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Thread: Detecting Water system problems before...

  1. #31

    Re: Detecting Water system problems before...

    Thought I would mention, that my procrastination on this topic has ended up with the water tank being empty again this week!.

    Usually takes something like that to get me to look at the problem again... Last time I was apprehensive to hook up the SParkfun Current sensors... Wondering now if I should try a more KISS solution.

    That is for the most part I don't really need to know the current... Would get most of the valid information from simply knowing when the pumps are on and off.

    Was wondering about setting up a 4 AC power outlet box in the well house.

    Where I tap into the circuits maybe something like:

    Run a GND and Neutral to the box for the 4 outlets.
    First Plug: Connect up to Pump saver for Well 1 on either S1 in or S2 in: When power is on, the Tank is not FULL.
    2nd plug: connect up to Well 1 to either S1 OUT or S2 Out: when powered, Well 1 is running.
    3rd Plug: Connect up to second pump saver, either S1 or s2 out: when powered, well 2 is running.
    4th plug: Connect up to one of the pressure pump legs, after the pressure switch. So again powered when Pressure pump running.

    Next question would be how to convert the AC signals to DC, either 5v or 3.3v... Could use AC relays? Or would it be reasonable to use 4 cell phone charger (USB) chargers, and run the output up to the Teensy (probably 3.5 as it is 5v tolerant.

    Then it is simply reading digital inputs... Maybe use bounce code to handle like buttons...

    Still need to test to see if I can get the signal from well house to the house... Plus write simple code to record the on/off times...

  2. #32

    Re: Detecting Water system problems before...

    Using a USB charger seems like a reasonable solution. They are generally sufficiently insulated from AC to be safe to hook to digital systems.
    Any other option should be galvanically insulated, because components fail and you don't want AC power into your low-voltage stuff! If you go that way, you could use a very small transformer plus a rectifier bridge plus a capacitor plus a resistor and a zener diode -- that'd make something like a charger, on your own. Another option is a resistive divider, plus a full rectifier bridge, plus an optoisolator. (Note you need the full rectifier bridge, else the opto will be back-biased by up to the full voltage, which will break it.)

  3. #33

    Re: Detecting Water system problems before...

    Thanks @jwatte , as I mentioned using the chargers appears like the simplest solution.

    Another option as mentioned by @dgranger (PJRC) was to maybe use an opto-isolated circuit like what was mentioned in the thread:

    I think the end diagram that person used was:

    There was an additional suggestion to the above image to:
    Move the vertical diode to the right hand side of the horizontal diode and cut the dissipation in 68k resistor in half.
    Not sure if he meant left hand side of resistor? Or the user updated the diagram...

  4. #34

    Re: Detecting Water system problems before...

    Yes, this is similar to the full-rectifier option I suggested, too!

    The vertical diode could be moved so it's parallel but different-direction from the optocoupler, so pointing "against" the other diode. This will cause approximately zero amps to flow (just leakage current) but because the forward voltage of the diode is only a volt or so, it will still make sure that the optocoupler isn't overvolted in the reverse direction.

    The resistor will dissipate about 0.3 Watts on 120V and 0.6 Watts on 240V, so the savings is not negligible. Also, you need to have a power-rated resistor for this! (power 1W, and one rated for 200+ Volts if using for 120V AC and 400+ Volts if using for 240V)
    Also note that you will get a 50 Hz pulse signal, rather than a steady on signal. You can perhaps make this better with a capacitor and another resistor and a bit of re-jiggering of the values involved.

    Cheap Chinese USB charger seems simpler and cheaper :-)

  5. #35
    Join Date
    Sep 2010
    Rep Power

    Re: Detecting Water system problems before...

    This install "four new AC outlets tapped into existing devices then plug in cheap USB chargers" crap is sounding way more expensive, dangerous, and complicated than just using the current sensors you already bought for the purpose. Those split core current sensors will never require you to touch mains AC and will never transmit mains AC beyond the existing wiring, so why so apprehensive? Rip the cable sheathing if necessary, clip onto a leg of the circuit (hot1 or hot2 for 240V split-phase; hot or neutral for single-phase), maybe wrap it with a bit of tape to keep it from sliding around, and you're done.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"

  6. #36

    Re: Detecting Water system problems before...

    Thanks Guys,

    In the end I hopefully will do some combination of all three...

    I was playing around with Diptrace with using the Opti... to connect... So far the schematic looks like:
    Click image for larger version. 

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    A quick and dirty board layout 3d looks like:
    Click image for larger version. 

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    I did not put any mounting holes on it yet... Could probably do a few other things like add PU resistors or use internal to processor...

    @Tician - you are probably right and maybe I will try one of these out on one of the pumps and make sure I don't create a voltage that fries the boards...

    Why I say maybe a combination of solutions. As maybe having a set of AC outlets for some of these power outputs, may not be a bad idea. Example: The "Contactor" circuit (I think it is called), is it's own 120v circuit, which runs to top level float valve in tank, and when down the switch is conducting (The tank is not full), the Contactor than allows 4 AC circuits to apply power. That is it applies 220v to both Wells. I am wondering for example if I mount a light on the outside of the Pump house, when this circuit is active, if I might notice that the light is on all of the time? Maybe/Maybe not...

    Anyway maybe something this time

  7. #37
    Join Date
    Sep 2010
    Rep Power

    Re: Detecting Water system problems before...

    It really is not difficult to prevent a low-power current transformer from producing a high voltage output. Hell, even the super cheap SCT-013-000 current transformers on ebay have an integrated bidirectional TVS to prevent high voltages (SCT-013 voltage output variants have integrated load/burden resistors instead). If the burden resistor is on your circuit board, then there is no way to hit the Teensy with a high voltage unless you use a burden resistor value that is too large or the burden resistor is not well soldered onto the board. If you are still afraid, you have several options: 1) add a bidirectional TVS in parallel with the burden resistor; 2) add a TVS to ground on the transformer output prior to the Teensy pin; 3) add a series resistor between the transformer output and the Teensy pin to limit current if there is an over-voltage event; 4) combine all of the above by adding a bidirectional TVS in parallel with the burden resistor, a series resistor between the output and Teensy pin, and a TVS to both sides of the series resistor; etc.

    If the transformer gets disconnected from the circuit board and the burden resistor, then the close spacing of the tip and sleeve of the audio connector pretty well limits the ability of the transformer to cause a dangerous shock and it would still be of far lower current than anything plugged directly into a mains AC circuit.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"

  8. #38

    Re: Detecting Water system problems before...

    Thanks Tician,

    I think I will give it another chance... I ordered 3 of the cheaper sensors from EBAY (did one from US as should get here next week)...
    I might also again try the sparkfun ones, but their spec sheet did not show everything like what is connected to the audio plug pins...

    The spec sheet, like the one up on Seeedstudio: is more clear. Also the examples for Arduino are more geared around the EBAY ones...

    My circuit currently looks like:
    Click image for larger version. 

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    I currently have it setup for 4 sensors. Currently I have voltage dividers for each one, Probably could use one for all 4? Would probably change the 10K resistors to something smaller like maybe 2.2K?

    With the sensor, does it make any difference on which connection goes where? i.e the EBAY one shows a K and an L output leads. So wondering if this maters?

    Thanks again!

  9. #39

    Re: Detecting Water system problems before...

    Am I reading this right?

    For one amp, you'll get 1/1800th of that out, which across 22 Ohms will generate +/- 0.012 Volts, which isn't enough to push the detector much, one way or another. Is that what the winding ratio means?

    If that's the case, I'd use a much higher source resistor, a bit depending on how much current your pumps really draw.
    And if you only want "is it running" rather than some kind of analog-input current reading, then I'd also suggest adding a comparator to clean up the signal.
    (You'll still get 60 Hz pulse trains, not instant readings, of course.)

  10. #40

    Re: Detecting Water system problems before...

    Yes - I am thinking that I probably don't need to size the burden resistor to handle 100amps. The pumps are on 30 or on I believe 30 and 20 amp circuits. Not sure if I should add a certain amount of overrun of that or not...

    So if I size if for 40 amps, I think the burden should be near 58
    or for 30 amps: 77
    or 20 amps: 116

    Wondering about maybe setting it up where I have a 20ohm resistor connected to 100ohm trimmer. That way could setup each one to handle the actual values seen...

    I have not setup to use comparators yet... May try first without, just in case I get ambitious and try to really know the current...

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