Switch on and off 12V sump pump with mosfet

Discussion in 'General Electronics Chat' started by french_guy, May 30, 2013.

  1. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    Hello
    I want to install a battery operated sump pump back-up. The Wayne ESP 25 is a good one. But the charger is not that great....
    I could just buy the 12V pump and do the sensor/controler mysefl, and buy a better trickle charger
    I was thinking to use a microcontroler (I have one) to switch the pump on and off depending on the value of a sensor (connected to one of the microcontroler's input - The Wayne controler detects a high level and turn the pump ON for a deternined amount of time - I can do the same or implement 2 sensors: low and high)
    I would prefer not to use a relay, but a mosfet
    How should I do?
    Thanks
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    Is there a reason for not using a relay, to use a Fet you need to know what the current is being drawn at full load, can you show us your circuit?
     
  3. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    Well, I thought it might more difficult to find a relay. And a Mosfet would be more "straight forward" (less components)
    Or I guess i can find an automotive relay at Radioshack and use a transistor to drive it....
    I am not sure about the pump...I will have to find the specs
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
    3,834
    Since you are turning on/off high current at infrequent intervals (seconds between cycles), then a relay is a better option. A transistor and relay from the shack will be perfect. Buy a project box to stuff it into while you are there. The board always takes more space than I plan so bigger boxes are better boxes.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,042
    3,243
    You could also use a DC-DC type solid-state-relay such as this. They have a long life and provide isolation between the input and output. They typically only take 10-20mA to turn on.
     
  6. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    So this type of relay can be directly driven by the microcontroller's output?
    I guess I still need a resistor, right?
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Yes, use a resistor and observe input polarity 330 ohm. 10 mA drive, these are optically isolated, LED. Available for less with free shipping on amazon http://www.amazon.com/dp/B009X14US0
     
  8. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    Wow.....cool
    Now, I need to figure out a good water level sensor (when I say good I mean reliable.....)
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Yes, they can be driven directly form the μC.

    You usually don't need a resistor with an SSR. The typically have a built-in input resistor, thus the input is rated for voltage, such as 3-32VDC. If you go above 32V for the input then you would need to add a resistor.
     
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  10. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    That's even better.......:)
     
  11. french_guy

    Thread Starter Active Member

    Apr 16, 2009
    42
    0
    Talking about sump pump, the choice for 12V pump is limited.....
    What is best for a 12V power supply (battery): 12V pump or 110V VAC pump+inverter?
    What will give the best life span out of a marine battery? I've heard a power inverter will draw current from the battery even when it is idle?
     
  12. french_guy

    Thread Starter Active Member

    Apr 16, 2009
    42
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    Could I find the same type of relay with a timer?
    I would need the relay to be ON for x sec (x being adjustable to something like 20 or 30 sec) when input is 1, then relay goes OFF?
     
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