Re: Stus-List Voltage / Amp Hours

Sat, 06 Jul 2019 09:38:28 -0700

Or this?

http://www.balmar.net/services-view/sg200/ill

Bill Coleman

On Jul 5, 2019 2:35 PM, Olivier Chatot via CnC-List <cnc-list@cnc-list.com> wrote:
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
-----------------------------------
914.774.9767   | Mobile
-----------------------------------


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