Quote Originally Posted by drumlin View Post
These are also great for sous vide cooking. In fact there's a relatively cheap out of the box model PID controller on amazon. It's called the dorkfood I think. I have one from auber instruments and love it.

Of course never mix food and developing chems. But sometimes the technologies of food and photo making are the same.
Unless it's caffenol!

I actually did use the contraption for sous vide eggs. But even though I used fresh water (I dump at the end of every session), I did put the eggs in a plastic bag to isolate them from the water (bag with air evacuated by carefully, slowly immersing it in water, sealing it as the water reached the seal. This can be done in a separate body of water.)

I tend not to spill much chemistry into the water bath - a drip here, drop there. So I'm not too worried about damage to the pump or heating element. Chems will be so dilute that I can't imagine any harm will come.

I find the little heater I have can maintain temps easily at "egg level" sous vide temperatures (I used 63.5 C for one hour). I haven't tried raising the temp to 80 C. I'm a bit concerned it will struggle a bit at that temperature, and I don't know if the aquarium pump will survive the heat. But try it I will at some point. I am considering inserting the whole tub inside a styrofoam cooler I have, in which it fits quite well. That should help with heat retention, especially at higher temps, and should generally allow me to use less electricity overall.

While the heater will bring up the water on its own, I also recommend helping it out by starting with water that is close to the desired temperature. Saves a lot of time, and energy. I think it also saves time to accelerate the chems to temperature by either starting them in a separate, much hotter bath, perhaps in a sink, and then transferring them to the tempered bath when they are close to the desired temp. It takes a long time for a jug of room temperature chemistry to come up to the working temperature, just sitting in 38 C water.

Regarding a bigger heater: I'm not sure it is necessary, but I do think you would want a PID that drives a higher capacity relay than the internal one if you use a big heater. For development, you mostly are interested in holding a constant temperature, rather than moving the water mass to different temperature levels. The former doesn't take a lot of energy, the latter benefits from a big heater. But you might also be using a much larger bath, so it really depends on your design's requirement.