Well Pump Controller

Well Pump Controller

So, here is the problem. My high-quality, German-made water level sensor in my water tank works some of the time. It's failure mode is to say the tank is empty so we regularly end up with a small flood near the water tank.

I was going to buy another sensor but guy who sells non-German ones in Estelí moved or vanished. So, Plan B. The in-tank sensor is a piece of copper-clad (both sides), fiberglass PC board. It's about 1 x 4 inches. I soldered wires to the two sides and covered the connection with RTV. It's mounted in the tank.

This monster then senses the change in resistance when the water reaches the sensor and turns off the pump. The pump is controlled by a solid state relay so I only need 5 or so volts at 10ma.

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What I did wrong

Just in case anyone is loco like me and decides to do something like this, let me add what I did wrong and the solution.

When the tank fills the water sloshes around. The result is that the sensor oscillates between full and not-full for a while. Even though there is hysteresis in the circuit, the problem still exists. In retrospect, two sensors at different levels would have been better.

The retrofit, however, amounts to adding a CMOS 555 timer IC as a monostable after the op amp. It will effectively ignore changes for 30 seconds at which time the water sloshing should have terminated. /end geek-stuff

low-tech solution

Just curious, why not use a low-tech solution... something like a toilet tank float. We have a 7,000 gallon tank used by 6 families and haven't replaced the switch in over 35 years. It's a small cage the size of a beer can with a small ball float in it. The ball float completes a circuit when it is at the bottom of the can and opens it at the other end. The can is on the end of a cable placed inside the tank. When the tank is empty the cage is at the bottom of its tether and the can tilts down, the float rises inside the can and completes the circuit turning the pump on. The only problem we've ever encountered is animals chewing through the ROMEX cable that runs from the tank a few hundred feet down to the submersible pump, controller and water source.

Different definitions of low tech

The float sensor I had was pretty similar and very low tech. For whatever reason, it failed.

For me, electronics (like this) is low tech. This is the same sort of thing I would have build 30 years ago (and the parts I built it with I have had for 30 years). The big plus, for me, is no moving parts.

That said, what I had, would I would have bought and what you have should work. But, mine failed.