12 Volt Toilet Tank Refiller

Description: A flushing toilet is often taken for granted by city dwellers, but it can be a luxury for those living off the grid without access to utility water and electricity. This circuit enables on-off pump switching for a small 12 Volt pump that fills a toilet tank from an external rainwater collection cistern. The power for the 12 Volt system is supplied by a small solar power setup. The cistern is positioned at ground level, necessitating the pump to lift water to the toilet tank. The Panasonic Hall effect sensor serves as the core component of the system. This sensor's output pulls to ground in the presence of a strong magnetic field. When the magnet is removed from the sensor's vicinity, the output returns to high through a 10K pull-up resistor, activating the IRFZ34N MOSFET transistor, which connects the negative lead of the 12V pump to ground, thereby turning the pump on and illuminating the LED. A 1N4004 diode protects against voltage spikes from the motor, while a 1000uF capacitor across the motor reduces brush noise in the DC wiring. Additionally, a 100uF capacitor filters noise from the 12V power source. As with any electrical circuit, a fuse and switch in series with the power source are recommended, although these are not shown in the schematic. A 10 amp silicon diode is included in a crowbar circuit to safeguard against reverse DC polarity, which would blow the fuse. This circuit is compatible with most momentary action (non-latching) Hall effect sensors, and experimentation with the sensor and magnet orientation may enhance sensitivity.

Construction of the initial version of this circuit placed all components inside the toilet, which proved problematic as water splashed onto the board, leading to corrosion. The second revision separated the circuit into two parts: the Hall effect sensor assembly and the remaining electronics. The Hall effect sensor was mounted on a small circuit board, secured with plumbing strap, and coated with epoxy for waterproofing. A 100nF capacitor connected between pins 1 and 3 of the sensor was also covered with epoxy to minimize interference from stray radio signals. The rest of the circuit was constructed on another board, mounted on the back of a standard electrical box, with wiring extending to the sensor, pump motor, and 12V supply. The magnet was attached to the toilet tank float using duct tape, although a more secure mounting method could be developed. In damp environments, sealing the magnet with silicone or epoxy paint is advisable. The pump inlet connects to a valve and reducer assembly at the bottom of the cistern tank, while the outlet runs through conduit into the building and into the toilet tank via bent copper tubing. The output should be positioned above the highest water level to prevent back-siphoning. Another modification in revision two included a water filter before the pump to prevent debris from clogging it. The pump's output tube and wiring feature connectors for easy removal when the building is unoccupied. A more permanent installation could involve mounting the pump in a metal box outside the building. The metal strap holding the PC board should be bent to align the Hall effect sensor directly above the magnet, and the board's height should be adjustable to ensure the circuit shuts off at the desired water level. Upon flushing, the red LED lights up, activating the pump to fill the toilet tank, which will shut off automatically once the water level reaches the top.A flushing toilet is something that most city dwellers take for granted, but it can be a luxury for those who live away from utility water and electricity. This circuit provides on-off pump switching for a small 12 Volt pump that is used to fill a toilet tank from an external rain water collection cistern.

The 12 Volt power comes from a small sola r power system. The cistern is located at ground level, so the pump is required to move the water up to the toilet tank. The Panasonic hall effect sensor is the heart of the system. The hall effect sensor`s output pulls to ground when in the presence of a relatively strong magnetic field.

When the magnet is pulled away from the hall effect sensor, the output goes high via the 10K pull up resistor. This turns on the IRFZ34N MOSFET transistor, which pulls the negative lead of the 12V pump to ground, turning on the pump.

The LED is also turned on. 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. Construction The rev 1 version of this circuit had all of the parts inside of the toilet. This turned out to be a bad idea as water splashed onto the board and electrolysis corroded the electrical connections.

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 the back side of a standard electrical box with wires running 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. Sometimes it is necessary to cheat when working in the field. If the magnet has a gap around the side, fill it with silicone sealant to prevent rust. People in damp climates may want to seal the magnet in epoxy paint. 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 copper tubing output should be above the highest water level to prevent back-siphoning. Another rev 2 modification was to put a water filter ahead of the pump, that prevents gunk from the tank from clogging the pump. The pump output tube and wiring were built with connectors so that the pump could be removed when we are away from the building.

A more permanent version could be made by mounting the pump in a metal box on the side of the building. Bend the metal strap that holds the PC board, so that the hall effect sensor is directly above the magnet.

Adjust the height of the PC board so that the circuit shuts off at the desired water level. Flush the toilet, the red LED will light up, and the pump will move water into the toilet tank. As soon as the water level reaches the top, the pump will shut off. Just like in th