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ATX Power Supply

Discussion in 'Power Electronics' started by somanshumehta, Nov 9, 2013.

  1. somanshumehta

    somanshumehta

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    Jun 22, 2013
    I have a 450W ATX power supply and I tried to connect an old PATA HDD but it's motor did not run.While I had powered up the SMPS using PS_ON green cable,which was made high.
    I saw the fan of my SMPS running,but HDD motor was not.
    I also tested the 4 pin molex connector ( 5 G G 12), which was workimg fine.
    What could possibly be the problem?
     
  2. somanshumehta

    somanshumehta

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    0
    Jun 22, 2013
    As my 450W ATX label reads,

    5V 28A
    12V 15A
    3.3 16A
    -5V 0.6A
    -12A 0.6A
    +5VSB 2A

    As you can see that at 12V the max current is 15 ampere,so can I use for charging my old car 12V lead-acid battery.Also,why -5 and -12 volts supply have been given as output when there is already +5 and +12 volts.Also explain +5VSB
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Perhaps the hard drive needs to receive a spin up command?

    In my experience, IDE drives spin up as soon as power is applied, but your drive could be different I guess.

    Many power supplies require a certain amount of load before they will operate. Typically people will connect a resistor across the 5V output to draw, say, 5% of the rated power. In your case, you should use five 5.6 ohm, 10 watt resistors in parallel, connected across the 5V output of the supply. They will get HOT.

    A power supply is not a battery charger. Also, "12V" lead-acid batteries have a nominal voltage of 13.8V not 12V.

    The ATX power supply has -5V and -12V because these voltages are needed by some motherboards. (I think very few need them nowadays.) These voltages are negative relative to the 0V rail so they are different from the +5V and +12V rails.

    The +5VSB rail is powered at all times (it stands for +5V Standby). It is designed to power parts of the motherboard that need to run at all times. When these circuits detect that the whole motherboard needs to be powered up, they drive the PS-ON signal low to tell the rest of the ATX power supply to power up.
     
  4. somanshumehta

    somanshumehta

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    Jun 22, 2013
    I have converted my 450W ATX into a 12V DC at 15A to charge my car battery,only the performance testing remains.I got procedures from instructibles.com and that made my way.
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Oh dear. Can you post the link to the article on instructables.com please?
     
  6. somanshumehta

    somanshumehta

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    0
    Jun 22, 2013
    I have gone through SMPS topologies and found that ATX is a push-pull topology.I also came across a crowbar circuit,can you explain it.
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    If you answer my question I will do that, yes.
     
    Last edited: Nov 10, 2013
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    A crowbar is a circuit that shorts out an output of the power supply if a problem is detected. Usually this problem is over-voltage, and the crowbar is there to protect components downstream of the power supply from damage due to overvoltage if the regulation in the power supply fails.

    The name comes from the idea of throwing a crowbar (a heavy metal bar) across the output of the power supply to short it out.

    https://en.wikipedia.org/wiki/Crowbar_(circuit)
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Well, butter my buns! That's not a bad instructable. He does say that he removed his fan altogether, which is not a good idea if you're going to be loading the power supply heavily, but apart from that it's OK.

    It will not be suitable for charging a sealed lead-acid battery though. As I said, these should be float charged at 13.8V not 12.0V.

    Also the power supply is not a charger and does not have current limiting; if your battery is undercharged, the power supply will trip out on overcurrent, restart, trip out, restart, and so on, making a ticking or "hiccuping" noise.
     
  10. Six_Shooter

    Six_Shooter

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    Nov 16, 2012
    Nominal voltage of an automotive battery is 12.6V, 6 cells at 2.1V = 12.6.

    Charge voltage should be 1V above that at 13.6V, and up to 14.4V.
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Huh, you're right. I assumed that automotive batteries would be the same voltage as sealed lead-acid (SLA) or valve-regulated lead-acid (VRLA) batteries, but they aren't.
     
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