Voltage drop at the water pump

In the middle of all the re-wiring work Dad and I did over the weekend, I noticed that the water pump didn’t sound like it normally does. It was only once or twice before it returned to sounding like normal, but it was enough of an anomaly for me to start poking at it.

With a voltmeter across the terminals at the pump end, Dad opened the tap, and to my dismay, the voltage went from 12.3 to 9.9. That’s a clear sign of something causing resistance issues.

We tried a few things to validate the hypothesis of undersized wiring.

  • Run fresh 12 AWG wire from the wiring locker to the pump
    • Small change in the voltage drop, for the better
  • Use the fresh 12 AWG in parallel with the existing wiring
    • Small change again, for the better. About 1/2 a volt
  • Change the chocolate block terminals for Wago connectors
    • Another 1/2 of a volt
  • Use the wandering lead to the PowerPole distribution point by the battery compartment; 20 amp circuit right next to the battery
    • Better again, but still dipping under 11 volts

Our conclusion is that the wiring running across from the battery compartment to the wiring locker is undersized for the current requirements of the Jabsco Par-Max4 pump; the Jabsco site says 15 amp draw, and the run of wire is probably too long given the size.

The easy solution will be to run a fresh 8 AWG cable from the battery compartment to the water pump compartment, for both the positive and negative lines. This should greatly reduce the run of cable. I have the positive run already, but will need to order a new negative run to suit.

We noticed that with shore power connected, and the Wago connectors in place, the pump runs much faster for a much shorter period of time; draws more amps when it does run, but my feeling is that the shorter run more than offsets the higher draw.

I’ll probably also work on replacing the cables that cross the boat in to the wiring locker with something a bit heavier, and put a heavier bridge between the negative bus bar and the fused bus in the wiring locker.