure out voltage % drop vs just reading voltage and just going to the datasheet, is that the datasheet is one measurement at a given current not necessarily the one you are using so it is of limited use. % drop gives you a rough idea of whats going on. ideally it reaches stability at a fraction of allowable Tj and you know youre good

you can also use the mfrs various calculator tools to try to glean good data on V vs Tj at various currents

So following what you said above regarding voltage drop.

Using a 185H-48A powering (at 100% Vo and Io) 1 1818 cob with the CUTTER-HS14080P heat sink I have, if I power it on with the multi meter across the cob, as it heats up up it should keep dropping because that heatsink without a fan is not capable of dissipating the heat fast enough? Is there a rule of thumb for how much it drops is the point where it might be damaging something on the COB?

Thanks

No one has commented on the parallel wiring, can I run the COB's I have in series off the driver I have if I want?

Is there any difference in efficiency or heat based on if they are in series or parallel?

So 3 - CLU048-1818 per 185-H-48A in series vs in parallel.

One thing I have noticed during the past week running them in parallel for 16+ hours at a time, not all of them run at the same temp at the heat sinks. I have one of the 6 that seems to run 10 degrees cooler in F then the others. Not sure if it has something to do with running them in parallel vs series.

samsung42 said:

So following what you said above regarding voltage drop.

Using a 185H-48A powering (at 100% Vo and Io) 1 1818 cob with the CUTTER-HS14080P heat sink I have, if I power it on with the multi meter across the cob, as it heats up up it should keep dropping because that heatsink without a fan is not capable of dissipating the heat fast enough? Is there a rule of thumb for how much it drops is the point where it might be damaging something on the COB?

Thanks

Click to expand...

thats what i meant by this:

CobKits said:

-if it levels off calculate voltage % drop and compare vs allowable on datasheet*

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lets take a look at
http://ce.citizen.co.jp/lighting_led/dl_data/datasheet/en/COB_5/CLU048-1818C4_P3703_0516.pdf

lets assume your ambient temp is 20-25C, and the first voltage measurement you can see upon firing up the cob is at 30C- on the chart at nominal 1620 mA current you can see were at 53.5V. im not at home or id post a screenie but look at the graph on pg 6 "case temp vs forward voltage"

per datasheet page 3 the limit of the cob is 105C so lets run it up to 90C max to be safe just in case. you can see from the case temp graph that at 90C the forward voltage is about 51.4V. so our allowable drop over ambient temp is (53.5-51.4)/53.5 = 3.9%

so measure your forward voltage at your desired current and if youre under say 3% droop relative to your initial measurement you should be good to go. theres a couple little safety factors there in that method (assuming initial measurement is 30C when its probably less, designing for 90C instead of 105, not utilizing the full 3.9% droop) that should account for this less-than-precise measurement method as were assuming that temp droop % is the same at all currents which may or may not be the case

so in your case if you want to push the cutter heatsink to the max incrementally increase current, let it stabilize (5-10 min), measure, repeat

samsung42 said:

No one has commented on the parallel wiring, can I run the COB's I have in series off the driver I have if I want?

Is there any difference in efficiency or heat based on if they are in series or parallel?

So 3 - CLU048-1818 per 185-H-48A in series vs in parallel.

One thing I have noticed during the past week running them in parallel for 16+ hours at a time, not all of them run at the same temp at the heat sinks. I have one of the 6 that seems to run 10 degrees cooler in F then the others. Not sure if it has something to do with running them in parallel vs series.

Click to expand...

assuming the cold cob isnt noticeably dimmer id be most concerned with poor heat transfer from cob to sink. put an ammeter in line and compare it to the other cobs in your rig

CobKits said:

assuming the cold cob isnt noticeably dimmer id be most concerned with poor heat transfer from cob to sink. put an ammeter in line and compare it to the other cobs in your rig

Click to expand...

I was looking back through my temp logs and it is weird it seems like the one that I was talking about running 10 degrees F cooler than the others a couple of days ago was running the same, then another day was 10 degrees cooler. Seems to move around. I am starting to wonder if it is just the sensor now.

So cobkits, you list on your website (which BTW, I bought some of my build through you, great service)

MeanWell HLG-185H-48:

3 1818@ 75.3W each (226W max) or 4@ 55W ea (220W max)

Does this mean I can run 3 of my 1818's in series off the 185H-48? I am considering trying that just to see how that works comparatively.

thanks for the kind words

as for running in sries, its not possible with that driver, youd need 150V. the configuration described is parallel.