Announcement

Collapse
No announcement yet.

The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

    So I picked up the cheapest ATX PSU I could find on Amazon that was Prime Eligible. It is listed as a KDMPower MIPC 775w and as of 09/30/2018 was selling for the low low price of $15.57 with free 2 day shipping (for Prime members). I'm sure the wattage claim is pure BS, but lets see how bad (or good) it is otherwise.


    The Packaging is about as basic as you can get, a plain cardboard box with the PSU wrapped in bubble wrap and a power cable inside:



    Looking at the PSU itself, this is a non-modular unit with a 120mm fan and basic black paint job:


    The Label is even more ambitious than the product listing page, claiming 875W :


    Lets take a look inside:
    Well that looks a bit sparse for "775W" or "875W" but overall not as bad as I expected for a $15 power supply:


    Primary:

    Line filtering consists of 2 X-Caps, 4 Y-Caps, 2 coils, and 1 MOV, honestly not bad at this price point,
    The bridge rectifier is a GBU806 8A 600V unit.
    Primary caps are a pair of Changx 560uf 200V
    Primary switchers are 2 4N50C MOSFETs rated at 4A 500V

    Secondary:

    2 MBR20100CT 20A 100V Schottky Rectifiers on the 12V Rail(s)
    1 STPS2045CT 20A 45V Schottky Rectifiers on the 5V Rail
    1 STPS2045CT 20A 45V Schottky Rectifiers on the 3.3V Rail

    3 Changx GR 1000uf 16v caps on the 12v Rail(s)
    2 Changx GR 1000uf 10v caps on the 5V rail
    1 Changx GR 1000uf 10v cap on the 3.3V rail
    1 Changx GR 470uf 16v cap on the 5vsb

    The fan is a BOK BDM1202S 120mm sleeve bearing fan.


    The soldering isn't too bad considering the price point:




    Lets see how it does under a 257W load (12V@14A, 5V@10A, 3.3V@12A):

    The 12V rail is at 12.221V:


    The 5V rail is at 4.8925V:


    The 3.3 V is at3.2239V:


    Lets take a look at the ripple, the scale on the oscilloscope is set to 10mv per division.
    The 12V rail has around 15-20ma ripple:


    The 5V rail also around 20mv ripple:


    Same story on the 3.3V rail around 15-20ma ripple:


    Efficiency is around 81% with the PSU drawing 317W at the mains for a 257W load:


    Honestly I was somewhat pleasantly surprised by this PSU, while it certainly isn't really a "775W" or "875W" unit as the manufacture claims (more like 350-400W at best) it isn't nearly as bad as I would have expected at this price point. Aside from rather questionable cap choices (Changx, and more capacitance would be nice) it isn't all that terrible for a "cheap" PSU (that being said the prices seem highly variable and it wouldn't be any kind of a "value" at a price above $25).
    Attached Files
    Last edited by dmill89; 10-03-2018, 05:22 PM.

    #2
    Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

    Haha! Always wondered what kind of "new math" these manufacturers use to come up with these outlandish wattage claims!
    Last edited by jetadm123; 10-03-2018, 05:34 PM.

    Comment


      #3
      Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

      Whoa, that looks stunningly reasonably, for 15€...

      Comment


        #4
        Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

        looks like a classic type 300w inside.
        right down to the double cap input circuit with the slide switch for voltage selection.
        no pfc, and has space for a second fan.

        Comment


          #5
          Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

          ripple isnt bad considering the use of changx junk caps but then it prolly isnt stressed much at 257w for the ripple to rear its ugly head. if only the voltages of the minor rails didnt sag that much, it would be a nice psu for powering a retro rig, after a recap of course...

          Comment


            #6
            Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

            Not bad for a 300W-350W PSU. The limiting factors are probably the 4A MOSFETs and maybe the main transformer core. I like the true Y caps. I didn't see MOVs protecting the input lytics, though. Interesting that the multi-output inductor is -52 material but what probably is the 3.3V inductor is -26 material. With a decent fan those low quality caps might actually last a while.

            But 775W would quickly result in a loud noise, bad smell, bright flash, and possibly shrapnel.
            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.
            ****************************

            Comment


              #7
              Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

              Originally posted by ChaosLegionnaire View Post
              ripple isnt bad considering the use of changx junk caps but then it prolly isnt stressed much at 257w for the ripple to rear its ugly head. if only the voltages of the minor rails didnt sag that much, it would be a nice psu for powering a retro rig, after a recap of course...
              Why recap, might as well buy a better PSU.

              Comment


                #8
                Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                Originally posted by Stefan Payne View Post
                Whoa, that looks stunningly reasonably, for 15€...
                Agreed!

                Looks like a 300-350W capable unit. It has has full input EMI/RFI filter with what appears to be genuine Y2-class caps. And it uses a fairly modern double-forward design, which is quite a bit more efficient than STF and H-bridge. 5VSB is done with a PWM-FET IC - none of that 2-transistor ancientness.

                But the best part IMO: No APFC.
                - Awesome! I hate APFC with a strong passion. Seems to kill primary caps for no reason - even good quality Japanese ones... at least some PSUs do. Might be due to bad design, of course, and not something common for all APFC designs. But meh... just adds more complexity IMO *and* drops PSU efficiency. So I'll take a PSU with no APFC and crappy primary caps any day over one with Japanese caps and APFC.

                Anyways, this PSU should work okay for a modern low to low-mid power rig. Probably alright for a mid-range CPU with a 1050TI or 1060TI video card and a single HDD or two... i.e. no more than 200-240 Watts load on the 12V rail.

                Only the Cheng/Chang/Chong +/-X caps on the output are a killer, I'd say. But at this price point... it's still a very good deal. New caps and off you got a decent PSU, I think.

                Oh, and for those of you who missed it: this PSU is for "Traimed service people only."

                Welp, I haven't been on any trams recently, so I guess this one is not for me.
                Last edited by momaka; 10-05-2018, 08:29 PM.

                Comment


                  #9
                  Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                  They still shrink the PCB to leave room for an 80mm fan?

                  Comment


                    #10
                    Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                    Originally posted by Heihachi_73 View Post
                    They still shrink the PCB to leave room for an 80mm fan?
                    That space is probably for the passive-PFC coil in markets where PFC is required. The board has spots for a passive PFC coil to connect and the case has unused mounting holes for one.



                    Attached Files

                    Comment


                      #11
                      Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                      PFC & BPFC never seen that before, are there PSU's that use two passive PFC coils?
                      "The one who says it cannot be done should never interrupt the one who is doing it."

                      Comment


                        #12
                        Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                        Originally posted by Per Hansson View Post
                        PFC & BPFC never seen that before, are there PSU's that use two passive PFC coils?
                        Maybe it's just a special PPFC coil with two windings: one for Live and one for Neutral. I recall HiPro doing something like that in one of their older 250W PSUs. There were even special taps on the PPFC that had to be shorted or separated, depending if you had the voltage switch @ the 115V or 230V position.

                        That said and looking at the solder-side shot of this PSU...
                        https://www.badcaps.net/forum/attach...1&d=1538606423
                        ... it looks like PFC and BPFC were indeed for Line and Neutral. But then BPFC is bypassed with the trace, so it looks like they got rid of that in the design.

                        Comment


                          #13
                          Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                          ah yes, no pfc. i forgot to mention that this psu will also work great behind a non pure sine wave ups. so if u have a ups that gives out a square sine wave waveform, this psu will work great on that too but after a recap of course lol!
                          Originally posted by momaka View Post
                          Oh, and for those of you who missed it: this PSU is for "Traimed service people only."
                          hahaha! good catch there on the chinglish!

                          jokes aside, i see it has two schottkys for the 12v rail. so is this a true dual rail design or is it another single 12v rail design split into two?

                          Comment


                            #14
                            Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                            Originally posted by ChaosLegionnaire View Post
                            jokes aside, i see it has two schottkys for the 12v rail. so is this a true dual rail design or is it another single 12v rail design split into two?
                            Looks like it is a single rail PSU that claims to be dual-rail. The 12V schottkys are connected in parallel with traces, and while there are markings on the board for 12V1 and 12V2 where the wires connect, when you turn over the board they are all connected to a single shared trace. There may be variants of this PSU with dual 12v rails but this one appears to be single rail.


                            Attached Files
                            Last edited by dmill89; 10-07-2018, 04:55 PM.

                            Comment


                              #15
                              Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                              Originally posted by Per Hansson View Post
                              PFC & BPFC never seen that before, are there PSU's that use two passive PFC coils?
                              There are PSU with multiple windings on the PFC Coil.

                              Comment


                                #16
                                Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                                Originally posted by dmill89 View Post
                                Looks like it is a single rail PSU that claims to be dual-rail. The 12V schottkys are connected in parallel with traces, and while there are markings on the board for 12V1 and 12V2 where the wires connect, when you turn over the board they are all connected to a single shared trace.
                                ack... its a dual rail design combined into a single rail... my fsp300-60ghs sfx psu is also something like that. when i opened it up, i saw that the 12v1 and 12v2 wires on the pcb were all soldered together using one big giant blob of solder! at that time, i was like, now i finally understood why people hated multiple 12v rail designs! because almost none of them were done correctly! that "combined 12v rail with a giant blob of solder" was one of the many examples!!

                                Comment


                                  #17
                                  Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                                  Lets see what a re-cap does.
                                  -1000uf 10v Changx GR replaced with 2200uf 10v Chemi-Con KY
                                  -1000uf 16v Changx GR replaced with 2200uf 16v Chemi-Con KYB
                                  -470uf 16v Changx GR replaced with 1000uf 16v Nichicon HE
                                  -"560uf" (really 480uf when I tested them) 200v Changx replaced with 820uf 200v Nichicon LGU



                                  Same 257W load (12V@14A, 5V@10A, 3.3V@12A) as before (my 137W Sesasonic tester with 12V@4A, 5V@10A, 3.3V@12A and two 60w [5A] each electronic loads on the 12V rail):

                                  The voltages improved, especially on the minor rails

                                  12.455V on the 12V rail:


                                  5.01V on the 5V rail:


                                  3.3415V on the 3.3V rail:


                                  and the ripple now all <10mv:

                                  12V:


                                  5V:


                                  3.3V:
                                  Attached Files
                                  Last edited by dmill89; 10-10-2018, 05:40 PM.

                                  Comment


                                    #18
                                    Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                                    You intend to replace the Protection IC and add a PS223 or so??

                                    Comment


                                      #19
                                      Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                                      Originally posted by Stefan Payne View Post
                                      You intend to replace the Protection IC and add a PS223 or so??
                                      Probably not, I really just got this to "play with" because it was so cheap and wondered how bad or good a $15 PSU could be, and then was curious what better caps would do and had some laying around that would work so I figured "what the heck" swapped the caps and re-tested. But I've got so many better PSUs (Delta, Seasonic, PC Power & Cooling, FSP, HiPro, etc.) that this likely won't be used for anything beyond testing.

                                      FYI: The protection IC in this PSU is a Weltrend wt751002 which appears to provide over voltage protection and under voltage protection but no over current protection (though even if I used this in a PC it wouldn't be in an application with enough load where OCP would be needed)
                                      Last edited by dmill89; 10-10-2018, 10:17 PM.

                                      Comment


                                        #20
                                        Re: The Cheapest ATX Power Supply on Amazon Prime, How bad can it be?

                                        Originally posted by dmill89 View Post
                                        Lets see what a re-cap does.
                                        woooow! what a difference a cap change makes! cant hardly believe it! ah well... i guess this is solid proof good caps do make a difference. from 15 dollar junk psu to a va-va-voom psu that can compete with even high quality units from seasonic and superflower. with that recap, i'd bet the psu can do 350-400w without the ripple getting out of control.

                                        if any nub or *gasp* even a nub engineer on another forum says all caps are created equal, i'd show them this forum topic! that'll blow 'em away and teach 'em good! lol!

                                        thanks for doing this jonny guru style review and test of this psu. this is actually an excellent psu for a newbie to practice their smps recapping skillz!

                                        Comment

                                        Working...
                                        X