XPost: alt.binaries.chatter   
   From: no@spam.com   
      
   On Mon, 16 May 2016 23:19:41 +0100, Wayne Chirnside  wrote:   
      
   > On Wed, 17 Feb 2016 15:54:29 +0000, Mr Macaw wrote:   
   >   
   >> On Tue, 16 Feb 2016 23:50:38 -0000, M Philbrook   
   >>  wrote:   
   >>   
   >>> In article , no@spam.com says...   
   >>>>   
   >>>> I have a pile of power supplies which used to power CCTV cameras.   
   >>>> They're rated at 12V 1A.  They're very light and give out precisely   
   >>>> 12V with no load, so they must be regulated switched mode.  So why is   
   >>>> it when I try to power a 0.15A 12V fan (a 120mm Corsair computer fan),   
   >>>> they fail very quickly?  The first one started whining and gave out   
   >>>> only 0.5 volts after only half an hour, and the second one went pop   
   >>>> after half an hour.  I've had two of the others powering door   
   >>> entry RFID coils and the door solenoids and they've been happy for a   
   >>> few years.   
   >>>   
   >>> Most likely bad caps , that is most common failure mode for them.   
   >>   
   >> But for two of them?  When another two (of the same age from the came   
   >> camera set) have worked for a couple of years powering door locks?   
   >>   
   >> I've opened them up, this is what they look like.  I can see the power   
   >> transistor in the top one (the one that whistled and produced bugger all   
   >> voltage) has been warm enough to discolour and crack the yellow wax   
   >> stuff (ringed in green), but the caps look fine.  In the one that went   
   >> pop, a fuse has exploded (ringed in red).   
   >> https://www.dropbox.com/s/q1sc56tx0vtmzuv/PSUs.jpg?dl=0   
   >   
   > Back EMF from the fan?   
      
   Which should be less than the 12V coming from the PSU, right?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)