Turn off water pump

Discussion in 'The Projects Forum' started by Rushdev, Feb 4, 2012.

  1. Rushdev

    Thread Starter New Member

    Feb 4, 2012
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    Hi, I'm new and hope that someone can help me. My electronic knowledge is limited, but I can solder...

    Last night my water pump stayed on all night long and drained my 3000 gal tank (Javelinas broke a faucet...) I'd like to have a circuit that sees when the 120vac pump has been on for 2 min and then A) shuts a relay off that is connected to the pump, does not reset and B) turns on a light signaling something is wrong.

    Is there a relatively easy circuit like this that I can build or buy?
    Thanks in advance.
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Sounds like Southern AZ? A preliminary wild thought from Tucson: To avoid contact with 120 V AC, a no-no here, look for a short section of hot lead where a clamp on induction pickup could be located. Or supply information on present relay drive circuit to include operating voltage. With an input signal available a 555, with a 2 min integrator on pin 6 will act as a flip-flop, output going high if signal lasts for more than 2 min. A NC relay on output would interupt control relay coil current, shutting off power, & turn on warning light. A high on pin 6, or power interuption would reset.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Don't know that there's anything off-the-shelf that will do exactly what you want, that is, a delay timer that will only time out if the pump is on more than two minutes but will not reset once a time-out has occurred. Thus you likely need to build some electronics like Bernard suggested with a time delay and a FF latch driving a motor relay. It's a reasonably simple circuit but will require building the circuit on some type of breadboard. We can give you more help with that if that's what you want to do.
     
  4. Rushdev

    Thread Starter New Member

    Feb 4, 2012
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    Bernard
    Good guess - I'm in Tucson also, well Three Points actually.
    I sort of understand what you're saying, but I'm not sure how to actually make it work, wires, connections, components etc. Is it possible to get a simple schematic?

    Crutschow - Right, I don't want it to reset. I want the light to go on and the NC relay to open, shutting the pump down. That way it will not run continously and I can take care of the problem and reset the circuit. I have no idea what a FF latch is... like I said, I can solder..
    So yes, any help would be greatfully appreciated.

    Thanks
    Rush
     
  5. Rushdev

    Thread Starter New Member

    Feb 4, 2012
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    So I've been doing a little googleing and from your words/descriptions above - I put a current transformer on the hot leg (no problem, I did the wiring from the panel to the pump), and there is a circuit that reads the current going thru, translates it to volts. If that current lasts more than 2 minutes the 555 in the form of a flip flop latch opens a relay, 120vac rated at 20 amps (or whatever the pump draw is) that is Nominally Closed, thereby stopping the pump. Also on the relay is a Nominally Open switch which closes to turn on a light, signaling that the pump has been turned off. And the relay will have to hold on till I come and turn it off, reset it, after seeing why the pump went more than 2 minutes.

    I think that is it, but I need the specifics, a schematic.
    Thanks
    Rush
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Still need relay operating voltage, AC or DC? Is relay controlled by a pressure sw? The more information available , the closer we can meet your need.
     
  7. Rushdev

    Thread Starter New Member

    Feb 4, 2012
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    The relay in the pump is a 120vac relay that is operated by a pressure switch, it is on a line with a 30A breaker.

    But isn't the circuit I want basically independent of the pump? I want to monitor the time that there is current flowing in the power line to the pump. When it exceeds 2 minutes, the monitoring circuit will open a NC relay that is in line with the power line, not the relay in the pump. Or am I missing something?
    Thanks
     
  8. crutschow

    Expert

    Mar 14, 2008
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    After some further thought I believe you can do it with off-the-shelf devices, namely an "ON" time-delay relay (such as this) and a standard DPDT relay. The time delay relay would be triggered by the pump turning on. If it times out, it applies power through its contacts to the standard relay which turns off the pump. To keep the standard relay latched you use the second set of contacts to apply power to its own coil when the contacts close. You release the relay with a momentary switch in series with the second contact.

    See attached for a schematic. I didn't have exact symbols for the devices so bear with me on that. The relays need to operate from 120VAC, of course.

    Edit: Corrected schematic.

    Pump Delay.gif
     
    Last edited: Feb 5, 2012
  9. Rushdev

    Thread Starter New Member

    Feb 4, 2012
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    Carl,
    I'm not sure the H3JA will work, the specs rate it at 120vac/7amps for either a conductive or resistive load (motors are resistive?). The name plate on the motor says 115vac/12.7A, Max Amps 17.4. I guess that is the running amps, not the lock-up or start amps. My understanding is that the lock-up amps can be double the run amps, that is why my pump guy told me to put it on a 30A Breaker.

    Rush
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Look at the schematic. The H3JA doesn't carry the pump current. Only the auxiliary relay controls the pump.
     
  11. Rushdev

    Thread Starter New Member

    Feb 4, 2012
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    OK, let's see if I understand the schematic..
    U2/Time Delay is the H3JA-8A (SPDT)
    U1/Aux Relay is a NC 120vac/30A relay or contactor with a 120vac coil
    U4/Pressure switch and L1/Motor is my existing Pump
    U3 is a switch (on-off)
    Indicator is the light

    My pressure switch actually has a throw for each leg of the power, so I modified your schematic, Revised schematic.jpg

    Is this how it works?

    AC_Pwr2 always flows to pressure switch U4-2 directly.
    AC_Pwr1 flows to pressure switch thru the top switch in Aux Relay U1, Nominally Closed
    When the Pressure switch turns on, it energizes the motor and also the time delay (which is set to 2 min), if after 2 min the motor is still running, the Time Delay relay energizes the coil, which in turn energizes the coil in the Aux Relay, disconnecting AC_Pwr1, and also lighting the Indicator.

    The Aux Relay coil holds the pump circut open and the indicator light closed until it is reset by U3 Reset.

    Thanks
    Rush
     
  12. crutschow

    Expert

    Mar 14, 2008
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    That should work, but if you want to switch both sides of the line with the relay, the same as the pressure switch does for safety reasons, see the revised schematic below.

    Pump Delay.gif
     
  13. Rushdev

    Thread Starter New Member

    Feb 4, 2012
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    Great! Thanks a lot.

    An electronic version using the 555 would be more educational (and fun to build) for me... how much more complicated is it to use that in a circuit?
    Thanks Rush
     
  14. crutschow

    Expert

    Mar 14, 2008
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    A 555 circuit would be somewhat more complex then the relay design. You need the 555 connected as a power-on-delay (Circuit #2, except connect to the relays NC contacts). The relay would be a DC coil type instead of AC. And you may need to add a transistor buffer to drive a large power relay from the 555 output. Of course, you also need a DC power supply to power the circuits (a wall-wort type supply would do).

    Adding the latch capability complicates the circuit and I don't think that you need it. If you power the 555 circuit from the output of the pressure switch and put the relay contacts between the pressure switch and the motor, then the relay will stay pulled in as long as the pressure switch is activated. Isn't that all you need?
     
    Last edited: Feb 7, 2012
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