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Good capacitors to put in HOT fanless PSU?

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    Good capacitors to put in HOT fanless PSU?

    Hi guys,
    I have a failed Silverstone Nightjar, 430W. A small ish cap (under where all the wires are connected to the PCB) has bulged out. This thing is a toaster. I read a suggestion on a thread here to use capacitors with non-aqueous electrolyte. I also heard you shouldn't use low-esr capacitors in switch mode power supplies in general because they will increase the ripple by deregulating the filter network. Could someone recommend a good capacitor family to use in this situation? This is seemingly a secondary cap, so I guess up to 50V, maybe even 12V? I haven't pulled the PCB out yet, because that's a lot of messing about. I would appreciate if you could recommend a part that can be ordered from Mouser without wait times.

    Thanks

    #2
    Re: Good capacitors to put in HOT fanless PSU?

    There is no good cap here. Just bad and worse for 'lytics.

    I'd avoid anything not 105C rated. I'd personally suggest Nichicon HE (or UHE, same thing) as that's my go-to PSU recapping cap; I've only blown them by getting them in backwards. Nichicon PW's are also generally durable for PSU usage.

    Poly caps CAN work in PSUs but it requires that the PSU be designed for it. Many recent designs use them out of the box in fact. However, without re-engineering the entire secondary (or at least the rail(s) in question), a direct Poly Swap probably is asking for trouble.
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      #3
      Re: Good capacitors to put in HOT fanless PSU?

      "I also heard you shouldn't use low-esr capacitors in switch mode power supplies in general because they will increase the ripple by deregulating the filter network."
      Can you please give us a link to this information?
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        #4
        Re: Good capacitors to put in HOT fanless PSU?

        You might even want to even look into 125C rated automotive grade caps in such a situation (Nichicon UBT, etc.), though they are a bit pricy compared to normal 105C electrolytics, they can be found with specs close enough to caps normally used in PSUs (UCC KY, Nichicon PW, etc.) that you shouldn't have to worry about messing with the circuit like with polymers.

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          #5
          Re: Good capacitors to put in HOT fanless PSU?

          you might also think about bolting a fan onto the thing!!

          a "fanless psu" is like "clean / safe nuclear power" - it's marketing bullshit.

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            #6
            Re: Good capacitors to put in HOT fanless PSU?

            Hi guys,
            I understand some electrolytic caps contain water based electrolyte, and in some caps the electrolyte is not water based - therefore much better for high heat situations. I think those are called "non-aqueous electrolyte" capacitors. Could someone confirm? What families of capacitors is based on this chemical compound?

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              #7
              Re: Good capacitors to put in HOT fanless PSU?

              Originally posted by budm View Post
              "I also heard you shouldn't use low-esr capacitors in switch mode power supplies in general because they will increase the ripple by deregulating the filter network."
              Can you please give us a link to this information?
              Sorry, I don't have time to find a competent article that explains this, but here's a thread:

              https://www.badcaps.net/forum/showpo...35&postcount=4

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                #8
                Re: Good capacitors to put in HOT fanless PSU?

                Water-base electrolyte vs. conventional electrolyte is not an imperative, so long as you stick to good parts from reputable manufacturers (Nichicon, Chemi-con, Rubycon, Panasonic). You could go with non-water base electrolyte capacitors for peace of mind, but I’m sure that even water-base parts from the above manufacturers will outlast the original caps. Capacitors that are too low impedance for the control loop are, as ratdude said, known as “ultra low impedance”, and are more suitable to motherboard use than filtering and smoothing the output of a SMPS. But that doesn’t mean all low impedance capacitors are no good for PSU use. It depends on what was originally installed in the unit (what was the brand, series, case size, voltage and capacitance, of the original caps that failed?).
                Last edited by Wester547; 11-25-2017, 10:29 AM.

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                  #9
                  Re: Good capacitors to put in HOT fanless PSU?

                  "Low impedance" is a term that covers a fair amount of history, and can mean different things in different applications. So you need to choose with some understanding of that or you can run into stability or reliability problems. Some practical examples:

                  Nichicon's ancient PM and PS series (PL and PR before RoHS) are "low impedance", but in modern times calling them low impedance is kind of charitable. They are probably the go-to series for pre-2000 PSUs.

                  Nichicon's PJ and United (or Nippon) Chemicon LXV series are newer and lower in impedance than PM or PS. I'd recommend them for late 90s and early 00s PSUs.

                  As an aside, I get the humor of "Nunya Biz", but it sets up some practical problems for folks trying to be helpful. Nippon Chemicon (NCC) is one of the best manufacturers of electrolytic capacitors. But in the US they do business as United Chemicon (UCC). Not knowing your country makes discussing the brand awkward. Further, when you know what you want to buy, it's helpful for folks here to know your country, because they know what distributors sell in various countries. Moving along ...

                  For PSUs manufactured in the past 10-15 years Nichicon PW, UCC LXZ, and Panasonic FC will probably do very well.

                  These all have solvent-based rather than water-based electrolytes.

                  For higher end PSUs made in the past 5-10 years, Nichicon PA (not water-based) or HE, UCC KY or KZE, Rubycon ZL, and Panasonic FM may be appropriate. Nichicon HD is similar in specs to UCC KZE, but I don't have much experience with the HD series. Also, there are some newer series in this range with which I have no experience. Except for PA, these are all water based but at the longer life end of the ultra low impedance spectrum. The PA series is almost the same specs as the HE series, but I'm not sure how easily it is to get them.
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