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Thread: computer psu powered by 12v battery

  1. #1 computer psu powered by 12v battery 
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    looking at the anatomy of a 240v psu the A/C signal is converted to a lower voltage then rectified........

    not meaning to sound too much like a noob but surely i can plumb a 12v car bettery in there somewhere!.............?

    i am trying to avoid purchase and use of an A/C inverter.........

    much obliged for any help.........


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  3. #2  
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    Path of least resistance would be to just use an Inverter.


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    nice post 'tom did'...................the first of many successful posts on this forum I am sure!

    an inverter costs money..................and i would have thought only adds to the overall energy loss in the system even if small......besides taking up lots of space...............

    since there are no moving parts (like would be found in a speaker) would some passive electronics be of use, say some resistors to feed the 5 and 3 v outputs and put the 12v rail straight on the battery - in this way the battery feeds the internal power cables directly?
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    Well you could use many 12 volt batteries in series to get the required voltage of the high voltage DC side of the PSU. This is normally over 200 volts DC. This would work the most efficiently. 12 volts could be used, but you would need heavy duty feed cables and a completely different PSU.
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    If I understand correctly, you want to power up your laptop or similar device from your car's 12 d-c power supply without having to use an inverter.

    A standard AT computer power supply has output voltages of +12, -12, +5, -5 volts and ATX has voltages of +12, -12 +3.3, +5.

    http://en.wikipedia.org/wiki/Power_supply_unit_(computer)#Wiring_diagrams

    I don't know of a way to get all those voltages directly from one 12 volt battery without an inverter.
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    please see link below..........

    http://arstechnica.com/hardware/news...gle-server.ars

    GOOGLE are using custom built motherboards but I am unsure how they are linking the 12v batteries to the servers they are powering........
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    I am guessing they custom build their power supplies, so no inverter is required, which would have dropped the efficiency down quite a bit AFAIK. . 12V in and +12, -12 +3.3, +5 out. I can't think of a reason they would do it any other way. See the thing with the red and black wires coming out of it on the top right hand side of the picture of the server box? I am guessing that is the 12V supply from the battery. If you look, you will see it goes into the PSU where the other wires come out. They must have it connected to a custom circuit that kicks in if the AC power dies.
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  10. #9  
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    Quote Originally Posted by Harold14370
    I don't know of a way to get all those voltages directly from one 12 volt battery without an inverter.
    You shold not try to answer this question then.
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  11. #10  
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    there is another article linked that shows a better side angle...........

    http://news.cnet.com/8301-1001_3-10209580-92.html
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  12. #11  
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    Ah, I think that thing is the battery. An interesting bit:

    "Another illustration of Google's obsession with efficiency comes through power supply design. Power supplies convert conventional AC (alternating current--what you get from a wall socket) electricity into the DC (direct current--what you get from a battery) electricity, and typical power supplies provide computers with both 5-volt and 12-volt DC power. Google's designs supply only 12-volt power, with the necessary conversions taking place on the motherboard."

    So, I guess you'll have to take a peak at their patent.

    Quote Originally Posted by Twit of wit
    Quote Originally Posted by Harold14370
    I don't know of a way to get all those voltages directly from one 12 volt battery without an inverter.
    You shold not try to answer this question then.
    It was still a hell of a lot more useful than you are being. Besides, he knows much more about this stuff than both of us combined.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
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  13. #12  
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    Quote Originally Posted by KALSTER

    Quote Originally Posted by Twit of wit
    Quote Originally Posted by Harold14370
    I don't know of a way to get all those voltages directly from one 12 volt battery without an inverter.
    You shold not try to answer this question then.
    It was still a hell of a lot more useful than you are being. Besides, he knows much more about this stuff than both of us combined.
    Are you sure? It's a basic thing in electricity.
    Edit: He claims to be an Electrical Engineer. That is weird, he should know.
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  14. #13  
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    Are you sure? It's a basic thing in electricity.
    He said you can't get 120V/240V from a 12V source without an inverter. That much is true. Do you know of another way? He was giving the only immediately possible solution for fatman57's question, which would be to get an inverter. Google's gadgetry is not for sale at the moment and nor is the motherboard that does the further converting AFAIK.
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  15. #14  
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    Quote Originally Posted by KALSTER
    Are you sure? It's a basic thing in electricity.
    He said you can't get 120V/240V from a 12V source without an inverter.
    That's not what he said.
    ATX has voltages of +12, -12 +3.3, +5.

    http://en.wikipedia.org/wiki/Power_supply_unit_(computer)#Wiring_diagrams

    I don't know of a way to get all those voltages directly from one 12 volt battery without an inverter.
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  16. #15  
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    Quote Originally Posted by Twit of wit
    Quote Originally Posted by KALSTER

    Quote Originally Posted by Twit of wit
    Quote Originally Posted by Harold14370
    I don't know of a way to get all those voltages directly from one 12 volt battery without an inverter.
    You shold not try to answer this question then.
    It was still a hell of a lot more useful than you are being. Besides, he knows much more about this stuff than both of us combined.
    Are you sure? It's a basic thing in electricity.
    Edit: He claims to be an Electrical Engineer. That is weird, he should know.
    You can't get +12 volts and -12 volts at the same time from a 12 volt battery, if you measure these voltages to the same reference point. That requires a 24 volt battery. My previous response allowed for the fact there might be some device I haven't heard of before.
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  17. #16  
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    just seems a little silly having an inverter though to run in a car for example as the PSU does the job anyway!

    with an A/C powered system does a normal computer PSU get its -12V from the negative of the A/C wave?
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  18. #17  
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    Quote Originally Posted by fatman57
    just seems a little silly having an inverter though to run in a car for example as the PSU does the job anyway!

    with an A/C powered system does a normal computer PSU get its -12V from the negative of the A/C wave?
    I wouldn't put it that way. A-c does not have a positive or negative. Depending on which way you connect the rectifier, either side of the a-c could be connected to the positive of the rectified d-c. And voltages are all relative. The reference point is arbitrary. If you have a 12 volt battery you could ground the positive, and call that the voltage reference. Then the negative terminal is -12 volts. Or ground the negative and you have +12 volts.
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  19. #18  
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    Quote Originally Posted by Harold14370
    You can't get +12 volts and -12 volts at the same time from a 12 volt battery, if you measure these voltages to the same reference point. That requires a 24 volt battery. My previous response allowed for the fact there might be some device I haven't heard of before.
    yes, you're right. sorry
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