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Capacitors 101

Discussion in 'Electronic Repair' started by Stevie D, Dec 19, 2006.

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  1. Stevie D

    Stevie D Guest

    TV on bench with vented main filter cap, (220uf @ 200v), and I've a
    simple query. Can I up the ante on this and replace with a 470uf @
    200v? It's a switched mode p. supply and the pop was a result of a
    power surge, didn't take anything else out. Is it just a question of
    economics when it comes to filtering, (cheap walmart tv), or might I
    disturb the fragile balance in the smps. My thought is, better filter,
    smoother dc. Any thoughts???
    Cheers, Steve
     
  2. DaveM

    DaveM Guest

    Well, your thought is correct about smoother DC, however, there are other
    considerations that are important as well. Inrush surge current is the first
    thing that comes to mind. When you first apply power to an uncharged capacitor,
    it looks like a dead short across the line. The higher the capacitance, the
    higher the surge current. If the surge is large enough, you'll blow the line
    fuse. Unless you just like digging around in a dead TV set just to change the
    fuse every few times it's powered on, it would definitely be a nuisance.


    --
    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
    address)

    Some days you're the dog, some days the hydrant.
     
  3. Eeyore

    Eeyore Guest

    Within certain limits. More likely it'll make the inrush current last longer, which
    could indeed also blow the fuse.

    Graham
     
  4. Stevie D

    Stevie D Guest

    Graham, Dave, thanks for the input. I'll consider replacing the cap
    with the initial value just err on the side of caution and avoid a call
    back. This being said, I've had better luck in the past with closer
    values, within 100uf or so. Happy Holidays
     
  5. I also wonder if the cap is the only problem.

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  6. Stevie D

    Stevie D Guest

    Thanks for the feedback/comment Sam, I've had the set on now since I've
    replaced the cap, no more "poof"! The client lives in a rural area with
    frequent surges in the supply line, (transmission lines affected by ice
    storms and the like, I'm in Canada ya know...eh). Pretty straight
    forward repair. Merry Happy Joyous Holidays one and all, health and
    happiness in the new year!
    Cheers, Steve
     
  7. Going higher on working voltage is a better (and very safe bet), but
    probably it was just a cheap physically small capacitor and replacing
    it will do the trick.


    Best regards,
    Spehro Pefhany
     
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