Hi Chuck, First off, 12V * 100 A*hr = 1200 W*hr. But keep in mind that A*hr battery ratings for a 100 A*hr battery is tested typical at 5 amps(or 0.05C). That is your 100 A*hr is 5A * 20hr. At this rate the battery is only providing 12.5V * 5A = 63 Watts. At higher current loads, your effective battery capacity will be much much less due to Peuket Effect losses. In fact, a 100 A*hr rated lead-acid battery at 100 amp load would only provide about 20 A*hr of energy(and lots of heat). To add to the insult, lead acid based batteries like AGM should not be depleted below 50% capacity to limit damage, so reserving 1 battery for start leaves only 50 A*hr for your house bank at loads of about 5 amps. At a 20A load, the 100 A*hr (50 A*hr effective) only provides 60 A*hr (30 A*hr effective). That’s about 30 A*hr / 20A = 1.5 hrs of use.
A 1000 W inverter could draw a max of 1000W / 12.5V = 80 Amps (but likely higher due to a voltage drop). This would drain your battery in 6 - 10 minutes. I gave a talk to some local Hams about Solar Off-Grid Systems. I posted the slides on my blog (see link below). On slides 5 & 6, I discuss battery discharge capacity and bank sizes. https://svjohannarose.blogspot.com/2021/10/solar-off-grid-system.html On Johanna Rose, I have a 2000W inverter charger. When I run my microwave, it draws about 100A from a 560 A*hr LiFePO4 battery. Like Dennis, I have my inverter connected to my panel powering all AC loads except for my A/C unit and water heater. The inverter has a built in transfer switch which automatically (and smoothly) transfers to shore power when available. - Paul E. 1981 C&C Landfall 38 S/V Johanna Rose Fort Walton Beach, FL http://svjohannarose.blogspot.com/ > On Oct 17, 2023, at 7:27 PM, via CnC-List <cnc-list@cnc-list.com> wrote: > > OK, an DC/AC Pure Sine Wave inverter looks attractive > > I've heard some boats have 1000 watt, some 2000watt and some 3000 or more. > What size inverter is right for a boat equipped with two 100Ah AGM batteries? > > One battery provides 12v x 100ah: 1200watts. My system can provide 2400 > watts but I usually reserve one battery to restart the engine and run on the > other battery. Does the inverter get fed from a bus common to both > batteries, or to the selector switch marked, "Off, 1, both, 2"? > > Thanks, > Chuck S >
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