i’ve been trying to figure out how to make one of these for a long time. the original idea was to use in-line style pumps and heaters for an aquarium or hot-tub to heat and circulate the water bath, but the hot tub equipment was too expensive and it was hard to find information on how it worked and how to connect the parts, and the problem with the fish tank heaters is that they don’t get hot enough to cook a fish. the temperature range that i was shooting for is 100-160 degrees, and the system needs to be able to maintain this temperature for up to 24-hrs (as a maximum). through some poking around on the internet, i found that some people have been using commercial rice cookers and crock pots. so i headed down to target and picked up the largest capacity crock pot for about $40. i’m not to psyched on the oval shape of the crock pot, i think that a more uniformed temperature gradient would be acheived through a round pot, but hey, it works. upon dissassembling the crock pot, i found that the heating element is just a resistance heating band that is wrapped around the chamber surrounding the ceramic pot (this is why nothing sticks to the bottom of the crock pot).
i spliced the relay loop of a love industries temperature control module into the AC power supply to the crock pot, and bored out one of the rivets on the glass lid, so that i could fish a j-type thermocouple into the water bath, for my feedback. i dropped a $20 recirculating fish pump into the bottom of the 5-qt crock, with some tubing to channel the water in a circular fashion around the bath. the one thing that i was concerned about was burning out the circulation pump, since aquarium pumps usually do not operate at 140-degrees F (i don’t doubt that the lifespan will be stunted, but it’s $20, and i’ll probably find something better). i did a few tests for extended periods of time, running the pump at high temperatures, and during the last test i actually threw in a chuck fillet and tested it out. i replaced the variable power supply with a 12Vdc transformer, and it has been running great. check out how the fillet turned out over here.
[ps: i’m going to put some better pics of the unit up when i finally get around to making a housing for the controls and common power supply… according to the done manifesto, this probably isn’t going to happen. see #5.]