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    #1

    DIY PSU load tester

    Since shovenose got me started on it, i'm going to build one. Most of the specs i decided upon you can see here: https://www.badcaps.net/forum/showth...?t=7319&page=3

    Considering the demand for cheap ATX PSUs here, i think i could even be in business. Time to give a friend of mine some competition hehehe. If anyone has something to contribute about the specs, comments are welcome. I'm thinking of something along these lines:
    • 700W loading capability. This should easily cover 90% of PSUs.
    • Adjustable load by means of a variable voltage source driving a bunch of MOSFETs thru their linear range.
    • Four amp meters and four MOSFET banks. Two for the 12v rails, one 5v and one 3.3v. Simple resistor loading for -12v, -5v and 5vsb, no amp meters needed there.
    • Opamp-based voltmeters and ripple detectors. Latched LED indicators that show whether any of the rails has gotten our of spec during the test, and what got out of spec (voltage or ripple).
    • No power supply required. The load tester shall derive all necessary voltages from the 12v rail of the PSU under test.
    • Output terminals for connecting an external voltmeter or oscilloscope to any of the rails.
    • Variable speed fans and over temperature protection.
    • Cost: Under $150.


    Other stuff you will need to borrow, steal or beg for to calibrate the tester:
    • Oscilloscope >10MHz
    • High current, high precision amp meter


    So whatcha think? I'll start designing the ripple meters and come with some schematics.
    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!
    Tags: None
    #2
    Re: DIY PSU load tester

    dont know how mosfets work

    and i have no oscillioscope.
    o.o what do i need that for?

    can i just attach the mosfets to a metal case? good enuff heatsink? or can i use psu heatsinks?
    please make one, post pictures, schematics, then i will be able to make one. thanks!

    Comment

      #3
      Re: DIY PSU load tester

      Originally posted by shovenose View Post
      dont know how mosfets work
      If not your PSU also, your current motherboard definitely uses MOSFETs for all its voltage regulation needs, so you should learn how they work. MOSFETs are esentially voltage controlled resistors, but they can also be used as switches. In a linear application, the resistor between drain and source is adjusted by varying the voltage going to the gate. This is called biasing.

      In a switching application, the MOSFET is intended to switch between the lowest (piece of wire) and highest (basically open) resistances. In a switch-mode power supply this switching must be done as quickly as possible, because if the MOSFET is in its linear range it does nothing more than dissipate heat. So to keep them cool in a SMPS application, high current drive circuits are used, that turn the gate voltage between 0 and maximum (usually 10 to 20 volts) at speeds in the 100s of nanoseconds.

      Originally posted by shovenose View Post
      and i have no oscillioscope.
      o.o what do i need that for?
      An oscilloscope is used to visualize the waveforms in your power supply. It is essential for you to have one if you're serious in doing SMPS work. If done right (1% tolerance resistors in the reference dividers, more on that later), the ripple indicators will work without needing a 'scope to calibrate them, but you'll still want to have one around.

      BTW i decided against using opamps for the ripple and voltage meters, i will use comparators instead, most likely the common LM339, which i hope will be accurate enough. Now you can build the power supply tester from power supply parts!
      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

        #4
        Re: DIY PSU load tester

        Couldn't you do it with resistors? I was thinking of doing that if I made one.
        I love putting bad caps and flat batteries in fire and watching them explode!!

        No wonder it doesn't work! You installed the jumper wires backwards

        Main PC: Core i7 3770K 3.5GHz, Gigabyte GA-Z77M-D3H-MVP, 8GB Kingston HyperX DDR3 1600, 240GB Intel 335 Series SSD, 750GB WD HDD, Sony Optiarc DVD RW, Palit nVidia GTX660 Ti, CoolerMaster N200 Case, Delta DPS-600MB 600W PSU, Hauppauge TV Tuner, Windows 7 Home Premium

        Office PC: HP ProLiant ML150 G3, 2x Xeon E5335 2GHz, 4GB DDR2 RAM, 120GB Intel 530 SSD, 2x 250GB HDD, 2x 450GB 15K SAS HDD in RAID 1, 1x 2TB HDD, nVidia 8400GS, Delta DPS-650BB 650W PSU, Windows 7 Pro

        Comment

          #5
          Re: DIY PSU load tester

          OK I've drawn up a quick diagram in paint of what I was thinking. Something like this for each rail.
          Attached Files
          I love putting bad caps and flat batteries in fire and watching them explode!!

          No wonder it doesn't work! You installed the jumper wires backwards

          Main PC: Core i7 3770K 3.5GHz, Gigabyte GA-Z77M-D3H-MVP, 8GB Kingston HyperX DDR3 1600, 240GB Intel 335 Series SSD, 750GB WD HDD, Sony Optiarc DVD RW, Palit nVidia GTX660 Ti, CoolerMaster N200 Case, Delta DPS-600MB 600W PSU, Hauppauge TV Tuner, Windows 7 Home Premium

          Office PC: HP ProLiant ML150 G3, 2x Xeon E5335 2GHz, 4GB DDR2 RAM, 120GB Intel 530 SSD, 2x 250GB HDD, 2x 450GB 15K SAS HDD in RAID 1, 1x 2TB HDD, nVidia 8400GS, Delta DPS-650BB 650W PSU, Windows 7 Pro

          Comment

            #6
            Re: DIY PSU load tester

            Originally posted by c_hegge View Post
            Couldn't you do it with resistors? I was thinking of doing that if I made one.
            Of course. But like i said, high power resistors are expensive, and don't offer the degree of control given by an active load. Right now, what i worry about is how much of a difference is actually required to trigger a comparator. LTSpice says it's a bit too much to be useful as a ripple indicator... But real parts are different, of course. We shall see.
            Last edited by Th3_uN1Qu3; 09-16-2010, 04:34 PM.
            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

              #7
              Re: DIY PSU load tester

              hey th3-uniqu3 did you get progress?

              Comment

                #8
                Re: DIY PSU load tester

                So um any luck?
                If you DO do this please make a parts list, schmetics, and how u did it. Then im gonna make one too!

                Comment

                  #9
                  Re: DIY PSU load tester

                  I'm not at home atm, will resume work on this thing when i get back (next Wednesday).
                  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

                    #10
                    Re: DIY PSU load tester

                    I tried a simulation with IRF530s (as they're cheap), but i will need 8-10 devices per rail, and the more devices in parallel the lower their resistance, which makes them extremely sensitive to gate voltage.

                    The sim shows 200mA load at 4v gate voltage (just above threshold), and 26A at 5v. The voltage range is too narrow and controlling it will get complicated. I'll have to find something with higher RDS(on).
                    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

                      #11
                      Re: DIY PSU load tester

                      I did eventually come to terms with the IRF530s and have completed the feedback circuit that keeps the load constant. It uses cheap opamps, a standard TL431 2.5 volt reference, and a 0.001 ohm current sense resistor. So basically the "power" part is done, all it needs now is metering.
                      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

                        #12
                        Re: DIY PSU load tester

                        Where are you dissipating the heat that is cheaper than resistors?
                        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

                          #13
                          Re: DIY PSU load tester

                          ok whats a irf530s? and a tl431? and i have no clue wtf ur talking about ???

                          Comment

                            #14
                            Re: DIY PSU load tester

                            Originally posted by PCBONEZ View Post
                            Where are you dissipating the heat that is cheaper than resistors?
                            In the 'fets internal resistance and some BIG heatsinks. Power resistors are more expensive and harder to find in usable values than a bunch of MOSFETs, at least in this part of the world.

                            Besides, if i don't like it, i can always turn it into a big ass power amplifier.
                            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

                              #15
                              Re: DIY PSU load tester

                              Originally posted by shovenose View Post
                              ok whats a irf530s? and a tl431?
                              They are both MOSFET Model numbers.
                              I love putting bad caps and flat batteries in fire and watching them explode!!

                              No wonder it doesn't work! You installed the jumper wires backwards

                              Main PC: Core i7 3770K 3.5GHz, Gigabyte GA-Z77M-D3H-MVP, 8GB Kingston HyperX DDR3 1600, 240GB Intel 335 Series SSD, 750GB WD HDD, Sony Optiarc DVD RW, Palit nVidia GTX660 Ti, CoolerMaster N200 Case, Delta DPS-600MB 600W PSU, Hauppauge TV Tuner, Windows 7 Home Premium

                              Office PC: HP ProLiant ML150 G3, 2x Xeon E5335 2GHz, 4GB DDR2 RAM, 120GB Intel 530 SSD, 2x 250GB HDD, 2x 450GB 15K SAS HDD in RAID 1, 1x 2TB HDD, nVidia 8400GS, Delta DPS-650BB 650W PSU, Windows 7 Pro

                              Comment

                                #16
                                Re: DIY PSU load tester

                                Close but not quite. The TL431 is a shunt regulator with 2.5v reference, which is commonly used as a 2.5v voltage reference.
                                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

                                  #17
                                  Re: DIY PSU load tester

                                  Can you make a schemtic?

                                  Comment

                                    #18
                                    Re: DIY PSU load tester

                                    Yes, that's what i'm working on atm.
                                    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

                                      #19
                                      Re: DIY PSU load tester

                                      ok
                                      and pictures too maybe?

                                      Comment

                                        #20
                                        Re: DIY PSU load tester

                                        I've decided I will build one too. I'll probably take the somewhat more expensive but easier apporach and use resistors. For now, though, I'm deciding on what resistors to use where and what to house it in, as it will need some fairly large heatsinks.
                                        I love putting bad caps and flat batteries in fire and watching them explode!!

                                        No wonder it doesn't work! You installed the jumper wires backwards

                                        Main PC: Core i7 3770K 3.5GHz, Gigabyte GA-Z77M-D3H-MVP, 8GB Kingston HyperX DDR3 1600, 240GB Intel 335 Series SSD, 750GB WD HDD, Sony Optiarc DVD RW, Palit nVidia GTX660 Ti, CoolerMaster N200 Case, Delta DPS-600MB 600W PSU, Hauppauge TV Tuner, Windows 7 Home Premium

                                        Office PC: HP ProLiant ML150 G3, 2x Xeon E5335 2GHz, 4GB DDR2 RAM, 120GB Intel 530 SSD, 2x 250GB HDD, 2x 450GB 15K SAS HDD in RAID 1, 1x 2TB HDD, nVidia 8400GS, Delta DPS-650BB 650W PSU, Windows 7 Pro

                                        Comment

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