voltage vs capacity

[timmbo]

Hi

I got a 200Ah LifePO4 Battery and on 70% Capacity the Battery has 12.7V, is that OK?
My PV-System charged it to 81% and it shows 13.1 V, and a few hours later 12.9V with 80%.
I got a small load on it.


Bye
Timm

 

[Sojourner1]

Using voltage to know your SOC is tough with LFP, LFP voltage is linear in between the knees.

What are you using for reading SOC or how are you getting the %? What are you charging to?

Your voltage seems low for SOC%, here is screen shot from some misc recent recordings from my system.


Column A_ Date
Column B_ Time
Column C_ SOC% (1%=5ah, 37%=185ah)
Column D_ Battery voltage
Column E_ Discharging amps
Column F_ Charging amps



I've been living off the batteries/ solar everday for 43+ months now. There is always a draw on the batteries.

 

[timmbo]

Hi,

thanks.
At the beginning for a few weeks, between 78 and 99% the Voltage stays everytime between 13.1 and 13.5. For a few days the SOC goes down to 64% and since then the voltage stays down.

Bye
Timm

 

[electric]

Is your SOC meter based on voltage or coulomb counting? Voltage based meters are designed for Lead Acid batteries and will not be accurate for LFP battery. Only coulomb counting SOC with frequent sync at 100% charge voltage can be reliable for LFP batteries.

 

[timmbo]

Hi,
I don´t know that the Info from the build in BMS. I see this information with my Tablet over BT.

Bye
Timm

 

[Sojourner1]

@timmbo, over the years reading different forums with folks that have dropin batteries. Some that have kept their batteries at a lower charge voltage the capacity % would get out of sync. After charging to a higher voltage (14.4 - 14.6)so the capacity can be reset to 100%.

What does your manufacturer of the batteries require charging to?

If you have been charging to a lower voltage this could be why it looks to be off.

I'll give an example of my EMS/ CPU, my batteries aren't dropin but this is how the capacity % is reset...
The EMS system has a minimum recorded resolution of +/- 0.5A so any current below that level is not accounted for. The system could be setup for a finer resolution, but the shunt value would have to be reduced which reduces the systems maximum current capability.

The system will reset the capacity to 100% whenever the pack voltage reaches 3.49 to 3.52 V/cell on average and the pack current must be negative (charging) and typically under 35A and then it will set the capacity to 100%.

 

[timmbo]

Hi Sojourner1

The Manufacturer said, i should set the VE MPPT 100|30 to 14.4V.
OK, that could be the reason, because my Battery is charged from a 330WP PV, but right now we don´t have sun since more weeks.
We got here cloudy or foggy, so no Voltage above 13.5V.
Only one time the Charger was in the Absorbtion Mode.
The max. power is now 140W, normally 40W.

In the summer i don´t know because i got the Battery in Oktober.

Bye
Timm

 

[Sojourner1]

If you could plug in and charge occasional when the sun isn't cooperating I'll bet you'll be back to normal capacity reading.

Not the end of the world and worst case would be that your battery will shut down till charged if the bms has that level of protection for the cells.

Which manufacturer is the battery?

 

[timmbo]

Hi,

Wattstunde.

WATTSTUNDE® Lithium 200Ah LiFePO4 Batterie LIX200, 1.690,00 €

WATTSTUNDE LIX200 Lithium Akku 200Ah 12V 200 Ah Nennkapazität LiFePO4 max Entladestrom: 150 A dauerhaft -> dies entspricht 1800 Watt Wechselricht

solarkontor.de

Thanks
Timm

 

[timmbo]

Hi,

now its 77% with 11.9V.
The Voltage is right, the % is wrong, because on my ICOM IC-7900 the Powerbar is in the red zone right now.

Bye
Timm

 

[Sojourner1]

You will need to charge to 14.4v to recalibrate or sync the V/ %. Do you have a way to charge from being plugged in?
Or you need more solar to feed the battery.

 

[timmbo]

Hi

Yes i got a 10amp Banner AGM Charger.
So i charge now with Landline.
Let´s see.

Bye
Timm

 

[Sojourner1]

Hook it up that should take care of you as long as it doesn't go over 14.6v not fimilar with settings of the charger.

 

[Sojourner1]

Let's us know how it turns out if it recalibrated the capacity.

 

[Bob B]

I have a battery with a Bluetooth BMS in it. Normally the %charge tracks via Amps in VS Amps out .... but, if I write a paramater change to it, it looses the Amp tracking memory and picks back up based on the voltage reading. If I fully re-charge the battery, it resets the tracking to normal.

 

[timmbo]

Hi,
so yesterday i got 14.4V with my AGM Charger.
On 14.4V it goes to 0amps current, so it was no problem to charge with the AGM Charger.
Also the SOC shows me 100%, so i hope is fixed now, but i´m still on it.

Bye
Timm

 

[Sojourner1]

You might on occasion have to do what you did with the plugin charger. It will recalibrate the capacity %.
It will just depend on your solar charging.

Glad it worked out.

 

[timmbo]

Hi

what you mean with occasionly, one time a month, or every 2 weeks?
Or every cycle?

Thanks
Timm

 

[Sojourner1]

Depending on how your solar is charging, if you start to see it stray (2-3 weeks?). Maybe adding more solar could help especially during the late fall/ winter/ early spring.

You'll have to get a feel for your system being charged with solar.

 

[Bob B]

I assume you have a Bluetooth connection to the battery ..... Does the App show current in and current out? If so, does the App have a calibration for the amp readings?
My Bluetooth battery amp readins were off when I first got it causing it to track the % incorrectly. I calibrated the Amp in and Amp out and it has tracked correctly since doing that.