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Creating a more inexpensive sous vide controller ($27)

While i was at home depot the other day, i noticed that a thermostat from an electronic
water heater could possibly used for (almost precise) sous vide. Temperature regulation
(it goes from 120 F to 150 F). The question is, i need your minds to help me in collaborating
on a circuit setup which makes this possible.

Thermostat: Costs: $14
Plug to plug your slow cooker in: $3
Pump to circulate water: $10
Total Cost: (without cooker): $27

*Future Instructable Contents*
-As the thermostat works through surface contact, Place the Thermostat
 near the top of the metal vessel.
-In order to better stabilize temperatures, make sure the heater is near 
 the bottom of the vessel. (we'll just use a heat plate or something like that)
-Use a pump to stabilize the temperature better.
-The knob just really requires better calibration.

Hystersis: 18 Degrees. The million dollar question

Just say i set it at 150 and the hystersis is 18 degrees, that means it will turn back on at 132. Especially with sous vide,
Is all that matters is that the food stay at the top temperature, (say 150) and it can go to 132 as long as the solution as a 
whole never goes above 150?
In theory, this setup will just require more time to to heat evenly and correctly.


Sources
question: http://www.privatedata.com/byb/rocketry/composites/ovens/Propellant%20and%20Composite%20Post%20Cure%20Oven.html






I'm in the process of trying to make a sous vide controller too. It looks like you must have a PID type controller for consistent temperature control without the big swings that a "normal" thermostat has.
I've ordered a PID controller from eBay that cost about double the home depot thermostat.
To minimize the temperature differences, some people use an air bubbler (like and aquarium) and others use a small fountain pump. I went with a pump since bubbling air will cool the water bath.
kelseymh6 years ago
Maybe you want to read all the MAKE magazine articles on sous vide cooking?

http://blog.makezine.com/archive/2010/01/cooking-sous-vide-the-diy-way.html
http://makeprojects.com/Project/Sous-Vide-Immersion-Cooker/471/1
http://blog.makezine.com/archive/2011/02/75-sous-vide-immersion-cooker.html
http://makeprojects.com/Project/Sous-Vide-Immersion-Heater-for-50/529/1

You will want a heat source that covers most of the "surface" of the water. Sous vide relies on both constant and uniform temperature of the water bath. If you have a localized heat source, then you can have substantial gradients in temperature.