This is an incubator I built to hatch out Ball Python eggs. It worked very well for me. It was about $150.00 in materials but if you had a cooler laying around, it would be cheaper.
I believe it would work well for other reptile eggs but you will need to read up on the requirements.
This incubator goes together quite quickly and will be able to hold three 10.5 x 7.5 x 4 inch "shoe boxes" per level. You can have two levels in a cooler of this size. It takes about 30 minutes total to assemble once you have all the supplies on hand. It also took about 15 minutes after it was complete to come up to temp and hold it. When you add the Egg boxes with media inside, it will take several hours to rise the media to the proper temperature so allow, at least 24 hours for all to come together prior to needing it!
I am not an electrician and I post this information for reference purposes only. This is simply what works for me. If you have any suggestions for improvements, please feel free to share.
Step 1: Materials
70 Qt Coleman (or similar brand) Xtreme Cooler
Flex Watt Heat Tape 11" Wide Tape (110V) (20 Watts per foot)
Flex Watt Cord With Attached Copper Clip Set
2" Wide Professional Foil Tape (UL Listed)
BAH-1000 Thermostat (1000 Watt Triple Plug-In)
Themometer with Probe
2 Racks (I used raised cookie racks for the bottom rack and a piece of closet rack for the top)
6 Plastic Egg Boxes (Tupperware is great!) around 10 x 8 x 4
Hatch Rite (egg container media)
Various self-tapping screws
Step 2: Assembly
The first step is to thread the power cord for the Flex Watt Cord in through the drain in the cooler. Do not attach the cord to the Flex Watt Tape prior to this step or you will not be able to get the plug through the small drain opening. Once the cord is through the drain so that the plug end is outside the cooler and the bare end is inside the cooler, connect the cord to the Flex Watt Tape as directed by the manufacturer. I then use Aluminum Tape to secure the Flex Watt Tape to the bottom of the Cooler. This is the only "Dangerous" step and you should understand how to safely wire the Flex Watt Tape prior to starting this project. Again, please FOLLOW THE MANUFACTURERS DIRECTIONS to complete the connection. Bear in mind that you are dealing with 110 volts when you plug this in. Do not leave any exposed metal showing either on the Flex Watt Tape or the cord or you will get a SHOCK!
Step 3: Installing the racking
Next you will need to add the lower wire rack to the bottom of the Cooler just above the heat tape. I like to use the Cooling Racks for Cookies on this level as they have their own raised stands raising them up off the heat source. NEVER PUT EGGS DIRECTLY ON THE HEAT SOURCE. Try to leave about 1 inch clearance between the heat tape and the racking. Measure the inside dimentions of your cooler clhttp://www.instructables.com/id/edit#osely as the walls taper in and trim the rack (if required). I use small tie wraps to ensure the legs on the cookie sheets do not fold shut. Once you have secured the legs, place this rack into the bottom of the Cooler. It will now look like the first picture.After you have completed mounting the lower rack, you are ready to install the upper rack. I use the white closet wire racks that you can buy at any Home Depot and Lowes for the upper rack. I measure and cut it to fit exactly into the internal shelf that is already built into the Cooler walls. If you did everything else up to this point as I have, it will fit perfectly. If you have modified anything up to this point you can use screws to mount the racking being sure to leave a minimum of 5.5 inches between the lower and upper racks (must make sure you can fit you egg boxes!) The second picture shows the setup with both racks installed.
Step 4: Temperature Control
You're almost done! Now you need your Thermostat. Attach the Thermostat to the front of the Cooler with screws or hooks and plug the Flex Watt Cord into the Thermostat unit. Drill a hole just large enough for the probe to fit through in the lid of the Cooler and feed the probe inside and let it extend down from the top a few inches. Set the desired temperature (88 - 90 degrees for Ball Pythons) on the dial and then plug it into the wall.
Step 5: Testing your Incubator
NOTE - please setup your cooler well in advance of egg laying to be sure everything is in working order when you need it. It can take some time for you to fine tune the temperature to where you need it and you do not want to have eggs waiting around for you to finish.
I like to put the media (not opening the bags yet) and my containers into the cooler as it would be when you have eggs. If I am expecting a full cooler with all six containers full, then that's how I set it up. If I only have three clutches expected then I only setup three. This way you can have the temperature ready to go for the volume that will be inside. I like to use Hatch Rite as it is pre-mixed and ready to go out of the bag. Set the cooler up as planned and then sit back and watch the Thermometer. You will need to set your Thermostat to the desired temperature to hatch your particular clutch. For Ball Pythons, I use 88 - 90 degrees.