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  • Help with 12V to 5V step down converter.

    I bought a 150 watt, 30amp, step down converter. Its supposed to take me from 12V to 5V. i am using this for all my hubs and many 5V based devices. My understanding is that this unit steps down the voltage by turning the extra energy into heat.

    Obviously I have to cool this thing down, so would it be ok to build an enclosure to cool the unit down? Basically it would have a fan to the right and left of it, so the air passes through the fins to cool it. Im just worried that cooling it to much will kill its function. If I cool it to much will that mess up its ability to stepdown to 5V?
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  • #2
    You can't over cool it with fans. Overcool would be putting it in a freezer, and then the problem would be condensation/moisture as it warmed.
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    • #3
      The only energy the device would dissipate would depend on the current it is sourcing.
      Many electronic converters just chop the 12V and then smooth it again to give the 5V required so there is little heat generated as you expect when dropping [email protected] across a drop-down resistor.
      I would connect it up to your load first in an open position and feel how much heat it generates by feeling the heatsink.
      Are there any specs which show the Watts dissipated ?
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      • #4
        Thanx, that all makes sence. Here are the stats listed on the website.

        Input Rage: 10 - 30 VDC
        Output: 5 VDC
        Output Current: 30A
        Size: 77*77*30(mm)

        Waterproof;
        Light compact, convenient to use and transport;
        Switching mode power supply, Non-isolated, efficiency:> 90%;
        Ambient temperature at -10 ℃ ~ 45 ℃;
        with overload / over-current / over / low voltage protection (some of the products have the protection of plus or minus reverse), stable performance.
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        • #5
          OK so 150W @ >90% efficiency means about 167W total at full-load from the 12V supply.
          This means that at full-load the converter will only need to dissipate about 16W and less if not at full-load of 30A @ 5V.
          Chances are with that large metal surface area heatsink it will only get warm to touch with normal convection cooling but give it a run to check before you stash it anywhere.
          VIA Pico ITX, M2-ATX clone, 7" Seform 800x480 LCD Touchscreen, Dual 2x75WRMS Mini Amps, IDE-CF & SATA-CF adapters, 8GB (Sys) & 32GB (MP3s) CF, ELMscan5USB, Slot-load DVD, Craig Brass DAB+/FM USB module, Odyssey Navigator
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          • #6
            All the devices will be pulling about 21 amps. So I should be good? I could just have the fans in case. This will be tucked in a tight space.
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            • #7
              You should have no heat issues with a switch-mode supply at that current, case fan air should be ample and as suggested, run it loaded for about 20 minutes and verify it holds at a stable temp in its installed location.
              Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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              • #8
                i would probably put a fan right next to it, so some directed airflow is going across it, but other then that, the case options are up to you.. i might need to pick one of those up for my 5v hub..
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                • #9
                  It should only dissipate ~16W - hence less than a 21W bulb. And in that finned-case, that should not be a problem.
                  It may have thermal limiting anyhow, but feeling it as comfortably warm should allay any fears.

                  If it were linear, then it would dissipate up to 300W, but it isn't - its an SMPS.


                  BTW - how $much & where from?

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                  • #10
                    http://www.current-logic.com/shop/index.php
                    Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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                    • #11
                      ^ What he said!
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                      • #12
                        wow, $17 for a switch mode 10A psu?!?! i almost bought a couple just for the price...
                        My OLD 2001 Mitsubishi Eclipse GT:
                        "The Project That Never Ended, until it did"


                        next project? subaru brz
                        carpc undecided

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                        • #13
                          Ditto.
                          It makes a farce of USB & 5V supply issues.

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                          • #14
                            Only thing I wonder is does this thing spit 5V right away? Does it have to get a certain heat before it drops to 5V or am I over thinking things again? I calculated out that everything on max will use 19.80 amps. So you think connecting 2 fans on the 5V side will be ok? They are the medium fans, found in most cases. I want to use two, but on 5V so its a steady breeze since you guys have me convinced it will not get extremely hot.
                            Nirwana Project, the Android/Win 7 hybrid system!

                            1X Ainol Novo Flame Tab
                            4X MK808b
                            3x Perixx Touchpads
                            3x 7 inch Screens
                            1X 7 inch motorized Screen
                            1x Win 7 PC

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                            • #15
                              So at 19.8A you'll use the 30A supply.


                              The heat is irrelevant.
                              They need a minimum load (typically ~10mA), but this should be inbuilt. Hence why "power on" LEDs are used, though otherwise 470 Ohm resistor. (That dissipates 1/20th of a Watt, hence trivial and cheap and should be built in.)

                              FYI - the same minimal loading is found on many PSUs and regulators. I know some (pathetic) ATX supplies do NOT include that load... (That's looking for trouble, or more sales!)
                              Even the linear LM317 requires it, but hence the choice of a "standard" 120 Ohm as one of its voltage-divider resistors - 120R across 1.2V is its 10mA minimum regulation current.


                              PS - BTW, thanks for the link.
                              Last edited by OldSpark; 10-06-2011, 07:27 PM. Reason: ps

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