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Current rise in 12v pump

Discussion in 'Sensors and Actuators' started by Alex Scott, Sep 18, 2018.

  1. Alex Scott

    Alex Scott

    18
    3
    Jul 3, 2014
    Hi everyone

    Got a DIY project I need some help with. I know very little of motors & pumps.

    I have a 12v water pump (link to pump: https://www.amazon.co.uk/gp/product/B00EIA8UPK/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1) that I'm running from a 12v SLA battery.

    I have a hose connected to the pump and it draws water fine, however on one end of the hose I have a connector with a tap. When the tap is open and water is flowing freely the pump draws about 1amp (even though the amazon page says it should be 3 amps). When I close the tap, the pump cuts out after maybe 5 seconds however the current draw shoots up to 4 amps. It doesn't make any noise and sounds like it's safely cut off, but still drawing a lot of current?

    Is this safe? This pump is going to be running in a car and the tap is definitely going to be closed for up to 5 minutes before I get back to to turn off the power supply to the pump.

    Advice needed please
     
  2. Tha fios agaibh

    Tha fios agaibh

    1,765
    575
    Aug 11, 2014
    Yes, that's a problem.
    Sounds like the pressure switch is not opening up under pressure and its deadheading (stalling) the motor.

    I'd investigate/contact seller if there's an adjustment screw for the pressure where this switch off limit can be lowered.
    If not I'd send it back.
     
  3. Alex Scott

    Alex Scott

    18
    3
    Jul 3, 2014
    Thanks very much, looking at that Amazon link does this product look like it shouldn't be stalling?

    If not, when ordering another one what should I be looking for?
     
  4. Externet

    Externet

    632
    131
    Aug 24, 2009
    Are you shutting off a tap at the suction hose end ? If so, the outlet pressure cut-out is not sensing pressure reached; will not turn off the motor unless the motor itself has a protection that trips after a while drawing 4 amperes.
     
  5. Alex Scott

    Alex Scott

    18
    3
    Jul 3, 2014
    Sorry I didn't make that clear the tap is on the discharge end, I couldn't put the tap on the suction end it could be up to 50metres away from me.
     
  6. Tha fios agaibh

    Tha fios agaibh

    1,765
    575
    Aug 11, 2014
    That's fine, you dont want it on the suction end. I think you got the correct type of motor, its just not turning off like it should.
    It should be pumping, and when spicket is turned off, pressure goes up and should open the normally closed pressure switch which turns off motor. Either the motor cant reach the pressure needed to trip the switch or the switch is bad or set too high.
     
  7. Alex Scott

    Alex Scott

    18
    3
    Jul 3, 2014
    I think the mechanical piece that engages the pressure switch is bad. There was a small housing at the top of the pump which I disassembled and found the pressure switch. The switch works fine and will turn off the pump however the mechanical piece behind it that actuates the switch doesn't seem to literally move far enough to press the switch. There was a screw which adjusted the point at which the switch engaged however it never stayed engaged for more than 5 seconds. I thought maybe there was a leak somewhere in the line that under the greater pressure was stopping the pressure building up in the pump but it all looks fine. I just think the design for actuating the pressure switch is bad.

    That is a shame, back to the seller I think it is.

    Thanks for everyones else.
     
    Tha fios agaibh likes this.
  8. Alec_t

    Alec_t

    2,487
    642
    Jul 7, 2015
    Can't you just modify the bit that actuates the switch? It's amazing what can be done with duct-tape, Blue-tak, hairpins, wire coat-hangers etc :).
     
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