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 > > > > _______________________________________________ > > Email address: > CnC-List@cnc-list.com > To change your list preferences, including unsubscribing -- go to the > bottom of page at: > http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com > > >
_______________________________________________ Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
