In addition to the above,
The MidNite Classic does have a Skip Day function, that allows a settable fixed number of days to Skip the Absorb stage (up to 32 days, IIRC).
So on a Skip day, the CC begins charging in Float-MPPT, until the Float voltage setpoint is reached, and spends the entire day trying to maintain that Float voltage.
BUT, still try for 100% charge on non-Skip days. All of the Surrette banks here are approaching 12 years of service. The battery efficiency has certainly dropped with advancing age, necessitating a bit of an increase in Vabs, and attendant increase in the EA settings, but these batteries seem to be doing fairly well ... knock on wood.
First, most all things regarding our systems and batteries seem to be relative.
Have never used the ReBulk function in MN, or OB CCs. This is the voltage setting where the CC will perform a, or a new Bulk.
Would say that lightly-cycled banks can benefit from Skipping Days -- due to Summer heat, and the lack of cool nights, have gone from Skipping 3 days, and completely charging on the fourth (with the Classics), to Skipping only one day.
Here, the goal is to try to get the bank down to about 85% SOC, or a bit lower. The main banks have a nominal Capacity of 1280 Ah. Need the available Capacity at times, but not daily, so the Skip function works great:http://forum.solar-electric.com/discussion/23052/quick-question-for-midnite-classic-owners
jonr, here is a Link to an old Discussion here on the Skip Days, beginning with Post #11. Believe that the Skip Day function may not be in the latest Classic Manual, but it is easily setup in the Classic Charge>Advanced menu page.
And I DID say that the Classic can Skip Absorb, I should have said Skip Bulk & Absorb. Skipping Bulk and Absorb seems to work fine. On an Ah returned to the battery basis, even when using the historic Surrette-recommended relatively low Vflt of 52.4 V (about 2.18 Vpc) one can return 50-60% of the Ah removed in the previous discharge (roughly .... depending upon a number of variables), and seldom do any of the battery banks here get below 75% SOC.
We all have our beliefs about battery behavior, AND there really seem to be few absolutes, regarding battery behavior, and the "best" thing to do in some certain situation ... IMO.
FWIW, YMMV, so on, Vic
IMO, once Gassing Voltage reached, Positive Plate corrosion has begun, but Stratification starts to lessen. Just my opinion, but Sulfation is quite reversible within a few days, unless the SOC has been reduced to somewhere around 70% SOC. The lower the SOC has been taken, the greater the difficulty there is in removing Sulfation by simply going through a normal charge cycle ... these things are relative to exactly what is the construction of the battery, and so on ... just my read on things.
Many years ago, like most off-gridders, I did strive to try to reach 100% SOC each day. Now, not so much.
As has been stated by BB Bill, NOT looking to do a complete recharge each day really does reduce the amount of heating that the battery experiences, heat is not good, and, of course almost all of heating from recharge occurs at/above the Gassing Voltage.
Even during heavy Bulk charging, have only noted a 1 - 1.5 degree C temp rise of the battery, even at about 18% of C. There is probably some lag in the heat soaking out to the BTSes, but still, almost all of the battery heating occurs from about Vgas and above, as one would expect ... (relative to an earlier wonderment you noted, [ Estragon ] ...
Just "throwing the dice" to see what happens. My read on things, Vic
It is a very good thing to not recharge an FLA unless the SOC is below (approximately) 90%. On some daily-used off grid systems, this will require more than one typical day's use.
Bulk does little heating, and very little Gassing. Avoiding Bulk and Absorb still allows a significant number of Ah to be returned to the battery (during the all-day Float, even at relatively low Vflt). This still counts as charging.
These things are all a matter of opinion. There are many, many opinions around, particularly regarding batteries.
The above comments from yours truly are just my opinions, which have evolved a bit over the years.
All of this is in the context of having about four typical days of Autonomy for these battery banks. Folks with relatively heavier discharge of their batteries, daily, will certainly have a different perspective.
Much of the generator run-time on systems here, are mostly just to exercise the gensets. And that was one of the goals of the design of these systems ... many other people will have completely differing perspectives.
SOMETIMES, we Skip charging when the approximate SOC IS below 85%. When this is done, it is because a genset needs exercising.
Occasional deeper discharges are good for Flooded batteries, perhaps to about 60% SOC. Here, these are intentional discharges, that usually result from shutting off the PV input, and sometimes running electric heaters, so that the battery does not spend much time at this lower SOC. Then, the genset recharges the battery into the Absorb stage, and the PV finishes recharge to 100% SOC, nominal.
This is just the way that it is done here, there are many ways to run off grid systems, and most every system is at least a bit different from most others ... and so on.