24v Lithium resting voltage

Or any combo of soc in cells that meets the pack voltage

Naturally an imbalance with little impact to capacity is not a problem

ie 3.65+3.65+3.65+3.45=14.4

Would be 99-100%full
 
leon.davibe said:
There is always a settle down

Post charging

If you were at float for long enough time to have the cells settle down to the 3.35

The float would sustain the one low cell at 3.35 and whe removed it would settle down to reflect it's state of charge and thus affect pack voltage
Click to expand...
There was no float because of 0V setting.

We need to clarify with multimeter and also whether we are talking about proper resting voltage (no load for extended period of several hours) or voltage with a load or with surface voltage left over from "bulk/float".
 
leon.davibe said:
Or any combo of soc in cells that meets the pack voltage

Naturally an imbalance with little impact to capacity is not a problem

ie 3.65+3.65+3.65+3.45=14.4

Would be 99-100%full
Click to expand...
Why the 0.2V difference? Why now all of a sudden is it out of balance when before it was balanced?
 
wingnut771 said:
Why the 0.2V difference? Why now all of a sudden is it out of balance when before it was balanced?
Click to expand...
Cells aren't equal they get resistance/capacity binned to build batteries

As long as the balance current is enough to deal with any slight differences it isn't a big deal

But sure you would get compromise batteries , due to stock constraints

ie they pair the last cells in a battery to have it out the door
Thinking the resistance match isn't perfect but we think the bms balance can cope with it
 
That would drift little bit over time

That is why i would always prefer a diy battery

Cause if this happens you can
Do something about it , ie pull them into proper balance ie once a year before certain cells get abused

Vs sealed you can't even know what the balance state is

At best you can charge as high as you can go and the closer you can get to 15v the better the balance state is

If the bms allows pack voltage that high


you would know that the imbalance is in the steep part and can't affect capacity

ie if you know the bms cuts at 3.75v 14.7v would be that point

If it cuts at 3.8v per cell 14.85 would be that point

Edit opinion change : after seeing the behaviour of another diy battery of mine it isn't as simple as charge to x voltage,
You would have to disconnect the battery to see if it actually hit that point

As the bms disconnects the charging circuit if one of the parameters is met ie cell high voltage

And the voktage in the pack stops rising at that point

And the charger is allowed to push the volts up so you think the battery is that voltage and the only way to know it isn't is to disconnect the battery
And measure at that time what it is
 
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Ok, none of that is resting voltage and we are just going around in circles.
 
Perfect/good enough balance would net you a resting voltage of 13.4v
On a 100soc battery as all cells could reach 100soc

Imbalance would give you lower voltage if charged 100soc according to charge controller

ie the voltage that can get a balanced battery to 100 soc would not get an imbalanced battery there
you can lift the charge voltage if the imbalance isn't too big you can get it to 100soc

but then you would always drive the high cells to the cut-off voltage of the bms on cell voltage every charge cycle

ie if the bms cuts at 3.8v you would need to charge an imbalanced pack to a higher voltage to get the lowest cell to 3.45 to be full

ie 3.45+3.8+3.8+3.8 =14.85
or if the imbalnce is smaller
ie 3.45+3.65+3.65+3.65= 14.4v

if you have an awesome pack and all are 3.45v at the same time charging to 13.8v would get you to 100soc
 
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If you don't get the capacity expected move closer to the 3.65v per cell for charging to compensate for voltage drops over longer battery
Cables

if you hit the 13.4v rest then You got it fully charged

though if you don't get the 13.4 rest on a charge voltage of 14.6 most likely you have imbalance inside one of the batteries

and will have less capacity because of it
How much less you would have to do capacity test to dead

You may find it is less than 1% and the imbalance is not a big deal
 
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wingnut771 said:
There was no float because of 0V setting.

We need to clarify with multimeter and also whether we are talking about proper resting voltage (no load for extended period of several hours) or voltage with a load or with surface voltage left over from "bulk/float".
Click to expand...
Can tell you my battery takes about 1.5 hrs to reach this 3.35v settle voltage

There is no way to know if it is done settling apart from ok voltage is stable seems it is done

But at best you get an avg
Voltage which means nothing
ie yes if you deal with 2 cells you can math the other

But since it is 4 cells it means nothing

If it rests lower the only thing you can do to see if imbalance is anything to worry about would be a capacity test

ie if that 0.2v be less is over 3 cells the impact would be less

If only one cell less so

And naturally manufacturing differences could mean that the resting voltage could be slightly different, no idea how wide the variance could be
 
FrozenToast said:
Howzit Everyone

My two Blue Nova batteries in series are reporting 26.4v on the inverter. The inverter is set to 28.8v bulk charge and no float as oddly enough my off grid Growatt provides PV power for load instead of the battery when using the USE2 mode. Ive read USE is normally chosen to have this work.

So the batteries last the full 2 or 4 hours load shedding but its just weird that its spikes up to 28.8v on charge then after an hour or two the inverter stops charging showing the batteries are full and the batteries show 26.4v.

I know its not wise to use the voltage to determine SOC on an axpert type inverter. So I just want to know if its something I should investigate or just leave it if it works type of thing.

Thank you for your time
Click to expand...
Can. Also scroll through the settings to see how the priority is set for what to do with the solar power

ie normally you get these options not sure if it applies to yours

LBU load battery utility
Or
BLU battery load utility

Though i think the LBU is the better one to go with
For ROi purposes

But hey loadshedding capacity the blu may be better

A person has to find what works best for you
 
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wingnut771 said:
13.4 is around the resting mark so 13.2 is a bit low imho. Double check with multimeter on battery to confirm? Are you using a balancer? How are the battery cables? Cable length and gauge? If it charges to 14.4V and is giving you your runtime then I don’t think there’s anything to worry about and it is what it is.
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Since i balanced the other battery can add another example at rest for a day

As most don't get that much settling time before next shedding session started
My pack after resting from last night is @ 13.38 this morning
 
leon.davibe said:
Since i balanced the other battery can add another example at rest for a day

As most don't get that much settling time before next shedding session started
My pack after resting from last night is @ 13.38 this morning
Click to expand...
Mine has been resting for 26 hours now and is on 13.67V (it was 13.71V this morning, from an overnight charge @ 14.6V).

I have LS at 2am mon morning, so I won't be able to complete the test but will take a final measurement before bed.
 
Mine is 13.37 now vs the 13.38 of this morning

Just recharged just wanted make sure what the pack overvoltage cutoff is
My daly cuts at 14.3
Ie 3.575v per cell
The buck inverter went to 14.6v upon disconnect of charging circuit again

Just realised i might have triggered a protect mode last night with the individual cells
Charging , so will dip the voltage , recharge en then check rest again

And will post if different
 
Howzit Guys

Sorry for the late reply but LS was just inconvenient when it came to testing.

Ok so I tested the voltages on both batteries and I got 13.4 and 13.5. The battery balancer light was flashing prior to the test so I imagine it was busy balancing the batteries before the test hence the slight voltage difference.
 
FrozenToast said:
Howzit Guys

Sorry for the late reply but LS was just inconvenient when it came to testing.

Ok so I tested the voltages on both batteries and I got 13.4 and 13.5. The battery balancer light was flashing prior to the test so I imagine it was busy balancing the batteries before the test hence the slight voltage difference.
Click to expand...
What has changed as it seems like we are back to the way it was? Where did the 13.2V come from? 13.4 + 13.5 = 26.9V. Is that the reading on the inverter?
 
wingnut771 said:
What has changed as it seems like we are back to the way it was? Where did the 13.2V come from? 13.4 + 13.5 = 26.9V. Is that the reading on the inverter?
Click to expand...
The inverter says 27v instead of the 26.4 I initially mentioned. The only thing that has changed is that I followed the Float and Bulk recommended by Blue Nova. Overall the voltage seems to be higher according to the Inverter and from the multi meter. Maybe these batteries needed those specific settings?
 
FrozenToast said:
The inverter says 27v instead of the 26.4 I initially mentioned. The only thing that has changed is that I followed the Float and Bulk recommended by Blue Nova. Overall the voltage seems to be higher according to the Inverter and from the multi meter. Maybe these batteries needed those specific settings?
Click to expand...
Can you put it back to the old settings (28.8V no float), I want to see something. I'm also confused how you have 27V when your float setting is 27.6V.

Next time it's at bulk voltage of 28 or 28.8 or whatever, can you measure the voltage at the battery terminals.

Thanks.
 
wingnut771 said:
Can you put it back to the old settings (28.8V no float), I want to see something. I'm also confused how you have 27V when your float setting is 27.6V.

Next time it's at bulk voltage of 28 or 28.8 or whatever, can you measure the voltage at the battery terminals.

Thanks.
Click to expand...
Sorry I should have said that 27v reading is when I connected the batteries to the inverter with no input from Eskom or PV to provide float. I just went to check now and the inverter is reporting a battery voltage of 27.5v, with a multimeter both batteries are reporting 13.5v and the total voltage is 27.1v.
 
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