Marginal OEM Power Supply
in [Chips]
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From: Robert Myers on 22 Jun 2010 10:19 Robert Redelmeier wrote: > In comp.sys.ibm.pc.hardware.chips Robert Myers <rbmyersusa(a)gmail.com> wrote in part: >> I had previously noted the puniness of power supplies on OEM >> boxes, but not by overloading them to the point where the machine >> wouldn't run. I don't think that upping the RAM by 50% and adding >> a HDD causing a power supply overload is a reasonable expectation. > > Agreed. HDDs (especially 10k) can cause a heavy motor-start > load on the 12V but should otherwise be fine. One problem with > big OEMs is they are also aiming at EPA EnergyStar targets > which cause them to tight-size PSUs for max efficiency. > The German TuV may also have powerfactor targets. > Energy efficiency is the new wild card. It's the only consideration I can imagine that would justify cutting it so close. > >> Something else about this machine that is shaved very close is >> the thermal design. It will not run for long with the side cover >> removed. That wouldn't surprise me if the side cover included a >> duct, but there are only holes strategically placed in the side >> panel. The CPU has an enormous heat sink, but no fan of its own! > > There is your clue, no CPU fan -- the cover is a duct. With the > cover off, air can bypass the CPU heatsink and slip straight to > [from] the PSU fan. I've built machines without CPU fans, and > you have to be very careful about airflow. > It's misleading for me to say that the CPU has no fan. The case fan draws air in such a way that the predominant flow is through the many horizontally stacked, spaced plates of the heat sink. It wouldn't seem that it would matter so much where the air comes from, but apparently it does. The heat sink stack is so tall it extends nearly to the edge of the case, so that air entering through the side holes (highly turbulent because it is a collection of small jets) encounters the top of the heat sink almost immediately. I suspect that those holes behave more like vorticity generators than like a duct. Take the cover off, and the relatively laminar flow through the heat sink doesn't create enough heat transfer. Robert.
From: Yousuf Khan on 21 Jun 2010 15:12 On 6/21/2010 12:57 AM, Robert Myers wrote: > I had previously noted the puniness of power supplies on OEM boxes, but > not by overloading them to the point where the machine wouldn't run. I > don't think that upping the RAM by 50% and adding a HDD causing a power > supply overload is a reasonable expectation. > > Something else about this machine that is shaved very close is the > thermal design. It will not run for long with the side cover removed. > That wouldn't surprise me if the side cover included a duct, but there > are only holes strategically placed in the side panel. The CPU has an > enormous heat sink, but no fan of its own! > > Robert. About a year ago, I bought a Zalman 600W PS, which other manufacturers apparently repackage and call a 750W PS. So I think there is probably some conservative design involved here. You might consider changing the power supply to something like this. From your other messages in this thread, it sounds like you got yourself a pretty high-end Core i7 of the original triple-channel variety. So you getting marginal PS with it, is pretty surprising, as it must be a pretty expensive machine otherwise. Regarding it having only a big heat sink with no fan, this would probably indicate to me that the heat sink depends on the power supply's own fan to move air over the CPU. This would also explain why keeping the case cover off is bad for it, as the cover is probably integral in directing the air over the CPU heat sink. Yousuf Khan
From: Bill Davidsen on 22 Jun 2010 16:31 Robert Myers wrote: > Bill Davidsen wrote: > > > Robert Myers wrote: >>> >>> DIMM slots 0 and 2 had been installed correctly and the "upgrade" was >>> installed to slot 3. >>> >> I would expect that to pass smoke test, then, incorrectly installed as >> in not full speed rather than upside down or something, I'm actually >> surprised that it didn't show up working on POST and only be obvious >> with the cover off or using dmidecode. Or whatever the Windows tool is >> to get the same information. >> > > I would have expected it to boot, too, but it didn't. I tried to boot > before opening the machine. It's been long enough that I don't remember > if it got past a power-on POST and stopped at a blank screen. Maybe > that would have constituted passing a smoke test. I can understand why > a tester in a hurry wouldn't want to wait for Vista to boot. > > Since I intended to add memory, I didn't hesitate to take the cover off > to see what was going on. Making what I thought would be a correct > memory install fixed the problem. > Glad you like it, I have been thinking of a 930 for a KVM server, drop in 12GB of RAM and 4TB of cheap disk and put all the boring little 512m servers on Earth on it.
From: Bill Davidsen on 22 Jun 2010 16:45 Robert Myers wrote: > Robert Redelmeier wrote: >> In comp.sys.ibm.pc.hardware.chips Robert Myers <rbmyersusa(a)gmail.com> >> wrote in part: >>> I had previously noted the puniness of power supplies on OEM >>> boxes, but not by overloading them to the point where the machine >>> wouldn't run. I don't think that upping the RAM by 50% and adding >>> a HDD causing a power supply overload is a reasonable expectation. >> >> Agreed. HDDs (especially 10k) can cause a heavy motor-start >> load on the 12V but should otherwise be fine. One problem with >> big OEMs is they are also aiming at EPA EnergyStar targets >> which cause them to tight-size PSUs for max efficiency. >> The German TuV may also have powerfactor targets. >> > Energy efficiency is the new wild card. It's the only consideration I > can imagine that would justify cutting it so close. > >> >>> Something else about this machine that is shaved very close is >>> the thermal design. It will not run for long with the side cover >>> removed. That wouldn't surprise me if the side cover included a >>> duct, but there are only holes strategically placed in the side >>> panel. The CPU has an enormous heat sink, but no fan of its own! >> >> There is your clue, no CPU fan -- the cover is a duct. With the >> cover off, air can bypass the CPU heatsink and slip straight to >> [from] the PSU fan. I've built machines without CPU fans, and >> you have to be very careful about airflow. >> > It's misleading for me to say that the CPU has no fan. The case fan > draws air in such a way that the predominant flow is through the many > horizontally stacked, spaced plates of the heat sink. It wouldn't seem > that it would matter so much where the air comes from, but apparently it > does. The heat sink stack is so tall it extends nearly to the edge of > the case, so that air entering through the side holes (highly turbulent > because it is a collection of small jets) encounters the top of the heat > sink almost immediately. I suspect that those holes behave more like > vorticity generators than like a duct. Take the cover off, and the > relatively laminar flow through the heat sink doesn't create enough heat > transfer. > Possible, but I think having the coolest outside air coming to the CPU first is probably the key. My problem has been running high ambient temperatures. With a 90F building temp keeping CPU and disk cool is an issue. I looked for a Peltier cooler, but didn't come up with one I really liked. And they draw a ton of power.
From: Robert Myers on 23 Jun 2010 13:33
Bill Davidsen wrote: > Robert Myers wrote: >> It's misleading for me to say that the CPU has no fan. The case fan >> draws air in such a way that the predominant flow is through the many >> horizontally stacked, spaced plates of the heat sink. It wouldn't >> seem that it would matter so much where the air comes from, but >> apparently it does. The heat sink stack is so tall it extends nearly >> to the edge of the case, so that air entering through the side holes >> (highly turbulent because it is a collection of small jets) encounters >> the top of the heat sink almost immediately. I suspect that those >> holes behave more like vorticity generators than like a duct. Take >> the cover off, and the relatively laminar flow through the heat sink >> doesn't create enough heat transfer. >> > Possible, but I think having the coolest outside air coming to the CPU > first is probably the key. > The short circuit to the air flow with the cover off is just a few inches between the heat sink stack and the exhausting case fan, which exhausts much greater heat than the power supply. A piece of cardboard or plastic that blocked that short circuit would be an interesting test. There are actually holes upstream of the CPU to cool the disk drive, and that air has to get through/around the CPU heat sink to exit the case. > My problem has been running high ambient temperatures. With a 90F > building temp keeping CPU and disk cool is an issue. I looked for a > Peltier cooler, but didn't come up with one I really liked. And they > draw a ton of power. These boxes have run without air conditioning in summer weather. I don't think 90F ambient should be a problem. Robert. |