It is way too hot this summer. I built this fan too keep me cool on the bus. It has a comfortable handle and rests easily on my leg.
Using a 12cm (12V, 6.8 watts) and 3 lithium ion cells from a used laptop batteries I made a powerful battery fan that lasts about 4 hours between charges.
Computer fan (12cm works best)
Batteries (used laptop cells, 3 cells for 12V)
2 fan covers
Step 1: Build the Handle
Cut out two T shapes from the plywood. Glue them to the fan.
Step 2: Make the Battery
I used hot glue to put 3 cells together. One cell should be pointed in the opposite direction. Wire the cells in series. Make sure there is extra wire at each connection for charging and balancing.
Wire the switch with the batteries.
Step 3: Finish and Charge
I used a 12V transformer to charge the batteries.
I use a 5V transformer to balance charge.
I also glued the switch between the handle sides so it is protected from accidental pushing. I positioned the switch so I could use my thumb to turn the fan on and off.