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Fra avatar image
Fra asked

Doubt about Victron adapative charging algorithm

I don't understand victronenergy's adaptive algorithm well.
Victronenergy says that the absorption time should be longer with a very discharged battery and shorter with a slightly discharged battery.
But why?
whatever the previous discharge, when the battery reaches the absorption voltage, eg 14.4v, it means that it is at 80% charged.

Case 1: 100 Ah 0% battery, charged with 10 A charger. After 8 hours of bulk, it will be around 80%. And the absorption begins.

Case 2: 100 Ah 60% battery, charged with 10 A charger. After 2 hours of bulk it will be about 80%, so as in case 1. And absorption begins.

Why, according to the victronenergy algorithm, must the absorption of case 1 last 8 hours, while the absorption of case 2 must last 2 hours?
Why,if both batteries are about 80% charged when absorption starts?

According to electrical physics, providing a constant current of 10 amperes, any battery, at any level of discharge, will have the same level of charge when the absorption voltage is reached. That is about 80%.
MPPT Controllersbattery chargingVRM
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Alexandra avatar image Alexandra ♦ commented ·

@Francesco

Battery charging is a pretty complicated subject. I hear what you are saying about electrical physics but it is not as linear or as simple as that, in battery charging there are many factors that affect a battery's ability to accept charge. And as a rule 10AH discharge takes way more than 10AH charge to replace. As a battery is charging its internal resistance changes, and also its ability to accept the charge. There is so much information on particularly lead acid as adaptive charging is mainly applied in that chemistry. The article linked explains a bit more about charging batteries.

https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery#:~:text=The%20charge%20time%20is%2012,quickly%20as%20other%20battery%20systems.

In short, the absorption phase is more about reversing the chemistry in the battery and obviously the more reaction the battery has had, the longer it takes to reverse it. The deeper the discharge the more sulfation of the plates has occurred and this is ultimately what renders them useless as it prevents chemical reactions from happening.

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Fra avatar image Fra Alexandra ♦ commented ·

thankyou for the reply,and for he article. I agree with you for sulfatation, internal resistance etc....

But a question: its true that in the moment the battery reach the absorbtion voltage is ever at the same state of charge, either if its being discharge a little,or a lot??


i see varius charging diagram of lead acid battery,in witch the absorbtion fase last the same, with a 50% DOD than with a 100%DOD, to reach the 100% SOC.

Meanwhile what is changing is the time of bulk phase.


i have charged 70% dod battery and 20% dod battery, both with 2hr of absorbtion time, and in both case were on 13.1 v after 24 h open circuit. These means they were compleatly fully charged...Corrrect??


Can you give me your opinion also in these my other post, please??

https://community.victronenergy.com/questions/84568/new-victron-agm-battery-accurate-solar-charging-pa.html?childToView=84676#comment-84676

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2 Answers
Paul B avatar image
Paul B answered ·

There are lots of variables but Alexandra is also correct,

how old are the batteries

whats the SG of all the cells

whats the Temperature.

different chemistry's

how fast they are charged

the list is long and varied between brands as well,


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Fra avatar image
Fra answered ·

The article say:

"" "full charge is reached when the current decreases to 3–5 percent of the Ah rating. A battery with high leakage may never attain this low saturation current, and a plateau timer takes over to end the charge" ""

My new victron 110ah, with 15/ 20% DOD(12.6 open circuit voltage), absorb 2A at the ond of 1hr of absorbtion at 14.4v. After, the current drop to 0.8/ 1A at the beginning of floating at 13.8v. And after 4hr of floating decrease at 0.4 A.

If I try to extend the absorption time to 3hr (maximum allowed by my mppt controller), the current does not decrease less than 1.5 / 2 A.
In my opinion it means that it is fully charged with 1 hr of absorption, and with 3 hr I am overloading it by generating only gas.
Other than that, I measured the open circuit voltage after 24 hours of recharging, and it is 13.14v.
Both with 1 hour of absorption, both With 2 hours of absorption, and with 3 hours of absorption.
What should I do?
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