Types of capacitor should be used

Discussion in 'General Electronics Chat' started by raychar, Dec 10, 2011.

  1. raychar

    Thread Starter Member

    Nov 8, 2011
    82
    0
    I found the following electroylic capacitors get very hot and have smell coming out, the related areas for that capacitors are working at +90VDC and at frequency 20KHz.
    - 1uf, 400V
    - 10uf, 400V

    I checked that there is no wrong polarity connection mistake involved and think that the type of capacitor I used is not suitable. What is the meaning for ESR for capacitor, are there such reading marked on capacitor for the distinction?

    Thanks,
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Change the caps to low ESR type with the same ratings

    Equivalent Series Resistance
     
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    It is also might be that the ripple current (the AC component of the current) is really too big even for the best electrolytic capacitors. Depending on what your circuit is, this might a design issue or the result of a component failure.

    If you post a schematic, somebody may be able to advise you further.
     
  4. raychar

    Thread Starter Member

    Nov 8, 2011
    82
    0
    Where can I buy ESR capacitor? I already bought a 1uF 400V capacitor of audio use type, there is no such ESR marking on it but it's price is five times the general capacitor of same rating. However, same high temperature and smelling happened when using. Can I use polypropene or mylar type or etc. instead of electroylic type? Of course, I don't prefer these because their sizes are much bigger bigger than the space available in the populated circuit board.

    P.S it is used in floating voltage supply in high side gate driver, so its voltage is shifted +90v to 0 at frequency 20KHz.


    Thanks,
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    If you bought an "audio grade" capacitor, take it back.

    They are generally dressed up standard capacitors, with average specs, but specially plated and had a virgin's tear land on it during a full moon in February.

    Digikey sells Low ESR capacitors, I'd suggest Nichonon or Panasonic lines
    www.digikey.com

    Mouser also carries those brands.
    www.mouser.com
     
  6. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Low ESR capacitors have current ratings at 120hZ and 10kHZ or 100kHZ indicated on the datasheet--in some applications, it requires parallel capacitors to increase the current rating.

    New observation:
    It appears that capacitors of this DC voltage rating (>150VDC) are not specified in terms of ESR, but current rating only.

    I did a quick search on DigiKey's search engine and located this 10uf 250V radial capacitor with a current rating of 350mA @ 100kHZ that was designed for nasty ballast applications--it may possibly work???

    http://search.digikey.com/us/en/products/EKXG251ELL100MJ20S/565-1441-ND/755957

    datasheet:
    http://www.chemi-con.co.jp/e/catalog/pdf/al-e/al-sepa-e/004-lead/al-kxg-e-110701.pdf

    The 450V version has a current rating of 450mA--higher probably due to increased surface area that enhances cooling.
     
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