# Using a COB LED panel: experiences



## lf-mark (Jul 22, 2016)

We have a folding camper (halfway between a trailer tent and a caravan) with an interior light that used two 8W fluorescents. Obviously, the only thing to do was to strip these out and replace with a more pleasant and less power-hungry LED.

The final result:







Some notes:



the LED I used was sold on eBay as a "10W 1000 lumen" unit with a Vf of "11–14V", for just £1.89 posted from Hong Kong. I did some research: from the spec sheet it's actually a "6.7W" unit intended to be driven with 560mA, no built-in resistors. That same spec sheet claims 1890–2430 lumens, a truly spectacular efficiency. What do you mean, of course it's true :ironic: 



it was actually a poor choice, as the camper's 12V supply could realistically be anywhere from 12V to 14V. The LED couldn't be driven directly from this, a simple series resistor wouldn't suit, and it'd take an unusual regulator to be able to cope 



so I used an unusual regulator: a Mean Well LDB-500LW (PDF) buck/boost regulator that'll take 9–30V in and provide 500mA at 2–32V out, with no restrictions on input versus output voltage. This slightly under-drives the LED, which'll be good for lifetime and heat. Turns out a 500mA drive current requires a whisker under 11V as you'd expect from the specs. 



I actually bought five of these regulators as the postage for a single one is horrific. I plan to recoup some of this via selling the remainder on eBay. 



The LED is heatsinked (heatsunk?) via a 3mm aluminium plate, cut to the maximum size that comfortably fits in the lamp unit. The LED is firmly bolted on with a super-thin smear of thermal compound between. The rear face of the plate is thinly sprayed to increase emissivity, and the plate is mounted with a gap behind it to allow some convection. In testing, this gets only warm, which bodes well for lifetime. 

I'm very pleased with the final result: the LED is nice and bright, a good match for the old tubes even through the diffuser, with a pleasant colour (it's a warm white unit) despite the poor-spec CRI. On its own, it should run for over a week non-stop from the 110Ah leisure battery...


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## CuriousOne (Jul 22, 2016)

In best case scenario, it will work for 2 years, in worst - for 2 days


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## lf-mark (Jul 22, 2016)

CuriousOne said:


> In best case scenario, it will work for 2 years, in worst - for 2 days



But it's an LED: we all know they last 20 years!

Seriously, though, thanks for the injection of realism. I will post any progress on its lifetime, hopefully proving you wrong in the long term. I've done everything I can: underdriven it with a stable constant current and heatsinked it well.

What do you suspect the failure mode will be?


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## CuriousOne (Jul 23, 2016)

The main issue with these COB modules is the fact, that they are made in china, and no one know how good they are made. From my previous 7 year experience, if used for serious project, Chinese leds should be avoided at any cost. Personally I prefer to use cob modules from Bridgelux - they are cheaper than tier 1 brands, but offer almost same performance. And for "firmly mounted", if you have noticed, brandanme led modules does not have mounting holes, they have mounting cutouts. You know why? when led heats up, it expands, and since you will never match thermal expansion ratio of led die metal and heatsink, one of them will expand a bit more, causing troubles. So appnotes for brand-named leds suggest that you should not firmly attach led to heatsink, but allow it to expand and "slide" a little. I've bought once 20cm x 1cm Chinese cob led strip, and firmly mounted it on heatsink with it's end. After it warmed up, center area rised about heatsink for about 1mm!


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## lf-mark (Aug 12, 2018)

CuriousOne said:


> In best case scenario, it will work for 2 years, in worst - for 2 days



Just exceeded your best case scenario 

Still working well with admittedly light duty cycle (couple of hours a year whilst camping).


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## Calina (Aug 29, 2018)

I would guess that you only use your folding camper occasionally, so your light will probably last for twenty years (worst case scenario) and 100 years or more (best case). ​​


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## lf-mark (Aug 29, 2018)

Calina said:


> I would guess that you only use your folding camper occasionally, so your light will probably last for twenty years (worst case scenario) and 100 years or more (best case). ​​



I shall reply and let you know at the appropriate times. Hey Siri: set a reminder for 2116AD please.


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## alpg88 (Aug 29, 2018)

i made under cabinet light for my kitchen using 14w cob panels from dx. got aluminum 4ft ruler from home depot, installed 3 panels, used step down driver, and power supply from laptop, wired 3 12v panels in parallel, set driver to 300ma, the lights are making plenty of light, the ruler never got even warm. stays at room temp. and the lights are on 24\7 for over a year, no sign of any degradation, or loss of brightness.


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## mercrazy (Aug 29, 2018)

hate to tell you but Cree are made in china too.
i haven't seen any made anywhere but china and taiwan.


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## KENN MOSSMAN (Sep 12, 2018)

CuriousOne said:


> The main issue with these COB modules is the fact, that they are made in china, and no one know how good they are made. From my previous 7 year experience, if used for serious project, Chinese leds should be avoided at any cost.



I STRONGLY disagree.There are very good factories in China but the problem is finding them.The ones you see on the popular B2C and B2B websites however cater to the low-end of the market. I spent Ten years in China and visited (in-depth) MANY LED factories and did QA.


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