Classic going to absorb at 92% SOC

[asdex]

When I looked at the system first thing in the morning batteries were 92% SOC
The Classic was in absorb when batteries were at 94%. Voltage was 29.8 volts current 8.2 amps. PV voltage 85.6 volts and 245 watts
Once SOC reached 100%, battery voltage was 27.7 volts.
I would have expected the Classic to be in bulk charge rather than absorb for longer. Should this be the case?
Also, just an off subject question. Before I changed my batteries I had a 12 volt 440 AH bank and now I have a 24 volt 300AH bank.
Will I have increased capacity or as I’m running a 24 volt inverter rather than a 12 volt inverter or will my available capacity have decreased?
Thanks,

[Vic]

When I looked at the system first thing in the morning batteries were 92% SOC
The Classic was in absorb when batteries were at 94%. Voltage was 29.8 volts current 8.2 amps. PV voltage 85.6 volts and 245 watts
Once SOC reached 100%, battery voltage was 27.7 volts.
I would have expected the Classic to be in bulk charge rather than absorb for longer. Should this be the case?
Also, just an off subject question. Before I changed my batteries I had a 12 volt 440 AH bank and now I have a 24 volt 300AH bank.
Will I have increased capacity or as I’m running a 24 volt inverter rather than a 12 volt inverter or will my available capacity have decreased?
Thanks,

Hi asdex,

Not exactly clear (to me)  just what was the sequence of events.

When the Classic makes its transition to Float,  the Net Ah should reset to zero,  and the SOC should be reset to 100%.   With AGMs,  the Vfloat seems about correct ...  depending on how weather the Classic was delivering any current,  etc.

You show a WBjr in your Signature,  so assume that you are using an EA setting to end Absorb (with a Absorb Time as a backup).   As you know,  when the EA has been reached for 30 - 60 seconds (forget which),  the transition to Float will occur.  If the batteries were not very deeply discharged,  the Bulk and Absorb times will not be too long.

Some questions;
What is the EA setting that you are using?
Roughly,  how long did that Absorb stage take?

SOC readings when using any Battery Monitoring device are only approximate,  as there are many,  many factors that affect the real SOC,  and quite a few of these factors are difficult to measure/calculate.

Also,  you are familiar that battery voltage varies considerably with variations in battery temperatures.  It might be possible that some of what is troubling you about the charge process this morning,  might,  possibly be partly due to a change in battery temperature ...   dunno ...

Speaking of Capacity,  this is a term assigned to batteries.  If you had a 12 V battery with 100 Ah Capacity,  it could deliver a certain amount of energy to a load.

If you had a 100 Ah 24 V battery it could deliver about twice the amount of power to a load,  and yet have the same nominal Capacity.

This is if both batteries were in the same condition,  charged to the same real SOC,  were discharged to the same ending parameter,  and so on,  but you get the idea.

[ClassicCrazy]

It is in Bulk until the Absorb setpoint is reached, then it goes to Absorb until it either reaches the end of Absorb time or ending amps if you have that set - then it goes to Float.

And like Vic said the SOC will go to 100% as soon as it reaches Float.

So it may not be in Bulk very long if the voltage climbs up fast to Absorb setpoint.

Larry

[zoneblue]

When I looked at the system first thing in the morning batteries were 92% SOC

We encourage phrasing that more like that "WBJr reported that the batteries were at 92%. Unfortunately its something of a rocket science to accurately measure SOC, and we need to be aware that what we are "measuring" with the classic is a rough guess only. You can after extensive tuning get it pretty close.

As a rough guide a battery will be in bulk until around 80% SOC, absorb for the last near 20%, then float for the final finish off.

[boB]

Unless you have a bad connection or questionable batteries,
what you described is perfectly normal for SOC% to be around
where you saw 92% when going into Absorb.  BULK/MPPT only
happens below set point voltage as crazy mentioned.

Your "energy" capacity is roughly battery amp-hours multiplied
by nominal battery voltage.

At 300 AH X 24V  you have around 7,200/4,800 watt-hours = 1.5
times your previous energy capacity.

It will take a bit longer than 1.5 times to charge than before if your PV array
is the same... Approximately...

boB

[asdex]

Hi, thanks for your replies. Thinks are a bit clearer now.
Below are the settings in the log.

4246   0   EndingAmps   0
4247   5   EndingSoc   5
4149   294   Absorb Set Point Voltage   29.4
4139   7107   AbsorbTime   7107
4153   0   Minimum Absorb Time   0
4154   7200   Maximum Absorb Time   7200
4236   7107   AbsorbTime   7107
4150   276   Float Voltage Set Point   27.6

I have seen the system in absorb for 4 or 5 hours.
I haven’t set absorb time or ending amps so maybe I should do this. Ending amps seems best I expect.
I’m up there again in a couple of weeks so will set ending amps and observe.
Any idea of an end amp figure? I would probably go for something like 5 amps.
I’m not sure why the ending SOC is 5 but all these settings except absorb and float voltage are default.
Thanks,

[mike90045]

....I have seen the system in absorb for 4 or 5 hours.....

How many sun hours on your planet ? Takes me 3 hours to get out of Bulk, there's not 4 hours left !

[asdex]

Well my panels don't actually need direct sun to start charging the batteries. They start at about 8am charging and the batteries are charged at around 11 or 12am. The sun goes off the panels at about 4:30pm at this time of the year. Even on a cloudy day they preform much the same. So 8am to 4:30, that's eight and half hours. I didn't realize this was unusual.
The Classic always looks to be in absorb most of the time. It does go to float but then the water heating starts and it cycles between absorb and float.
Cheers,

[ClassicCrazy]

Do you use Mymidnite ?  Perhaps you can take a screenshot of the graph and share that -  showing battery volts, SOC, system amps, etc. That really helps see what is going on over time.
example of mine from yesterday


Larry

[asdex]

Thanks, nice looking graph. I'll give it a go next weekend when I'm there,
Cheers,

[asdex]

Oh, it looks like I need to be on the internet to run My Midnite which I can't do unless its just for a short time. I have only 3G at the farm.

[boB]

asdex, what is the size of your batteries in amp-hours ?

Next, around how many kW-Hours or amp-hours of energy
from the classic do you see at the end of a good sunny day ?
This is a nice little sanity check on the system.

To get an idea of ending amps, what is the lowest output current
that you see towards the end of an absorb cycle ?
The EA will be somewhere close to that low value.

Without a Whizbang Junior the value will not be perfect though.

Also, even though you may have a good ending amps value,
your batteries will still want a nice long absorb cycle once in
a while (days) to keep them from sulfating which , unfortunately,
ending amps  by itself can keep from happening.

boB

[asdex]

Hi boB, I have 3 strings of 2 x 12volt batteries so 24 volts and 300 AH in total.
I'll take better note of the AH of energy and absorb amps when I'm there next time.
Is the picture attached, the AH per day which resets when the controller goes to rest?
Thanks,

[ClassicCrazy]

In your photo that is the daily kWh which resets at midnight .

Larry

[boB]

Yes, that shown is the energy or kilowatt-hours but you can see the amp-hours by
pressing the STATUS key once.  The status screens go one by one and wrap back
around to the kW-Hour screen shown in your picture.  There is not enough space
on one screen to show all of the pertinent information without switching screens.

But kW-Hours as shown is maybe close enough.  0.7 kW-H isn't all that
much but maybe that doesn't matter depending on the size of your batteries
and how many amp-hours your pull from those batteries before re-charging.

But to go from 100% SOC down to say, 75% SOC, you have to put back
at least 25% and then some more amp-hours because the amp-hour
efficiency is not 100%.  That efficiency is fairly good though, say, somewhere
in the 90 percent area.

For instance if you went down to 75% SOC, you would have to put somewhere
around 32% back in to get back up to 100% SOC rather than just 25% amp-hours
taken out.

boB