Bulk, Absorption, Float

[teddysx3]

Hello everyone,

A little confused on the charging cycles on lithium iron phosphate, I think I understand them, but need you to confirm.

Bulk and Absorption, are basically the same from my knowledge, some use Bulk, some use Absorption, this is the cycle the charger puts out specified voltage into the battery, let's say 14.4 volt.

The part I don't fully understand is, when the battery reaches 14.4 volts, and if Float is set to 13.6 let's say, does it immediately drop to 13.6 volts? I was checking during the charging, it was charging at 14.4 volts, and after some time I check it with a multimeter, and it's at 13.6. Does this mean that the battery is fully charged, if it goes into the Float setting?

These 14.4 that are pushing are only to pump high voltage until it reaches, and then it drops down to 13.6 (float) but why does it drop, and does not stay at 14.4?

I'm basically trying to understand when and at what voltage my battery is fully charged.

Thanks!

 

[John Frum]

Hello everyone,

A little confused on the charging cycles on lithium iron phosphate, I think I understand them, but need you to confirm.

Bulk and Absorption, are basically the same from my knowledge, some use Bulk, some use Absorption, this is the cycle the charger puts out specified voltage into the battery, let's say 14.4 volt.

The part I don't fully understand is, when the battery reaches 14.4 volts, and if Float is set to 13.6 let's say, does it immediately drop to 13.6 volts? I was checking during the charging, it was charging at 14.4 volts, and after some time I check it with a multimeter, and it's at 13.6. Does this mean that the battery is fully charged, if it goes into the Float setting?

These 14.4 that are pushing are only to pump high voltage until it reaches, and then it drops down to 13.6 (float) but why does it drop, and does not stay at 14.4?

I'm basically trying to understand when and at what voltage my battery is fully charged.

Thanks!

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

 

[John Frum]

I will be glad to answer any follow up questions you may have.

 

[Zil]

LiFePo: Charge to your set 'high' voltage. Stop charging. Discharge to your set 'low' voltage. Repeat.

 

[mikefitz]

For some resion my complete reply disappeared.

I was attempting to explain the different terminology, for example Epever use the term 'boost' for absorbtion.

Bulk stage, where the majority of energy is put into the battery, is not necessarily a constant current Into the battery. With charger types, for example solar, the current can vary considerably and with some battery types the current will fall during the bulk stage.

The absorbtion stage, ( boost duration), is where the battery is topped up. The charger holds the voltage constant and as the battery Internal voltage source increases, with increasing SOC, the current falls due to the decreasing voltage difference.

Float volts is usually applied by the charger following termination of the absorbtion period (boost duration).

Historically needed for lead acid batteries that need to be maintained fully charged. Not needed for LFP lithium batteries but since most chargers need a value set up, it's set to the battery resting voltage or slightly higher.

Where there is a load on the battery such that the battery volts fall below float voltage, many chargers have a 're bulk' ( re boost) set voltage, this is set slight.y below float volts.


Care is needed when inversigating the charging of lithium batteries is that charge termination may be due to BMS disable of charge path.

Mike


.

 

[Ampster]

A little confused on the charging cycles on lithium iron phosphate, I think I understand them, but need you to confirm.

Bulk and Absorption, are basically the same from my knowledge, some use Bulk, some use Absorption, this is the cycle the charger puts out specified voltage into the battery, let's say 14.4 volt.

The part I don't fully understand is, when the battery reaches 14.4 volts, and if Float is set to 13.6 let's say, does it immediately drop to 13.6 volts? I was checking during the charging, it was charging at 14.4 volts, and after some time I check it with a multimeter, and it's at 13.6.

This is explained in detail in the stickie linked in post #2 As explained in that stickie it is easier for me to define those terms as what they actually do electrically.
Bulk is a Constant Current stage that has a voltage and a current setting. The voltage is the voltage at which the charger transitions to Aborb.
Absorb is a Constant Voltage setting and to keep the voltage from increasing the current continually gets cut back. This is sometimes called the tail current and often chargers limit this by time or a tail current setting at which the charger stops charging.
Float is a Constant Voltage stage that is lower current than bulk. It is similar to trickle charging. In the above example it is set to 13.6 volts.

 

[Tomthumb62]

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

Do you have a new link for the post you linked to? It seems to no longer work. Thanks.