Capacitor Polarity

Discussion in 'General Technical Questions and Answers' started by KW4RP, Oct 13, 2017.

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  1. KW4RP

    KW4RP Ham Member QRZ Page

    To my fellow Hams: I have a simple question regarding this capacitor since it does not display a minus or positive symbol. With the attached photo you see below, you will see an oblong symbol, does that represent the negative - side? With the second photo, its labeled negative and black as you can see. In this case, would I follow what the capacitor label states the negative is negative and the black is positive? Thanks, MC Parise
     

    Attached Files:

  2. K0OKS

    K0OKS Ham Member QRZ Page

    That white stripe with the big (weird looking) minus sign in it denotes the negative side of the capacitor.

    There should also be a black dot on the negative terminal itself on those snap in caps ("negative black").
     
  3. KW4RP

    KW4RP Ham Member QRZ Page


    Joesph, that's what I figured, I wanted to be totally sure before I recap my HP-23A P/S. Instead of the black dot, the base of the terminal had a raised pattern on it which may be the same indicator as the "Black Dot" you were referring to. I thought I'd better be safe than sorry asking one of you guys before I started the project. BTW, we had a QSO within the last two weeks or so, I remember your name! Thank you for the heads-up and your time answering my question. Thank you again, MC Parise
     

    Attached Files:

  4. K8ERV

    K8ERV Ham Member QRZ Page

    You can also check it by applying a small voltage and measuring the current. A reversed voltage will draw more current that a correct polarity.

    TOM K8ERV Montrose Colo
     
  5. K0OKS

    K0OKS Ham Member QRZ Page

    The stripe side should be the negative. Did you perhaps buy that off eBay? I am not saying yours is, because I am not an expert on the topic, but many caps sold on eBay are counterfeit. Since the price difference between cheapcaps and good ones is so great the scammers can make a lot of money. Best to buy from Mouser or Digikey and get a datasheet, etc.

    A trusted ham source on eBay I am sure would be fine, though.
     
  6. W9GB

    W9GB Ham Member QRZ Page

    Mark -
    By this time, hanging around QRZ, you should be aware of the Capacitor Plague at turn of millennium (1997-2007). Industrial espionage gone bad by Taiwan and Chinese counterfeiters.
    https://en.m.wikipedia.org/wiki/Capacitor_plague
    The problem was featured in IEEE magazine (Electrical Engineers) in 2003.
    https://spectrum.ieee.org/computing/hardware/leaking-capacitors-muck-up-motherboards

    Last estimate, that I saw, over a Billion dollars (USD) of damaged electrical, test, and computer equipment. Guardian (2010) noted that it cost Dell (financial write-off) ~ $300 million.
    https://www.theguardian.com/technology/blog/2010/jun/29/dell-problems-capacitors
    EE Times (2016)
    https://www.eetimes.com/author.asp?doc_id=1329037

    It destroyed Abit, an OEM Taiwan motherboard mfg. for HP, Dell, and others.
    My nephew’s HP computer suffered the issue, which I repaired over a decade ago.
    ==

    I see two (2) issues with current radio amateur restorers:
    1.) Looking for “cheap parts” in HV power supply refresh. Failure of HV supply will often damage the amplifier, transmitter, or transceiver attached to it.

    2.) Blind capacitor replacement (shotgunning), within entire HF transceivers.
    The work, that I have seen, has been sub-standard and introduced NEW problems in radios.
    Soldering and component dressing similar to poor quality observed during CB Craze (1970’s).
     
    WA7PRC likes this.
  7. KF5FEI

    KF5FEI Ham Member QRZ Page

    With the exception of tantalum caps, the stripe denotes the negative terminal. That cap looks pretty small for the rating printed on it tho.
     
    WA7PRC likes this.
  8. K8JD

    K8JD Ham Member QRZ Page

    Test Method
    Hook it to a DC voltage source with the neg polarity to the lead on the striped side and if it smokes it is mismarked.
     
  9. N2UHC

    N2UHC Ham Member QRZ Page

    Or pops.
     
  10. G4COE

    G4COE Ham Member QRZ Page

    No guessing required...!
    Read what it says on the tin - 'negative black', look at the connection and the one with the negative sign in the strip is the negative, is the there not a black spot on the terminal?

    Come to think, looking at that negative sign in the strip, Shamwa electrolytic caps. uses the same format.... in gold on a green plastic sleeving.

    Dave
     

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