I have 11 spotlights in my kitchen which are 12V MR16 fittings. Recently they've started giving me trouble. Only 5 out of the 11 still work correctly, the rest have gone

I decided it must be a heat issue - the halogen bulbs I had get seriously hot and I thought they might be burning out the fittings. I bought 1 new LED bulb and tested it, and it worked perfectly.

I went ahead and ordered another 4 of a slightly different brand. After installing them this morning, they stopped working. They work when I first hit the switch, then about 5 seconds later they cut out. Worse, now the one that worked fine is also doing this

Has anyone any idea what could be going on here? I intend to call an electrician to sort it out but I'm curious if anyone's seen this happen before. It's made me think the 240V - 12V transformers on each fitting may be the issue

  • Is the switch a regular "on/off" switch, or is it a dimmer? Commented Feb 13, 2015 at 13:34
  • @Paulster2 just an on/off
    – roryok
    Commented Feb 13, 2015 at 14:30
  • I would first try to replace the 12V power supply. I suspect those are switched mode power supplies, and one particular defect leads to not holding output voltage under low load. In the meantime leave at least one 12V halogen bulb.
    – Dan
    Commented Feb 14, 2015 at 18:28
  • @Dan, each bulb has its own 12V power supply...
    – roryok
    Commented Feb 16, 2015 at 10:12
  • Oh sorry missed that. How old are they? Can you try with a new or not-very-old power supply? It's either defective power supply (I suppose it's a switching mode power supply - those have electrolitics caps inside that go bad really fast especially in high temperature areas) or it was not designed for low load. Have the same issue with a string of bulbs on a single power supply, need to keep one real bulb to work. Will dismantle the psu and check what's inside.
    – Dan
    Commented Feb 16, 2015 at 16:09

2 Answers 2


This question is old, but it just hit 1000 views so I thought I'd post the answer.

The 12V PSUs were all at end of life, and were failing. It may have been that the 3.5W bulbs were too low power to work, but either way I ended up replacing the lot with new sockets and LEDs. If I recall these are not stepped down 12V but run off 240V so don't need transformers. I could be wrong about that, it's over a year since all this happened


I have just had the same problem with some g4 LED bulbs. I ordered 3.5w (equivalent to 35w halogen) and put 2 in and they worked fine. Proceeded to put all 5 in and the light would turn off instantly. I left 3 in and they turned off after 5 seconds and buzzed whilst they were on. On the light fitting I noticed it said max 20w bulbs. I presume as they are equivalent to 35w they are too powerful for the fitting. Will be getting some 2w ones and trying that.

Hopefully this helps someone else in the future and they don't make the silly mistake I did of thinking that as they are 3.5w they will work in a max 20w fitting. Do not take this as gospel though, its just an assumption.

  • 1
    That's not how wattage works, of the fixture states 20w you could put a 20w led in and it would be fine you might be blinded by the amount of light but the fixture can handle 20w.
    – Ed Beal
    Commented Jan 27, 2019 at 18:16

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