question

This is an interesting topic. I had also the same doubts. In time, I developped my current opinion:

- If you have cells that were well top-balanced, you can live almost without absorption time.

- The absorption time has 2 goals: (1) finish the last 5~10% of charging and mainly (2) give time for the equalization circuitry (that normally only works in the higher voltage band) to do its job of balancing the cells. So, if cells don't need balance, you can skip this phase. And you also avoid charging to high SOC.

- But, the threshold voltage you select bulk->Absorprtion -> float also plays an inportant role.

My current settings are:

Summer (long days): bulk up to 3.45V/ cell, 5 min Abs time, 3.35 V/ cell FLOAT

Winter: (short/cloudy days): bulk up to 3.45/cell, 30min Abs time, 3.36 v/ cell Float.

In reality, absorption in my system lasts far less than the preset value. Absorption ends when the absorption voltage is reached and the charge current drops to the tail threshold.

You are correct that you probably don't need to cell balance with each cycle or partial cycle. But then you need to decide when to do it.

Battle Born says that charging their batteries to 100% does not shorten their life. I can't speak to other batteries.

I believe Victron recommends fixed absorption for LFPs. I also think the absorption time is the maximum time.

Hi Elimac & Kevin

Thanks for the feedback

What I did now 5 minutes ago is the max absorption current set from 14,2v to max. 13,8volts.

I did not change the float-current from 13,5volts it remains standard...for Lifepo4

Both MPPT-chargers were already in float-modus so, after I changed the max absorption current they started both in bulk-modus....is normal

I set the "absorption time" yesterday in "adapitive-modus" so I, must see tomorrow in the "each-day" history that this is enough for both MPPT to arrive at 13,8v max absorption-time

If not than I will set the absorption time "fixed" and max. 1h00

Until now the SoC was always 100% so, I am gonna see the coming days how much de SoC wil drop in % with the new setting of 13,8volts

My argument to set the max. absorption current to 13,8v was because the cells don't need every day to be loaded to 14,2v....

I am looking now with pleasure how the Victron engineers will react here what I described here

Regards from Belgium

Frank

Dear all,

What I have done is the following:

Battery voltage: 12V (LiFePO4)

Max charge current 20A (I use a smart MPPT 100/20). I could set a bit lower.

Expert mode on

Charge voltages:

Absorption voltage set to 14.10 Volts. (that is 3.525V per cell and is a bit on the high side 14.00 would be better)

Float at 13.70V (we do not need to float these Litium Iron Phosphate batteries)

Equ voltage greyed out

Bulk:

Re-bulk offset 0.20V (is maybe a bit too low - just testing for the moment)

Absorption:

Duration 5 minutes (could be lower - just testing it while monitoring each cell in the BMS)

Tail current: disabled

equalization stop mode: fixed time

Eq duration: 0 minutes

Voltage compensation:

Temperature compensation disabled

The BMS controller is a bit more complex but I use my cells between max 3.60V and 3.00 V. Which relates to the steep inflection points in the IU curve and the state of charge (SOC) is then somewhere between 95% and 5%.

I use an Overkill BMS also known as LLT power or JBD type bms.

4S LiFePO4/120A bms with bluetooth. I have it for only one week and it works with Android and my iPad. I still have to tests it with an uart.

Base parameters:

Cell number: 4

Nominal capacity: 75 Ah

Galvanometer resistance: 0.20 milliOhm

Protection params:

Overvoltage: 3.60 Volts (V from now on)

Overvoltage release 3.45V

Overvoltage release delay 2.0 seconds (s from now on)

Undervoltage: 3.00V

Undervoltage release 3.25V

Undervoltage release delay 2s

Pack undervoltage 12.00V

Pack undervoltage release 13.00 V

Pack undervoltage release delay 2s.

Charging over temperature: 50 degrees Celcius (C from now on)

Charging over temp release 40C.

Charging over temp delay: 2s.

Charging under temp 5C

Charging under temp release 7C

Chargeing under temp delay 2s

Discharge over temperature: 50C

Discharge over temp release: 45C

Discharge over temp release delay 2s

Discharge under temperature -10C

Discharge under temp release 0C

Discharge under temp delay 2s

Charge over current 40 Ampere (A from now on)

Charge overcurrent release 32A

Charge overcurrent release delay 10s

Discharge overcurrent 60A

Discharge overcurrent release 32A

Discharge overcurrent delay 10s

Balance turn-on voltage: 3.20V

Balance precision 0.001V

Hardware protection:

hardware overcurrent protection 67A @ 160 milliseconds

hardware short circuit protection 89A@ 70 microseconds

short-circuit protection release delay 32s

Hardware overvoltage protection 3.70V

Hardware overvoltage protection delay 8s

hardware undervoltage protection 2.70V

Hardware undervoltage delay 16s

Small lecture point (I could not resist after reading one of the answers)

Electrical current does not have the unit of volts. Electrical potential differences (U) do have the unit of Volt (V). Electrical currents (I) have a unit of Amperes (A).

Screenshot_20210725-235801_xiaoxiang.jpgScreenshot_20210725-235808_xiaoxiang.jpgScreenshot_20210725-235814_xiaoxiang.jpgScreenshot_20210725-235819_xiaoxiang.jpgScreenshot_20210725-235825_xiaoxiang.jpgScreenshot_20210726-000115.jpgScreenshot_20210726-000139.jpgScreenshot_20210726-000145.jpg

Dear all

I checked this morning the history

The absorption-time is still in "adaptive" mode

The max absorption-current is 13,83v so that seems better for de cells than keep the cells every day for a certain time up to 14,2v

Maybe I increase also the float-current up to 13,6volts to keep the "gap" between max absorption-current from 13,8volts and the float-current (now 13,5volts) a little shorter

When the both MPPT's starts more often in bulk-modus the max absorption current will never rise above the 13,8volts

To keep the cells in a good balance I will start every month the IP22/30 and charge the Lifepo4 up to 14,2v (for that I added an automatic message in my iPhone agenda)

Best Regards from Belgium

Frank

For charging LiFePO4, ideally you have 2 + 1 stages:

• Charging from empty with a constant current - such as 0.5C - (if possible to maintain a constant current), until a certain cell/battery voltage is reached (this voltage is the one which you set as "absorption voltage"). This stage is referenced as "Bulk". This voltage should not be set greater than 3.6V (cell voltage). It can be set lower, such as 3.55V, 3.50V, even 3.45V (depending on the actual cells used and the BMS - if any).
• Then you maintain a constant voltage (the one set as "Absorption voltage") and continue charging. Because the voltage is kept more or less at a fixed and limited value, the current the battery absorbs will naturally drop over time. This is also referred as the "Absorption" stage. This would be best ended using the "Tail current" setting (when this setting is available). For instance the constant voltage stage (absorption stage) will be ended when the current taken by the battery drops under 0.05C (this means 5A for a 100Ah cell). If the tail current is not available to be set, you use a time limit (chosen based on manually monitoring the constant voltage stage - you check how much time it takes to the current to drop to that "tail current" limit you would want).
• After ending the constant voltage stage, you just want to keep the fully charged battery at its "natural equilibrium voltage"© (name made up by me), which is around 3.35V (cell voltage). This would be the "Float" stage. No charging takes place anymore (more or less), but you want to also avoid discharging (if you still have solar power from the PV panels to power the loads). By maintaining this "Float" voltage, the loads should be powered directly by the PV panels, keeping the battery fully charged for when the Sun goes down.

In practice you can't always follow this algorithm. For instance, when you have cloudy weather, the charging current during constant voltage stage/absorption can drop at a value lower than the "Tail current" value not because the battery can't take higher current, but because the PV power production drops due to the clouds. So some adjustments of the settings (those settings related to the end of constant voltage/absorption stage) are usually required.

Regarding discharging - you should avoid dropping under 3.0V (cell voltage). This limit can be set higher, but do not set it lower.

Dear all,

Since my last reaction I used again the standard settings for Lifepo4 in both MPPT's

My Victron supplier advised me select the settings for Lifepo4 without make any changes .

The MPPT settings for Lifepo4 are developed bij Victron.

In the standard setting for Lifepo4 the absorption-time is "fixed" for 2h00

But during this 2 hours the current is very low and the voltage stays never higher than 14,20v

My question is shall I use the adaptive absorption for Lifepo4 ?

I think is more useful for lead-acid Gel of AGM battery....?

I buyed a 180Ah Lifepo4 to have more comfort in my motorhome

Nespresso 4 x a day , a 650watt water kettle, a 850watt toaster an even a induction plate that I starting up max on 1400watt and I use the plate only when we have enough sun on the 535Wp solar panels

Continously and directly plugged in on the 12V supply : 2 iPad's ,2 iPhone's a Mac-book Air, a 16 liter compressor cooling box

I have also Ctek MXS 10 charger (also continuously) plugged in a 350/700 Phoenix inverter...to keep the 90Ah starter battery all the time in float-modus between 13,5 and 13,6v

But I am considering to buy & install a Victron Orion 12/12/9 adjusted to max. 13,6v for the starter battery

So, I use my 180Ah Lifepo4 every day but I keep my eye also on the app of the Smart Shunt

The best investment ever..

Regards

Frank

Dear all

Many thanks for all the reactions

Before I start a new topic about Lifepo4 and absorption-time..

I mentioned also in my previous reactions that I use also a Victron IP22/30.

And I selected since i use this charger the Lifepo settings no more no less

Until now I did not searching further in the IP22 menu , but I found today also the possibility to reduce the absorption-time for max 1 hour instead to use the standard 2 hours for Lifepo .

What shallI do?.....use the standard selection for Lifepo4 of shall I change the settings by using "user defining" and reduce the absorption time to max. 1 hour

What I further see in the menu is that de reconditioning is 'switched off" so that is ok

But down below I can not set the de reconditioning-time to zero..?

It seems logical when the reconditioning is "switched off" that the recond-time down below must be also come to zero...

A time from 15 min will stays visible even when the reconditioning-time is "switched-off"