[HELP] Lifepo4 parameters on inverter with AC charging option (UPS mode)

[narmenia]

Setup:
12v 1000w pure sinewave inverter with AC charging (set to mode#1 - UPS mode)
4s prismatic sinopoly 90ah (2nd hand cells)
30a/15a deligreen bms
4s capacitor type active balancer


NO SOLAR (the thing is powered by grid electricity all the time)

My load is very very small. roughly 40-60watts. 70watts max.

Blackouts are uncommon just around 2x 30-60mins blackout every month.
But every 2-3months an 8-10hour scheduled maintenance blackout do happen.
I want them to last a good 12hours of battery backup.

Now i want to get the "most life" of these lifepo4 batteries as i have used lead acid and they last just 2-3years and i am pretty feedup of replacing them.

The inverter has these options available to adjust.


Defaults are:
B1 - 13.8v
B2 - 13.6v
B3 - 12.0v
B4 - 10.8v
B5 - 10.8v
B6 - 12.0v

Do i need to change any of these?

THANK YOU

 

[John Frum]

B1 - 13.8v
B2 - 13.6v
B3 - 12.0v
B4 - 10.8v
B5 - 10.8v
B6 - 12.0v

b01 - charging voltage = 14.6 volts (make sure to compute the voltage offset so your bms and inverter/charger agree on battery voltage)
b02 - recover voltage = 12.8 volts (this is flexible)
b03 - low voltage alarm = 12.2 volts
b04 - low voltage cutoff = 12.1 volts
b05 - 0% = 10.0 volts
b06 - 100% = 14.6 volts

I can explain the calibration procedure if you wish.
Set your BMS low battery cutoff to 12.00 volts
set your BMS low cell cutoff to 2.90 volts
set your BMS high cell cutoff to 3.70 volts
set your BMS high battery cutoff to 14.6 volts

You have not mention float and re-bulk parameters.
Does this unit do float voltage?
You also don't mention charge termination parameters.

 

[narmenia]

b01 - charging voltage = 14.6 volts (make sure to compute the voltage offset so your bms and inverter/charger agree on battery voltage)
b02 - recover voltage = 12.8 volts (this is flexible)
b03 - low voltage alarm = 12.2 volts
b04 - low voltage cutoff = 12.1 volts
b05 - 0% = 10.0 volts
b06 - 100% = 14.6 volts

14.6v - is this kind of high?
most suggest 14.4v
i also seen a suggestion of 14 or 14.1v so as to keep the SOC below 100%

Set your BMS low battery cutoff to 12.00 volts
set your BMS low cell cutoff to 2.90 volts
set your BMS high cell cutoff to 3.70 volts
set your BMS high battery cutoff to 14.6 volts

Deligreen BMS. I dont think this has any adjustments.

You have not mention float and re-bulk parameters.
Does this unit do float voltage?
You also don't mention charge termination parameters.

not sure.

 

[John Frum]

14.6v - is this kind of high?
most suggest 14.4v
i also seen a suggestion of 14 or 14.1v so as to keep the SOC below 100%

Not IMO.
3.65 volts is the max voltage for a lifpo4 cell.
The reason to charge at 3.65 volts per cell is to minimize the time that the battery is exposed to the voltage stress of charging.
At odds with the wisdom of the crowd, but there it is.
Also lifepo4 is a bit more tolerant of over-voltage than of under-voltage.

 

[narmenia]

So it would still be better in the long run if i stay with 13.8v?

The batteries would be just on "standby" all the time.
As they would only be needed in case of a blackout.

 

[John Frum]

View attachment 25492

So it would still be better in the long run if i stay with 13.8v?

The batteries would be just on "standby" all the time.
As they would only be needed in case of a blackout.

If you have 3 stage charging(bulk, absorb and float), I don't think so.
bulk and absorb should both be 14.6 volts and float should be 13.8 or less.
That is why its important to know how your charge terminates to float.
At this point you should have focused questions and/or objections.

 

[narmenia]

If you have 3 stage charging(bulk, absorb and float), I don't think so.
bulk and absorb should both be 14.6 volts and float should be 13.8 or less.
That is why its important to know how your charge terminates to float.
At this point you should have focused questions and/or objections.

how to check if the charger is doing float voltage of 13.8?

 

[John Frum]

how to check if the charger is doing float voltage of 13.8?

This is where a shunt based battery monitor or a smart bms comes in handy.
Either one of those will show current going into or out of the battery.
The inverter/charger should show the voltage from its perspective.
The usually show the charge stage explicity as well.
But the shunt will tell you have much of a know load it is servicing.
If its not supplying the whole lead then the charger is making up the difference.
For lifepo4 batteries float mode is better understood as battery assist mode.
The charger helps the batteries service the load in float mode.

 

[narmenia]

This is where a shunt based battery monitor or a smart bms comes in handy.
Either one of those will show current going into or out of the battery.
The inverter/charger should show the voltage from its perspective.
The usually show the charge stage explicity as well.
But the shunt will tell you have much of a know load it is servicing.
If its not supplying the whole lead then the charger is making up the difference.
For lifepo4 batteries float mode is better understood as battery assist mode.
The charger helps the batteries service the load in float mode.

but during this time the battery voltage will always stay at 100% or 14.6volts?

 

[John Frum]

but during this time the battery voltage will always stay at 100% or 14.6volts?

No.
When the battery voltage is higher the battery will service the vast majority of the load.
As the battery and charger converge on float voltage the charger will service more of the load.
If the load exceeds the float voltage the battery will be discharged.
If the battery voltage gets low enough the charger should re-enter bulk mode.
And now have a pretty good understanding of how charging works.

 

[gnubie]

I think that's a bit of a poor lead acid charger style. For lifepo4 Victron chargers pull up to 14.2V but then release back down to 13.5V once 14.2V stage is completed. This inverter doesn't appear to have a multi-stage charger configuration. It looks like a dumb single voltage charger, and that wouldn't even be good for lead acid.

If I've formed the right opinion of the charger, and as bluck as it seems, I'd set the charger for 13.5V, cop the lost capacity on the chin and periodically reconfigure the charger for 14.2V and let the battery charge up (observe tail current) to allow the BMS / balancer to do its thing, then reconfigure for 13.5

What do you think of that @smoothJoey ?

 

[narmenia]

I think that's a bit of a poor lead acid charger style. Victron chargers pull up to 14.2V but then release back down to 13.5V once 14.2V stage is completed. This inverter doesn't appear to have a multi-stage charger configuration. It looks like a dumb single voltage charger, and that wouldn't even be good for lead acid.

probably.
so i should set the charging voltage to a lower number?

I used a multimeter and the battery now sits at 14.6volts. The charger is keeping the battery at that voltage.
Is this bad?

 

[gnubie]

IMO yes, it's not good to hold a lifepo4 cell at elevated voltages indefinitely. At least that's what everyone seems to agree on. 13.5 is generally held as being a safe 'float' voltage if the battery is periodically put under load.

 

[John Frum]

probably.
so i should set the charging voltage to a lower number?

I used a what meter and the battery now sits at 14.6volts. The charger is keeping the battery at that voltage.
Is this bad?

How much charge current is going into the battery?
If its below the recommended tail current for the battery then its bad.
The longer it goes the worse it gets.
If your inverter/charger doesn't terminate the charge and switch to float then its not really fit for purpose IMO.

 

[narmenia]

IMO yes, it's not good to hold a lifepo4 cell at elevated voltages indefinitely. At least that's what everyone seems to agree on. 13.5 is generally held as being a safe 'float' voltage if the battery is periodically put under load.

so if the float voltage is 13.6v or 13.8v.
theoretically my voltage should drop to below 14volts after couple of days while still connected to the charger?

 

[snoobler]

Late to the game - thinking out load for a bit...

13.8V screams UPS function, i.e., for batteries that are cycled, 14.4-14.8V is recommended but for batteries, particularly AGM, that are backup/standby for infrequent discharges, 13.8V is the only voltage given. That's what I'm seeing.

You have enough capacity for about 16 hours of a 70W load.

Essentially in agreement with @gnubie - I vote to set it at 13.6V and see how it performs. This way the batteries are only charged to 3.4V and floated there as well, which is regarded as safe. If they sit for extended periods, they will take on a wee bit of charge slowly and possibly inch even higher until near fully charged.

If you have enough capacity to make it through your 8-10 hour maintenance once per month, then nothing needs to be done. Otherwise, get a different inverter.

 

[narmenia]

Defaults are:
B1 - 13.8v
B2 - 13.6v
B3 - 12.0v
B4 - 10.8v
B5 - 10.8v
B6 - 12.0v

MY SETTING:
B1 - 13.6v
B2 - 12.8v
B3 - 12.0v (highest possible)
B4 - 11.5v (highest possible)
B5 - 10.0v
B6 - 13.5v (highest possible)

 

[John Frum]

Ooops, totally missed the fact that this is an online UPS.

b01 - charging voltage = 13.6 volts (make sure to compute the voltage offset so your bms and inverter/charger agree on battery voltage)
b02 - recover voltage = 11.2 volts
b03 - low voltage alarm = 11.1 volts
b04 - low voltage cutoff = 11.0 volts
b05 - 0% = 10.0 volts
b06 - 100% = 13.5 volts

 

[narmenia]

MY SETTING:

B1 - 13.6v
B2 - 12.1v (lowest possible)
B3 - 11.1v
B4 - 11.0v
B5 - 10.0v
B6 - 13.5v

Thanks to all who helped.

 

[narmenia]

You have enough capacity for about 16 hours of a 70W load.



If you have enough capacity to make it through your 8-10 hour maintenance once per month, then nothing needs to be done. Otherwise, get a different inverter.

I tested today with my watt meter and i may have under estimated my figures.

It is now around 90+watts.

I may need to recalculate my battery time.