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Please help me recognize clamp-meter's cap ratings for replacement

Discussion in 'Repairing Electronics' started by BGAmodz, Sep 18, 2013.

  1. BGAmodz

    BGAmodz Member

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    Hi everyone in this forum .

    So 2 days ago i was trying to repair a microwave , i decided to check a big AC capacitor with a clamp meter , i used AC voltage mode , and the meter just shut down as soon as i connected the probes to the AC capacitor .
    I opened the clamp meter and found that 2 tracks were out of place and a small capacitor was burned but only 4 symbols were visible in it : YP and 02 , i wonder what rating would be safer to use , this capacitor is attached to a small daughter board making connection between the probes holes and the meters motherboard .
    this is how the capacitors looks like :

    Microwave's cap :
    [​IMG]
    Meter's cap :
    [​IMG]




    Multimetrix CM600
    [​IMG]
     
  2. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Not quite sure what you did. How do you connect a clamp probe to an out of circuit capacitor?

    John
     
  3. BGAmodz

    BGAmodz Member

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    The capacitor was on circuit when i checked it , the microwave was turned on .
     
  4. dave

    Dave New Member

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  5. debe

    debe Active Member

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    Sounds like what you measured exceeded the voltage rating of your meter.
     
  6. BGAmodz

    BGAmodz Member

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    I think so
     
  7. tunedwolf

    tunedwolf Well-Known Member

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    If the blown "capacitor" is connected between the probes then it's not likely to be a capacitor but much more likely to be a varistor, used to protect the meter input against excess voltage. In any good design I would have expected a fuse in the input circuit somewhere between the varistor and probes to also protect against over current situations. Take some photos of the input and surrounding circuitry and post them here :)
     
  8. BGAmodz

    BGAmodz Member

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    i will , and your quite right , its a varistor , but i don't know its ratings
     
  9. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I would SERIOUSLY suggest you leave microwave ovens alone, you obviously have no clue about how they work (it was an incredibly stupid thing to do, and was guaranteed to blow your meter). Microwaves are the most dangerous of all household appliances, and the shock from that capacitor WILL kill you.
     
  11. BGAmodz

    BGAmodz Member

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    I admit it i really acted stupid and could have killed my self
     
  12. BGAmodz

    BGAmodz Member

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    Last edited: Sep 19, 2013
  13. BGAmodz

    BGAmodz Member

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    The unit does not turn on , am sure if its not the varistor , its some damaged tracks .
    I have just read about this varistor's behavior :
    actually varistors may not be able to successfully limit a very large surge from an event like a lightning strike where the energy involved is many orders of magnitude greater than it can handle. The high current resulting from the strike generated excessive current that destroyed the varistor in my case .
     
    Last edited: Sep 19, 2013
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I would suggest buying a new meter - you've probably caused extensive damage to it, far beyond anything it's 'protection' is capable of handling.

    They aren't designed to have 3000V high current applied to them :arghh:
     
  15. BGAmodz

    BGAmodz Member

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    the card contain small amount of SMD parts , i checked them and they seem fine , just some resistors and zener diodes , am pretty sure it will work again when i replace the varistor .
     
  16. BGAmodz

    BGAmodz Member

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    I taught that the CAPACITOR was only delivering 220 V ac !!!
     
  17. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You thought VERY badly wrong! :eek:
     
  18. BGAmodz

    BGAmodz Member

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    Thanks for the worries ,
    A member (KeepItSimpleStupid ) suggested me to use a varistor with 660 Volts max ac on the link in his post , but what about the capacity in farads ?? i dont have any ratings on it , the cap i got is burned .
     
  19. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I thought the part INSIDE your meter is a (Transient Voltage Suppressor), not a cap. The TVS basically ACTS like back to back Zenier diodes. It's physical size determines how much energy it can absorb.

    It is usually placed in Parallel with what's being measured to act as a clamp. Removing it, should allow the meter to work without any protection. So, your first step is to remove it, repair the tracks and see if the meter works.

    As for the cap in the microwave, here is a pic of one. http://www.appliance-parts-experts.com/13QBP21090-capacitor.html Note the 2,100 Volts AC rating. That should be enough to SCARE you and easy enough voltage and current to kill you.

    I worked on stuff a but more scary. An X-ray diffraction set with a 100 KV, 0.1 A power supply and an electron beam evaporator that had a 15 KV, 1 Amp supply with a Shunt Tube/Valve regulator and a 1000 W rube RF transmitter. If you don't know what your doing, you don't mess with it.
     
    Last edited: Sep 19, 2013
  20. BGAmodz

    BGAmodz Member

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    I hope this picture could give you a clear idea , here is where the component is connected ( between positive hole and the motherboard ) :

    [​IMG]
     
    Last edited: Sep 19, 2013
  21. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    It should basically be across the input which I can't tell. A cap would just be used for the AC scale.

    So. are those binding post jacks used for AC only? If so, then it could be an "X" or "Y" capacitor. Probably "Y".

    If it is a capacitor, I'd pick it out of this list http://www.digikey.com/product-search/en?pv14=1140&FV=fff40002,fff8000b,654056a&k=capacitor&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25 by diameter.

    The cap picked is a a "safety capacitor". The value probably isn't critical. So, I'd try to pick it by size.

    I can't quite see what the circuit looks like, but if in series, it may be a cap. If in parallel, its probably a TVS. If the posts are only used for AC, thats another hint.

    Temporarily, you can connect a ceramic cap of a high enough voltage, but I would only use a safety cap for a final repair.
     
    Last edited: Sep 19, 2013

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