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    #1

    need help finding 'small' caps

    Sorta. I have an Antec PSU that blew its caps. Was able to replace some with same value but little larger diameter caps but I'm running into a prob replacing these 4700uf 10v 10mm dia Fuhjyyu caps. I can't find 10mm 4700uf caps. Even at 6.3v. 12.5mm is too large for the four all together. Tried digikey, newark, and mouser.

    Anyone know of a place? Or maybe an idea to replace them? They aren't really parallel on the board. I can post pics if needed.

    thanks!!
    Tags: None
    #2
    Re: need help finding 'small' caps

    Use Samxon RS series in 16v or 10v at 3300uF & 10mm.
    Can get here:
    https://www.badcaps.net/store/index....h6b28gfmo5omm6

    The claimed ratings on the Fuhjyyu are not realistic and they are very inconsistent.
    Fuhjyyu 4700uF pulled from brand new equipment and tested have measured anywhere from 3100uF to 4800uF. [And they degrade quickly which means uF goes down.]

    Given you have the 10mm diameter issue the RS series is about the only realistic choice to keep ESR and Ripple rear the original -design- ratings.
    [ESR matters more than uF in-so-far as tuning the PI Output filter to the expected Ripple Frequency.]
    -
    Some folks will use something like MBZ but that's a big jump in ESR and may throw the PI filter off [meaning you'd need to change the coils to keep it right in the ripple frequency range.] - I'm too lazy to do all that math and possibly change coils. It's easier to just match the caps as close as you can.
    .
    Mann-Made Global Warming.
    - We should be more concerned about the Intellectual Climate.
    -
    Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
    - Dr Seuss
    -
    You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
    -

    Comment

      #3
      Re: need help finding 'small' caps

      PCBonez, thank you! Yeah, I'm too lazy to do the math AND change the coils. This PSU is so damn packed its crazy.

      My uneducated worry is that the 3300uf will be too little. Otherwise, these seem to be for the 5v rail so 10v should be fine. Right? Great. I'm doubting myself again.

      Comment

        #4
        Re: need help finding 'small' caps

        Yes, a 10v cap is fine for the 3.3v or 5v Rail.
        A 16v cap will work for the 3.3v, 5v, or 12v Rails.

        The voltage marked on the cap is just it's limit.
        You can use a cap rated for any voltage higher than the actual circuit voltage.
        On a 5v circuit you could use caps rated for 6.3v, 10v, 16v or even higher.

        ~~
        As I said before, Fuhjyyu's marked 4700uF have actually measured as little as 3100uF when new.
        [As in the '4700' is in Fuhjyyu's dreams.]
        Replacing 4700uF Fuhjyyu with 3300uF has been tried and tested by ~many~ folks [including me] in here in ~many~ different PSUs [including Antec] and it's well known to work.
        - As in, "thoroughly tested".

        ~~
        In most PSUs the OP filter is designed to be most effective at around 200 kHz.
        - 200 kHz is a typical Ripple frequency in many kinds of SMPS world wide, not just those in PC gear.
        - That is why cap data-sheets show ESR at 200kHz. It's the standard frequency in the tables because it's the one designers usually care about.

        At 200 kHz ESR has as much [usually more] effect on the cap's total Reactance as uF.
        Reactance is basically 'AC Resistance' but unlike true Resistance it changes when frequency changes.
        -
        - When they teach Capacitive Reactance [Xc] in schools they use higher frequencies and they disregard ESR because the -effect- of ESR is tiny [insignificant] at those frequencies. They leave the 'ESR part' out of the equations to simplify and the subject of ESR [if it even gets mentioned] almost never comes up again later.
        - Problem is, when the frequency goes down where ESR matters people forget to [or weren't trained to] use the complete equation that includes ESR. Many techs and even engineers [if they aren't SMPS specialists] don't even know ESR exists because all their training used the abbreviated equations and by-passed the whole subject.

        You can think of it like the Reactance due to uF [Xc-Ohms] and the Reactance due to ESR [ESR-Ohms] work like parallel resistors inside the cap to achieve the over-all Reactance.
        - Looking at the math for two resistors in parallel you can see that when a big resistor is in parallel with a small resistor it is the small resistor that has the most affect on total resistance.
        [The total resistance is always smaller than the smallest resistor.]
        [A huge resistor in parallel with a very small one makes almost no difference to the total.]
        http://www.1728.com/resistrs.htm

        Now - As frequency goes down...
        - the ESR-Ohms gets smaller.
        - the Xc-Ohms [from uF] gets larger.
        [At Zero Hz [which is DC] Xc-Ohms = Infinity [Open Circuit].

        [Depending on the specific part.]
        Somewhere between 200kHz and 1000kHz: ESR-Ohms = Xc-Ohms.

        At frequencies less than where they are equal ESR-Ohms will be less than Xc-Ohms.
        Most PC SMPS Switch at 100-200 kHz or so.
        [I think it's 200 kHz to say 'most' but I'm having a geriatric moment. - It does vary.]

        At that low of Frequency the ESR-Ohms is equal to or smaller than Xc-Ohms and so has a major effect on Ripple current expected in a PSU.

        ~~~ Now the point of all that:
        Changing uF doesn't matter that much *for the issue of passing Ripple to ground* because you can make Xc-Ohms pretty huge but the total Ohms will still be less than ESR-Ohms. That is why keeping the ESR the same or less matters more than keeping uF the same.

        ~~~~
        The other way uF affects things is hold-up time.
        That is basically how long voltage will stay in spec after a power loss.
        [This is the cap's battery-like behavior.]
        It only really matters for momentary power loss where you want the system to stay up because the power is coming right back anyway.
        3300uF is perfectly fine for that in the OP Filters.
        We know this because 3300uF is what the vast majority of PSU's use there.
        -
        The drain on the stored energy is due to the load/drain put on it. The motherboard, drives, etc...
        If 3300 uF stores enough for adequate hold-up time from one PSU then it's enough to hold-up the same load from some other PSU for about the same time.
        .
        Mann-Made Global Warming.
        - We should be more concerned about the Intellectual Climate.
        -
        Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
        - Dr Seuss
        -
        You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
        -

        Comment

          #5
          Re: need help finding 'small' caps

          PCBonez, again, thank you! The crash course on ESR was very enlightening even though I think it hasn't totally sunk in and will need to refer to this again.

          I found out I will be a daddy soon so haven't tackled this yet (and why I've been away) but am needing to do this soon as I need that PSU and buying a new one is just not worth it compared to just getting the caps from here.

          Comment

            #6
            Re: need help finding 'small' caps

            Congratulations Dad!
            Mann-Made Global Warming.
            - We should be more concerned about the Intellectual Climate.
            -
            Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
            - Dr Seuss
            -
            You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
            -

            Comment

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