Forgive my ignorance on the subject of 12 volt charging, but I want to be sure that I've been doing the right things to treat our batteries well.
After our recent grounding/extraction I noticed that the original 28 year old 20 amp (not-so-smart, always-on), 2 bank charger was humming loudly and damaged some vinyl items down the stern lazarette due to heat, so I decided to replace it with a smart 3 bank charger by Xantrex and added the temperature warning attachment and the remote read-out unit (see photos, note: I added a 4" square vent in the foreward, outboard-most wall of that under-seat cubby to release the heat of the charger fan/heat sink -- VERY quiet). After a 1.5 hour trip under power with all three batteries turned on to start and while underway, once back at the dock all three were showing as charging, while I had naively expected the alternator to have topped them up to replace the energy I'd used to heat the glow plugs. Clearly my expectations were incorrect, hence these questions:
- Is it the case that, unless the switch is set to "ALL" and the independent starter battery is also switched on (all three batteries are then being used to start the engine and are under some load while underway from the USB power to the phones, instruments, the Admiral using the water pump, etc.), that the alternator is NOT charging them while underway? (i.e. The batteries will not get charged while the motor is running if they are not turned on at the switches.)
- I believe I've read a warning that, once the engine is started, the battery switches should not be turned on or off. If this is the case, what damage can be done by doing so?
- If I am doing the right thing in order to charge the batteries while underway by turning them all on (I realize that this is not necessary, but if #2 is true and I do not switch the starter battery off and turn the house batteries on once the engine is started, then we would be tapping into the starter battery and alternator for any load while underway), then how long, theoretically, would it take before all are back to fully charged by the alternator (seems to reliably output 14+ volts)?
We regularly cross Lake Ontario by motor (5 to 8 hours, depending on the destination) and, after early disasters while we were brand new to the boat with the two batteries dead and no backup or generator available, I am a tad paranoid about making sure the batteries are as well charged as possible. Any feedback would be appreciated!
'91 C-36 Mk. "1.5" Tall Rig, Fin Keel, Hull #1120, Universal M-35 original (not "A" or "B")
CBYC, Scarborough, Lake Ontario, Canada