matt23 avatar image
matt23 asked

Absorption voltage

If I was to lower the absorption voltage on LiFePO4 batteries what would the affect be? it is currently set to 56.8 as standard but i'm intrigued to know.

MultiPlus Quattro Inverter Chargerbattery charging
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klim8skeptic avatar image klim8skeptic ♦ commented ·

16 cell battery?

What C rates are you charging your battery at?

Solar charging (variable output current), or mains charging (fixed output).?

How much time spent at absorption voltage?

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2 Answers
Alexandra avatar image
Alexandra answered ·


It depends on if your cells are actively or passively balanced and the trigger voltage for the balance circuit. You can go lower for bulk/absorption but it does need to be high enough for the circuit design.

The other effect being a lower capacity stored in the battery.

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kirby avatar image kirby commented ·

I found this manual. But it's related to MPPT. In my understanding, it does not matter what thing charges batteries.

So, what we have:

Setting \ System: 12V 24V 48V

Absorption voltage




Absorption time




Float voltage




Are these settings relevant? Shall we use them?

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Alexandra avatar image Alexandra ♦ kirby commented ·

What is relevant is what the manufacturer of the battery you are using recommends.

The MPPT or inverter will come with a base setting, but in my experience i have found that with all the different batteries i have installed over the years, the base settings are always altered to match battery manufacturers recommended ones.

If you are building your own pack, then absorption should always be set at a voltage that triggers the cell balancing.

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ahtrimble avatar image
ahtrimble answered ·

From my experience and training for 16-cell LifePO4 batteries Bulk & Absorption charging rates can be the same since they are the same function with LifePO4 batteries. And, baring any difference stated by the battery manufacturer, the charging rate should be about 57 - 57.6v (remember, battery capacity while charging is 58.4v).

I have seen some folks state that the Bulk should be 57.6v and Absorption can be stepped down to 56.6v - 56.8v to lighten the incoming power on the battery.

The Float charging rate should normally be set at 54.4v (the resting 100% SOC). This comes from my 150/70 manual "During this stage the float voltage is applied to the battery to maintain a fully-charged state. When the battery voltage drops below float voltage during at least 1 minute, a new charge cycle will be triggered. "

But 56.8v Bulk setting is fine, just will take a little longer to get the batteries up to full charge. And, 54.4v on the Float will keep your battery at 100% resting SOC.

FWIW...charging control is more about voltages than length of time. Although some folks preset absorption time. But I haven't seen any benefit to that.

If you have a 15-cell LifePO4 battery let me know and I will look up those voltages for you if you would like.

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andrii avatar image andrii commented ·

Hi, Ahtrimble! I have 2 batteries Uhome - LFP 5000. How do I choose the right voltage and time for floating charge and absorption. Thanks!

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