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Spare Time Project: "Improving" Delta 100w PSU

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    Spare Time Project: "Improving" Delta 100w PSU

    (click on all pictures to zoom them)

    So I posted this power supply in the "PSU discussion thread" some time ago...

    This is a 100w power supply made by Delta, which I pulled from a HP Vectra system 486 66 Mhz about 5 years ago.

    The basic idea is to convert this psu (well, add to it as there's room inside the case) to make it adjustable power supply with current limiting.

    It's a cool psu, almost silent as fan doesn't spin much (there's thermal sensor on the schottky diodes so it probably adjusts fan as well but I'm not sure, may just be protection)



    As the label says, there's 5v @ 13.5 A, 12v @ 4.5 A, 100w in total. There's also -5v @0.1A and -12v @ 0.3A , but they use linear regulators for those L7905CV and L7912CV which I believe are rated for max 1A so who knows... anyway, not interested in those.



    Decent mains filtering, main capacitor is Rubycon USB 270uF , 400v - enough for the wattage, with ~1.7 ripple and 2000 hours @ 85c if i remember the datasheet values correctly.
    Bridge rectifier with one of those things (the proper name escapes me now) glued to it that I assume will limit current when the rectifier overheats)

    The Schottky diodes are s30sc40m (40v 30a) which seems to be used for the 5v and a much smaller one that has BY208 written on it, for which I couldn't find a datasheet (but I guess it's enough for 12v 4.5v) ... there's a thermal sensor attached to the small metal heatsink and the metal heatsink is screwed to the case so there's plenty of heatsink.

    Can't determine the main switcher chip due to heatsink, but there's a 1-3w resistor in shrinkwrap almost glued to it that looks to be a bit burned. On the right of the transformer there's another to220 chip that I can't tell what it is due to the heatsink clip.

    The controller is uc3842an, 500Khz frequency.

    Front pictures:



    Back :



    The capacitors are all UCC SXE, KME... the large ones are 2200uF 16v (1) and 10v (2) in the mains section, in the secondary there's another set of 2200uF 10v for the 5v lines, a lonely Rubycon 1000uF 10v, and a Taicon 1000uF 16v for the 12v...
    The -12v has a UCC 220uF 35v and the -5v I think has... nothing, don't see any capacitor by the regulator larger than 10uF... the 5v stand by with the "huge" 5 mA rating has a 47uF 25v.

    All the other small capacitors are UCC and a few Taicon spread around.

    I started it by shorting the ps/on wire to ground and the 5v line measures 5.3v but the 12v line measures 10.96v. 5v standby was 5.03v. Obviously 10.96v on the 12v rail is bad, but right now I can't tell if this is due to no load or for other reasons.
    Your thoughts?

    Like I said, I started it with no load, and I don't really have something to put load on it right now (besides 12v fans which is not enough to be sure). Planning to buy some 12v 5-10w light bulbs from some car parts store so that there's gonna be some load.

    So basically, I'm planning to replace all the 2200uF 10v and 16v with UCC KZE 3300uF 16v as I have about 40 of those here and I don't really use them - they're larger than the common 10mm diameter so don't have a chance to use them much.

    I don't think it would affect the stability of this power supply to go from 2 x 2200 to 2x 3300, right?

    I'll have to test the capacitors ESR after desoldering them from the board.. wouldn't surprise me if they have high esr, considering they're from around 1995.

    Other suggestions for solving the 12v rail issue?
    Attached Files

    #2
    Re: Spare Time Project: "Improving" Delta 100w PSU

    Originally posted by mariushm View Post
    I started it by shorting the ps/on wire to ground and the 5v line measures 5.3v but the 12v line measures 10.96v. 5v standby was 5.03v. Obviously 10.96v on the 12v rail is bad, but right now I can't tell if this is due to no load or for other reasons.
    Your thoughts?
    It's due to no load. On an unit this old with almost all the capacity on the 5v rail, it absolutely needs a bit of load (1A or so) on 5v, for 12v to be in spec.
    Originally posted by PeteS in CA
    Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
    A working TV? How boring!

    Comment


      #3
      Re: Spare Time Project: "Improving" Delta 100w PSU

      Originally posted by mariushm View Post
      (click on all pictures to zoom them)
      I have no techncial value to add in this subject area, but I will say this is the BEST example of how to tell a story using small inline thumbnail images I have seen on this forum.

      It is the best of both worlds. I get to read a coherent story supplemented with thumbnail inline pictures and can see the full size image IF I WANT to.

      Thank you.

      PS. Bookmarked as an example for others to follow.
      --- begin sig file ---

      If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

      We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

      Please do not post inline and offsite as they slow down the loading of pages.

      --- end sig file ---

      Comment


        #4
        Re: Spare Time Project: "Improving" Delta 100w PSU

        Thank you for the compliments.

        Well, I had some free time today and replaced the large capacitors with the 3300uF capacitors I planned to use.

        The capacitors were still relatively OK, 3000uF for the 3300uF, ~2050uF for the 2200uF ones, esr was 30mOhm 40-60 mOhm for the 2200uF ones, the largest was the Taicon 1000uF that was on the 12v line, at 100 mOhm.

        But... the ones on the secondary will have to go because they're about 4-5 mm taller than the case... The case is taller on the primary side, the fan is at 45 degrees between the primary side and the secondary...
        It was designed so that the fan would sit just above the 486 cpu heatsink... pulling air from the front of the pc, over the heatsink of the cpu, through the psu over the primary side and outside.

        And... the bad thing is when I tested it I accidentally shorted it, didn't screw the pcb onto the case so the case hit one of the traces on the back and the fuse popped.

        There's nothing looking like it's burned but I'll have to get some fuses and see if I screwed something else tomorrow.

        Comment


          #5
          Re: Spare Time Project: "Improving" Delta 100w PSU

          A very minor update on this, just to show I didn't lose interest on this.

          I went out and bought a few light bulbs, they're 12v each, some 5 watts and some 21 watts.

          After recapping with the UCC KZE caps, the voltage on 12v was 10.98v, a smidge better than the 10.95v it was before.

          The power supply itself just connected to the mains pulls 3.9 watts. When powered up with just the fan running and nothing connected to it, it pulls 9.1 watts.
          So it won't win the most ergonomical psu contest

          I had very little time to work but patched something really quick for a small test - got one of the 12v 5w bulbs and connected it to the 5v line and it barely lits up: the meter read 0.24 A so just about 1.2 watts of load.

          BUT... the voltage on the 12v line rose up from 10.98v to 11.4v! ... so it's definitely what I thought - it needs to a bit of load on the 5v to get close to 12v on the other rail.

          So I'll connect two of these 5w bulbs in series to see how much it improves and if it's still much lower than 12v, I may try one of those 21 watts bulbs - on 5v, it should eat about 5-10 watts and that should be almost 1-2A out of the 13.5 amps the psu says it supports.

          Next step would probably be to find a resistor that I can attach to that 5v to keep the 12v up... I think i have a 5.6 5w resistor from an old psu somewhere but I have to check. Not sure that's right, have to look up ohm's law and do the math for that.

          Comment

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