So you're keeping a dog/rabbit/cat/... outside and their water keeps freezing in the winter. Now normally you'd bring them inside or buy a heated water dish, but this animal is probably smelly, you don't have the room, and you can't afford to pay $40 for a single heated water dish. Well have no fear, because you can buy all the suppliers to make about 3 heated water dishes for about $40.
1. Stainless steel dog dish ($0.75 at the dollar store)
2. Tupperware ($0.75 at the dollar store)
a. the dog dish fits partially inside it, but has a gap at the bottom for the heater
b. is able to keep your pet from messing around with the heating element
3. A 200 Ohm 100 Watt Resistor ($10 on ebay)
4. A Thermal shutoff safety thermostat with the correct temperature range ($3.80 from Radio Shack)
a. Temperature open/off: 59°F or 15°C (below room temp which is 60-80°F, thus to cold to burn anything including your plastic Tupperware dish)
b. Temperature close/on: 41°F or 5°C (above freezing so the water/drink is always liquid)
5. Old power cables (Free, Recycled from old radios and such)
6. Thermal glue (Free, Left over from another project)
7. Cable protector (Free, recycled aluminum cans and/or sheet metal)
a. To keep the animal from chewing on the wires
b. be sure the gaps are extremely small or over lap is large, see following steps
Step 1: Thermal Glueing
Take the resistor and the thermal shutoff switch and thermal glue/paste (or weld if you're careful) them to the bottom of the stainless steel bowl. Be careful that the Tupperware still fits over the bottom of it such that there is space for the wires and so that it is protected from tampering. Note: do not attempt to solder the components to the bottom of the bowl, because solder does not stick to stainless steel.
Step 2: Securing the components
Use hot glue or an industrial adhesive (don't drill holes in the bowl) to adhere the components to the bowl. The reason for doing this is that you should not trust the thermal glue/paste to be strong enough to hole the components down. If you picked welding in step one, then congratulations you may skip this step.
Step 3: 1st Connection
Solder a wire (I used 12 AWG) between the two components. Wiring them in series like this will allow the heater to be turned on and off by the thermal safety switch.
Step 4: The Case
Melt a hole in the plastic case using a soldering iron or another tool (drilling the hole may cause the plastic to shatter). Make sure the hole is larger than the wire and leave a gap/extra-space for for the sheathing/wire protector. Run the wires through the hole so that the are on the inside of the Tupperware.
Step 5: 2nd and 3rd connections
Note: Make sure the wires are still coming through the Tupperware, because you'll have to de-solder the components if you goof this up.
Solder the power wires to the unconnected ends of the resistor and thermal protection components.
Step 6: Wire Protection and sealing
Wrap the aluminum/sheet metal around the wires so that the animal cannot chew through them. Make sure the metal is not touching the solder joints or copper wires at any point. zip tie the metal in place so that it does not move. Pull the wire through the tupper ware while seating the tupper ware on the metal bowl. Seal the tupper ware entrance area with adhesive so that no water can get into the component area.
Also seal the area between the Tupperware and metal dog dish.
Step 7: Success
Now you have 3 water dishes for the cost of buying one, way to go!!!!