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Everyone knows that LED tail-lights are very bright and are not supposed to "burn out" like incandescent bulbs. In automotive tail-lights things seem to be going according to plan. However, on (boat) trailers, many people are having trouble with individual LEDs going "out". I've bought at least 3 pairs of LED lights and have had them fail in ~10 hours of use. The same thing turns up in online reviews of a different tail-light.

Apparently, it has nothing to do with submersion. I've disassembled two different lights. In one, the electronics are "potted". In another, they are sealed in a clear plastic container with wires "potted" at the entry point.

The housing on both of these lights fills with water on submersion and drains when brought out.

So, what's going on? Is "load dumping" in the tow vehicle causing transients? Are resistors burning out? LEDs being driven over rated current? Inductive "kicks" from the trailer wiring?

Finally, why can't these manufacturers hire a well-qualified electrical engineer to find out what the problem is - and fix it?

Seems the problem is not due to the LEDs! It is other circuitry. Does anyone have a schematic for these tail-lights? Migrate back to Electrical Engineering??

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migrated from electronics.stackexchange.com Apr 17 '17 at 1:30

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  • In a word: MONEY! The automotive lights do frequently have problems (count the number of semi trucks & passenger cars with 1+ "dead" LEDs in their taillights, you might be surprised how many you'll see when you're looking for them), but the trailer lights, being that they're sold for often less than 1/20th the price, are simply not made with "quality control" and "durability" being words that are allowed to be spoken in the plants. In the end, if your trailer light goes out, you buy another cheap, imported trailer light, and the cheap imported company makes money whether they work or fail... – Robherc KV5ROB Apr 17 '17 at 0:29
  • Unfortunately, there just isn't enough market demand for "expensive trailer lights," so the manufacturers aren't motivated to put in the small amount of R&D + QC it would take to make dependable LED taillights that would last for 25years. :S – Robherc KV5ROB Apr 17 '17 at 0:30
  • potted in what? even epoxy took 30 yrs for the best in the biz. , Sumitomo to make moisture grade for freezing. Early vintage TTL and CMOS was all ceramic below -C due to moisture absorpion and freezing. Silicone can be a problem too along the interface wires or leads. – Sunnyskyguy EE75 Apr 17 '17 at 0:48
  • clear epoxy is hydroscopic along leads. moisture ingress will destroy chip if submerged unless proper potting is is used – Sunnyskyguy EE75 Apr 17 '17 at 1:24
  • most LEDstrip makers, (not all) use this for outdoor use only. BUYER BEWARE. Some engineers already know the solutions – Sunnyskyguy EE75 Apr 17 '17 at 1:25
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More than likely, the leds in the light assembly are being over driven for reasonable light output. Typical 5mm and smaller leds, including the typical 5050 or 0805 SMD leds used in these assemblies are only rated for 20mA at their typical forward voltage, and at 12V for the assembly are already over driven. I bought many different models to replace car dashboard lights, and found them to be 30 to 35 mA at 14.5V of the typical fully working alternator supported voltage. This means they are overheating and overdriven and will burn out much much faster than their 5k to 15k hour life span.

Higher quality led assemblies do not require overdriving for decent light output.

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  • I'm thinking that they do not need to overdrive the LEDs. The brightness is way over what it needs to be. Compare it to an incandesant tail-light...you can hardly see them in full sunlight. The high-brightness red LEDs are more than adequate. – whitegreg56 Apr 18 '17 at 1:20
  • You'd be surprised. Break out a multimeter and measure it out. – cde Apr 18 '17 at 1:42
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Based on the answer by @cde, consider fitting a small voltage regulator to feed each light - these are available quite cheap and see if the lifetime changes.

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If you can be totally certain that not moisture is getting into any part of the circuit, then the answer is most likely overpower as mentioned by cde. As Solar Mike said, you can remedy that by using a voltage regulator module like this (fully packaged module) or you can make your own for less money too if you have the know-how.

To answer the question of why this still happens, as mentioned in the comments - money. The manufacturers do plenty of R&D and QC but you're still going to have the .1% of bad diodes. And when you're talking about BILLIONS of units, they add up. There may be nothing wrong with the design of the lights or their power source! It could simply be that when you buy 2 taillight modules (guessing ~144 LEDs total) that you get a couple bad diodes that don't deal with the workload correctly... then, a few days later, you have a "dead" LED.

So, unfortunately, there's no way to guarantee a 100% working part for this. There are just too many points of variability - especially when the problem is reduced life of a diode. That unit was probably tested and worked just fine! But give it 5-10 hours of use and boom - no more light off that diode. Even with a voltage regulator, you're still face with the inevitable fact that some diodes will be bad and unless you're willing to open the module and replace a single diode yourself, you may never get the fully functioning 15k life hours you should... then again, maybe you do, that the beauty of probability. ;)

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  • Highly dependant on the manufacturer. Legit brands will have longer or better life and warranty than the bottom bargain bin eBay sellers. Of course you end up paying for it. – cde Apr 17 '17 at 17:43
  • That's true. But even with the best brands, my point is that you will still have the occasional defect. That's the nature of large-scale manufacturing. The biggest difference is warranty in my experience, and secondarily, lamp life. The problem is that no manufacturer can test for 15k, or 20k or as high as 50k hours to actually be sure that it works that long. If they did they'd be sitting on a product for 10+ years before selling it. I will agree that you will get better items from better manufacturers, but no matter how good they are, there will always be the defective parts. – kyle_engineer Apr 17 '17 at 18:10
  • Not even near that many LEDs! Twelve facing rear and four for the side-light. That makes 16 on each lamp, times 2 lamps = 32 LEDs. With half of the LEDs going out on each lamp, something is not right! My guess is that if it "lights up" in the factory, it is shipped.... – whitegreg56 Apr 18 '17 at 1:26
  • @whitegreg56 you're absolutely right. If that's how many are going out then it's more than just standard defect parts. Can you link the ones that you've purchased? – kyle_engineer Apr 18 '17 at 16:33
  • @whitegreg56 also, do you unplug your harness before launching or not? I'm not a boat guy but I know a lot of people do that. Finally, is it the same halves of the lights that are blowing on all of the lights? – kyle_engineer Apr 18 '17 at 16:44

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