I also cut the cord leading to the 12V power supply (the 120V end of the power supply) at around 1 foot from where it would attach to the power supply. (Note that I also stripped the green wire, but didn't need to do this and had to tape it back up). A small section of black wire should be stripped back. The white wire is cut as this will be switched by the solid state relay. Around 1.5" of insulation is stripped back on the pump cord around 1 foot from the pump, exposing the three wires inside. Power for the 12V power supply will be taken from the fountain pump cord to allow the entire system to utilize a single power cord.
Since the two floats are located at different levels, the water in the tube does not turn the pump on when it drains back into the tank, even if the bottom float switch closes. When the water level falls low enough to open the bottom float switch, this circuit is interrupted and the pump shuts off. As the water level falls and the top float switch opens, current continues to flow through the bottom float switch, through the COM and NO pins and back to the relay coil, keeping the relay energized and the pump on. However, a feedback loop is added between the NO pin and the + side of the relay coil. At this point, the pump would shut off as soon as the water level fell to the point where the top float switch would open.
#Minitube controller for automated disp pump free
Current is now free to flow to the 120V relay, which energizes the pump. When the water level rises further and closes the top float switch (Float 2), current is supplied to the coil of the 12V relay, which closes the connection between the COM and NO pins. Since the control wire to the 120V relay is connected to the normally open (NO) pin of the relay, current does not pass through the relay and onto the 120V relay (The pump remains off). This sends current to the common (COM) pin of the 12V relay. As the water level rises it lifts the bottom float (Float 1) and closes it. 12V DC is supplied to the float switches, which are normally open when not being floated. This system utilizes two levels of float switches, a 12V relay and a 120V relay to drive the pump. I did a bit of digging online and found the relatively simple pump controller circuit seen above. The pump would constantly cycle on and off, which would destroy it very quickly. However, when the pump shut off, the water in the tube would flow back into the bucket and raise the float, turning the pump on again. It did turn the pump on when water was added to the bucket and it also turned the pump off when the water level fell low enough. We connected the switch to the pump and tried it out. However, on I found some small stainless steel float switches and ordered one. Since the bucket we were using was quite small (2-3 gallons), most commercially available float switches were too large for the system. These pumps work great, but they lack a control system to turn them on when the water level rises, and more importantly, shut them off when the water is pumped out of the bucket. For a pump I chose a very small fountain pump.
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