The order of ROM is based on your individual cell voltages and the answer lies therein considering the well defined maxim of avoiding thus the upper and lower knee of the cycle. 3.0v per cell as plainly you can see of course the alarm
will trigger below that and the cells fall quickly out of proportion after that.
Consider first though how you normally used your pack. An applied constant float charge without discharge as you surmise has degraded capacity and of course your data suggest plainly 400 is the capacity from what you surmise to be your rated capacity of 3.325 volts per cell.
Now question how long the cells sat at 3.325 volts before the test commenced? Question also how and when the cells came to be at your opinion 100% state of charge at 3.325 volts per cell? Question also how long after reaching the theoretical state of 100% charge was the test conducted? Straight up did you only charge your batteries to 3.325 volts and then immediately start the test or were the batteries found in this condition after sitting for some time and then you decided to do the test?
Perhaps as you surmise voltage is not a good indicator of state of charge and I would concur but on the lower knee only. To be more succinct you have I believe conducted a test on a 2/3 full bank and only realize the amount of amps you have placed in the bank. Question what it is about your charging that only allows you to store this amount of energy?
Ask yourself what is 100% state of charge anyhow? In an automobile charging cycle for lithium
batteries top balanced the end charge voltage per cell for 100% state of charge should very well be 3.5 volts per cell safely and proceeding any further is unwise because of the acceptance factor and certainly the ability of your chargers to actually push the constant charge constant current higher. It is simply only worth going to the upper extremes only during initial calibration of top balance of all new cells.
To charge or not to charge to 3.5 volts per cell before using the stored energy that is the question? In a living environment
utilizing the stored energy in a matter of fact. Will you always have the luxury to charge to 3.5 volts per cell before you disconnect a charge source? I contend no you will not depending on your system that is unique to you the owner.
Oft missed in this thread and briefly ever so touched on is constant draw constant charge buffering. Recently one would say use a lead acid buffer and or advocate the separation of lithium
from propulsive and house loads. Considering the only various advantages and disadvantages of the school
of thought as it pertains to the inherent individualized solutions mariners have implemented is the difference between splitting the 2-ply or simply buying
the best Charmin.
Real use dictates otherwise. From personal experience there is zero possibility of any lead acid bank buffering for long an extended, prolonged constant 30 +/- 20 amp draw of four months 24/7 with any reasonable amount of fail safe operation given the fluctuation of daily living. Simply put the ability to buffer amps in versus amps out is what lithium was made for. Eventually due to usage the bank will be full when the cooking
is done and there is only one heater
running and you have retired for the evening. The charger will then stop happily to where you have set it hopefully at roughly 3.325 volts per cell which is not full and not empty but the resting voltage of the cells.
But then what is the state of charge? Why contemplate it then in a static dockside situation? If for some reason during the night you get a low voltage cutoff and are awakened by alarms you realize your bank is now more empty then full. Start the chargers, turn the heater
back on and go to bed
. But now how does your charging solution come into play? How long does it take you to put back in 700 Ah back into that bank and should you today is the decision.
Without knowing how much charging potential you have I can't begin to say how long it will take you to actually charge your bank back to full 3.5v 700 Ah as I interpret your bank. How many amps can you throw at it continuous and does it keep up with your daily usage?
In my case recharging fully a 480ah 48v pack is a needless and lengthy affair usually aside from a voyage of any distance. With only two chargers each at 15amps it is 16 hours at 30amps continuous. In reality this translates into 10 amp charge considering the heater is usually going and there is some variations in the amp usage I'm simply rounding as the heater may be 16 amps and the chargers may only produce 27 amps but you get the idea.
Consider also the extra charging that must occur at times to fully or quickly augment your bank state of charge when needed to 100%. Do you have enough solar, wind
to make your bank full? In some situations dockside if I wanted to I could put 150 amps back into my batteries continuous for some duration based on voltage for my specific generator
and the solar charge potential of any given day with 2160 watts of solar. But that is never reality only a theoretical maximum.
In real life away from a dock the system must function without the luxury of a 30 amp electrical
outlet. Are you able to buffer accordingly with enough solar, wind or generating capacity to keep your batteries fat and happy 3.28v to 3.3v and to never let them reach the lower knee? That is the successful implementation of a lithium battery boat from a safety
To surmise would an active Captain
take the chance whilst watching voltage drop beneath 3.1 volts per cell without starting a generator during a night voyage or in fog
or otherwise? I submit to you that no you would not and foolish if you did.
Dockside as others have concluded certainly use what is stored and understand what potential is stored in terms of your vessel and system. Understand the deficits produced by turning on the 50amp water
heaters and then cranking the induction cooktop up as well. Most induction cooking
can be maintained around 1 or 2 setting for a small but efficient still cooking amp draw. Perhaps wait until the water is hot before cooking and or wait until the water heaters are cycled off or simply control them yourself by breaker. If you don't know how much energy is in your bank off by heart can you sleep comfortably at night in freezing temperatures or hot temperatures knowing that the heater or air conditioner is using 20 amps per hour and how many hours can you sustain.
Most nights I would buffer energy usage with one charger and run a small deficit on the bank. This is the proper way for lithium utilization. Easily sustainable and recoverable without major ah loss from the bank towards the bottom knee with anticipated usage and acceptable full capacity realized during the daylight hours when your up and about and the heaters are turned off or the energy is used for other things sporadically whilst your charging is supplemented from other sources perhaps another charger, solar or wind.
Use the energy storage you have purchased without abandon. Enjoy it. 3000 cycles of daily use at a minimum is eight years. With that figure alone they are counting full cycles not partial or static use. Perhaps the next test of the calb 100ah now degraded from being held in full state compass marine
batteries should be how long they can have a charge applied and simultaneously discharged and still maintain a modicum of capacity.
When I go back to read the specifics of your batteries and your choice of lead acid charger I realize Joe from looking at the specifications on your calb 180's they list a recommended charging current of 54A .3C. When I open the PDF of your Battery Test Phase I see that and according to the Victron literature you are utilizing the 170 amp charge rate. Could this be where the capacity loss is coming from?