| Electronics > Repair |
| Why/how do these LED lamps fail so fast? |
| (1/9) > >> |
| soldar:
We are told LED lights are eternal and will last more than 10,000 incandescent lamps but not in my experience. About a year BP (Before the Pandemic) I bought a bunch of round flat ceiling LED lights and I installed some of them in a second home where I do not spend that much time. Today the third one out of seven has failed. They all fail in the same way. The flicker but do not start up. The symptoms are that the PSU is failing but it is the string of LEDs that fails and the PSU is fine. If I exchange PSUs between lamps the problem stays with the lamp, not the PSU. I do not know how to interpret these symptoms except that the LEDs are demanding more current and the PSU is limited and shuts down. So I have three PSUs to play with. I am talking from memory but IIRC they provide a constant current of about 240 mA at about 60V. Not isolated from mains so care is recommended. I am assuming the LEDs fail because they are being driven too hard. But for the brief moment they are on I do not see any one of them not lighting. This time I might test the string of LEDs with a DC power supply (which I do not have and will have to rig). My experience with LED lamps is not being good. And what ticks me off is that these are complete ceiling fixtures where you can't just change the light-bulb like in the good old days. Any ideas or knowledge on this topic? I am thinking that, with a constant current PSU, I could divert some of the current through a resistor in parallel and this would lower the dissipation in the LEDs. Suppose it is putting 240 mA at 60 V. If I put in parallel a 2K4 resistor it will take away 25 mA from the LEDs (and dissipate 1.5W). |
| Grandchuck:
I don't know if it is relevent to your lights, but if an LED in a series string shorts out the others draw more current if the power supply is a CV type. |
| artag:
Big Clive often autopsies (biopsies ? some aren't broken when he starts) LED lamps and looks into the current control. Often, there is a resistor whose value sets the LED current. A while ago he investigated some Philips lamps only available in Dubai which were underrun for longer life. So he often explains how a given lamp can be modified to run at lower current. |
| soldar:
--- Quote from: Grandchuck on September 20, 2023, 05:06:12 pm ---I don't know if it is relevent to your lights, but if an LED in a series string shorts out the others draw more current if the power supply is a CV type. --- End quote --- I was thinking along those lines. If one LED fails open then none will light. If it fails shorted then the other will draw more current depending on the PSU. This one seems to be more like constant current, variable voltage. If one or more LEDs short out then the current should stay the same but the voltage should drop. It could be that if the voltage drops then the PSU shuts down as detecting a short. But, without looking too closely, I did not see any individual LEDs obviously not lighting. I think I need to do some more testing with both the LED string and with the PSU. |
| dobsonr741:
I saw electrolytics causing the trouble many times. Usually, the simple plastic encased bulbs. So my working theory is overheating, caps blowing up or getting leaky and cascading into semiconductor and LED failure. |
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