I recently received a used dell inspiron 5100 laptop. now for those of you who dont know - this is the laptop that heats up like there's no tomorrow due to some design flaw (i think i read somewhere there's a class action against dell). anyway free is free so i wouldnt go out an buy a $50 cooler for that!
instead i decided to spend some time and build one preferably as easily and cheap as possible!
note that you will need some minor electrical experience (if you ever added a light switch or outlet you should be OK)
EDIT(dec07): the laptop finally died this week. the hdd is dead by overheating. i may replace it but it's probably a question of time until it dies completely.
EDIT(xmas07): i replaced the dead hdd with one i had around and now i'm running the internal fan at high speed all the time to keep it cool. i also got a clearance fanless logitech laptop pad for less than $10 and dremel'd a hole into it to allow air intake for cooling. hopefully it will last longer this time :)
Step 1: What you need
Step 2: Mark & cut the acrylic
you need to mark and cut the base (acrylic) depending where your bottom fan(s) is located on your laptop. make sure your hole is big enough to fit your fan.
if your laptop has multiple fans on the bottom you need to have a hole in the acrylic for each of them! if you dont you risk overheating it. you can however just add a single fan (preferably under the bigger laptop fan)
Step 3: Cut the cable & add the fan
cut the USB cable making sure you have enough length from the "normal" USB connector (which will power the fan). the USB cable will have 4 wires inside. you need to use the RED (+5 volt) and black (ground) to connect to same color cables of your fan. ignore the green and white wires. test before you make the final setup to confirm the fan is spinning. add the electrical tape over the connections.
make a note of the direction of the airflow! then check your laptop's fan. the cooler needs to drive air in the same direction as the laptop's fan. this is very important!
mount the fan in the appropriate direction (inlet or outlet).
Important note about the fan: USB ports can support up to 500mA (0.5A). your fan needs to be below this limit or it could damage your computer. most fans are rated 100-150mA (0.1-0.15A) which should be fine. fans that include LEDs may have higher power requirements however.
Step 4: Verify your work
do a visual check and be proud of the result! unless you really messed up your measurements you should be all set on this step :)
Step 5: Final touches
now remove the protective plastic foil off the acrylic. you can add some felt to assure some spacing between the hot laptop and the plastic. this will allow some of the air blown by the fan to cool the rest of the laptop's bottom.
the book you see in the picture is the final touch. it's giving you the inclined surface you need to type comfortably and allows the fan to pull/blow air. i know you can add another piece of acrylic instead of the book but this is really meant to be cheap and fast :)
Step 6: Start using your laptop!
you're pretty much done. plug in the USB cable into the USB port of your laptop, power up and enjoy! assuming you tested your electric connections before you should be all set.