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    #1

    Recommend primary capacitor ratings

    Here are some values I recommend for the two 200V/250V primary capacitors used in most PC power supplies, board space permitting:

    <200W: 220uF
    200-250W: 330uF
    251W-350W: 470uF
    351-400W: 680uF
    401W-450W: 820uF
    451-550W: 1000uF
    551-650W: 1200uF
    651-750W: 1500uF
    751-850W: 1800uF
    851W-1000W: 2200uF

    Some of these have been overrated, especially at the higher wattage end.
    My first choice in quality Japanese electrolytics is Nippon Chemi-Con, which has been in business since 1931... the quality of electronics is dependent on the quality of the electrolytics.
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    #2
    Re: Recommend primary capacitor ratings

    Some values I've seen:

    220uF: 90W Gateway/Newton, 250W cheapo (PC P&C's prime example of a bad PSU)
    470uF: 200W Dell/Delta, 550W Q-tec
    680uF: 300W Antec & Fortron/Sparkle, 350W Enermax
    820uF: 300W Delta (oddly, rated for down to 100VAC, not the usual 90VAC)
    1000uF: 350W Fortron/Sparkle

    Comment

      #3
      Re: Recommend primary capacitor ratings

      Well, here my question comes again then ;-)

      Originally posted by Per Hansson
      Can someone more knowledgeable than me please comment on the very small rating of the Primary bulk cap, only 270uF in the S12 430w PSU, and 220uF in the 350w Seasonic?

      Is it due to the active PFC or something? I mean I've seen Primary caps in L&C powersupplies with almost twice the farad rating!!!
      "The one who says it cannot be done should never interrupt the one who is doing it."

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        #4
        Re: Recommend primary capacitor ratings

        It's the active PFC I'm sure. My FSP 600W with active PFC has a single 470uf 400v Capxon on the primary side, while the older 530W with no PFC has two Teapo 1200uf 200v capacitors.

        Comment

          #5
          Re: Recommend primary capacitor ratings

          Which would explain the Q-tec's abnormally low primary cap.
          The great capacitor showdown!

          Comment

            #6
            Re: Recommend primary capacitor ratings

            Per, there are two factors involved.

            First, in P/Ss without active PFC, the two I/P lytics are connected in series (necessary for the I/P voltage range switch). This means that the net capacitance is cut in half. IOW, if you have two 470uF lytics, the net capacitance is 235uF.

            Second, when you have active PFC, the voltage on the lytic is typically in the 325V-350V range (and regulated). Without PFC, the voltage across the I/P lytics is typically in the 260V-270V range (unregulated). The formula to calculate the energy stored in the lytics is .5(C)(V^2). Thus, for the same net capacitance, if the PFC bus voltage is only 325V and the non-PFC bus voltage is 265V, the lytic in the PFC is storing ~50% more energy.
            PeteS in CA

            Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
            ****************************
            To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
            ****************************

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              #7
              Re: Recommend primary capacitor ratings

              Thanks for the explanation Pete, I really appreciate it!
              "The one who says it cannot be done should never interrupt the one who is doing it."

              Comment

                #8
                Re: Recommend primary capacitor ratings

                Me too

                Just remembered something about my 530W - next to the two 1200uf Teapos, there is a place for a PFC board... I wonder how much that would have affected Fortron's choice of input capacitors had the PFC circuitry been added. Then again, now that I think about it, that may just have been a soldering point for a passive PFC coil...
                Last edited by Oklahoma Wolf; 02-01-2006, 03:53 PM.

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                  #9
                  Re: Recommend primary capacitor ratings

                  An SMPS I know told me pretty much the same thing OP is posting. He said that 1000uF in a 500W and 1500uF in a 550W is widely accepted, but said that it's more "accepted" to use a 1500uF in a 600W.

                  Of course, that doesn't take into account the 470uF~820uF caps found in 500W and up active PFC PSU's.
                  Rest in peace BFG. You were... a job...

                  Comment

                    #10
                    Re: Recommend primary capacitor ratings

                    I have a Topower server PSU that's supposed to be 420w... has two CapXon 1200uf 200v primary caps...
                    Ludicrous gibs!

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