We dropped the hook on a couple of hot summer overnights last year and left the refrigerator/freezer (Adler-Barbour) on all night which ran down our house battery quite a bit.
Considering that your house bank should really never dip below about 12.2V, even under your average house loads, what is "
ran down our house battery quite a bit." actually mean?? What was your voltage come morning?
even though the p.o had updated to an 8D AGM in 2013.
A single 8D AGM, pushing 4+ years old, is likely already getting quite tired unless it has been treated very well. You don't say what
brand it is, and this can make a huge difference in cycle life, as many of the 8DAGM's out there are not a deep-cycle product but rather a "dual purpose" battery stickered as "deep cycle".
A typical 8D AGM is rated at around 250Ah's of capacity. If you cycle to 50% DOD then the most "usable capacity" you'll have, from a 100% SOC starting point, is approx 125Ah's. IF THE BATTERY CAN DELIVER ITS
RATED CAPACITY. This is very unlikely at 4+ yeas old.
Now stack crusing on top of that and your average daily usable capacity shrinks to just 30-35% of the banks actual capacity because to properly charge a battery back to 100% SOC takes 5.5+ hours in "perfect conditions" but more like 7+ hours on a boat, even for AGM's. Thus, when cruising your average daily usable capacity will be about 30-35% of the banks actual capacity.
Let's assume your bank can deliver 200 Ah's at this point in its life.
30% of 200Ah = 60Ah's (this is if you get back to 80% SOC Each day)
35% of 200Ah = 70 Ah's (this is if you can get back to 85% SOC each day)
As can be seen quite easily a singly 8D on a boat with refrigeration is rather grosssly undersized for even one day let alone 3-4 days...
Furthermore, a 3 hour run motoring back to our marina, didn't fully recharge the battery.
Of course not, and it never will, no matter how much charge current you can throw at it. Charging lead acid batteries to 100% SOC takes a LONG time. In perfectly optimal lab conditions, see link below, at a .2C charge rate it took 5:45 to go from 50% DOD to 100% SOC and at .4C it took 5:30.... Once out of bulk the battery determines how fast it can be charged, not the charge sources....
How Fast Can an AGM Battery be Charged (LINK)
We will be retiring in a few weeks and our plan for this summer is to be quasi-liveaboards and explore the Chesapeake Bay from top to bottom and the many gunkholes in between. We would like to be able to stay out at anchor for 3 or 4 nights at a time before having to pull into a marina to plug in. To that end, here are few things I'm considering. Replacing the original, built in 11 watt solar charger that is connected to the starting battery with this 30 watt unit and connecting it to the house battery:
https://shop.hunterowners.com/hp/part.php?m=376&c=15&p=55119 Also, replacing the current Balmar 90 - 75 amp alternator with a 100 amp model.
For your described desires, 3-4 nights before recharging to 100% SOC you'll want a....
#1 Considerably larger house bank 450-600 Ah's (follow the 30-35% rule for 3-4 days of usable capacity)
#2 Considerably larger alternator than *100A, but this will entail a dual belt or serpentine pulley kit
#3 A Generator & massive inverter/charger if you don't do the alternator
#4 200W + of solar...
*Going from 75A to 100A is money
unwisely spent. You could do more just
properly programming your external regulator, if it is a good one like a Balmar.. Approx 98% of the boats I set foot on, with external regulators, are not optimally programmed...
On the consumption side, I'm thinking of buying a Yeti cooler, filling it with ice and then filling ziploc bags with ice from the cooler and placing the bags in the refrigerator/freezer to take up any empty air space and then turning the refrigerator off at night. Any thoughts or suggestions would be appreciated.
Minimizing consumption is always the money best spent. LED bulbs are one of the biggest savers of energy on a boat and one of the first energy saver that should be considered.. Making sure your fridge is running optimally and is well insulated is also key. These days computers, tablets and other electronic gadgetry have eclipsed daily refrigeration consumption for many families. Most boat owners don't believe it, until you show them how much energy it takes to keep these things charged and running.... I have one family who burns over 65Ah per day just on phones, tablets, computers etc......
