Help With Varistor ID

Discussion in 'The Projects Forum' started by apprenticemart2, Aug 26, 2013.

  1. apprenticemart2

    Thread Starter Member

    May 7, 2013
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    I am trying to spec this mov that has blown in my PC power supply and is not powering up now after I removed the component.

    I didn't like the arcing I was getting on applying power.I'm not sure if it would be a good idea to put a jumper wire in until I actually know what's happening.

    I have found a datasheet that could be a contender but the dimensions are incorrect. This component is about 10mm in diameter.http://www.thinking.com.tw/documents/en-sck.pdf?osCsid=34b263dd15120e68c25e6b8e8e4156ee

    The only ID I can make out on the component is SCK, then an unknown digit, then the number 5.

    The MOV goes between GND (I think) and the Cathode of an STTH8S06 ultrafast high voltage rectifier.

    Can anyone suggest what rating or even component Is most likely to be used in this application?

    Thanks.
     
    Last edited: Aug 26, 2013
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Normally you would not replace a Transient Voltage Suppressor with a jumper, in most case these act as a virtual open until the suppression level is reached, where they start to conduct.
    The main spec's are operating voltage and energy level of suppression (Joules) in watt-secs.
    Google: general electric transient suppression manual ch17
    Max.
     
  3. apprenticemart2

    Thread Starter Member

    May 7, 2013
    67
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    Thanks for your reply. I have been sifting through google images until I find something similar to what I have.

    There seems to be a few pictures of varistors with the part number SCK 054 so it could be that this is the same part that I have. I'm just trying now to find some kind of datasheet so that I can cross reference a replacement.

    I'm thinking that the part number is now SCK10054.
     
  4. apprenticemart2

    Thread Starter Member

    May 7, 2013
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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It is very hard to second guess when the original device parameters and requirements of the original are not known?
    Max.
     
  6. apprenticemart2

    Thread Starter Member

    May 7, 2013
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    Yes that's very true. I'm having a lot of trouble trying to find a mov for a Yamaha Virago 400 electronic ignition box. When these things blow they tend to take all the identification markings with them.There's a million different ratings that I could choose from.

    It's almost as if they deliberately made them with failing in mind. A couple of pennies worth of electronic component failing means something that's worth a good deal of cash gets bricked.

    As for my PC power supply MOV, I will take the 20 or so pictures of exploded SCK 054 MOV's I found on the internet as a good indication that I may be on the right track. Classic bad batch/poor manufacturing signs, although I would have expected better from a Corsair branded power supply.

    What other options do I have other than buying a brand new PC power supply?
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    This is one of the problems with this type of device, they are by definition Transient Suppression devices, but if a larger, or longer duration energy pulse happens to occur, they MAY save the devices they are protecting, but in the process, themselves destruct!
    R/C snubbers are a little less energy-rating defined, but usually do not destruct that easily.
    In many instances, these are used in parallel with a MOV.
    Max.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    If this thing was really a MOV, as it appears to have been, your PS should run fine without it. That's easy to test. If it does, just choose a new one. It doesn't do anything in normal operation, so its exact details aren't all that important. Like choosing a fuse you just want one that doesn't blow all the time but still protects against an event that would damage other, harder to replace, components.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The energy (Watt-Sec) could be approximated from the dimensions, but is is the constant voltage rating that could be tricky, unless there was a steady even DC/AC signal across it that could be measure for peak amplitude.
    Max.
     
  10. apprenticemart2

    Thread Starter Member

    May 7, 2013
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    The power supply won't power up now I've removed the part so that means it isn't a MOV then?

    While the part was still in the pcb I was getting a popping sound and a flash at the location of the component, then the green power LED on the motherboard would light up.

     
  11. debe

    Well-Known Member

    Sep 21, 2010
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    I would say its a NTC thermistor, they are used to limit switch on current. Used a lot in SMPS to limit switch on surge current. The symbol on the board is for a resistance not an MOV.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    I've been trying to figure out what else it might be. I think you've nailed it.
     
  13. apprenticemart2

    Thread Starter Member

    May 7, 2013
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    I see you have the trusty Mk I eyeball in your tool kit.

    Thanks.
     
  14. apprenticemart2

    Thread Starter Member

    May 7, 2013
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