# Re: Stus-List Battery power

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From: Josh Muckley via CnC-List <cnc-list@cnc-list.com>
To: C&C List <cnc-list@cnc-list.com>
Cc: Josh Muckley <muckl...@gmail.com>
Sent: Monday, February 12, 2018 5:44 PM
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 MuckleyS/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
Aries1990 C&C 34+New London, CT

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 MuckleyS/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 FreefallPreviously 1984 C&C 34 GhostBass Harbor,
Maine______________________________ _________________

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______________________________ _________________

Thanks everyone for supporting this list with your contributions.  Each and
every one is greatly appreciated.  If you want to support the list - use PayPal
to send contribution --   https://www.paypal.me/ stumurray

______________________________ _________________

Thanks everyone for supporting this list with your contributions.  Each and
every one is greatly appreciated.  If you want to support the list - use PayPal
to send contribution --   https://www.paypal.me/ stumurray

_______________________________________________

Thanks everyone for supporting this list with your contributions.  Each and
every one is greatly appreciated.  If you want to support the list - use PayPal
to send contribution --  https://www.paypal.me/stumurray

```
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Thanks everyone for supporting this list with your contributions.  Each and
every one is greatly appreciated.  If you want to support the list - use PayPal
to send contribution --   https://www.paypal.me/stumurray

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