Safety Float Switch
I considered version three of my immersion circulator a success, I had used it sous vide several meals. One morning before work we turned it on for meal that night, and left before the water had come up to temperature. When we got home that night we found a hot mess. I don’t know for sure what happened, but I suspect that the PID overshot its temperature and boiled away most of the water to the point where the heating element burnt out. By that time the entire plastic enclosure was melted including the SSR and the PID. At this point I didn’t have a heat sink on my SSR, so it’s possible that the heat from the SSR is what melted the components within the enclosure.
After this I learned to make sure that my water bath is holding a temperature before I leave. Once it’s holding a temperature it’s relatively safe to leave. The heating element is only coming on for short bursts and the PID shouldn’t have a problem. However, the fact that we weren’t home when this happened scared the bejeezus out of me. So I decided to add a failsafe into version four. That’s where the float switch comes in.
If the water starts to boil away, before it drops to a dangerously low level, the float switch will cutoff power to the heating element, stopping the chain reaction before the element burns out or my house burns down.
Following are the instructions for mounting the float switch and wiring it up:
- Screw one end of the brass pipe into the brass coupling, the screw the float switch into the other end of the brass coupling.
- Drill a hole into the bottom of your enclosure (I drilled my hole between the clamp and the heating element, just make sure it’s out of the way of the pump); make sure that you start small and work up to the size of the brass pipe.
- Screw the brass pipe, into the bottom of the enclosure. (If the hole is to large, you may need to use plastic epoxy to hold the pipe in place.
- Once the switch is mounted, you should wire it in line between your PID SSR output and your SSR. The wiring on the switch is too small to handle the current that will be drawn through the heating element. The current through the control path is much smaller on the other hand and the net effect is the same. When the float is down, the relay will not be powered and the heating element will not be on.