I should be able to leave equipment like the refrigerator on during the week as long as shore power is plugged in, shouldn't I?
Mike
Mike,
Couple of thoughts.
While convenient to have the fridge
always on there is
always risk in doing so.
Risks:
* Marina power is anything but reliable. Muffy & Skippy unplug your cord when heading out on the Sea Ray and forget to plug it back in. A breaker trips because the pedestal was over loaded etc.. Darrell & Darrell are working on the dock system and forget to re-power your finger pier..Your own boat develops a fault and AC is interrupted etc.. A transient boater comes in and trips the docks ELCI or GF circuit taking your finger pier out. These are
not at all rare incidents especially when you do this sort of work for a living. While folks can & do get lucky, sometimes for many years, this still represents and n=1 data set and is not something to rely on. Running dockside DC loads, that relay on the battery charger, are simply risky.
* Not all chargers are actually
smart. A fridge compressor load can kick many chargers back into absorption mode and wind up actually over charging the batteries. One would think that boats plugged into shore power would see longer battery life but due to loads rebooting absorption I frequently see batteries that get abused, and have short life, even when tied to shore power. In a perfect world the charger would stay in float but they don't all do this. With no DC loads the charger can easily stay in float and you run a much lower risk of over-charging the batteries.
* When plugged in, and the batteries are full, the charger is supplying 100% of the fridge load, but during start up the battery usually kicks in some because the power supply in the battery charger is a bit too slow to keep up with the in-rush. In theory the batteries should just sit there and float but the reality is far too many chargers are not smart enough to know the batteries are full and they can get triggered back into a higher absorption voltage when the fridge compressor kicks on. Some will drop back to float quickly others may start a two plus hour timer once absorption has been re-triggered.
* If you do lose AC power, not uncommon and becoming more & more common everyday with the new NEC/NFPA requirements for GF interrupters in marinas, your batteries can be sucked below the chargers safe "
turn on" voltage. Even though AC power was restored the charger may not resume charging the batteries because the charger assumes there is a "fault" because the battery voltage is so low.. This is a built in safety feature to prevent chargers from charging into a shorted battery.
*Chargers can and do fail.. The failure rate for marine battery chargers is routinely on the higher side of the failure spectrum for marine electrical items...
Options:
* Add a low voltage cut off to the fridge circuit. Set it at 12.1V and this will prevent your batteries ever being sucked below about 50% SOC regardless of whether or not you lose shore power. It will also ensure your batteries will have enough voltage to allow the battery charger to re-boot when the fault or power has been restored. The Blue Sea m-LVD is a good choice in a low voltage cut off. IMHO, as a marine electrician, every single boat owner who leaves DC loads on dockside should install a low voltage disconnect at a bare minimum. Battery banks can get very, very, very expensive and I replace thousands of dollars of batteries destroyed each year to to leaving DC loads running on shore power.
* Use a good quality charger that has a
power supply setting or
force to float feature or
custom programming ability where you can manually set it at your float voltage when you leave the vessel. Often times a custom setting can be configured so the bank won't go above 13.XX volts no matter what. This prevents overcharging due to fridges rebooting absorption.
* You could use an AC to DC power supply but you'll still want/need a battery in the circuit, as a buffer for start up loads. Ones that can handle motor in-rush, without a battery can get a bit expensive.
Safest Option:
*When you leave your boat, turn all DC loads off. This is the lowest risk for ruining a battery bank.