I hope this is not taken personal at all - this is just how I might deal with the fridge - it certainly would be nice for this trip I would take with my wife and dogs. Its a couple years off so I’m still undecided.. leaning towards the simple side of things (ice chest only). But anyhow I had made this spread sheet that made looking at some options somewhat easy so Ill post them.
This is based on the battery test numbers that Maine Sail provided in this thread and scaled for two golf cart batteries with a capacity of 225 amp hours.
50% capacity = 112.5 amp hours
80% capacity = 180 amp hours
40 amps charging current = 0.18C
Delta between 50 to 80% = 67.5 amp hours
The charging numbers (Maine Sail) showed you could charge at .2C from 50 to 83% battery capacity. So this assumes that with the 225 amp hour battery, you could charge between 112.5 to 180 amp hours with a constant 40 amps - with batteries in good condition. To get 40 amps charging, I would use a 40 amp three stage battery charger (AC input) and a 1000 watt gas genset. Genset somewhere near the rear of the boat, battery charger near the batteries at the front of the boat. This would require 110 AC to be strung along the lenght of the boat - which is almost no issue for power loss in cables (higher voltage is better for long runs) but would have some safety considerations.
The solar estimate here should not be taken too seriously as this can vary a lot - but at least you can see what was used. MPPT vs PWM would change the solar output by about 10% but daily variations are likely a fair amount larger than that so I didnt bother with that detail. For the larger panel, use MPPT, I currently only need PWM for my smaller setup. Since solar can vary a lot, I think if you stay out very long, you pretty much need to bring along some method (such as a gas genset and charger) to compensate for a string of cloudy days. The more solar you add, the less chance of needing the gas genset - but you probably still need to bring it along if there is any chance of more than two or three cloudy days. Total daily amp hours used is based on my normal 15 amp hours plus 35 for the fridge = 50.. The fridge certainly complicates things, the charging is way simpler with just an ice chest.
Keep in mind this is a sailboat with an under 10 hp outboard and corresponding small charging system. Also another thing this points out - being able to tell the battery state is "kind of" important here. You probably could get by just watching voltage.. but either a charge monitor or something like the Balmar battery voltage monitor might also be good to have (and make the boat more complicated.. more expense.).
The first configuration is with my current 50 watt solar panel (40+10). I could go for about four days without using the genset and then would need to run it about an hour every other day.
The config below is with a 100 watt solar panel. It pretty much would supply all the power I needed (still plenty of power after nine days)
Finally the last one (below) is with 50 watts of solar and no extra charging. I could go for about 4 days starting with a full charge and getting good solar everyday.
This is based on the battery test numbers that Maine Sail provided in this thread and scaled for two golf cart batteries with a capacity of 225 amp hours.
50% capacity = 112.5 amp hours
80% capacity = 180 amp hours
40 amps charging current = 0.18C
Delta between 50 to 80% = 67.5 amp hours
The charging numbers (Maine Sail) showed you could charge at .2C from 50 to 83% battery capacity. So this assumes that with the 225 amp hour battery, you could charge between 112.5 to 180 amp hours with a constant 40 amps - with batteries in good condition. To get 40 amps charging, I would use a 40 amp three stage battery charger (AC input) and a 1000 watt gas genset. Genset somewhere near the rear of the boat, battery charger near the batteries at the front of the boat. This would require 110 AC to be strung along the lenght of the boat - which is almost no issue for power loss in cables (higher voltage is better for long runs) but would have some safety considerations.
The solar estimate here should not be taken too seriously as this can vary a lot - but at least you can see what was used. MPPT vs PWM would change the solar output by about 10% but daily variations are likely a fair amount larger than that so I didnt bother with that detail. For the larger panel, use MPPT, I currently only need PWM for my smaller setup. Since solar can vary a lot, I think if you stay out very long, you pretty much need to bring along some method (such as a gas genset and charger) to compensate for a string of cloudy days. The more solar you add, the less chance of needing the gas genset - but you probably still need to bring it along if there is any chance of more than two or three cloudy days. Total daily amp hours used is based on my normal 15 amp hours plus 35 for the fridge = 50.. The fridge certainly complicates things, the charging is way simpler with just an ice chest.
Keep in mind this is a sailboat with an under 10 hp outboard and corresponding small charging system. Also another thing this points out - being able to tell the battery state is "kind of" important here. You probably could get by just watching voltage.. but either a charge monitor or something like the Balmar battery voltage monitor might also be good to have (and make the boat more complicated.. more expense.).
The first configuration is with my current 50 watt solar panel (40+10). I could go for about four days without using the genset and then would need to run it about an hour every other day.
The config below is with a 100 watt solar panel. It pretty much would supply all the power I needed (still plenty of power after nine days)
Finally the last one (below) is with 50 watts of solar and no extra charging. I could go for about 4 days starting with a full charge and getting good solar everyday.
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