3.3V water flow meter on batteries?

  • Is there a 3.3V water flow sensor available somewhere and is it possible to run one with battery power for atleast 4-6 months?
    I guess I would want to send average values about every 5 minutes.

  • Mod

    How big is the max flow, and how small flow do you want to be able to measure?
    https://www.aichitokei.net/products/microflow-sensor-of-z/ have a range of sensors.

    Two measurement methods:

    • interrupt driven: sleep, wake by interrupt for each pulse: increase a counter and go back to sleep again
    • sample driven: sleep for x time. wake up, measure time between two interrupts, go to sleep again

    Depending on the power consumption of the sensor, the number of interrupts and the desired accuracy, method 1 or 2 can be more efficient.

  • @raptorjr A bit vague on flow range, pipe/channel, inside/outside, accuracy required....
    If it is a piped flow of clean water, a standard domestic water meter (new or second-hand) with a pulse output (reed or fet) would be my choice. Usually the meter design dictates pulse (1, 10, 100 litres) accuracy, the advantage is that no power is consumed other than to respond to the interrupt as @mfalkvidd outlined, and you have the register to cross-check results.
    I have a plastic bodied fet type (not cheap for the sensor) in the house reporting every litre back to Domoticz since last November, two AA cells currently read 3v, they will die at 0.9v sometime in late 2019 or 2020.
    I also have a gas meter reed sensor (same principle) reporting over the same period, with the same battery condition).
    Zenner and B-meter etc water meters are available down to 10 litres/pulse, the Zenner sensors are silly money but the pocket for them takes a cheap small reed switch which serves the same purpose. There are also cheap chinese apartment style domestic meters also around with reed built in.

    IMHO anything else is going to bring more problems over power supplies and accuracy...

  • Thank you for the answers.

    Of course I should have been more precise about the usage of the sensor.

    It will be a outside sensor. I want to measure the output of my water cleaning filter for my little fish pond. When the output decreases too much I know it is time to clean the filter.
    I’m guessing that the output with a clean filter is somewhere between 5-10 liters a minute. Hard to estimate. And I also guess when it gets close to 2-3 litres a minute it would be time to clean it.

    The goal would be a sensor that runs on battery for the season which would be about 6 months. During late autumn/winter/early spring the filter will not be used.

  • Mod

    @raptorjr then you could probably use the sample driven method and let the sensor node sleep for 6 or even 24 hours between each sample (and power the flow sensor through a mosfet). Getting 6 months should be easy.

  • @raptorjr You are not looking for water flow at all, you simply assumed you were...
    Perhaps a sampled differential pressure sensor, or a differential pressure switch might be your solution ? 😉

  • Mod

    @raptorjr maybe a bit out of the box, but I think a tipping bucket (like they are used in rain sensors) could be a simple, sleeping solution for your application.
    The bucket would slowly fill and produce an interrupt to the arduino once it's emptied. More flow gives more frequent interrupts.
    If you choose the size of the bucket & fill rate of the bucket wisely you can go for e.g. an interrupt per hour, which can easily be handled by a battery powered sensor.

  • Thank you for the answers. Maybe you are right and I don’t need to measure the actual waterflow. I realize now that this could be solved in a smarter way. A way that would give me 6 months of runtime.
    Maybe I need to just start testing and see what works best.

  • @raptorjr If you can figure out what the filter differential pressure should be when requiring serviced (perhaps from the filter manufacturer or a manual?), it should be possible to find a pressure switch which triggers alarm on the supply side of the filter.
    If I recall correctly, some water supply pump pressure switch controllers can be turned down to trigger between 5 and 30 psi, perhaps an old one can be found and re-purposed if it fits the range you are aiming for, however fugly they are...

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