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What is this component please?

Discussion in 'General Electronics Discussion' started by 1025478, Nov 25, 2012.

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  1. 1025478

    1025478

    4
    0
    Nov 25, 2012
    Excuse my ignorance, zero knowledge of electronics here, but what are the three red sausage rolls shaped components in this picture of the inside of an inverter welder and why is there smoke coming from them? I want to get it fixed if possible.


    2012-11-25 11.35.12.jpg
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    I would say those sausage rolls are capacitors. Do they have anything written on them?
     
  3. 1025478

    1025478

    4
    0
    Nov 25, 2012
    I think it says MPP 250v 4775J. Why would they have smoke coming from them? Some overload or something? One of them was sitting crooked

    g (450 x 600).jpg
     
  4. Externet

    Externet

    762
    166
    Aug 24, 2009
    It is a 4.7uF at 250VDC capacitor, metallized polypropylene. Widely available, cheap, and it would be good to buy a few in case after replacing it blows up again because of an external cause of damage that will have to be fixed before replacement.
    Digi-Key or Mouser should sell them.
     
    Last edited: Nov 25, 2012
  5. 1025478

    1025478

    4
    0
    Nov 25, 2012
    Thanks, now i know what it is, Looks like it might be easy to replace, but I can't find any online in the UK.
     
  6. 1025478

    1025478

    4
    0
    Nov 25, 2012
    thanks, final question is if this component holds a charge of 250 volts is it safe to replace. How do you discharge a capacitor?
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    Very good (and wise) question.

    They're a low capacitance(so they're not going to kill you), and almost certainly will discharge after power is removed (so you may have to do nothing).

    BUT... I never rely on either of those things.

    Turn off the power and unplug.

    Leave for as long as practicable (an hour or so is fine).

    Use a multimeter (carefully) to measure the voltage across the capacitors (under 20V and you'll be fine for small caps).

    optional... Take something conductive and place it across the leads of the capacitor. For small (low value and lowish voltage) capacitors a screwdriver piece of wire is sufficient. For anything larger, you should use something designed to safely discharge them.

    In this case, what you need to avoid is discharging the capacitor through your finger. That could be a little uncomfortable.

    This procedure is probably not required for these capacitors, however there are capacitors of a similar physical size which could give you a sizeable zap. As a beginner it's best not to rely on luck :)

    Also, wherever possible (when working on equipment that may still harbour a hazardous voltage/charge), get used to working with one hand so that you don't discharge anything across your chest. That is what can change a nasty shock into a deadly one.

    The above is part of what we mean when we tell people to "Be sensible" or "Be careful". It's shorthand for stuff you may not even have thought about.
     
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