I have an Eccotemp L10 2.6 GPM portable tankless water heater that has two adjustment knobs, one for cold water flow and one for hot water flow. This heater is bolted to the outside of a shed due to venting requirements (uses propane). Inside the shed I have a rudimentary shower set up. Trouble is, based on input water temperatures and ambient outside temperatures the “shower” can be to hot or to cold, and adjusting it requires stepping outside the shed, walking around to the heater, adjusting the hot knob, going back in, and testing. I know there are other ways to solve this issue (cut hole in wall and reach thru, move heater inside and install appropriate vents, etc), but what fun is a simple solution when I can complicate things a bit!
This seems like a perfect opportunity for me to learn about stepper motors! What I want to do is get a stepper with the same shaft size as the knob shaft, couple the knob shaft to the stepper, then wire it to an Arduino I can mount inside the shed, and use a potentiometer or similar “adjustment” tool (maybe even a temp sensor for self regulation) to control the stepper and adjust the hot water knob.
Here’s the concern. I know nothing about steppers. When I look at steppers in the NEMA 17 or 23 range it looks like they are really low torque. The knob on the heater is easily turned by hand, but I have no way to easily determine the torque required to do this, and I have no idea what the usable torque is on these NEMA steppers. It looks like the “holding torque” is in the range of 50Ncm to maybe 2Nm, and that doesn’t seem like much. I figure a stepper is a good choice as I only need to turn the knob around 150°-180° of rotation, so having good control on how far the stepper turns is a good thing.
Any advice on what the usable torque is on these NEMA 17 or 23 motors would be helpful. Do you think they’d “turn a knob”. I suppose I could use gearing or something (belt drive), but I don’t want to create a Rube Goldberg machine (well, maybe I do).