Trying to build a power supply and need some guidance

Discussion in 'Power Electronics' started by tgrantjr, Sep 5, 2019.

  1. tgrantjr

    Thread Starter New Member

    Sep 5, 2019
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    0
    I am new here and have been trying to get this to work. I have an old dell 300w power supply for my project. I bought all the parts but want to make sure it works before i put everything together. I wired in a switch to the main power on the neutral side so i didnt have it on the hot side. I was getting the fan to spin with the green and ground just twisted together to test. I then went and put 2 10w 10ohm resistors in series for the dummy load on the 5v rail with a ground and red wire. Now it wont power on at all. This is the second supply i have tried. I have watched quite a few videos on youtube and some tutorials online i could find. Nothing is working here for me. I want to use this for electronics as well as the 5v output for electroplating custom parts. Does anyone have some insight on this? Thanks in advance.
     
  2. BobTPH

    Senior Member

    Jun 5, 2013
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    542
    Are you sure of the value of the resistors? Is it possible they are 1Ω or .1Ω instead?

    Bob
     
  3. tgrantjr

    Thread Starter New Member

    Sep 5, 2019
    4
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    they are the ceramic body resistors. They clearly state 10w 10ohm on the top
     
  4. BobTPH

    Senior Member

    Jun 5, 2013
    1,960
    542
    Maybe the power supply is defective then?

    Bob
     
  5. tgrantjr

    Thread Starter New Member

    Sep 5, 2019
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    it turned on and spun before i added the resistors so i could test at every step. I am wondering if 2 of those are too much load and it trips. I will take one out and try just one to see what happens.
     
  6. tgrantjr

    Thread Starter New Member

    Sep 5, 2019
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    I went ahead and wired it up and i had fan spin. I have a single resistor on the 5 volt rail and ground. I connected it to the wires for my plating and the fan dies. I am trying to figure this out and coming up short.
     
  7. TeeKay6

    Member

    Apr 20, 2019
    351
    88
    You are aware that most PC power supplies have safety lockouts that prevent operation in the case of too low or too high current load? Or too low or too high voltage output? A too low load on the +5V output would very likely prevent operation (as would a problem with load on some other output).
     
  8. LesJones

    Well-Known Member

    Jan 8, 2017
    2,304
    693
    You say that you originally had two 10 ohm resistors in SERIES (Making the load 20 ohms.) as a load on the 5 volt output. You then say that you are taking one out to REDUCE the load. This will INCREASE the load. I am guessing that you are trying to use the +12 volt output as you have not said. Normally in a PC the main part of the load is on the 5 volt rail. So even if we say that the 5 volt rail is supplying 150 watts that is still a current of 30 amps. Your 20 ohm load would only draw 0.25 amps and your 10 ohm load would only draw 0.5 amps. I think it is likely that you load is too little rather than too much.

    Les.
     
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