how to make a thermostated waterbath for sous vide for under $150

1. buy a temperature controller, directly from manufacturer or for less from mcmaster-carr.
2. this device runs on a logic controller programmed up to 60 C, and operates on a thermistor temperature probe, the resistance of which varies with temperature. add a constant 10 kOhm resistor in series with the thermistor in order to extend the operating range above 60 C.
3. buy an electric heating element, such as a single cup water boiler or a crock pot, but one that uses less than 1.8 kW of power or draws less than 15 Amps of current at 120 V.
4. calculate an instrument response function by measuring water temperature in an appropriate vessel such as a pot. here is one obtained by using a 8 quart pot with a 300 W heating coil.

1. 

• the linear fit in the temperature range of interest yields: Actual = 6.4 * Read - 57
• attempt to reproduce pierre gagnaire's egg cooked at 68 C (for 20 minutes) yields a most delicious entity with a delicate and uniform texture, neither "soft" nor "hard"
  

q.e.d.
thanks to emil for the controller-resistor fix
digg it