Battery Wiring

Battery Wiring Notes

3 batteries:

  • #1 Bank (from house bank selector) is STARBOARD Battery

    • 8D battery

    • House, Starter, and charger connections

      • Older, thicker wire appears to be the house wire.

      • Newer, smaller cable appears to go to starter / engine wiring

    • Battery appears to be VERY WEAK - will NOT start starboard engine on it's own, must be paralleled.

  • #2 Bank (from house bank selector) is PORT Battery

    • 8D battery

    • House, Starter, and charger connections

      • Older, thicker cable appears to be house wire.

      • Newer, smaller cable appears to go to starter / engine wiring

    • Appears to be in acceptable condition

  • Generator Battery

  • Battery Selectors

    • Engine Room / Engine Selector

      • Port (left hand) switch turns on batteries - BOTH batteries disabled if switch is OFF.

      • Starboard (right hand) switch selects whether to jump the batteries or not.

    • House Bank Selector - at top of main electrical panel.

      • #1 is starboard battery, #2 is port battery

      • Switch has historically been in "both" position (starboard battery is bad)


Observations

  • Engines MUST have port/starboard respective house wire to be able to start. Apparently, some of the engine functions are run from the "house wire".

    • Therefore, it is not obvious that it will be easy to separate out the "house" load and put it on a separate battery, without significant re-wiring.

REPLACING THE BATTERIES

  • The 8D batteries were removed 6-6-22, and replaced with golf cart batteries. Two batteries in each box, to give 12V at over 100AH. After batteries replaced, found that engines still would not start on a single battery bank - both batteries had to be wired in parallel to start either engine.

  • 7-3-22 Battery connections moved to terminal strips at the two main battery banks and the generator. A new Group 27 AGM battery was installed in the generator battery box, and wired to the house (running cables from the "generator battery" to the bus terminals at the starboard battery position. Main battery connections removed from the starters on the port and starboard engines, and terminated. 4 Ga wire cable was run from each engine to it's (isolated) golf cart battery set.

  • Mid July 2022 New 150Ah 12V Lithium battery purchased for the house battery, to replace the AGM group 27 house battery.

BATTERY STRATEGY:

Ultimately, I would like to have a single group 27 AGM starting battery for each engine, and a large lithium bank for the house.

The AGM starting batteries are needed to work most effectively with the alternators on the engines. Lithium batteries have two issues that prevent them from being easily used as starting batteries: 1) when they are fully charged, the internal BMS will cut of the battery, resulting in no load on the alternator, which would most likely fry the diodes in the alternator. 2) Lithium batteries can suck HUGE amounts of current when charging, and would most likely overload a typical old school alternator. The FL120 engine is expected to start with a very modest 420 cranking amps (ASSUMING the wiring is reasonably short! which was clearly not the case with the way the boat was wired when I purchased it!!). Thus, a single group 27 AGM battery should be PLENTY as a stating battery for these engines - but MUST be isolated from the house loads that would quickly drain it.

The house has a number of high loads. The engine blowers may be as much as 10Amps. The refrigerators are currently wired to run on DC only, and easily draw up to 10A. I don't yet know what the real drain of the GPS, radar, and other instruments are - but expect that to be several amps. I have replaced the running lights with LED equivalents - saving about 10A of drain in that action!

After shopping batteries, it seemed a 150A LifeP04 (Lithium Iron Phosphate) battery was the best bang for the buck to start with. The 150AH 12V lithium fits in a Group 31 battery box (barely), and only weighs 26 pounds! (as opposed to the ~120-160 pounds of an 8D battery that has perhaps less available capacity!)

I bought a Victron battery monitor to put on the lithium house bank (the monitor also has a spare voltage monitor lead that I can used to keep an eye on at least one of the stating batteries). This will allow me to install the lithium battery and then start monitoring the real loads/drain.