As some of you recall from my last post (#15), I purchased a 12V submersible water pump. This pump provides excellent pressure. On the negative side, it needs to be mounted vertically to the bottom of a container and although submersed it is still noisy. For the vertical mounting I designed a pump mount that keeps it stable. For a container I chose a 5-gallon bucket with a matching lid and made three holes for the water input, output, and DC power. Each hole was enlarged to accommodate a rubber grommet. On my CNC controller box, I replaced my SS AC relay with a SS DC relay so I can turn on cooling when the spindle is energized. After I got it running, I was very pleased by the amount of flow. However, I don't think this pump has the reliability that the AC pond pump offers and including a coolant alarm wouldn't be a bad idea. I gave it some thought and decided to add a water flow meter that produces a pulse tachometer output. I designed a circuit that converts the pulses from the flow meter output to a DC voltage using a charge pump. The output from the charge pump drives a transistor so that when the pump stops it drives an LED (Coolant Alarm) to illuminate. I have the circuit debugged and it is now running on a breadboard. Below is the vertical bracket for the pump:
The schematic for the alarm is shown below:
Some key features are C1 which prevents a stalled high tach signal from charging the pump. D1 and D2 are used to rectify the pulses into pulsating DC, while C2 converts the signal into smooth DC. When the charge goes high, the voltage at the collector of Q1 goes low preventing the LED from illuminating. However, when the pulses stop, the voltage drops allowing the collector to go high, hence drive the LED on.
The flow meter is shown below:
These meters are available on Amazon for $8.30 ea.
Regards,
Rick