How to design a Transfer pump on/off circuit

Discussion in 'Digital Circuit Design' started by ralphspa, Sep 20, 2016.

  1. ralphspa

    Thread Starter New Member

    Sep 12, 2016
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    I have a 12 volt oil transfer pump that a computer controls on/off. It transfers oil from main tank on boat to remote tank on outboard motor.
    remote tank on motor has low/full level pair of switches that send a ground signal to computer depending on oil level. i would like to design an electronic circuit that will trigger pump to come on when low level switch grounds out and keep pump on until full level switch tell curcuit to turn pump back off.
    I am unable to come up with an idea that will do this.
    Any help would be appreciated
    Thanks in advance
    Ralph
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Welcome to AAC
    It is easy.
    Need some info though.
    1. Operating Power of pump and available battery voltage.
    2. What kinda limit sensors are used to sense empty and full conditions.
    3. Do you have excess to these sensors wire terminals, if not do you plan on to install sensors.
    And any other info you have will help.
     
  3. ralphspa

    Thread Starter New Member

    Sep 12, 2016
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    So I finally have some info needed.
    Pump only draws 1 amp at 12 volts dc.
    I have sensors accessible. Low level sensor pulses a ground when level low. A second pulses ground when full.
    I'm not sure what kind of sensors they are tho. I can't seem to find info on that.
    Any help would be appreciated.
    Thanks
    Ralph
     
  4. ralphspa

    Thread Starter New Member

    Sep 12, 2016
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    Oh I forgot to mention pump needs a ground output from circuit.
    Thanks again
     
  5. crutschow

    Expert

    Mar 14, 2008
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    A RS latch circuit driving a MOSFET should do the job.

    Since you didn't post where you live I don't know what electronic parts suppliers you have ready access to. :confused:
     
  6. ralphspa

    Thread Starter New Member

    Sep 12, 2016
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    I can get most electronic parts here in Hamilton Ontario
     
  7. ralphspa

    Thread Starter New Member

    Sep 12, 2016
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    Can anyone help me out please?
     
  8. R!f@@

    AAC Fanatic!

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    @crutschow suggested a simple method.
    Since I can program simple code I would use a small micro (PIC) to do the job.
    If you can program I can write you a little code for the Job
     
  9. R!f@@

    AAC Fanatic!

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    By the way what is the voltage at the sensor output when the sensor in not active?
    That is when sensor is not grounded or not it limit.
    And I believe the system is a 12VDC one.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Below is he LTspice simulation of a circuit that I think does what you want.
    The simulation shows the motor current for the Full and MT (Empty) switch operation.

    I picked a common N-MOSFET to drive the motor, but any N-MOSFET with a voltage rating of ≥50V and an ON resistance of <0.5Ω should work.

    The CD4011B is a CMOS NAND gate configured as a latch (4 gates in one package). The actual part number may contain some additional letters depending upon the manufacturer.
    Note that you need to connect pin 14 of the IC to V+ and pin 7, as well as all unused inputs (not outputs) to ground.

    R_Motor simulates the motor load and is not part of the built circuit.
    D1 absorbs any motor transient voltages to protect the MOSFET.

    upload_2016-11-2_15-47-42.png
     
    Last edited: Nov 2, 2016
  11. ralphspa

    Thread Starter New Member

    Sep 12, 2016
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    Unfortunately I have knowledge of programming whatsoever. I only have automotive electrical experience and some basic electronics experience. I could build a circuit on a breadboard if I have a diagram and parts list tho.
     
  12. ralphspa

    Thread Starter New Member

    Sep 12, 2016
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    I will look into sensor relaxed voltages and energized voltages tomoro if that helps

    Thank you
     
  13. crutschow

    Expert

    Mar 14, 2008
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    My circuit requires no programming (why did you think it does).
    It operates as shown, nothing else required.
    Where would you buy the parts (Digikey, Mouser, Jameco...)?
    Can you wire it following the schematic I posted?
     
    Last edited: Nov 2, 2016
  14. R!f@@

    AAC Fanatic!

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    @crutschow
    I think OP missed your post.
    He was replying to my post
     
  15. crutschow

    Expert

    Mar 14, 2008
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    Apparently.
    Although he quoted from my post. ;)
     
  16. ralphspa

    Thread Starter New Member

    Sep 12, 2016
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    Sorry got confused with other poster R!f@@
    My bad.
    I'll look into parts
    Thank you very much
     
  17. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    First pass at an alternate solution.

    The ULN2003 has seven individual small power darlington transistors, with a common ground and a transient protection diode on each output. Each one is rated for 50 V and 0.5 A. It makes a great logic device for rugged environments, with each section acting as a high voltage open collector inverter. The small schematic in the corner shows the internal connections of each section. Two sections back-to-back form a flipflop, and five sections in parallel form the output motor driver. One chip, 2 resistors, no capacitors.

    ak
    Transfer-Pump-1-c.gif
     
    crutschow likes this.
  18. crutschow

    Expert

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    Hard to beat just one component. :)
     
  19. R!f@@

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    I admit, that is unbeatable.
     
  20. crutschow

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    Mar 14, 2008
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    Actually I forgot about the two resistors. :rolleyes:
     
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