question

electro-skipper avatar image
electro-skipper asked

Increase battery life - No daily absorption voltage.

I have a sailboat where I keep a 12 V lead acid battery bank of 100 Ah charged by a MPPT 75/10 and solar cells of 50 W. The battery is only used for 25 days per year when I am out with the boat. There is no consumption the rest of the days. I find it non-optimal that the battery is daily taken up to 14,4 V absorption voltage by a bulk charge step. Even if the actual absorption step is only one minute long, the journey there will expose the battery for an increasing voltage of 13,7 to 14,4 V every day, although the battery has not been used during the day. I have ruined (dried out) two lead acid batteries and replaced them through the years. I think the daily absorption could play a role. I have now decreased absorption voltage to 13,7 V too eliminate the daily voltage increase. I think the algorithm with adaptive absorption time is sophisticated, but has Victron not fully considered my type of application with only intermittent usage of battery and actual no need to go above float voltage every single day.

MPPT SmartSolar
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electro-skipper avatar image
electro-skipper answered ·

…I think that if the adaptive absorption time is calculated to zero, the charger should not make the climb up to absorption voltage, but stay at float voltage.

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JohnC avatar image
JohnC answered ·

@Electro skipper

Victron mppts are shipped with charge defaults that don't suit everyone. So you change them.

And some battery makers recommend different charge profiles for Cycling vs Standby use.

I use a flat 13.9V for about 3hrs a day to charge a lightly loaded 675Ah fla bank. I use the graphed current they'll accept to check on them. All 7yo+ veterans, but still need to top em up sometimes.

It's your choice to make as to how to treat them..

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electro-skipper avatar image
electro-skipper answered ·

Thank you for your response. Interesting to read how you have set it up.

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Alexandra avatar image Alexandra ♦ commented ·

@Electro skipper

You can also adjust the re bulk offset- or the battery voltage at which a new charge cycle is started.

Then it wont rebulk/absorb every day.

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electro-skipper avatar image electro-skipper Alexandra ♦ commented ·
Alexandra, that was an excellent advice. I thought I had investigated all settings possibilities, but I might not considered this one in detail. I guess I need to set the re-bulk offset to something like 1,2 V or so. Even with no load during a night the battery voltage goes down to approx 1 volt below float voltage. If I used some charge It will be lower and I will welcome a bulk charge up to absorption. Thank you.
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kevgermany avatar image kevgermany ♦♦ Alexandra ♦ commented ·
I'm not sure this will work as expected. The charger detects sunrise and starts a new charge cycle each time. As well as for long periods of charging inactivity due to low PV voltage.

Setting a shorter max absorption time and lower absorption voltage is probably the way to go.

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