One way to make your batteries last longer and still guarantee starting in the morning is to go to a dedicated start battery and combine the existing pair into one house bank. Your depth of discharge will be much less for a given draw, so the house batteries last much longer, and if you wire it right you will never draw your starting battery down. I have 3 Group 31's in my house bank (345 AH) and a Group 24 starting battery. The starting battery dates from the purchase of the boat, so 12 years; it's time to replace it.
Jim Watts Paradigm Shift C&C 35 Mk III Victoria, BC On 12 February 2018 at 20:23, Marek Dziedzic via CnC-List < cnc-list@cnc-list.com> wrote: > One thing that should not be overlooked is that your big alternator could > hardly ever be used at full power. Your batteries won’t absorb even half of > that in the last 20% of the charging capacity. Since you have solar, you > can use it for long (and slow) final charging. Also, your alternator may > quite easily overheat if used at full power over longer time and without > good cooling. > > > > I might be stating the obvious, but if you don’t have the time or capacity > to fully charge your batteries, you should really consider that what you > have available is roughly 30% of your (current or real (vs. the nominal)) > battery capacity (between 50% and 80% of SOC). > > > > Another obvious thing is to make sure that for a large capacity alternator > you have an external regulator with proper temperature sending and that > your v-belt can drive it (serpentine or double). > > > > Just a few thoughts > > > > Marek > > 1994 C270 “legato” > > Ottawa > > > > Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for > Windows 10 > > > > *From: *Josh Muckley via CnC-List <cnc-list@cnc-list.com> > *Sent: *Monday, February 12, 2018 17:44 > *To: *C&C List <cnc-list@cnc-list.com> > *Cc: *Josh Muckley <muckl...@gmail.com> > *Subject: *Re: Stus-List Battery power > > > > First, I completely agree with everyone else about amp hours and meters > and the sort. > > > > But.... > > > > Just looking at the voltage, the easiest way is to think of the available > capacity as 1 volt from 11.7v to 12.7v. Each 0.1 (tenth) of a volt is > roughly equal to 10% of usable capacity. > > > > *Long winded explanation:* > > This is actually pretty conservative since minimum voltage of a dead > battery is 10.5v (0%) Full is 12.7v (100%). A difference of 2.2v battery > service life (think warranty or years before replacement) decreases > exponentially the further discharged you get. Normally a service life > measurement is based on 50% discharge cycles. Imagine that the battery is > rated for 200 cycles @ 50% for its entire life. That number might drop to > 100 cycles @ 70%, and increase to 400 @ 20%. Because of all of this, *the > typical recommendation is to minimize depth of discharge overall but to > absolutely avoid discharging deeper than 50%*. Using the assumption of a > linear relationship of 2.2v between 0% and 100% we can extrapolate that our > 50% minimum to 100% is equal to 1.1v. Since its just easier to say one > volt, and 12.7v is easy to associate with 11.7v. I come full circle to the > 10% = 0.1v. > > > > Did I explain that well enough? > > > > Josh Muckley > > S/V Sea Hawk > > 1989 C&C 37+ > > Solomons, MD > > > > > > > > On Feb 12, 2018 3:02 PM, "David Knecht via CnC-List" < > cnc-list@cnc-list.com> wrote: > > This discussion raises an issue I have struggled with as I have started > cruising more: deciding how much battery power I have. I have 2 AGM > batteries, one house, one starting and a panel voltmeter for monitoring. > My batteries are now separated so I no longer have to worry about being > able to start the engine if I run the house too low. The fridge is the only > major power draw, so I usually am just conservative, running it only > periodically to make sure I don’t overdraw the battery. So what is the > most efficient way to figure out how much I can safely run the fridge? If > I just watch the voltage, how do I decide if I can leave the fridge on > overnight? Dave > > > > Aries > > 1990 C&C 34+ > > New London, CT > > > pastedGraphic.tiff > > > > On Feb 12, 2018, at 2:33 PM, Josh Muckley via CnC-List < > cnc-list@cnc-list.com> wrote: > > > > Much of your problem is a matter of battery capacity as much as a matter > of charging capacity. I have ~450 Ah of capacity on one bank, a 90 Amp > alternator that never reaches full load, and 200 watts of solar. Even > without the solar I was able to comfortably keep the the fridge running and > the lights on when cruising for ~2 weeks. The half hour to hour of engine > operation to anchor or moore in the evening and the same in the morning was > always enough to keep the batteries charged. > > > > Keep in mind that the battery capacity should be at least 4x of the charge > capacity for flooded lead acid and at least 2x for AGM. So a 400 Ah or 200 > Ah respectively for a 100 amp alternator. > > > > Josh Muckley > > S/V Sea Hawk > > 1989 C&C 37+ > > Solomons, MD > > > > > > On Mon, Feb 12, 2018, 12:55 PM Damian Greene via CnC-List < > cnc-list@cnc-list.com> wrote: > > A question for your collective wisdom: > > > > I am scoping out upgrading my stock 55A alternator to a 100A Balmar, and > related upgrades to the controls. I had a very productive discussion with > Rod Collins at Compass Marine (mainesail), and we worked out the details. > Unfortunately he's booked out through the spring, so this job will wait > until next winter. > > > > So thinking then about keeping the batteries charged, and the fridge > running on our long summer cruise - where we may go for weeks without > access to shore power, I got wondering about using a portable generator to > charge the batteries - as an alternative to many hours of running the > diesel. There are a couple of Hondas that might do the trick 2000 Watt, > weighing 47#, 1000 Watt weighing 29#. > > > > Have any of you tried this? What could (would) go wrong if I plugged this > generator into my inverter, to charge the batteries? > > > > Regards, > > > > Damian > > > > 1986 Sabre 38 Freefall > > Previously 1984 C&C 34 Ghost > > Bass Harbor, Maine > > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each > and every one is greatly appreciated. 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