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Electronics PSU Pasive Cooling Idea - Possible?

Discussion in 'Modding' started by Skylined, 26 Jul 2004.

  1. Skylined

    Skylined Minimodder

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    The idea is to eliminate as many fans in my case as possible.
    I cannot run totally fanless because I have a SLK900-A on a 1700+ @ 2.1GHz, but that's ok, I have it with a 92mm fan @ 6.5V, totally silent, so that doesn't matter.

    Now to the idea.
    I want to rip the transistors (?) off the PCB, get big heatsinks and put them there, and of course, make it a fanless PSU.
    About the PSU, it's a crappy no name PSU, sorry but I cannot get branded PSUs here, this is my ONLY option.
    The idea is to make the PSU's cover a lil bit taller and make holes or make big grills so that I won't get air traped in there.
    I would wire the transistors and then I'll put them on big heatsinks.

    What do you think?
    Any piece of advice you want to give me?

    I can make the PSU cover in acrilic and I can get a router, so I can make grills or holes in that piece of acrilic.
     
  2. Smilodon

    Smilodon The Antagonist

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    yeah, that's possible... i have seen passive cooled PSUs before, but those are really expensive!

    As long as you have a large enough heatsink and mount it a place where it can get enough cool air, i can't really see any problems with that...

    I think the best place for the heatsink would be at the back of the PSU... That way it will be on the outside of the case..
     
  3. whypick1

    whypick1 The über-Pick

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    Just remember that the metal tabs of transistors are connected to one of the terminals. They may be grounded, or they may be live. The point is, you need to make sure that you don't connect them all to one big heatsink recklessly or you'll short something out. You can either use a nonconductive TIM in place between the tab and the heatsink or determine which ones will be at the same potential and use the same heatsink for those.
     
  4. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    The heatsinks are floating with high frequency hight voltage. You would have to isolate them with mica shims or something like that. (diamond would be the preferred insulator but you don't seem to have access to a lab to make the diamond sheet :D )

    I would also use an anodized aluminum heatsink, not copper or bare aluminum. If you can afford it, mount the mosfets/diodes using the appropriate bolts, (plastic washer on the back to keep it from gouging though the anodizing) than take it to a anodizing shop and get a nice hard anodizing done to it to make sure it is insulated and will stay that way.
     
  5. infernis

    infernis What's a Dremel?

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  6. Skylined

    Skylined Minimodder

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    NO, this isn't a thread revival. :)

    I haven't done this in my main rig yet, but now I want to do it with my server (see signature).
    I've already taken a look at both SPCR links.

    I have to replace the heatsinks on my PSU because it gets really hot.
    I'll check if they are grounded, live or if they're doing something in the circuit, but not now, it's 6am. :p

    I won't be able to anodize and I don't even know if I'll be able to get anodized heatsinks.

    Right now I have a couple of questions.
    Can I use the mica that is in the PSU or do I have to get new one?
    Is there any way to calculate which kind of heatsink I should get?
    Is there any other part that gets hot apart from the MOSFETs?
     
  7. Xiachunyi

    Xiachunyi What's a Dremel?

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    I recommend that you obtain new mica insulators but re-using old ones, as long as they still serve their job, is acceptable.

    Good information here about selecting and sizing heatsinks

    All the components in a PSU become hot but the ones that generate the most heat, besides the onboard regulators, would be the transformers, resistors, and possibly the capacitors - you can't really tell since they are in layers and usually a warm cap means a hot one inside.
     
  8. cpemma

    cpemma Ecky thump

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    The mod shown in the second link is very similar-looking to this SilentMax psu.

    And I note the comment at SPCR: "CAUTION: There are many reports of heat-related failures." :worried:

    Note on mica - there are far better insulating pads these days.
     
  9. Skylined

    Skylined Minimodder

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    I've also taken a look at this other site http://web.telia.com/~u85920178/begin/heat-0.htm#use

    But I'm still confused, I didn't get how to calculate which heatsink I need.
    I won't use a heatsink I already have, my plan is to get a new big heatsink and put the 6 transistors on it, but I don't want to get a huge heatsink just because I don't know what I need, the smaller the heatsink, the better it's going to be.

    Unfortunately I don't have any online shop here, well, there is one, but it doesn't have pics of the heatsinks nor the specs of them.
    I have to go downtown, where all electronics shops are, but before going there I want to know which heatsink I should get, and there I'll see what those shops have in stock.
     
  10. cpemma

    cpemma Ecky thump

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    At a guesstimate, your system will be drawing around 150-200W max. A typical generic psu will have efficiency around 70%, so that's 45-60W of heat to get rid off. It won't all be generated in the 6 transistors, but most will.

    Sounds a lot for passive cooling in the space available. Maybe you should be under-clocking. ;)

    I'd be looking for something a bit bigger than this . :eeek:
     
    Last edited: 12 Jan 2005
  11. Skylined

    Skylined Minimodder

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    I think I'll be under that W.

    CPU (P2 350MHz) rated ~20W.
    Video card, it's set to turn off the monitor after 1 minute since I don't plug a monitor to it, I use VNC.
    PATA HDD.
    2 NICs
    1 stick of RAM.

    I'm not into underclocking since the CPU can run fanless and has a very low W rating.

    And before anybody says something, I've already tried to run the PSU without a fan and it gets very hot, it has tiny heatsinks.
     
  12. cpemma

    cpemma Ecky thump

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    :confused:
     
  13. malfunction

    malfunction What's a Dremel?

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    Just a thought. But how about buying a passive PSU instead of killing yourself / your PC?
     
  14. Skylined

    Skylined Minimodder

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    Now you get it? :)

    I'm doing it to my server, take a look at my siggy. ;)
     
  15. Skylined

    Skylined Minimodder

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    Killing myself?
    I would be already dead, I'm a car mechanic. ;)

    Kill my PC?
    Nope, I'll test the PSU alone before pluggin everything. :)

    Buying a fanless PSU.
    1. I cannot get them here.
    2. They're expensive.
    3. I don't want to waste that money.
     
  16. malfunction

    malfunction What's a Dremel?

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    I'm not saying it's impossible to make a passive PSU that works. I would suggest you have some temperature monitoring built in and maybe a fan you can either switch on manually or that can come on once the internal temperature reaches a certain level. Outside of that if you only have low end requirements have you considered going the mini itx route? Failing that an old laptop may save you a lot of hassle.
     

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