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Physical size of cap's

Discussion in 'General Electronics Discussion' started by Ric, Mar 6, 2017.

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  1. Ric

    Ric

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    Mar 6, 2017
    I have a cap on a board that is 405v 47uf 105'c and is 50mm long by 10mm (2" x 3/8").
    Can I replace it with a cap of the same value but physically smaller ? Half the size.
    It is in a switch mode psu.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Generally speaking, a physically smaller cap with the same voltage and capacitance is likely to have worse specs in other areas.

    Is the new cap 105C or 85C? They typically operate in a warm environment.

    Another important rating is ripple current. The smaller cap is likely to have a lower rating.

    However, in most cases this cap is, relatively, under lower stress than other caps (especially for 220V operation), so it may be OK.

    I had to replace a pair of calls in my oscilloscope. The original caps were unobtainable. The replacements we physically smaller. I do note a slightly higher amount of residual ripple, but it's not significant.
     
  3. Ric

    Ric

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    Mar 6, 2017
    Thanks. I was wondering about the ability of the smaller one to dissipate any heat that might be in the larger cap.
    I will look for one that is closer size to the original.
    Hard to find here.
     
  4. davenn

    davenn Moderator

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    It's not a hugely major issue
    More modern manufacturing techniques have also meant that the physical size has shrunk for a given value and voltage rating

    Dave
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Yeah, I should have mentioned that. The relationship exists (roughly) for a cap you purchase today. The older the equipment the less it applies.

    I guess I should have asked about the age of the equipment.

    In more direct answer to your question, newer caps generally have lower internal losses, so the self-heating, and hence heat to dissipate is lower.
     
  6. Ric

    Ric

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    Mar 6, 2017
    I will give the smaller ones a chance this time.
    Thanks for the replies.
     
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