What you are looking for is an amp-hour meter.
Discharging a flooded deep cycle battery rated at 100 Ahrs
below 50% should be avoided. This roughly equates to 50 Ahrs
of use. 5amp for 10hours or 50 amps for 1 hour....you get the
jist. Discharging a flooded deep cycle below 50% will
decrease its effective useful service life. Many batteries
publish a the number of cycles and depth of discharge. One
loose rating convention is that a deep cycle will survive 200
charge/discharge cycles of 50%. The cycle number increases
when the depth of discharge is reduced.
When using a voltage meter, it is important to take
a "no load" voltage after the battery has had time to
"recover". The easy way to remember a capacity to voltage
conversion is 0.1v per 10%. A fully charged battery will read
12.7v and a fully discharged one will read ~11.7v. By this
convention one should avoid voltage readings below 12.2v. I
have a total of 500Ahrs between 2 banks so when one gets to a
"loaded" voltage of 12.2v I start considering a switch to the
other battery. I can go about 2 days in the middle of summer
with no charging source before I start to worry. The engine
charges at 100amps so motoring on and of the hook keeps me
pretty well topped up.
I put one of these in my first sailboat. It is
similar to the Link 2000 that Edd suggested. I have a Link
2000 installed on my current boat but it has never worked
right. I believe the current shunt is bad or somehow bypassed
on the charge or discharge circuit.....I'll get to it...
http://www.altestore.com/store/Meters-Communications-Site-Analysis/Meters-Battery-Monitors/Ammeters-Voltmeters-Battery-Monitors/Bogart-Engineering-TM-2025-A-F-TriMetric-Meter-Includes-fuse-and-fuse-holder/p10112/
Josh Muckley
S/V Sea Hawk
1989 C&C 37+
Solomons, MD
On Feb 2, 2015 8:27 AM, "David Knecht
via CnC-List" <
cnc-list@cnc-list.com>
wrote:
Looking at the wiring
diagrams reminded me of a question I am sure this list can
answer. I have not done much cruising yet, but plan to do
more in the future. One of the things I am unsure of is
how people monitor the state of their batteries when you
know shore power is not going to be available. I have a
digital voltmeter on the panel that I can check the
batteries and a chart that translates voltage into percent
charge and I have used that as a rough guide, but that
seems crude for such an important function. My
understanding is that you have let the batteries sit for a
while if they have been charging to get an accurate
reading. I am not sure if current draws also have to be
off. For instance, how would I know if it is safe to run
the refrigeration while sailing to the next destination?
Can you get a meter that gives you “hours of battery life
remaining”? What strategies to listers use to solve this
problem? Thanks- Dave
Aries
1990
C&C 34+
New
London, CT
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