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DC-DC converter for Desktops?

Discussion in 'Electronics & Electrics' started by lukhangcheng, Nov 8, 2006.

  1. lukhangcheng

    lukhangcheng Member

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    Is there something like this in the market?

    Input 12-24V DC (actually anything in this range will do)

    Output 12V,5V,3V (am i missing anything?)

    about 65W total load,

    ALSO, i would like if this powersupply could charge (drip?) a 12v SLA (sealed lead acid), and be able to use this 12v battery for emergency power?

    This is in everyway similar to what a laptop does, but for a desktop, the peak power rating should not be a problem, as planning on running this with A64 2X 3600+ EE, and with laptop HDD and no optical drive.

    Does anyone know anything similar?
     
  2. Sadow

    Sadow Member

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    I have seen a 12vDC ATX PSU, think it was on this forum, but they didnt have a charger or battery backup capabilities.
     
  3. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    Yeah i have seen similar stuff (no charging battery) for those VIA mini-itx boards. but they are generally quite expensive.
     
  4. RILEYP

    RILEYP Member

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    where are you going to get 12-24 vdc on the desktop from with the current capacity you are after for a start unless your in a vehicle
    And no I dont believe ther is anything out there
    The problem is this:
    to change 24 dc to 12 dc or to 5 volt dc or 3 volts etc with the current capacity your after in a computer large amounts of heat are dissapated! Unless you convert the dc back into ac then step it down with a switchmode psu like in your desktop atx psu...
    so basically what you asking for is a an invertor to convert 12/ 24 dc in to 240 ac to run the switchmode psu already in your pc as they dont make a switch mode psu for a 12/ 24 ac supply...nor do they make an off the shelf 12.24 dc to ac invertor that i know of..
    But then again Im a sparky not an electronics guru that knows every gadget out there...
    But if there is something I'd love to see it!
    cheers rileyp
     
  5. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    I think you misunderstand something in my "requirements"
    I am just after inputs of anything from 12v to 24v,
    since if its less then 12v it would have efficenecy problems with DC/DC converter.
    And 24v was just an arbertory upper limit.

    True to some extends, that DC/DC is inefficent,
    but would DC->AC->DC be more/less efficent?
    (hard to say, i know AC/DC is efficient, but DC/AC isnt.?)

    What i am after is similar to the result of using a laptop, if anyone have any ideas as to how it works in a laptop, then that is what i want :D,

    Current My laptop takes 18.5v input and has a 14.4v battery :D
     
  6. RILEYP

    RILEYP Member

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    What do you mean by this? :confused:
    dc/dc is inefficient
    dc/ac is inefficient
    ac/ac/ac/ac (as many as required)/dc is the way the entire planet is wired up and set up...
    eg 220kv/22kv/240v/to dc
    Less those horrid things we had to invent for to keep the pc's running when the generators failed called invertors!....
    If there was a more efficient way of supplying your pc with power they would be selling them on every corner.....
     
  7. SKiB

    SKiB Member

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    The M2-ATX does DC to DC and I believe meets your original specifications.

    There's no reason why you couldn't use the 12v to trickle charge the battery. Unless of course you were using power from the battery to charge it. In which case the battery would just run flat over time.

    Try this guide instead.
     
  8. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    Well as you said, DC to DC converters exsist, but at the cost of generating fair amount of heat (more heat = less efficient!)
    AC/AC/AC/DC is perfect! (for a desktop)

    I am after something that can make a whitebox (with my choice of lower power components), with laptop type power behaviour.
    (so it can use a battery basicly)

    In a laptop type system, u have a power brick that converts 240v AC to 12-24v DC (mine is 18.5v), which then in turn charges the battery and power your system, if your 240v disappear for some reason, the laptop runs on battery!

    Also power bricks dont tend to have fans!
     
    Last edited: Nov 9, 2006
  9. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    Thanks SKiB,
    I was looking at somthing similar, granted that u can use 14v to 12v on something like this.

    But what of the 240v + the battery?

    DIY UPS would be good, but usage time is still limited? and a bit expensive still
     
  10. SKiB

    SKiB Member

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    I'd buy a $20 car battery trickle charger to get the 240v to 12v.

    That'd keep the car battery charged.

    But you could buy a 600W ATX PSU and charge the battery from the 12v rail. It'd also have enough steam to power the other PSU. That means the M2-ATX would be run from the big PSU, and when the power cuts out, the 12v battery would immediately start supplying the M2 with current. But doing it like this is just plain silly.
     
  11. LethalCorpse

    LethalCorpse Member

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    wow, you guys are talking some shit. It is not efficient to invert from 12VDC to 240VAC, back down to 12, 3, 5VDC. A DC-DC converter is able to achieve very high (>85%, at least) efficiency by using a simple single stage switchmode design. An inverter and ATX PSU has a far more complex switchmode circuit to convert the 12VDC into a modified square wave, then a transformer (inefficient) to get it up to 240VAC, then another complex switchmode circuit in the PSU to get down to the required levels. Add to this the fact that the modified square wave has a whole lot of high frequency harmonics which will, over time, demolish the filtering caps in the PSU, and you've got yourself a less than ideal power supply situation.

    Lukhangchang, you can use the M2-ATX, or thisPSU to power the PC in the car. You can also set up a dual battery system for backup, however this is designed more to protect the main battery from going flat, so you can still start the car after playing warcraft all night instead of camping.
     
  12. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    Humm yeah i think you guys are reading into this too much.....

    wat i want.

    240V AV -> 14V DC -> ATX power supply
    <-> Sealed Lead Acid Battery

    so that is 240V a one supply of power, and SLA as the other,

    why step down to 14V?
    to be able to charge the SLA battery.

    LethalCorpse's suggestion is not bad, but not as elegant as i like.
     
  13. RILEYP

    RILEYP Member

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    1 You cannot charge a 12volt battery at 12 volts IE from the 12 volt rail of the computer ...It will always be almost dead flat...
    2 For an lead acid battery the ideal charge voltage is~1.4-1.5 volts per cell
    which means you would need 14 or 15 volts dc.
    3 For your info.. a car alternators regulators is normally set at 14.4 volts..
    4 Stationary batteries like in a telstra excahange etc are set at 15 volts...

    That mini dc /dc convertor for $80 is very inpressive!
     
  14. dakiller

    dakiller (Oscillating & Impeding)

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    That is basically a UPS you want? Checkout this for some DIY action then - http://www.dansdata.com/diyups.htm
     
  15. OP
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    lukhangcheng

    lukhangcheng Member

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    Yeah basicly want a UPS, but ... but one which supplies DC....
    instead of AC.

    I had a look at the Dan's Data site but just reakon this could be more easily/cheaper done?
     
  16. OP
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    lukhangcheng

    lukhangcheng Member

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    I think thats $80 USD rite?
     
  17. nux

    nux Member

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    What exactly do you want? Just a way to provide backup power for your PC like an UPS?

    This plugged into a car battery continuosly charged with something like this would probably work.

    The problem is you need to be able to charge your battery faster than its being used up.

    An UPS is definately a much smarter way to go.
     
  18. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    I want a desktop, to behave like a laptop, in terms of power supply goes.

    Reason's includes.
    I want to use a power brick because its fanless, and easier to cool (placing it on a steel case for example.)
    I feel that using a DC supply is more flexiable in terms of modding into a small form factor case.

    The alternative includes just using a low end laptop, like the HP and Acer ones with added ram.
     
  19. fad

    fad Member

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    You realise inside a Computer PSU, is a bridge recitifier. Inside the PSU is a DC->DC circuit.
     
  20. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    Yeap, but inside a PC it goest 240VAC - > 12VDC - > other voltages

    having 240VAC -> 14VDC - > 12VDC -> other voltages

    would be LESS efficient cos its got one more step.
     

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