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DPS5020 dual power supply build

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    #61
    Re: DPS5020 dual power supply build

    You short each winding and measure capacitance from pri-sec, pri-core, sec-core.
    It's good to know how much the leakage currents might be. Some 600VA big toroids are 100's nF pri-sec.

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      #62
      Re: DPS5020 dual power supply build

      Originally posted by redwire View Post
      You short each winding and measure capacitance from pri-sec, pri-core, sec-core.
      It's good to know how much the leakage currents might be. Some 600VA big toroids are 100's nF pri-sec.
      Does "core" in this case refer to the metal chassis of the transformer where earth would go ?
      Wattevah...

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        #63
        Re: DPS5020 dual power supply build

        Got the caps today. As you can see, they claim to be Nippon Chemi Cons
        Attached Files
        Wattevah...

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          #64
          Re: DPS5020 dual power supply build

          What makes you think that they are not real
          9 PC LCD Monitor
          6 LCD Flat Screen TV
          30 Desk Top Switching Power Supply
          10 Battery Charger Switching Power Supply for Power Tool
          6 18v Lithium Battery Power Boards for Tool Battery Packs
          1 XBox 360 Switching Power Supply and M Board
          25 Servo Drives 220/460 3 Phase
          6 De-soldering Station Switching Power Supply 1 Power Supply
          1 Dell Mother Board
          15 Computer Power Supply
          1 HP Printer Supply & Control Board * lighting finished it *


          These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

          1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
          2 Hem Saw Computer Stack Board

          All of these had CAPs POOF
          All of the mosfet that are taken out by bad caps

          Comment


            #65
            Re: DPS5020 dual power supply build

            Originally posted by sam_sam_sam View Post
            What makes you think that they are not real
            Ok, maybe I was a bit harsh on Ali with that statement. Funny thing is that I once saw a video of Dave from EEV Blog where the took apart a cheap subwoofer and projector and he found some Elna and NCC caps inside and he was having a very hard time believing they were real. The people in the comments however disagreed with him and pointed out that it's unlikely they'd counterfeit the logos on the caps as well, so it could be the same in my case
            Wattevah...

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              #66
              Re: DPS5020 dual power supply build

              i'v not seen fakes with snap-in style base.

              i suppose a company could re-sleeve another brand, but it's unlikely - they arent cheap to begin with.

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                #67
                Re: DPS5020 dual power supply build

                Originally posted by stj View Post
                they arent cheap to begin with.
                Correct - they were not exactly cheap, so here's hoping they don't bulge after a few hours
                Wattevah...

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                  #68
                  Re: DPS5020 dual power supply build

                  Back on this project, I was thinking of adding an NTC thermistor in series with the secondary of the transformer to limit inrush on those large caps after the bridge rectifier.
                  Wattevah...

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                    #69
                    Re: DPS5020 dual power supply build

                    i wouldnt bother, the Q of the transformer will limit the inrush.

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                      #70
                      Re: DPS5020 dual power supply build

                      If the primary fuse is slow-blow and it can handle it, then I would keep it simple.
                      Above around 20,000uF is when I add a soft-start to a mains transformer, or just listen to the mains wiring rattle in the walls when I turn on power.

                      Comment


                        #71
                        Re: DPS5020 dual power supply build

                        Speaking of fuses and stuff "blowing". I once had a freak mishap with my existing supply made from the same UPS transformer: it tripped the main breaker when I plugged it into the wall outlet. To this day I have no idea why it happened, but it hasn't happened since...I thought inrush current caused it, but that means it should've tripped again after that as well, which it hasn't done so far, so I have no idea what that was all about I saw a little spark flying out of the wall socket as well, so maybe it was a faulty outlet, though I remember wiring that outlet myself and plugging in lots of stuff in it before without a care....strange :|
                        Wattevah...

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                          #72
                          Re: DPS5020 dual power supply build

                          Big power transformers, they can be magnetized when you switch off power.
                          The flux alternates between N and S at 50/60Hz but say you unplug it when the core is at peak N. Then you plug it in for peak S, and you get a bigger than usual inrush current. The core has to flip magnetic polarity.
                          It just depends on the mains sine wave phase when you unplugged it and when you plugged it in again.

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                            #73
                            Re: DPS5020 dual power supply build

                            Ok, but how long can it remain magnetized like that ? It had been more than a couple of days when it happened
                            Wattevah...

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                              #74
                              Re: DPS5020 dual power supply build

                              The core is steel, it can stay magnetized for a very long time.

                              Comment


                                #75
                                Re: DPS5020 dual power supply build

                                I see. Any way to "de"magnetize it ? Like shorting out the primary ?
                                Wattevah...

                                Comment


                                  #76
                                  Re: DPS5020 dual power supply build

                                  It happens in all transformers, residual magnetism in the core. The only way to demagnetize is apply a lower voltage sine wave and then slowly dial voltage down. It's kind of like demagnetizing a screwdriver or cassette tape.

                                  The formal name is "magnetizing inrush current" and it's why some transformers literally jump up in the air or blow primary fuses for no reason when they are energized, on the odd occasion. The core has a high (up to 90%) flux, just sitting there and then applying power the sine wave adds flux on top of that. I think some cores can saturate when that happens.
                                  Attached Files

                                  Comment


                                    #77
                                    Re: DPS5020 dual power supply build

                                    Interesting. Transformers go a bit over my head as far as electronics theory goes - a LOT of math in there, but at least I got the basics One of the more complex electronic components, with a lot of stuff going on in that little heavy metal box - flux, current, capacitance, resistance, turn ratio....etc. it's got it all
                                    Wattevah...

                                    Comment


                                      #78
                                      Re: DPS5020 dual power supply build

                                      Ok folks, I'm back on this project. I started working on the case today (or rather my old man did according to my instructions and tastes, as I'm a bit of a noob when it comes to machining metal stuff at this great precision ) and in the meantime I was gathering whatever parts might still be required. I've hit a bit of a snag however when it comes to those USB ports: remember the two modules can be connected via USB to a piece of software that controls them from a PC....pretty useless in the grand scheme of things, but if it has the option, I'd surely like it to work too. Trouble is, if I connect the two modules to USB, the grounds would become common through the PC or hub or whatever. It's not a problem if I'm powering something like a TV main board which requires two supplies (5 and 12v for instance), since the GND is common by default there, but if I want to go split-supply (+/- 12v for instance), that's not going to work, is it ? I found this isolator thing on Ali which according to the datasheet for the ADuM3160 chip it uses has separate GNDs and might do the job. Pretty pricey for my taste and I'd need two of them ! Am I at least looking at the right thing ?
                                      Last edited by Dannyx; 08-16-2019, 05:07 AM.
                                      Wattevah...

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                                        #79
                                        Re: DPS5020 dual power supply build

                                        no, the usb to serial boards are optically isolated.
                                        as long as they are not touching the metal case the pc wont be referenced to the psu's

                                        Comment


                                          #80
                                          Re: DPS5020 dual power supply build

                                          But doesn't the outer shell of the USB connectors do just that ? Plus, isn't the black GND wire inside the USB lead common across all devices ?
                                          Wattevah...

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