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Newbie: Auto shut-off for water pump based on water-level

Discussion in 'Electronic Basics' started by [email protected], Dec 7, 2004.

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  1. Guest

    Hi there,

    I am a complete newbie to electronics but am a computer geek (the
    software side). I am trying to get my feet wet with an electronics

    The problem:
    There is a electrical water-pump in my house that fills a water-tank
    that's up on the third floor. You need to climb a million stairs to
    check the level in that tank so that the water doesn't spill.

    I intend to do it all by myself using basic components and no ready
    made kits.

    The solution?
    I am thinking on the lines of a float-ball attached with a lever that
    closes a circuit when a certail level is reached. Now i know that the
    tank is full but how do i turn off the motor? Do i use a circuit
    breaker? if so how do i trip it?

    Ok, all of the above is just theory. I've never touched electronics
    before... any advice much appreciated.

    So, in summary i am looking for:
    1. How to turn off the motor when tank is full?
    2. Any info about how to do it?
    3. What equipment would i need to do it?

    ps. If this is the wrong group to be posting this to, could you guide
    me to the right one...

  2. Guest

    There is a float device you can get which looks like a flattened ball
    with a cable out of one end. You mount it with the cable tethered to
    the side of the tank. It has a switch built in which activates when the
    float is tilted downward from the cable end, ie: when the level is low.
    Connect a device like this to a small mains /motor rated relay and
    you have the whole problem solved.
    Regards, KT
  3. It's not clear to me how it works at *present*? What switches the pump
    off? And on again? Presumably you don't switch it on manually and then
    periodically traipse upstairs to see whether the tank is full?

    Anyway, I reckon you could easily adapt this circuit I suggested a
    while ago:

    Just remove Float switch 1 for the extra 'reservoir' that was needed
    in that aquarium application, and the associated components D1, D2 and

    If you'd prefer to use an NPN transistor to drive the relay, use pin 3
    instead of pin 4.

    This is just a simple bistable circuit, edge-triggered by the float
    switches so that it latches into an appropriate state until the
    alternative switch is triggered.

    You don't mention any need for a second float switch (hence my
    question about how the pump gets switched on at present). If you don't
    need one then you could replace that switch with a push-button to
    start the pump manually.

    If you want an even simpler approach (or an added precaution), wire
    the supply to the motor relay through contacts activated by the float,
    guaranteeing that the pump cannot operate above a certain level.

    And check your overflow pipe!
  4. Bob Masta

    Bob Masta Guest

    Take a look at Electronic Design, Nov 29,2004, page 90:
    "Simple Circuit Maintains Water Level Between Two Preset Limits".
    No floats needed!

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  5. Mike

    Mike Guest

    I think your schematic is beyond the abilities of a beginner that has never
    touched electronics. Even to me your schematic is a bit fuzzy, and I have
    had my feet wet in "basic" electronics for some time now... Isn't that a
    little extreme?

  6. CFoley1064

    CFoley1064 Guest

    Subject: Re: Newbie: Auto shut-off for water pump based on water-level
    I'd like to second the motion. Grainger has the Dayton 3BY58 for $22.84 USD,
    just as described in KT's response, which is made to switch pump motor loads
    (60 amp starting, 15A running). This is a trivial low cost solution to your


    * As a "newbie", you're going to have to be careful with the presence of water
    around electronics for various reasons, safety being the first. Starting out
    your career in practical electronics with a line voltage project isn't a good

    * In switching a motor, you may have problems with switch/contact arcing which
    might cause a complex circuit to be upset because of EMI

    * Even if you do have an overflow pipe, something experimental that can cost
    you significantly usually isn't a good idea for someone new to the art. In the
    event of device failure, best case is an astronomical water bill. Worst case,
    a swamped house. Pass on this one.

    Look up the device on the Grainger site and see if you can find anything like
    this locally -- I don't think you'll have any problem:

    I'm not trying to sound harsh, but if you'd just like to try a simple
    educational circuit "to get your feet wet", look at something else.

    Good luck
  7. Rich Grise

    Rich Grise Guest

    Go to your local home warehouse store and take a look at some sump pumps.
    They have a float with a couple of switches or maybe even a mechanical
    actuator. You could even ask around for a worn-out sump pump and just take
    off the switch assembly.

    Good Luck!
  8. Terry

    Terry Guest

    Exactly; it's not electronics; unless you want to make it so! It's simple
    on/off switch logic; controlled by the water level.

    Electricity flows through a normally 'ON' closed (in the low/empty position)
    float switch to actuate the pump.
    A true float switch will be designed to switch off and on the somewhat
    inductive load of, for example, a one third HP pump motor. Typically such a
    switch will last for 15 to 20 years, depending how often it cycles on/off.

    Water flows to tank, float rises, when water reaches the level you have
    preset the float switch 'OFF' and opens the circuit and electricity ceases
    to flow to the pump.
    That in its simplest form is how it would work. The float switch may have
    some sort of mechanical adjustment so that after the water is at the level
    you want it is allowed to fall again to certain extent before the pump
    operates again to refill the tank. If float switch is too sensitive to the
    water level the float switch will operate the pump every time someone takes
    one cup of water! And the pump will operate too many times.

    Also if the pumping rate is very fast/high and someone is running water
    continuously (to fill a bath tub say) the pump may fill the tank more
    quickly than the outflow so it will cut in and out several times. This may
    or may not be a problem for you? You may be able to adjust the pump flow
    rate with a simple water valve, to avoid that.

    MOST IMPORTANT. Have a gravity overflow; very slightly above your desired
    water level! Something may misoperate; without overflow there will be steady
    flow of water over the lip of the tank down through the ceilings and house
    structure until pump is manually turned off. (BTW I've seen software that
    omits that kind of 'what happens if' thinking!).
    Also make sure the overflow can't (depending on your climate?) freeze
    shut/blocked! Or goes to a drain that cannot block or backup. That is the
    over flow pipe should be of sufficient size to handle the gravity overflow.
    Whereas the fill pipe from the pump is at pressure!

    If it is undesirable to run household AC up to the float switch on the tank
    and thence down to the pump, a more complicated (perhaps low voltage )
    circuit could be devised' that could operate a relay that would actually
    switch on the pump? But that means more components (I can think of at least
    three more electrical parts and more cost) and insufficient info is
    available about what you are trying to accomplish?

    However I would comment that in all these situations 'The simpler the
    better'. If possible use standard and available parts. It's a waste of time
    to spend a long weekend trying to analyze why something doesn't work when a
    quick trip to the hardware store or building supplier, perhaps fifteen years
    from now, by someone will provide a most likely similar/identical standard
    float switch etc.

    Sounds like this is a practical plumbing and float switch job.
  9. Rich Grise

    Rich Grise Guest

    How about a toilet tank float and a pressure switch?

  10. ali

    ali Guest

    Thanks everyone, this was enlightening...

    My main motivation was not to solve the problem, but to learn some
    electronics. If the problem got solved, that's just a side-effect ;).
    So based on all of your kind input, i think i will change the project a

    I think i'll just hook the float to a rheostat or pot (i don't really
    know which at the moment) and hook the pot to an LED display which
    would be downstairs and would tell me about the level of water. I can
    turn off the pump manually with the help of the display. Surely, i hope
    this is electronics and not just plumbing ;).

    Anyway, i'll read up on all these links and be back when i get stuck...
    Thanks once again...
  11. Rich Grise

    Rich Grise Guest

    Here's some data sheets for bar graph displays:

    If the position of the pot is really proportional to the water level,
    this chip makes a really cool "gas gauge." Of course, you stilll have to
    learn enough of Ohm's Law to know what voltages to apply at the pot and
    how its position actually affects the voltage at the error amp input...

    Good Luck!
  12. Gordon Youd

    Gordon Youd Guest

    HI, I would suggest a normal float valve to let the water into the tank and
    a simple pressure switch(RS Supplies) downstairs on the feed pipe to the

    Tank empty, = floatvalve open = no back pressure, = pump on.

    Tank full, = floatvalve closed = back pressure = pump off.

    Just a suggestion :)

    Kind regards, Gordon.
  13. Raul

    Raul Guest

    Hi, I realize you want to build something yourself but you might try a
    marine store to get some ideas. They have all kinds of water
    activated/deactivated switches for pumps.
  14. Louis Bybee

    Louis Bybee Guest

    One easy to find switch that might be ideal for his application is the water
    level sensing switch used on most washing machines. Although suitable for
    pilot duty only, a visit to any appliance junk yard should be rewarding. The
    cost, flexibility of application, and availability, should make one a good

    Remove the two fish in address to respond
  15. kevreh

    kevreh Guest

    Go to this site:

    And do a search in the DIY forum. Reef tank folks (including myself) have
    discussed this quite a bit. I don't want to sound like I'm sending you
    somewhere else but there's so many different ways to approach it and issues
    to consider.

    Personally, I use a float switch from grainger that controls a solenoid
    valve. I use it to let RO water into my tank. Some people take an extra step
    and use both a low limit and high level limit float switch. As mentioned
    previously simplicity is key since water + electricity a)don't mix and b)are
    prone to failure.

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