System Cooling: A Dual Pronged Approach

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"System Cooling; a dual pronged approach"

by David Nixon

10/28/98


I have tried many ways to cool a system, on the CPU level, and on the case. You really need to take care of both of these items, as doing great on one and poorly on the other, will just be a waste of your time.

First of all let’s look at the CPU.

Everybody has their own preference. Some like a good old fan and heatsink, while some prefer the active type coolers, such as a Peltier chip. I have used both, and my personal favorite is a good heatsink and fan. The Peltier chip itself works great, but it creates alot of additional heat inside your case, which in turn means your case cooling needs to be that much better to dissipate it.

You may have heard talk about making a “Heatsink Sandwich”. This configuration is where you place a specialty heatsink and fan combo on the FRONT of your CPU, with a standard OEM heatsink and fan on the BACKSIDE of the CPU. Note: This only really works well with a CELERON processor, as the chip is not encased in plastic, as we see in the Pentium II chips. This “sandwich” works extremely well. You have only to touch the back of your Celeron chip after an hour of Quake2 to see how much heat it actually gives off.

What you need to do is get a good heatsink and fan combo. I like the ComputerNerd 2Fan Cooler. On the heatsink, you will need to drill out 4 holes that line up with the four mounting holes found on the Celeron chip itself, and also on the OEM type heatsink that is going to be mounted to the back of the CPU. Most heatsinks are made of aluminum, and are very easy to drill out.

You should use about a 3/16 inch drill bit. For screws, I used four leftover screws that came with my case fans. They were the right width, and long enough. The size is not that critical, so long as it fits. You need to cover the backside of the CPU with a THIN layer of insulation. This is to prevent the heatsink from making contact with the board and possibly shorting anything out. I used high temperature “Duct Tape”. Anything along those lines will work.

You need to put ONE layer of such tape, on the back of the CPU board, WITH THE EXCEPTION of the area(about 1.25 inches square) DIRECTLY BEHIND the CPU chip itself. This is where you apply your thermal grease. Next apply your thermal grease to the front of the CPU, and place the front heatsink onto the chip, and then slide your four screws through the front heatsink, through the CPU board, and through the back heatsink.

Then put on the 4 washers and nuts, and only tighten down untill SNUG! Do NOT torque down these screws as it will apply alot of pressure to the CPU board. We are now done with the CPU cooling.

Next we need to look at the case.

There are a ton of different cases out there, and some are better than others. What you need to do is get one that has plenty of room to work within. We don’t want all of the area that we need for air flow to be clogged with wires and drive cables. We want a large open area in there, with enough room to tie-wrap our wires out of the way once we are done.

Before we get into the actual design, we need to clearly state our goal here. An overclocked system generates quite a bit of heat that we need to dissipate. Our “sandwich” design generates just as much heat as a cheap OEM fan, but the difference is that our design removes it from the chip. The heat energy is still present, it is just trapped within our case, and unless it is taken out of there, the sandwich design, or any other CPU cooling design for that matter, will be rendered useless.

We want to create a wind tunnel effect in the case. We want cool air to rush in from the front and bottom of the case, and to flow over our peripherals and CPU, and be exhausted out the back. To accomplish this we need a fan for the front of the case, that moves A LOT of air. I have found that 60CFM is adequate, but sometimes you might want up to 100CFM just to be safe.

Before you mount this fan, we need to make sure that it has enough breathing holes to actually get the CFM that the fan is rated for. There won’t be much air flow through those tiny holes the manufacturer puts there.

Remove the front PLASTIC cover of the case, to get to the metal plate. I actually cut a big square hole the size of the fan in this metal plate. If you can get your hands on a little Dremel Tool, with a cutting wheel (fiberglass wheel works best), this is a piece of cake. However you accomplish this, get that hole big enough. Don’t worry about how it looks, it will all be covered by the plastic plate.

Once done, make sure that the plastic piece has enough holes to breathe also. Now on this, you want to be careful so it looks nice…just drill out several larger holes, and clean out the holes with a small file. Make sure the holes are even and lined up nice. Mount your fan to the metal plate, attach power to the fan, and put the plastic cover on. We are now done with the INTAKE portion of the case cooling.

Now we need to remove all of this air we are pumping into the case, only now that air will contain most of the heat energy our system is creating.

First, see if your power supply fan is blowing air INTO the case or OUT. Most new ones blow out, as they should, and this is what we want. If you have an older unit, open it up(with the power disconnected!!!) and simply turn the fan around. Put the supply back in the case, and seal up any openings on the unit. The only openings you want are the intake next to the CPU, and the exhaust port on the outside back of the case, as we don’t want any heat to leak back into the case.

Right behind the CPU, and above your PCI cards, is ideal for the “Radio Shack DC Blower” You need to cut a square hole that barely fits the square port on the blower, into the back of the case. You will need to find the best location depending on your particular case, but most cases should have a free spot there. If this is not feasible, ComputerNerd sells DC blowers already mounted to a metal plate that just slides into a free expansion slot. This blower will draw heated air from the CPU and PCI cards and exhaust it out of the case, as well as help draw the air from the front fan, through the case.

If your case has room(most FULL tower cases will) mount a normal 4inch (I used TWO 4 inch case fans) in the back of the case, and at the very top, above the power supply if possible, to exhaust heat that rises from the power supply and hard drives. If your power supply is at the top of the case, get a hard drive cooler that mounts in a 5 1/4 inch drive bay, and reverse the fans so that they blow air OUT of the case, and mount it in the uppermost free drive bay possible. Last, tie-wrap loose wires neatly out of the way.

This is the basic design to follow. You can move a fan if space requires it, or change the CFM of the fan to accomodate your particular needs, but you need to try to keep as close to this model as you can, to get the maximum benefit. Below is my system, and the CPU temperature that I achieve.

  • Celeron333@100×5(500Mhz) on an Abit BH6
  • 160MB generic SDRAM(max timings used)
  • Creative Labs TNT O/C’d to 112Mhz
  • Diamond Sonic Impact PCI soundcard
  • WinTV PCI card
  • 3Com EtherLink III LAN card
  • Western Digital 8.4G UDMA2
  • Western Digital 2.1G PIO4
  • Panasonic 24X CD-ROM
  • Memorex 2x4x6 CDRW, model 2642
  • DigitalDoc- thermal sensing system
  • Generic ATX Full Tower case, w/slideout MoBo tray and 300W

P/S



"System Cooling; a dual pronged approach"


page 2


I used the Sandwich design for the CPU, and for the case I have a 5inch,12VDC, 130CFM fan for the intake fan, a DC Blower from Radio shack above the PCI cards, P/S fan reversed, and two 4inch case fans in the top and back of case, above the P/S, plus a 120VAC 60CFM fan right on the top of the case to draw air up and out, like a chimney.

My thermal Sensor is set to turn on an extra DC Blower(when CPU temp hits 80F) that is pointed right at the CPU heatsinks. This aides in cooling, and is crucial in case your CPU fans ever died, the thermal sensor would kick on the emergency blower and flashes a big LED to let you know that the primary CPU cooling has failed… it may very well save you a chip someday!

The results: For temperature, in a room with 72F ambient temperature, the highest I can get the CPU to is 80F(after playing Quake2 Demo1 at 1600×1200 for over an hour straight), and the case only gets up to 74F!

WinTune 98:
CPU (1) Intel Pentium II with MMX@500 MHz
Video Board Graphics Blaster RIVA TNT (110/115)
Video Mode 1280×1024@16bits/pixel
RAM 160 MB
OS Windows 98 4.10.1998
CPU Integer 1398.985 MIPS
CPU Floating Point 558.9189 MFLOPS
Video(2D) 109.9342 MPixels/s
Direct3D 110.6907 MPixels/s
OpenGL 86.12973 MPixels/s
Memory 840.1092 MB/s
Cached Disk 86.3784 MB/s
Uncached Disk 1.266436 MB/s

Quake2:
640×480=85fps
800×600=73fps
1024×768=48fps
1152×864=38fps

Forsaken:
800×600=160fps
1024×768=105fps
1152×864=90fps

Viper Racing:
1024×768=61fps

David Nixon


squiresca@erols.com

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