100 uf dose size matter?

Discussion in 'General Electronics Chat' started by Boomer2506, Nov 12, 2011.

  1. Boomer2506

    Thread Starter New Member

    Oct 20, 2011
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    I have been using some 100 uf 35 volt caps, but today found some 100 uf 16 volt caps that are about 1/4 the size.Since they are both 100 uf will they work the same?Or do the bigger ones have more storage?I am using them in a 3.7 volt boost to 5 volt circuit.
     
  2. K7GUH

    Member

    Jan 28, 2011
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    The larger ones will store the same amount of energy, but have a higher voltage rating. That means that the larger ones can withstand roughly twice the voltage "working voltage" that the smaller ones can handle.
    It would be very helpful if you would read up on the meanings of microfarad and working voltage. Otherwise you are likely to ruin a few components. In the information you gave, the 16 volt caps will probably be OK for the purpose.
     
  3. tom66

    Senior Member

    May 9, 2009
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    No, energy in a capacitor is 0.5CV^2. Doubling the voltage quadruples the energy. And more energy don't come from nowhere ;) so the can is bigger.

    You could get away with using 6.3V or 10V caps. Most newer capacitors are not adversely affected by voltages up to their rating.

    If you circuit has a high output current and/or needs low output voltage ripple, you would do best with some low impedance capacitors and probably a higher value of cap.
     
  4. steveb

    Senior Member

    Jul 3, 2008
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    That's a good point to consider AC ripple when choosing the capacitor. People often forget about that. AC voltage implies current flow continuously which leads to heating which results in reduced lifetime.

    I would recommend that 10 V is a better choice than 6.3 V for reliability, if he is talking about 5 VDC for the working voltage. A factor of two margin for voltage is a good rule of thumb because it is very effective to improve reliability. It provides orders of magnitude increase in mean time before failure, with the actual improvement dependent on the capacitor type. This is particularly important with electrolytics and tantalums, when there will be high frequency ripple.
     
    Last edited: Nov 12, 2011
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    As far as Boomer2506's question, either cap is good there.

    I agree with steveb, I always pick caps to have at least twice the voltage rating as they ever see. Newer caps may be better as tom66 suggests but I'm old school on this.

    One rule of thumb taught to me is the physical size of a cap is proportional to the capacitance times the voltage rating. That may come in handy if you're trying to build something very dense.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I think cap size changes with the manufacturers size ..u know ?

    Or is it the other way around ?
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    Yes, physical size does matter. Besides the fact that the higher voltage cap will take up more space and cost more, there are other factors to consider.
    Yes, do make sure that the max applied voltage is covered and give yourself a margin of safety. But you would not put a 100uF 100V cap in a 5V circuit if you have one rated at 16V. As others have said above, when you take into consideration the increase in internal resistance and inductance, the lower voltage rating cap will provide better filtering performance.
     
  8. Boomer2506

    Thread Starter New Member

    Oct 20, 2011
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    Thanks guys for the reply's.Ripple is not a concern really only the size.The bigger ones fit very tight in my limited space so any little gain size really helps.
     
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