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Mounting HX750W in a Bottom Mount Case


Lady Fitzgerald

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I would like to be able to mount my new HX750 fan down in a bottom mount case to avoid dropping screws, small birds, etc. into the PSU. Mounting it that way also allows easier cable management and avoids sucking hot air from the GPU. The case doesn't have ventilation holes in the bottom. I could fairly easily cut a hole in the bottom of the case but would rather not do so since I would have to raise the case higher off the desktop or floor (leaving room for more air but also more crud and small objects), depending on where I wind up putting it, and it would be more difficult to filter the incoming air and to clean the filter (I live in a very dusty place). I would rather the air came from inside the case because the case is fairly easily filtered. When mounted fan down, there is a 1/4" (6 mm) x 3 1/2" (9 cm) space under the cable end of the PSU where air can get to the fan. There is only 1/16" (1 mm) of space under the rest of the PSU.

 

I saw an older post where the poster asked something similar and was told it would be alright as long as some air could get under the case. Still, I would like to verify this since there doesn't seem to be a whole lot of room for the air to get in without the fan revving up and sounding like a B-17 at full throttle. I also don't want to fry eggs on the PSU and replace it frequently.

 

Jeannie

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Thanks for the suggestion but all I have in my new case right now are three fans which isn't going to make this PSU blink. Even once I move components from my old case to the new case, the load is going to be light until I'm ready to upgrade and stuff in hard drives so I wouldn't be able to do a fair test using your suggestion. Once the PSU is installed and all the cables hacked and routed, I don't want to have to do anything over because it starts to heat up once the load does increase. Mayhap one of the Corsair guys will chime in.
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  • 2 weeks later...

I decided to expand on MJinZ's suggestion of running the PSU in both positions and feel the out going air except I went a step further and put a load on it. I cobbled together two 1.2 ohm and three 1.0 ohm 25 watt resistors on a board and ran leads to five 12v cable connector pins. Theoretically, this was a 56 amp load. Add a hair under an amp for the four case fans I was running (there is another one on the case side but I wanted to be able to watch for possible minor insignificant events such as flames) and that comes up to a theoretical 684 watts (I keep saying theoretical because of tolerance variations).

 

Running the PSU fan up gave no discernable temperature rise in the air blowing out the back (ambient was 72C). There was little air flow out the back using the highly scientific back of the hand test.

 

Running the PSU fan down resulted in a 7-8C temperature rise (measured with a probe type thermometer) in about three minutes and maintained that for the next seven minutes after which I terminated the test because the resistors started self distructing (weird; these were 25 watt units). I couldn't discern any increase in air output. Fan noise from the PSU (which was low to begin with) didn't appear to increase (haven't calibrated my ears lately). My thermometer isn't a type that can give an decent reading on the PSU case but it felt barely warm when I touched it, about how the exiting air felt (some day I'll calibrate my various senses).

 

One variable that might skew my highly technical tests (sarcasm off) is the lack of a GPU during the test cranking out nice, toasty air the PSU could be sucking in when mounted fan up. When mounted fan down, it will be pulling air from the theoretically cooler air at the very bottom of the case being blown in from a front mounted 120mm fan after passing over the hard drives (only two of which will be actually working at a time).

 

I'm not likely to ever use more than that 684 watts on my present system (I'll be swapping it into the new case along with the new PSU) once I load it up with HDDs (more like 530 watts until I upgrade the mobo, video card, etc.; the new GPU will be rated only for watching movies from two HDMI outlets so it won't draw much). I won't be overclocking so case temperatures should be low even after upgrading. The rig will never be in a room running hotter than 29.5C so the 7-8C temperature rise shouldn't be a problem. I deliberately chose an oversized PSU so it wouldn't be stressed to ensure long life.

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