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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