randynealpetersen:
Peter_I:
I have used the "Fotek SSR 25DA" for most of the sous vide controllers I have built.
You can find it at dealxtreme or ebay at a very reasonable price.It needs a low current for switching, meaning that you can connect the Arduino directly to it. Furthermore, being able to handle 25A, I've controlled a 2kW heater with it, and it just got luke warm in spite of only using a piece of aluminium plate for a cooling fin.
Thanks for the help, I am waiting for a 10A SSR I bought off of Fleabay. If it gets hot I will definitely buy the one you recommend, it sounds tough. You use a 2kW heater? Interested in knowing more about the controllers you have built. Did you share you process anywhere, or would you care to? Thanks! Randy
Very simple:
Commercial PID-controllers (My first one was a second-hand Eurotherm, the next four has been cheap chinese controllers... they all work fine, but the eurotherm is the best by a small margin).
The eurotherm did not have an autotune function. It was fun to do the datalogging and Ziegler-Nichols, but it is so much easier to push AT and lean back.
I use a slowcooker controlled by the PID through the aforementioned SSR, and it works great.
I have also used a ricecooker (higher wattage, easier tuning) and a BIG pot insulated with a towel and heated by an immersion heater.
Tuning is important for stable temperature.... and do not trust the temperature calibration! One of the controllers were 4° off when I got it. Thermocouples can be a little tricky too, and be a couple of degrees of the mark.
(Relative temperature is easy, absolute temperature is a little harder)
I have used Type K couples, but Pt1000 or LM35 would be a wiser choice for the low temperature region of gastronomy.