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Grundfos Pump MQ3-45 110v

Discussion in 'Technical Discussion' started by CSkipR, Apr 25, 2012.

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  1. CSkipR, Apr 25, 2012
    #1
    CSkipR

    CSkipR Member

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    Just installed my second pump in 3 years and it has quit. Great pump when it worked. Any ideas it keeps tripping the breaker and will not start. Naturally it is located in a tight spot in the boat so its difficult to get to. Have tried to find an internal diagram of the pump with no success. Any ideas?
  2. Capt J, Apr 25, 2012
    #2
    Capt J

    Capt J Senior Member

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    Check the breaker and make sure that the breaker isn't getting weak. I usually see 110 volt freshwater pumps only go 2-3 years on most boats.....I just replaced a Grundsfos a year ago in a boat that was built in 2007.....So it went 4 years.
  3. Beau, Apr 25, 2012
    #3
    Beau

    Beau Senior Member

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    Skip
    My 110v has been operating since 1998. Next time I'm at the boat, I'll try to note the manufacturer if I can get my fat butt past the gennie
  4. C4ENG, Apr 27, 2012
    #4
    C4ENG

    C4ENG Senior Member

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    When I have a breaker tripping one of the first steps I do is test for a ground fault. Very easy to do, get a voltage meter and set it to continuity (I like it where it beeps for a close circuit). Open the breaker panel and with the breaker off, put one test lead on the 110V out put and the other test lead on the ground bar or any other ground. You should have no continuity. If you do, your shorted some where and your breaker is doing it's job. You might find a wire chaffed or a million other things but that's when it gets fun!
  5. captholli, Apr 27, 2012
    #5
    captholli

    captholli Senior Member

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    Unless you have a faulty circuit breaker (possible) MQ3-45 rated for 9.2 amps on start up. but if you have a spare or another same amp rated breaker close by in the panel than move the load side (pump) wires to the spare/ breaker and test the pump. If it blows than your gonna have to pull the pump and go a bit further .
    This Grundfos has a proprietary run dry protection circuit and a pressure sensor so in the old days that would have been a thermistor or a thermocouple but in todays technology who knows , LED switched sensors??
    I dont know but outside of the obvious like the windings shorted to ground or the wires being loose in the j- box sounds like a motor issue as the pump head is a multi stage centrifugal deflector/impellor type that takes alot of abuse before its capable of binding so hard that it would stall a motor and blow the breaker and as I said before the pump has run dry protection so it shouldnt have melted any plastic-poly parts in the pump head. Its down to pulling the pump and breaking it down in components to investigate or just take it to your local dealer and get the best possible price on a new unit and rebuild this one for a spare.
  6. CSkipR, Apr 27, 2012
    #6
    CSkipR

    CSkipR Member

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    Will check the breaker. If I'm not mistaken the pump draws about 29 amps at startup. 115v. If I don't find faults with breaker will pull pump. Would like to be able to turn shaft with screwdriver but cannot get to backside of pump. Thanks
  7. Capt J, Apr 27, 2012
    #7
    Capt J

    Capt J Senior Member

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    I did a search under the model on the one we had and they had circuit board issues for the first few years. Ours did the same thing yours did, the motor was siezed and it blew the breaker instantly.