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Thread: tweaking power supply

  1. #1

    Default tweaking power supply

    I read few articles that computer power supply can be tweaked to get higher voltage. Is that possible to have 13.6 volt or more from the 12 volt output ? Pics of my AT & ATX power supply, let me which resistor to change. Thanks.

    ATX power supply


    AT power supply

    One told me find a variable resistor, found none on both power supply

  2. #2
    Flashaholic*
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    Default Re: tweaking power supply

    That variable resistor is probably just two resistors in series somewhere acting a voltage divider. If you find out which and your PS is fairly simple built, yes, you probably can mod it to output higher voltage. My advice is to find the switch regulator, check the datasheet on it, find which legs on the IC are "SENSE" or something similar and follow the routes on the PCB from those legs.

    Good luck!
    Still no response to that PM or e-mail you sent me two months ago? Try sending it again. I'm terrible at keeping track of messages.

  3. #3
    Flashaholic*
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    Default Re: tweaking power supply

    Short answer, it depends... Many supplies will closely regulate, for example, the +5VDC and simply make the 12VDC just 2.4x higher than the +5vdc. It is cheaper, fewer components, and, probably, a bit more reliable. The high volume supplies are going to have less ability to adjust their outputs simply because that increases costs.

    If a supply has remote sense wires, you can tweak them a bit by placing a resistor divider circuit in the sense leads (divider takes 13.6v down to 12 volts and the power supply thinks it is still regulating at 12 volts even though it is outputting 13.6v). Don't think the AT power supply spec. includes 12 volt sense leads.

    The better question is what do you want to use the 13.6 volts for? If it is for charging a, for example, lead acid storage battery--this is probably not a good way to go for various reasons.

    -Bill

  4. #4
    Flashaholic*
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    Default Re: tweaking power supply

    +1 to all that. Listen to what BB says!
    Still no response to that PM or e-mail you sent me two months ago? Try sending it again. I'm terrible at keeping track of messages.

  5. #5

    Default Re: tweaking power supply

    you would probably find yourself tripping over voltage protection on the other outputs if you do that if the supply is any good. theres probably at least an scr crowbar in there somewhere if its a cheapy. also you would need a dummy load on the 5v line at least , maybe others, to keep it in regulation.
    buy a proper bench supply matey, if you dont know exactly what your doing your best not pissing around with line connected electronics. if you inadvertantly defeat the isolation barrier you`ll end up charred and crispy and sitting on the roof.

  6. #6

    Default Re: tweaking power supply

    BB : I'll try the ATX power supply and leave alone the AT.
    winny : I'm reading BB post carefully
    copiertech : dummy load is a must, hope I don't get electrocuted, always play safety.

    Thank you for your support guys. If unable to work it up, I think it's time to get a bigger lab PSU.

  7. #7

    Default Re: tweaking power supply

    to get an atx to run outside of a pc youll need to ground PS_on, usually the green wire. you might also need a very small load on 5Vsb(normally violet) and a load on 3.3v (normally orange) depending on how sensitive the protection is.

  8. #8

    Default Re: tweaking power supply

    You can change the output voltage of any ATX power supply with sense wires (the thin wires that go to the mobo connector, yellow is 12v. red is 5v and orange is 3.3v). As mentioned, how far you can change it is dependent on whatever the manufacturer set the protection to, and the 12v + 5v circuits are frequently interdependent.

    Lot of guides available: http://www.xtremesystems.org/forums/...threadid=37574
    http://www.xbitlabs.com/articles/oth...ltmodding.html

  9. #9

    Default Re: tweaking power supply

    Quote Originally Posted by BB
    Short answer, it depends... Many supplies will closely regulate, for example, the +5VDC and simply make the 12VDC just 2.4x higher than the +5vdc. It is cheaper, fewer components, and, probably, a bit more reliable. The high volume supplies are going to have less ability to adjust their outputs simply because that increases costs.

    If a supply has remote sense wires, you can tweak them a bit by placing a resistor divider circuit in the sense leads (divider takes 13.6v down to 12 volts and the power supply thinks it is still regulating at 12 volts even though it is outputting 13.6v). Don't think the AT power supply spec. includes 12 volt sense leads.

    The better question is what do you want to use the 13.6 volts for? If it is for charging a, for example, lead acid storage battery--this is probably not a good way to go for various reasons.

    -Bill
    ~13.6v is the voltage that car alternator's regulator tries to maintain. As you can imagine, even though we commonly refer to car electrical system voltage as 12v, much like we say alkaline batteries are 1.5v, real items are designed to work best around real conditions.

    Car stereo, CB are designed to perform their best at 13.6v ish, so its common for people to use a 13.6v power suppy to power them from the grid. The problem is that such power supply is more expensive due to lower demand.

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