| Electronics > Repair |
| Why/how do these LED lamps fail so fast? |
| << < (6/9) > >> |
| soldar:
--- Quote from: Zero999 on September 24, 2023, 09:19:34 am ---Have you measured the voltage across the LEDs which do work? --- End quote --- I did some testing with the first few LEDs of the strip and, apparently they are grouped in groups of 4 LEDs in parallel. I put about 40 or 50mA through the first group , which would mean 10 or 12 mA through each LED and they light OK and measure about 2.8V. I then connected the two first groups and, sure enough, at the same current level I get about 5.6V. So those two groups are in series. If all the groups of 4 LEDs were all connected in series we would have about 25 groups adding up to about 70V. The PSU says 240mA and 40 to 76V which would mean a max of 18 W which is less than the 20W listed on the fixture. 240mA which would mean 60mA through each LED. Hmmmm.... But 60mA x 2.8V x 100 LEDs= 16.8W which is less than the 20 W nominal for the fixture. In any case it does seem like the LEDs are being driven with too much power. If the group of failed LEDs were shorted the others would just light normally. If they were open circuit the others could not light at all. I measured the failed LEDs and they are opened, not shorted. I then soldered a 68 ohm resistor across in the hope that it may repair the problem but it does the same thing, it blinks on for just a moment. Quite baffling to me. ETA: I shorted the bad LEDs and the others now work correctly. I might shunt some current away. I will keep experimenting. |
| soldar:
I measured the current the PSU puts out and it is about 275mA which is in excess of the nominal 240mA. That is about 69mA per LED. If I put a 1K resistor in parallel it shunts about 70 mA away from the LEDs ... wasting about 5W but making life easier for the LEDs. I might do that on all the other similar LED fixtures I have. That should prolong their life. It would be better to adjust the PSU to output less current but I have no idea how to do it. I am attaching a photo. |
| T3sl4co1l:
Probably there is a shunt resistor towards the output that could be increased, but if you can't identify the circuit and ICs, probably better not to screw with it. You might also just have poor quality LEDs. Tim |
| hobbylad:
I was equally puzzled seeing so many of my LED lamps fail. I could not resist doing an autopsy. Posted the results in my blog below: https://hobbylad.wordpress.com/2024/11/17/the-curse-of-the-failing-led-lamps/ |
| tunk:
If you double the resistor value, the current will be halved, reducing the temperature. This should increase the bulb life. |
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