Hello, I have an Eco Worthy 24V 100Ah lifepo4 battery and a Vevor 3.5KVA inverter/charger system. I have tried to charge it at 35A and 20A rates with AC source, but after less than an hour, the charger drops the current down to 0-1A as if the battery were almost full, but it seems that the battery never gets charged well. The charge and floating voltages of the charger are set to 28.8V. The last time, the Vevor system charged it at 20A for only 50min and then goes down. The initial voltage of battery was 26.3V and, after charged it and leaving it for some time, the voltage was 27v disconnected. In addition, when I connected it back to the inverter system, after 15min the voltage dropped from 27 to 26,5v. The voltage vs SOC table of this lifepo4 battery is different for what I have seen in the forums and I've never been absolutely sure about the state of charge of the the battery  

Any idea of what is happening? why does the charger is not charging it for more time?

Using a chart like this on lifepo4 is folly it is almost impossible to determine SOC from voltage if the battery isn't at either side of the flat voltage curve, ie when it hits the spike up at the top when full or the knee at the bottom when basically empty

People try to recreate a chart , that worked on batteries with steep discharge curves for a lifepo4  it is a joke

 

 

If you hit full voltage it is normal for the amps to drop, the charger will charge max amps until voltage is hit then Limit the voltage and charge slower rate until the charge amps drops to a certain % of charge rate the y is garded as full and switches to float mode

Some inverters on USE/Li settings doesn't apply a float voltage  it use the float voltage as a trigger only

 

My one inverter works like this, it will charge , change to float mode ie apply no voltage and let the battery come to a rest voltage and once the voltage drops x amount under set float voltage it would trigger a charge cycle again, so setting a high float would see that inverter charge leave battery to settle to rest voltage once it triggers it would charge again

Setting the float lower allowed the battery to rest until next shedding (battery backup only had no panels at the time)

 

Instead of repeating this loop

 

The charts are useless

Resting/float approx 26.8v is full

 

ie 

My system is 48v i will charge to 53.9v  and my battery will come to rest at about 50.5

The voltage can shift a bit if moving from charge/discharge/charge again

Both those voltages are full

All you explain sounds normal for a lifepo4 battery

 

So as an example look at battery soc chart when resting full voltage, then simulate shedding  switch of mains look at chart, then switch power back on look at chart again compare  voltages 

 

Now did your battery truly discharge 20% and charge 20% in a blink of an eye, probably not, that should highlight how much a joke the charts is

Edited May 17, 20242 yr by Leondavibe

On 2024/05/06 at 3:56 PM, ed47 said:

Hello, I have an Eco Worthy 24V 100Ah lifepo4 battery and a Vevor 3.5KVA inverter/charger system. I have tried to charge it at 35A and 20A rates with AC source, but after less than an hour, the charger drops the current down to 0-1A as if the battery were almost full, but it seems that the battery never gets charged well. The charge and floating voltages of the charger are set to 28.8V. The last time, the Vevor system charged it at 20A for only 50min and then goes down. The initial voltage of battery was 26.3V and, after charged it and leaving it for some time, the voltage was 27v disconnected. In addition, when I connected it back to the inverter system, after 15min the voltage dropped from 27 to 26,5v. The voltage vs SOC table of this lifepo4 battery is different for what I have seen in the forums and I've never been absolutely sure about the state of charge of the the battery  

Any idea of what is happening? why does the charger is not charging it for more time?

Do you perhaps have charts showing the battery voltage and the battery current during a charge cycle?

On 2024/05/06 at 3:56 PM, ed47 said:

Hello, I have an Eco Worthy 24V 100Ah lifepo4 battery and a Vevor 3.5KVA inverter/charger system. I have tried to charge it at 35A and 20A rates with AC source, but after less than an hour, the charger drops the current down to 0-1A as if the battery were almost full, but it seems that the battery never gets charged well. The charge and floating voltages of the charger are set to 28.8V. The last time, the Vevor system charged it at 20A for only 50min and then goes down. The initial voltage of battery was 26.3V and, after charged it and leaving it for some time, the voltage was 27v disconnected. In addition, when I connected it back to the inverter system, after 15min the voltage dropped from 27 to 26,5v. The voltage vs SOC table of this lifepo4 battery is different for what I have seen in the forums and I've never been absolutely sure about the state of charge of the the battery  

Any idea of what is happening? why does the charger is not charging it for more time?

The charts are not very accurate .

On my 51.2 system the volts will settle at 53.4v after about an hour.

On my mother in law 25.6v system the lithium will settle at 26.6v  after about an hour . 

Edited May 23, 20242 yr by GMAC

I agree these charts are bogus! You can never determine the soc using a voltage scale if you look at the flat charge discharge curve. The only way of accurately determining the soc is by coulomb counting(amp/sec) incorporated into logic equations by the bms or a smart shunt. The bms algorithms will apply "learn"method where continuous charge and discharge currents will be recorded from each cell in the pack and then constantly applying small changes to the soc until a point where it becomes quite accurate. See below mistake on chart in op post highlighted in yellow.

 

Edited May 23, 20242 yr by TaliaB

3 hours ago, TaliaB said:

I agree these charts are bogus! You can never determine the soc using a voltage scale if you look at the flat charge discharge curve. The only way of accurately determining the soc is by coulomb counting(amp/sec) incorporated into logic equations by the bms or a smart shunt. The bms algorithms will apply "teach"method where continuous charge and discharge currents will be recorded from each cell in the pack and then constantly applying small changes to the soc until a point where it becomes quite accurate. See below mistake on chart in op post highlighted in yellow.

 

A quick glance at the figures in yellow it seems only the 25.12V has a typo and should be 26.12V

On 2024/05/23 at 12:02 PM, TaliaB said:

I agree these charts are bogus! You can never determine the soc using a voltage scale if you look at the flat charge discharge curve. The only way of accurately determining the soc is by coulomb counting(amp/sec) incorporated into logic equations by the bms or a smart shunt. The bms algorithms will apply "learn"method where continuous charge and discharge currents will be recorded from each cell in the pack and then constantly applying small changes to the soc until a point where it becomes quite accurate. See below mistake on chart in op post highlighted in yellow.

 

yea the graph is bogus there is no way the battery will be at 3.21v per cell ie 26.12v  at 10% soc

and fully charged no way you will see battery full while charging with a voltage of 26.92v

yes if you keep it at that voltage after charging forever it may end being full 

 

a lifepo4 battery 25.6v 8S(8 cells in series) ie to be certain the battery is full you need to hit 3.55-3.6v  per cell to be sure it is full

ie 28.8v, the same full battery will settle once charging has stopped to 27v if the float settings allow it 

thus 28.8v is full and 27v too just under different conditions

On 2024/05/17 at 8:50 AM, HendrikBigChief said:

Do you perhaps have charts showing the battery voltage and the battery current during a charge cycle?

yes with a nice high charging voltage ie 28.8  3.6v per cell, most charging will happen in the constant current mode and very little in the cv phase

when the charging current drops low you know it has switched over from CC mode to CV mode and is basicaly full ie 99-100 % probably

 

the moment you hit 28.8v you know the battery is full

and if you did not use it at the settled voltage of 27v it is still full

 

with a flat curve 70-99% soc can be very close to resting full voltage, hence why

the reason why we say it is full when it hits 28.8v is because we know that it entered the steep section of the SOC graph

ie the battery cannot hit this voltage if not full

 

but if it settles to rest after being full then 27v is still full which baffles people 27v is full and 28.8v is full so which is it and then enters all these graphs trying to explain this sitting the pot miss most of the time

 

especially since you can see a 0.5v voltage drop due to length of battery cable  when under load

and 0.5v makes a big difference hence why i say just ignore these graphs when it peaks it is full when it dips below 3v close to empty anywhere in between you are fooling yourself

can get a rule of thumb based on your own system ie if you see your system hang at x maybe 26v voltage most of the time and the moment it drops below 25v not long before you get low warnings then you know ok that is you signals

 

even the bms that coulomb counts can lose a bit and drift ie 1-3% in a cycle

ie it can't count what is lost due to battery losses ie as heat in bus bars and as balancing losses, it only counts what flows through it

 

Edited July 24, 20241 yr by Leondavibe

On 2024/05/17 at 8:50 AM, HendrikBigChief said:

Do you perhaps have charts showing the battery voltage and the battery current during a charge cycle?

the battery will charge at the amps you specified in your charging settings, if the charge voltage is high enough then the moment the amps drop you know it is full, ie any charge  voltage  above 3.55v  per cell x8= 28.4v for 25.6/24v battery you are good to say amp drop= full

 

while a voltage under 3.5v per cell ie 3.45v may be hit with a high charging amps when battery is above 70% soc so then the amp drop means nothing 

most inverters have a charging algo that kinda goes like this , keep amps constant until it hits the charge voltage max

that is the CC phase constant current

then it will switch to CV and keep charging with whatever amps the battery takes without exceeding  max voltage until the amps drops to x% of max charging amps

ie normally 10% so it will maintain the max voltage until the charging amps drops below 2A ie10%of the 20A charge rate

 

some have a time limit on the CV phase too ie it will stay in CV for lets say 30 min max 

so if the amps does not drop below 2A by then because the charge voltage was maybe too low to have the battery full by then it just stops charging

 

hence why it is important to have a higher charge voltage of at least 28.4v

 

most of the charging is based on if else type programming, and hence why some inverters can get stuck in a float voltage if panels are present and it charges over a long period of time, (axpert inverters has what is called a float bug)

 

a person can get it out of the stuck position by momentarily lifting the float voltage

i just left my float voltage the same as charge voltage then it doesn't happen, i don't want my battery to stay at that high float though so i just set my inverter to charge solar only x amount of time after dark and since no solar it just lets battery rest

Edited July 25, 20241 yr by Leondavibe