Batteries Discharge while in Float

[santanaaviles]

Hello. I've seen this issue in another post but the user had lithium batteries. I have regular FLA Batteries and once the Midnite enters the Float Stage, instead of maintaining the charge to keep the baterry charged it let's the battery be discharged even when there is plantey of sun outside. Is this normal? Is there a way to fix it? Thanks in advance for any assistance.

[Vic]

Hi santan..,

This is not the normal way to set the Float Voltage (Vflt).

For Flooded batteries  it is customary to set a Vflt that will just barely keep a fully-charged battery,   fully-charged.

Finding this setting will take a bit of experimenting.

Be certain to use the correct Temperature Compensation value in the Charge menu,   or in the Local App (Status Panel).

How are you determining that the SOC is not being maintained in Float,   via the WbJr SOC reading ?   Have you tried taking SG measurements,   periodically while the CC reports that the battery IS Floating?

The amount of time spent in Float,    and the adequacy of the Absorb time and voltage,  could also have an impact on the battery appearing to loose charge in Float.

Does your battery manufacturer give a range of suggest Float voltages,  or,  just one value?

Just a few thoughts,   FWIW,   Vic

[ClassicCrazy]

Vic,
I think Santana is talking about how with lithium batteries the voltage will stay high after being fully charged and give a reason for resting code of 38 , so it takes some time for the battery voltage to drop enough so the Classic figures out to go to Float MPPT . So what happens is that instead of keeping up with the loads like it would in Float MPPT the SOC has to drop down to like 97 or 95% before that Float MPPT happens. 

I have never seen that happen with lead acid batteries though . So I would also like to know what setpoints Santana has the Classic set for .

Larry

[Vic]

OK Larry,

I missed all of that in santanaaviles'  Post above.   It was stated that Flooded batteries were in use there ...

And,  upon the transition to Float,  with the main battery banks here,   the Classic CCs immediately go to Float for 60,  or about 90 seconds,  with the Green MNGP LEDs lit.   Then they Rest for some minutes,  until loads,  or time removes the surface charge,   and the battery voltage descends to the set Float voltage (Vflt).   But,  the amount of the Ah deficit  does not seem to be any more than about 1 Ah,  until the Classic begins supplying enough current (limited to available PV power) to maintain Vflt.

I was unable to real all of what you noted into the OP ...   FWIW,   Thanks,  Vic

[australsolarier]

i think i might have mentioned this before here. on my 12v system after float and light use, so about 150w, the midnite classic often does not keep to the float V and slowly discharges the battery. i mean over 5 hours. i get home, force bulk, to get a full charge before sunset. if however i let the computer run (added wattage) , this does not happen. the setting is "legacy".
now, you will say try "solar". ah, yes i will not have that problem  anymore. but !!!!!!    then it malfunctions during bulk and the classic decides after a while to reduce charging to 50% of possible charge.
i am quite happy to concede that those symptoms might have something to do with lithium batteries and i have too much time on my hands  watching things too much.

lithium batteries have very stiff voltages. 2 tenths can mean 30% less SOC. so in float when you throw a major load on your system, the midnites are very sluggish in compensating that load even though there might be 3 times of solar available. it then takes hours to recuperate that loss in float mode. now i understand when they designed the midnite classics lithium batteries were not an option and were probably most certainly not considered. with lithium batteries the midnite seems to have a strong inner life and starts to make decisions on its own that are "irrational".
there is certainly something to be said for sense wires.

all in all the midnite is still a premium product, quality and prices wise and would definitively recommend.

[Westbranch]

OK, just happened that yesterday I mentioned that 'now' would be an opportune time to start up the old vacuum  instead of the broom, as I saw from  the plot on Grahams app that the Absorb limits were going to be reached soon... TOO LATE....the Classic  dropped into Float and then the battery turned on and 40 Amps(Max) was being pulled out of the AGM bank plus a lesser amount out of the SUN, we also had some intermittent clouds come our way.... 45 minutes later the erratic graph returned to its original level and FLOAT continued with declining Amps.... never did get up to 99% SoC as the Amps were a hair over 5A at the time,target 4.0A, and ~4 hrs to sun disappearing  behind the Mtn... All the time in Float MPPT.  I expected that it would drop back into ABSORB...??
CC set for SOLAR.

Will try a more exacting test of the issue after we return on Friday...  Re-provisioning trip right now.

[ClassicCrazy]

Why do you think it would  go back to Absorb ? Not once it gets to Float right ?

Larry

[Vic]

OK, just happened that yesterday I mentioned that 'now' would be an opportune time to start up the old vacuum  instead of the broom, as I saw from  the plot on Grahams app that the Absorb limits were going to be reached soon... TOO LATE....the Classic  dropped into Float and then the battery turned on and 40 Amps(Max) was being pulled out of the AGM bank plus a lesser amount out of the SUN, we also had some intermittent clouds come our way.... 45 minutes later the erratic graph returned to its original level and FLOAT continued with declining Amps.... never did get up to 99% SoC as the Amps were a hair over 5A at the time,target 4.0A, and ~4 hrs to sun disappearing  behind the Mtn... All the time in Float MPPT.  I expected that it would drop back into ABSORB...??
CC set for SOLAR.

Will try a more exacting test of the issue after we return on Friday...  Re-provisioning trip right now.

Hi wb,

Would only expect that you would see a second attempt at Absorb,   in a single day,  would be if you had set ReBulk to a meaningful value for the conditions that you describe.

AND,  if there was insufficient PV power to maintain Float,   then   there would be NO gain,  even if the CC tried to do a ReBulk.   Float MPPT,   means that there is too little input power (usually PV),  to even maintain Float voltage,   let alone reaching Absorb voltage again.

The above,   depends upon just why  the CC was in Float MPPT  --  if it was because of some clouds,   and not fading sun,   then,   a second Absorb might have been able to restore a full charge before sunset ...   and so on ...

Normally,   SOC  should be set to 100% upon the CC making its transition  to Float.

FWIW,    Vic