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I was changing some light bulbs at my mom's house and I noticed that a (water resistant) LED strip she has had turned stiff and almost black. As expected, it hardly gave out any light. The LEDs seem to be working so I think the reason it's hardly giving out any light is the decoloration of the insulation which was once transparent.

I also noticed its power supply (230V -> 12V, 5A) was buzzing and was quite hot to the touch. The strip is about 2m with LEDs every 5cm, so approximately 40 LEDs. Although I don't have a datasheet (since it was installed many years ago by someone else), if we assume each LED to be drawing 50mA, it adds up to 2A - way bellow the 5A of the power supply. Even if they use up 100mA, which does seem a bit much, it would still add up to 4A which should still be fine for the power supply but might explain the heat.

Could the LED strip turn black because of normal use/heat or should I have a better look at the power supply? I didn't notice any obviously busted electrolytic caps with a quick inspection (the top is full of venting holes so I could look inside) but there could be ones where I couldn't look without disassembling it.

I did notice a trimmer on it but I didn't have a multimeter with me to test the output voltage so I have a suspicion the output is somewhat larger than 12V but not enough to blow the strip instantly.

Last bit of information that I found odd but it could be nothing, the electrician had used a 5 core piece of cable, using 3 of them (blue, brown, green/yellow) to connect the power supply to mains and the remaining 2 (blue and brown) to go back and connect to the LED strip. So you have 230V and 12V running through the same cable. Could this have anything to do with it?

I will go back with my multimeter so I can find out myself if the power supply is not set correctly or acting up.

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    \$\begingroup\$ It's not uncommon for these strips to darken quite a bit with age. They're just cheap crap, not much you can do. Same goes for the power supply, cheap ones are often way overrated, so it can get quite hot with only half the rated load. The way it's installed sounds dangerous to me though... \$\endgroup\$
    – svens
    Aug 22, 2017 at 14:46
  • \$\begingroup\$ You give the LED 12V and hoped each drawed 50mA and that obviously didn't happen. \$\endgroup\$
    – user3528438
    Aug 22, 2017 at 14:47
  • \$\begingroup\$ #svens Thanks. I haven't been using them so I didn't know this was common. About the installation: It's something I've never seen done before and when I asked my mom she said the electrician that installed it was not yet certified as he was still studying for it. She does have good breakers though. \$\endgroup\$
    – Schizomorph
    Aug 22, 2017 at 14:52
  • \$\begingroup\$ I'd suspect that a cheap power supply reaches efficiencies of around 70%, especially when not fully loaded. At 24 W that would be around 10 W heat in the supply, plenty to make it warm. Buzzing can be a sign of bad design but I've encountered a few good power supplies which started to buzz after some time. \$\endgroup\$
    – Arsenal
    Aug 22, 2017 at 14:58
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    \$\begingroup\$ Buzzing can be a sign of too high ripple current through an inductor, that can happen when filter caps go bad. So sometimes it helps to replace those (big electrolytic caps). On other occasions it's just that the winding got loose over time and can move now. You can fix that with glue (I heard epoxy is working well for that). \$\endgroup\$
    – Arsenal
    Aug 22, 2017 at 15:14

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Could the LED strip turn black because of normal use/heat or should I have a better look at the power supply?

Yes, it can. Cheap plastic can warp and discolor under summer weather, and will do so faster when it has trapped the heat of the led and the FPC the strip is made of. Frankly. I've had cheap waterproof led strip yellow in room temperature over time.

The power supply can definitely be suspect as well. Without at least a multimeter. You cannot tell if it is under or over voltage, if it is stable, etc. Keep in mind that you can drive these led strips at more than 12V, up to 15V and they will work, at a significantly lower life time.

As to the wiring, unless there is a short, that's not too much of an issue.

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  • \$\begingroup\$ Thanks. I think I will replace the strip with a normal one. There's about 0 chances of water splashing up there. Is the buzzing normal for an 8 yo power supply? Is it something I could fix? I'm very good with soldering if I know what to look for. \$\endgroup\$
    – Schizomorph
    Aug 22, 2017 at 14:58
  • \$\begingroup\$ Depends on how loud of a buzz. \$\endgroup\$
    – Passerby
    Aug 22, 2017 at 16:20
  • \$\begingroup\$ 30-40dB SPL approximately. You can hear it when the room is calm but not when people are talking or a TV is on. \$\endgroup\$
    – Schizomorph
    Aug 22, 2017 at 16:24

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