Power Supply -commerical power supply has a problem

Discussion in 'General Electronics Chat' started by pujulde, Aug 17, 2015.

  1. pujulde

    Thread Starter Member

    Jul 24, 2013
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    Hi every one, I have a Siemens power supply 5Amp 24 volt output and 120volts , 220 volts input. The problem is I think in transformer. It creates voice like ticking. Output voltage keeps 24 volts for about a minute and after fluctuation begins (22.x-23.x). I tried to change capacitors but the same problem. I could not find any manual or drawinds. Can anybody suggest something, may be some additional information would required , in that case I will write, thanks in advance
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Assuming it is a low-voltage linear supply; not a Switch-Mode Off-line one, remove cover, and measure the AC voltage out of the transformer secondary right where it goes into rectifiers. Two possibilities: if transformer secondary is center tapped, you will find two rectifiers; else a potted full-wave bridge rectifier with four connections. See if the AC voltage at the secondary drops after things heat up?
     
  3. pujulde

    Thread Starter Member

    Jul 24, 2013
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    Thanks I will try,
     
  4. pujulde

    Thread Starter Member

    Jul 24, 2013
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    But what can make it ticking?
     
  5. pujulde

    Thread Starter Member

    Jul 24, 2013
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    I could not understand the scheme, because it seems that the voltage from supply is going to choke and capacitor, after to rectifier without stepping down. I measure the voltage on bridge rectifier and its about 320 volts. Is that kind of scheme possible?
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    A ticking SMPSU is usually repeatedly starting up and detecting a fault that makes it shut down again.

    The most likely source of the actual sound is the ferrite core in the transformer.

    It usually suggests a shorted output or basically an overcurrent fault - but the PSU could be designed to shut down if not properly loaded.
     
  7. pujulde

    Thread Starter Member

    Jul 24, 2013
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  8. pujulde

    Thread Starter Member

    Jul 24, 2013
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    I have no load, just switch it on and it begins ticking at the same time the led is flashing in tact with that ticks . when I switch it of the choke I think keep the voltage and the ticking rate slowly goes down and I see how the led is flashing in ticking time
     
  9. pujulde

    Thread Starter Member

    Jul 24, 2013
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    Led is just for indication of power on
     
  10. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Can you post some pictures or a brand name and model number?
     
  11. pujulde

    Thread Starter Member

    Jul 24, 2013
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    IMG_20150818_061505.jpg
     
  12. pujulde

    Thread Starter Member

    Jul 24, 2013
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    PS 307 siemens
     
  13. ScottWang

    Moderator

    Aug 23, 2012
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  14. gerty

    AAC Fanatic!

    Aug 30, 2007
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    The black disc in the picture, above the bridge rectifier, appears to have some sort of hole in the center. Is that correct? Do you see any arcing when it's powered up?
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
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    Looks like maybe a MOV, or more likely a NTC inrush limiter.

    Defects in the epoxy dip coating can happen - close inspection should reveal whether its a burst void in the coating as it set, or a crater blown out by an internal "event".
     
  16. pujulde

    Thread Starter Member

    Jul 24, 2013
    95
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    It's an NTC
     
  17. pujulde

    Thread Starter Member

    Jul 24, 2013
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    No arcing, just voice
     
  18. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Could it be relay chatter??
     
  19. pujulde

    Thread Starter Member

    Jul 24, 2013
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    OK, thanks everybody for assistance , I will try to find out problem. Some of your advice was important to me .
     
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