[Ham-Computers] Computer fan

Tue May 8 13:09:08 EDT 2007

>>> KA5BKG asked: 
"...what would happen to a computer if for example it has 2 cooling fans, and one 
would quit working?"

>>> My reply:
It would depend on which fan and how well ventilated the case is.  Most modern PC's have at least two fans, many with three, and some with more.  These fans are the CPU fan, Power Supply fan, and a case fan (or 2/3/etc).  Some have a "northbridge" fan (the memory/data bus controller).  High powered video cards also have a fan (or 2).  What happens would also depend on where the fans are mounted.  Luckily most fans rarely fail without "notice" - typically the bearings get *very* noisy before total failure.

If the CPU fan were to fail, then you could be in deep caca, depending on the CPU.  Older CPU's had no thermal safeties and would burn up if the heat sink system failed.  Newer CPU's will "throttle" down to a slower speed (typ 50%) once a certain temp is reached and will completely shutdown once a critical temp was reached.  A thermal shutdown can manifest itself as either a complete "lock" of the system, a system reboot, or an instant power-down, depending on how the system is configured.

Power supply fan failure would often lead to high temps inside the PC's case as it's typically the only "system" fan.  This can lead to higher CPU temps as the CPU is relies on ambient air for cooling.  The system will probably run fine until some component in the power supply fails due to termal conditions.  "Cheaper" power supplies with light-weight (or no) heat-sinking of the switching regulators will probably fail sooner than better power supplies.

Northbridge fans are generally just an extra precaution and typically not necessary - therefore, a NB fan failure doesn't usually cause any harm.  However, if you're overclocking the Front Side Bus (FSB), NB fan failure might cause random locks, reboots, or shutdowns.  The higher speeds (and the higher voltages often needed to OC) raise the operating temp of all OC'd components.  In some settings, every tenth (0.1) of a volt increase can lead to a component temp rise of 3 to 4 degrees Celsius.  The NB often runs near max operating temp without OC'ing, so the extra few degress could affect NB operation.

The fan on a video card is EXTREMEMLY important in high-powered video cards and less so on "basic" video cards.  The video card I have runs at 52 degrees C idle and is spec'd to go upto 140 degrees C before thermal throtlling.  When gaming, it's averaging 80 degrees C and the fan is running full speed - I definitely don't want a fan failure on this card!  I have an older video card where the fan failed - it's still working off the heatsink by itself with no problems.  It gets pretty hot, but it seems OK.  Why not replace the fan?  Because it's integrated into the heatsink and the heatsink has a unique mount.  No big deal for me as it's just an extra PC - if the card dies, so be it.

Case fans - typically, case fans are just to keep the temp inside the PC cool - the primary purpose of which is to keep the CPU cool.  A case fan failure generally doesn't cause any major problem other than a few degree rise in the internal case temp.  If the case fan fails, the Power Supply fan then becomes the primary ventilation source.  However, if you're OC'ing, then case fans become more important as there's a lot more heat being generated by the CPU/NB/RAM and whatever else you might be OC'ing.  Remember, 0.1v can lead to a rise of 4 degrees C per component - that's a lot of heat!

Remember, heat is the primary cause of component failure, so the better your case cooling, the longer your PC will last.  How much longer?  Who knows.

And, as mentioned in a previous post, if you have more than one fan, make sure they're not working against each other.  And check your airflow to make sure air is really circulating through your PC.  PC cooling is an art - mount your fans the wrong way and you're actually making things worse.  For example, mounting 5 fans as exhaust fans - where the heck is the air comming in from?  Ditto with 5 intake fans...where's the air going?

There are many websites describing case cooling...just Google them.  As always, be careful though as a lot of people sound like they know what they're doing, but actually don't have a clue (I'm like that...sometimes...<g>).  Here are a couple sites from Google...

Quick intro on air flow:
http://www.heatsink-guide.com/casecool.htm

Review of a "high-end" case with intro on thermal management:
http://www.madshrimps.be/?action=getarticle&articID=535

Yes, as typical, I've answered a short question with a *LONG* reply.  I generally like covering everything so less assumptions are made by the reader.  I hope I've answered your question, Brian, without going overboard!

73,

  - Aaron Hsu, NN6O