How hot should LED driver output caps get?

Discussion in 'General Electronics Chat' started by TamasK, Dec 30, 2014.

  1. TamasK

    Thread Starter New Member

    Dec 30, 2014
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    I have an LED light fixture with a 12V/18W power supply in it (an Eaglerise ELP18-12LS). The PS started overheating and switching off, so I looked inside if I could spot any obvious issues. Indeed, one of the output caps (a 330uF/16V part) was bulging, so I replaced it. But even after replacing the cap, the replacement cap (and the other original cap) keeps getting pretty warm (about 55C in 21C ambient).

    The PS also makes a louder than normal buzzing sound. I've heard this type of hum from other switching power supplies, so by itself it wouldn't make me worry, but combined with the overheating issue it is concerning.

    So my questions are:
    1. Is it normal for the output caps to get this warm? If not, is there a potential easy fix?
    2. Is there something I can do to reduce the buzz?

    Thanks in advance!
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,432
    3,360
    Scrap that fixture and get a new one. You are at risk of starting a house fire.
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
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    If its a high speed switching supply - you can't just use any old electrolytics as replacements. They have to be low ESR types.

    Sometimes I've got away with it by adding SMD multilayer ceramic chip capacitors to the electrolytic by mounting them on the print side.
     
  4. TamasK

    Thread Starter New Member

    Dec 30, 2014
    2
    0
    Yes, of course I used a low ESR part. Unfortunately this seems to be a somewhat uncommon size cap, so my local shop only had an off-brand part, but at least it is low ESR.
     
  5. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    When I serviced PC monitors for a living, I sometimes encountered certain makes/models that didn't have a particularly good record where the SMPSU electrolytics were concerned - the 6.3V CRT heater supply in particular.

    Whenever there were persistent problems, I'd examine whether or not a Shottky diode was used, if a regular fast silicon diode was used - a SB diode could make all the difference.

    You have to watch the reverse voltage rating (especially in flyback PSUs) SB diodes start at 20V and start getting pricey at only 60V.

    In most flyback converters; I used the diode I took out, in a snubber circuit to damp the reverse voltage peaks.
     
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