Hi Edd, I agree with Marek and Gary about the voltage reading not being a reliable indication of the state of charge. Here's an example from my boat. At noon my battery bank is normally back to full charge and the voltmeter shows 14.01V, cool. A second later the fridge starts and the voltage drops to close to 13V.
Best, Olivier On Fri, Jul 5, 2019, 13:46 Marek Dziedzic via CnC-List < cnc-list@cnc-list.com> wrote: > Edd, > to add to what Gary said... > > any measurement of the remaining capacity of the battery bank is tricky, > because it depends on how accurate your in- and out- meters are, what the > actual (current) total battery bank capacity is (it changes over time, > never up) and at what SoC (state of charge) you started the measurements. > > I assume that your 450 Ah is a nominal capacity, but you don’t know how > much of that is left. > > The 6 A you mention, is it 6 A over several hours (let’s say 3), i.e. 6 A > times “several (3)” hours = ~18 Ah or just 6 Ah? However, on a 450 Ah > battery bank, even 20 Ah is just under 5%, so if you started with 100% SoC > you should be at 95% (if it was 6 Ah, the SoC should be 98.5%). > > As Gary mentioned, re-synchronisation is a must. > > The voltage you are seeing depends heavily on what is using the battery at > the given time (as you check it). I can almost guarantee that if you were > watching the monitor at the time of starting the motor, the voltage meter > would show some number much lower than 12 V (even if the SoC was almost > 100%). > > I am not sure if it helped you much, though > > Marek > 1994 C270 Legato > Ottawa, ON > > *From:* Gary Russell via CnC-List > *Sent:* Friday, July 5, 2019 13:08 > *To:* C&C List > *Cc:* Gary Russell > *Subject:* Re: Stus-List Voltage / Amp Hours > > Hi Edd, > The battery voltage is only an indication of the state of charge of a > lead-acid battery when the battery has been without load (or charge) for > several hours. Otherwise, the voltage is pretty much meaningless. Many > devices measure the state of charge by noting the difference between the > number of amp-hours drawn and the number of amp-hours charged into the > battery. It is a more accurate indication of the state of charge but has > it's limitations as well. Any inaccuracy in measuring the current into or > out of the battery will accumulate over time requiring the device to be > "re-synchronized". > > Gary > S/V Kaylarah > '90 C&C 37+ > East Greenwich, RI, USA > ~~~~~~~_/)~~~~~~ > > > > On Fri, Jul 5, 2019 at 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 >> >> _______________________________________________ > > 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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