The 12V pump on the side of the cistern
This project can be used with a CirKits solar circuit kit.
The 12V pump on the side of the cistern
The rev 1 circuit in action
The rev 2 circuit board and sensor
The schematic
Nominal operating voltage: 12V Idle current: < 1 ma Pump Current: < 5A
The 1N4004 diode snubs out potential spikes from the motor, and the 1000uF capacitor across the motor eliminates motor brush noise from the DC wiring. The 100uF capacitor filters noise from the 12V power source. As with all electrical circuitry, it is important to have a fuse and a switch in series with the power source, that is not shown in the schematic.
The 10 amp silicon diode is used in a crowbar circuit. Its purpose is to protect the circuit from reverse DC polarity on the power terminals. Reverse polarity causes the fuse to blow.
This circuit will work with most momentary action (non-latching) hall effect sensors, you may want to experiment with the sensor and magnet to find the most sensitive orientation for both parts.
Rev 2 involved splitting the circuit into two parts, the hall effect sensor assembly, and the rest of the electronics. The hall effect sensor was soldered to a small piece of circuit board, that was then screwed onto a piece of plumbing strap. The entire sensor assembly was then coated in epoxy glue to make it waterproof. A 100nF capacitor was connected from pins 1-3 on the hall effect sensor and also covered with epoxy, it reduces the chance of the sensor picking up stray radio signals.
The rest of the circuit was built on another circuit board, that was mounted on a cover plate for a standard 4"x4" electrical box. Wires from the box connect to the sensor, the pump motor and the 12V supply.
The magnet was connected to the toilet tank float with duct tape. A better magnet mount could certainly be fashioned, but this arrangement has held up for many years. Sometimes it is necessary to cheat when working in the field. The magnet was removed from an old miniature speaker. The voice coil gap around the magnet's pole-piece was filled with silicone sealant to prevent rust. People in damp climates may want to coat the entire magnet with epoxy paint or silicone caulk.
The pump inlet is connected to a valve and reducer assembly at the bottom of the cistern tank. The pump outlet travels through a short section of conduit, into the building, and into the toilet tank via a piece of bent copper tubing. The pump inlet should be near the bottom of the supply tank, it is a good idea to run the water source through a filter made with some metal screen in a PVC pipe to prevent debris from clogging the pump. The copper tubing output in the toilet tank should be above the tank's full water level, this prevents back-siphoning.
The pump output tube and wiring is built with connectors so that the pump can be removed when the building is unoccupied. A more permanent installation can be done by mounting the pump in a metal box on the side of the building.
Another failure can occur if the supply tank runs dry. In this situation, the pump will run continuously and the motor commutator will eventually wear out. This problem could be corrected by either adding a pressure switch to the water line, or adding a timer that shuts off the motor power after a few minutes of operation.
Jameco 1-800-831-4242 http://www.jameco.com/ Digi-Key 1-800-DIGIKEY http://www.digikey.com/A 12V automotive windshield wiper fluid pump is suitable for use with this circuit. These can be found on eBay or at an automotive junk yard. A "universal replacement" style of windshield washer pump can often be found at an auto parts store, such a device is suitable for this application.