Edd, As I recall you are still on a mooring right? You're using the motor and solar to keep the batteries "charged"? If so then it is unlikely that you are ever really getting all the way 100% charged.
As others have mentioned the only good way to use voltage as a measure of the state of charge is by reading the NO LOAD (and No CHARGE) voltage. Seems simple enough.... But it's not. There is also a effect known as surface charge. This is the residual voltage that is greater than 12.7v read after applying a charge. Immediately after charge you'll see 14.7v and slowly dropping over 24 hours until it stabilizes at 12.7v. The surface charge can represent ~1% of battery capacity. To remove the surface charge you need to apply a relatively small load. In your case 4.5A-hrs....so 4.5 amps for 1 hour...or just let the battery sit disconnected for ~24 hours. With the surface charge removed the volts should read 12.7v and every 0.1v below 12.7v is roughly equal to 10% capacity. So during charge there are 3 different stages of charge (bulk, acceptance, float). You'll see volts climb steadily through the first stage finally stopping at ~14.7v. At the end of the first stage a lay person might casually look at the battery voltage, see 14.7v, and think that the battery is fully charged. The reality is that it is only about 80% charged. Most battery monitors like your blue sea are kinda dumb. At best they measure A-Hr in VS A-Hr out. Some reset to 100% charged when 14.7v is reached. Some keep accumulating A-Hrs from a pseudo-float while actually still in the acceptance (2nd stage). Some can be reset to 100% manually. Some need to be reset. I say pseudo-float since charge sources like solar can be sized insufficiently to actually change the chemical state of charge to get the batteries out of the 2nd stage and sometimes not even out of the 1st stage. So while a charge current IS being applied (and measured/accumulated by the battery monitor) the state of ACTUAL state of charge is not actually changing. I believe this is probably what is happening in your case. Summary of stages of charge: 1st = BULK = constant current and charger max current with steadily climbing voltage up to ~14.7v 2nd = ACCEPTANCE = constant voltage at ~14.7v with current steadily lowering from max to ~2 amps. 3rd = voltage maintained at ~13.6v. If the current required to maintain 13.6v goes above ~2amps then the charger will switch back to stage 2 mode a d you'll see volts jump up to ~14.7. I know you asked for simple... Sorry. Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Fri, Jul 5, 2019, 12:23 PM Edd Schillay via CnC-List < cnc-list@cnc-list.com> wrote: > Listers, > > Last year, I installed a Blue Sea battery monitor and I’m a little > perplexed about the readings I am seeing. > > Last night, before an amazing fireworks display at Hempstead Harbor > (thanks to fellow Lister Neal Gallagher for the guest mooring), I looked at > the display. Out of the 450 amp hours in the House bank, we had used around > 6 amps between using the electric head, cell phone charging, etc. for > several hours — with the display showing 99% capacity. But the voltage was > showing 12.38, which I understand to mean closer to 75%. > > Someone on a YouTube video said that the Voltage reading is not really the > one to go by, as the voltage will increase when you start switching things > off. > > Is that all true? Is what I’m seeing normal? Can one of you Amperage Aces > or Voltage Vixens explain this to me? (Please keep it simple - way too much > Romulan Ale and Klingon Blood Wine flowing last night.) > > - Confused on City Island > > All the best, > > Edd > > -------------------------------—- > Edd M. Schillay > Captain of the “Starship Enterprise” > C&C 37+ | Sail No: NCC-1701-B > Venice Yacht Club | Venice, FL > www.StarshipSailing.com > ----------------------------------- > 914.774.9767 | Mobile > ----------------------------------- > > > Sent via iPhone X > iPhone. iTypos. iApologize > > _______________________________________________ > > 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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