A little late to this thread, but here goes: Batteries, alternators, and regulators are a SYSTEM and you need to pick them all to work together for best results. A big alternator does you absolutely NO GOOD without a good temperature sensing 3 stage regulator. With a stock fixed set point regulator, you’ll either be set too low and get very little benefit from a big alternator, or too high and ruin expensive batteries. The 3-stage regulator charges fast when batteries are low and then backs off when they get full. The temperature sensors allow the regulator to back off if either the batteries or the alternator overheat. AGM batteries are far from a cure-all for battery issues and I personally do not like them. Quick rundown of battery types:
1. Car batteries. Die quickly in marine service, but they are cheap. 2. Gel batteries. These were the first commonly available gelled electrolyte batteries. They can charge quickly and their self-discharge is very low. They don’t leak and don’t off-gas unless badly abused. They won’t leak acid if damaged. Their cycle life is good in deep cycle use. Their big drawback is over-charging kills them very fast. They have very specific charge voltages that must be used. 3. AGM batteries. These are now the most common gelled/solid electrolyte batteries. They are popular for the same reasons gels are but without the sensitivity to high charge voltages. They can drop-in to boats, cars, and airplanes without a special regulator. Their drawbacks are significant compared to gels. The cycle-life of the commonly available AGMs is about half that of gels at the same discharge levels. They too have very specific charge requirements, but the opposite way that gels do. They *have to* be brought to 100% charge every so often or they lose capacity quickly. Boats not on shore power and without significant solar will have a very hard time with this. Please note that neither gel nor AGM have any advantage over wet cells for amp-hours per cubic inch, i.e. a 4D gel, 4D agm, and 4D wet cell are all about the same capacity. 4. Traction batteries. These batteries are designed for electric cars, electric golf carts, floor sweepers, fork lifts, and other types of electric vehicles. They are made for rough service in both senses, they routinely get discharged deeply and get banged around. The most commonly used size is the 6 volt golf cart battery and they are – by a HUGE margin – the cheapest batteries if you analyze the cost per AH, even when deeply discharged. They can be boiled to death or sulfated to death if you really try, but they are pretty tolerant of charging issues over the short term. You can always add water or equalize. Their drawbacks are higher self-discharge (not a big deal anymore with solar IMHO) and the big one IMHO – they contain liquid and off-gas hydrogen and acid fumes. The safe mounting requirements for wet cells are much more stringent than gel types. Long story made short - I had a wet cell crack and leak all the acid into the bilge during a hurricane and the smell did not add to the enjoyment of the trip at all. Oh – did I mention they are cheap? 220 AH for maybe $160 or so. 5. Lithium-Ion batteries are far superior in all ways to any of the above if you have a large container of $100 bills to devote to the project. Please keep in mind $1 of insulation in your icebox is probably worth $3 of electrical work ☺ Joe Coquina From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Dreuge via CnC-List Sent: Monday, October 16, 2017 9:20 AM To: cnc-list@cnc-list.com Cc: Dreuge Subject: Re: Stus-List New Engine, now what size alternator If you have a refrigeration load of 120AH/day, don’t waist money on increasing battery and charging capacity. Spend a little cash on better insulation or rebuild your box with more and better insulation. It is not unreasonable to shoot for a refrigeration load under 30AH/day. Just have a look at Wally’s Stella Blue page titled “Marine refrigeration and freezer on 22AH/day”(I recall he has a Frigoboat unit with keel cooler). Technautics claim that their CoolBlue system consumes “24AH/Day for a 7 cubic foot fridge/freezer with R-30” and “operates at ambient temperatures up to 120F without a loss in system efficiency.” Even the Isotherm claims their ASU SP3751 can achieve loads under 20AH/day. Now making ice or cooling down warm beer on a really hot day will likely have higher load demands, but the message is still the same. Insulation is cheaper than batteries and lasts a lot longer too. - Paul E. 1981 C&C 38 Landfall S/V Johanna Rose Fort Walton Beach, FL http://svjohannarose.blogspot.com/ On Oct 14, 2017, at 2:02 PM, cnc-list-requ...@cnc-list.com<mailto:cnc-list-requ...@cnc-list.com> wrote: Lets consider some hypothetical numbers based on the rep's info. If a 100w panel were %100 effective and operated for 8 hours, you would get 800w-hrs of power per day. 800w divided by 12v = 67amp-hrs. 67 divided by 24hrs = 2.8amps current draw on average. That kinda gives you a ball park for what type of loads you'll be facing. Round up to 5amps/hr if you like for margin. 5 *24=120AHr per day.
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