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DC-DC converter for Desktops?

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

  1. dakiller

    dakiller (Oscillating & Impeding)

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    Computer PSU's go 240VAC (via full wave rectifier) -> 340VDC -> 12, 5 and 3.3VDC (usually on the one transformer, sometimes 2)

    DC-DC computer psu's, they take 8-16V or so don't they? They would have a flyback switcher to give the regulated 12, 5 and 3.3, probably in just about the same fashion as the regular mains powered ones just with a modified primary supply section
     
  2. newSpeak

    newSpeak Member

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    Yeah. I've seen ATX PSUs retrofitted to operate from a 12V input. As you might imagine this involves removing the rectifier and PF correction stuff and rewinding the transformer.

    I gather what lukhangcheng wants is a UPS that has a PSU built into it. Dont think such a think exists as a regular consumer product. Unless he is gun at power electronics, think the best option is just to go the regular UPS and regular power supply route. If it must be external maybe put the UPS and PSU in a seperate box together.

    Also 65W doesn't sound like enough for a modern desktop system.
     
  3. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    yeah i think retrofitting a PSU is a bit beyond me,
    my level of electronics skills is just basic soldering and the introduction to electrical engineering subject i did a couple of years back (i used to do mechanical eng)

    Was thinking of using the A64 X2 3600+ with Asus motherboard, with a CF card (via IDE adopter) as the boot drive. (no optical drive or 3.5' HDD)
    it seems to be do able according some reviews and all the max consumption of all the hardware.

    Maybe 80W is better?
    I have been looking at the PicoPSU, that requires 12v in order to run.
    Maybe I can build another circult to add the functions that i want.
     
  4. nux

    nux Member

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    I would think an A64 with motherboard would require at least 80W if not more. I dont really see why you're bothering when you can buy an UPS much cheaper?
     
  5. RILEYP

    RILEYP Member

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    Maybe he thinks he can make it with things you can buy off the shelf quieter than a standard psu with an integrated battery charger and a sealed lead acid battery with a good four hours capacity and patent it and sell it to everyone else thats wants this set up for a small price...
    Thats why big companies use massive ups sytems to keep there pc's up and running for the short while between change over between mains and generator supply...
    If it was simple enough to do and compact enough for an extra couple of hunderd dollars per pc dont you think big companies would insist all there pc's with some level of importance would have a psu like this installed rather than being dependant on an individual ups that when it falls over everything falls over.
    Im sorry for being pesimistic lukhangcheng but I do believe what you want is pie in the sky!
    Im sure there are plenty of people with much more knowledge about psu's than you or I out there smacking ther heads together trying to put together an uber quiet psu with a battery back up that they can flog to the big computer dependant companies out there as the greatest revolution to computer reliability in years.
    UPS are horrid things as they dont every truely get tested as companies cant afford to test them on work days and if your a bank for example thats 7 days a week 24 hrs a day...
    They can only be tested with dummy loads...
    Which means when when it actually happens (loss of power) it may still fail!(the ups that is) due to some electrical glitch like a faulty contactor coil etc.. and there you have it disaster... they cant trade...they are losing hundreds of thousands if not millions of dollars with every second their system is down...
    Which is why they have dual UPS's I spose... ;)
     
  6. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    Well not quite, but its already been done in laptops,
    I just want to know HOW it works in laptops and make something like that for a desktop!!

    the problem is.. a normal cheapass PSU for desktop cost less then $30 to ppl like DELL, HP etc...

    This system is INFIERIOR to a proper UPS because it (if its like a laptop) lack surge protection and other things that a UPS offers
     
  7. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    Really? had a look at UPS mostly aorund the $200 mark?
     
  8. nux

    nux Member

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  9. RILEYP

    RILEYP Member

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    Luk... how are you going to run your monitor without 240V?
    Or
    Do you just want your box to stay up during this dreaded power outage your expecting?

    Why dont you just rip the guts out of laptop.....put it in a desktop case and plug in a usb keyboard and mouse... and glue the screen to the desktop case and get one of OCAU's uber case modders to make it look trick!
    Problem solved! :lol: ;)
     
  10. LethalCorpse

    LethalCorpse Member

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    Decide what you want, and then post. Quit wasting everyone's time. No one can understand whether you want a UPS, a desktop to run off a brick instead of a PSU, or a perpetual motion machine, where the PC is charging the battery which is used to power it (doesn't exist). Start talking sense, and you'll get some reasonable answers. Draw a diagram if you have to. But this thread has turned into a game of celebrity head - guess the OP's objective.
     
  11. OP
    OP
    lukhangcheng

    lukhangcheng Member

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    Oh yes dreaded power outage, had a 6 hour one last week!!

    I guess there is a chance that would happen.. this summer is looking hot..
     
  12. Goth

    Goth Grumpy Member

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    240VAC---->Trickle Charger----> 12V Pb-Acid Battery---->DC-DC PSU

    That's really what you want, isn't it?

    Or you could have a setup whereby a normal 240VAC SMPS is used, but when a loss of mains power is sensed, the DC-DC PSU is switched on, and switched in to the computers power supply with a relay, but i really don't think that's needed.

    For an output load of say 70W, i would guesstimate that a PSU such as the Jaycar one could pull as much as 8A at 12V - LethalCorpse probably knows the figure more accurately.

    An 18Ah SLA - the largest one in the Jaycar line - would thus last for a little over two hours. Car batteries are typically 40-50Ah, IIRC.
     
  13. ViPeR-7

    ViPeR-7 Member

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    It could have been my DC-DC PSU you were reading about on these forums, havent played with it in a while but heres what you wanna know :p :

    Theres 3 main ways to turn your ~12VDC into the standard PC spectrum of voltages.

    Switchmode DC-DC Regulator :
    Best option for efficiency, but the worse for price, difficulty, etc. You can buy them prebuilt at a few online stores (check out mp3car.com). And building one yourself involves about $20 from an electronics store, an old desktop PSU, and a moderate expertise with electronics.

    Linear DC-DC Regulator :
    This is the method i used, it requires that either your input power is at least 14VDC, or the 12v rail will be unregulated. Other than that the whole kit costs around $20, you can build it yourself, and its a good project for anyone 'modding up' their car ;) Downsides are : It does generate some heat, so a fan will probably be required. And it wont suppy negative (-ve) voltages to your pc (you'll lose your serial ports, thats about it)

    Power Inverter / Standard AC/DC PSU
    Using either a UPS or a dedicated Inverter you can step your input 8-16VDC up to 240v and back down with a standard PC PSU. Yeah it sounds wasteful, but you can often pickup old UPS's with dead batteries for free (just ask Dan) and if you want a reliable setup with battery backup, etc, this is definately the way to go.
     

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