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perplexing one-way problem on Jabsco pumps

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  • #16
    In terms of amps / volts the pump actually sees, you might want to start with that first. Voltage going from the battery, through a switch, through smaller wires and to the pump could see a significant drop in voltage.

    It makes sense that your pumps would run no problem straight from the battery, there is essentially no voltage drop.

    In terms of current needed by the motor when running, the motor does not require too much. However in terms of locked rotor current, the level of amps needed to break the rotor loose (impeller vanes inside the pump housing) can be up to 10 times higher. (thats why your lights dim when your A/C unit starts up)

    The motors in these pumps dont have much giddy up in them to help them from a dead stop. Any degradation in the power supply simply will not break the rotor loose (pump vanes) and the pump will remain locked up.

    When my factory impellers failed, I went to install new ones and took note of the very small wire running from the ballast switch to the pumps themselves. Think of the wire as a hose. The bigger the wire, the more current that can pass through them.

    In terms of the pumps starting in one rotation but not the other, that may be a factor of where the rubber vanes are and in which direction they are pointed. Breaking them loose when they are pointed in the wrong direction requires more starting current.

    Good luck with it.
    16' X-10
    04' X-9.
    91' Maristar 210.


    • #17

      So I found a post that point to the problem being the relays:

      and another referenced post that discusses the relays:

      When I took off the relay / fuse box and laid it on its side, all pumps worked in both directions. So I am thinking the relays are old and got stuck. They would get stuck again and hitting the relay with a wrench solved the problem. I have ordered new relays from here:

      I will put them in and see if that finally solves the problem. Just wanted to update any future folks with the same problem.

      odd that the wires to the pump were getting proper voltages yet if they ran was dictated by the relays. I guess I don't understand the purpose of the relays...

      Previous Boats:
      2006 Mastercraft X2
      1995 Mastercraft ProStar 190, New Dimension Tower
      1990 Supra Conbrio


      • #18
        That's great is finally solved.

        High load devices need relays using full battery power / triggered by small wire & load switches at long distance.
        Picture the main battery & switches sitting next to pump.
        If switches can handle the load of the pumps - fine.

        But that's not the case - switches have very low load ability in that amp range.
        They would get hot & melt.
        You could use phone cable as the trigger voltage to the relays & relays would have the 10G wire to run the pumps.
        Of course - the relay's main power source would also need 10G wire from battery.

        Similar to key switch to starter - it can be any distance from starter - it's just the trigger voltage going there.