capacitor questions

Discussion in 'General Electronics Chat' started by electronis whiz, Aug 17, 2010.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    the capacitors that look like ceramic ones but have slipery plastic cover are these mylar capacitors. some are also longer oval shaped. will a electrolitic capacitor explode if polarity is wrong or voltage exceded.
     
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    I don't know about slippery caps, but I can definitely tell you reversing the polarity on an electrolytic could cause it to blow up. Do it to a large filter capacitor and the results are pretty spectacular.
     
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
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    201
    They could be mylar if they're old but chances are they're both common Polyester Film Capacitors which have replaced most smallish - mid value caps. They're relaible, inexpensive and spec out pretty good for their price.

    Caps in the low pF range are usually still ceramic and most anything above 1 uF is usually an electrolytic.
     
  4. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    Not everything that looks like a Capacitor is a Capacitor.

    Some times you need to see the schematic in order to identify a vaguely marked item.
     
    PackratKing likes this.
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
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    True, the markings should tell all, even pictures would be a great help. For instance the long oval ones could also be tantalums but there should be a + sign on it somewhere. If you're fast enough with an ohmmeter you can sometimes deduce an unknown component but it really pays to spend $20 or so for an inexpensive LC meter to have around. Although I have bench gear I bought one of these because it's a heck of a lot handier to deal with, especially if I need to take it to work for something:

    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380024081247

    Testing with known values it appears to be pretty darn accurate, the case is thick, switch feels durable too.
     
  6. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    I wouldn't buy a multimeter unless it had an LC function or it was intended as a cheap extra meters.

    After a few accidents I prefer to always use cheap meters for measuring currents.
    :(
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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    An LC meter is little more than a spot check device for me to catch mismarked items or the value of questionable electrolytics. I generally just order new if I don't have something already in stock. They do come in handy when you have to hand wind RF coils though..
     
  8. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    519
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    i know i usiwaly check the shematic symbols before pulling off the part. if your are wondering how i do this i use a small carved needlenose. this is ok for parts with longer wires. butfor relags and electrolitiscs i desolder those. i have learned to chack thi because i have taken apart 3 old crt monitors and found veristors that look like ceramic caps but usiwaly have no or a odd number. also usuwaly labeled vr on the board. i have also found a rectangle plastic part thought was one and checked the symbol and it shows 2 diodes arows pointing tords eachother. any idea what this is it only has 2 wires so it is not a shockety diode. i looked it up online and the site said that was the symbol for a gunn diode. but thay make microwares so i don't think that's right.
     
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