caps measured in volts?

Discussion in 'General Electronics Chat' started by fbchurch2009, Sep 9, 2010.

  1. fbchurch2009

    Thread Starter New Member

    Jan 10, 2010
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    0
    Quick Question! why are some electrolytic caps not only measured in farads, but also volts? ex. one of my caps says 10µF and then 16 Volts.... I need help understanding that. Thanks!
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    All caps have a maximum voltage. That is what you are reading on the can.

    What do I win?
     
  3. tom66

    Senior Member

    May 9, 2009
    2,613
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    This is the maximum voltage the cap can be exposed to before the dielectric breaks down. Actually, you can slightly exceed this, but it is not recommended, because the cap will have a reduced service life. If the cap bulges (e.g. from over voltage), it can leak corrosive electrolyte out.
     
  4. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    Its the maximum voltage you can put to the two terminals of the capacitor.Normally we dont exceed this rating for example if you have a circuit and at any two point of the circuit you need to add a 10mfd cap.. and at the two points you have a max voltage of 10 Volt then we will use a 10mfd 10volt or greater then 10 volt like 10mfd 16volt cap.. but not a 10mfd 6 volt cap.. as the volt rating is less and it will be damaged,now their are many ratings of higher voltage like 10mfd 63 volt,10mfd 100volt,etc you could use it on the above example as the voltage rating is higher but the size of the cap.. will be larger and cost will be higher than a 10mfd 16volt cap.. or 10mfd 10volt

    So the main stuff is that always have your capacitor's volt rating a bit higher than the input terminal voltage of the capacitor.

    Good Luck
     
  5. tom66

    Senior Member

    May 9, 2009
    2,613
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    It's important to note that it's a Bad Idea to run a cap at its maximum working voltage. A general rule of thumb is 1.5x to 2x the voltage you expect the cap to be exposed to. For example, for 10V, select 16V, or even better, 25V. This rule does not apply to high voltage caps (>200V) usually.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    .. and if using or replacing an electrolytic make sure you install it with the polarity correct.
     
  7. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    I think I already mentioned that.....

     
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    I always go at least one step up in voltage on aluminum electrolytics, sometimes two depending on the circuit - especially if any AC is involved. If the circuit presents a maximum of:

    6.3V - use 10V but 16V is better (never really trusted 10V caps)
    10V - use 16V or 25V
    16V - use 25V or 35V
    25V - use 35V or 50V
    35V - use 50V or 63V
    50V - use 63V but 100V is definitely better.

    You can however overdo this. You wouldn't want to use a 100V electrolytic in a circuit where it will only see 10V, not enough voltage to keep the plates formed.

    I also pay the extra 0.02 to purchase 105*C electrolytics, they can exhibit 10 - 100s times the life of a common 85* rated one.

    The info is out on the internet somewhere, don't remember it exactly so someone should go look this up:
    An electrolytic rated for 85*C will last about 2,000 hours at that temperature but around 10 - 20 times as long at room temperature. One rated for 105*C will last for 2,000 hours at that temperature but around 100 - 200 times as long at room temperature.

    I'm just guessing from something I saw in passing a long time ago, can anyone find more valid data for these figures?
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Did anyone mention they can occasionally explode (and make excellent stink bombs)? Or if they are tantalum, catch on fire like a match head?

    50% rule applies just like resistor wattage ratings, allow for more capacity than you will use.
     
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