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martin-haemmerli avatar image
martin-haemmerli asked

Absorption voltage LiFePo4

Hi everyone

I read that the max voltage for a 3S LiFePo4 battery is defined at 12.60 volts. (Absolute maximum is set to 4.20 volts per cell)

So I wonder, why is the default absorption voltage in the SmartSolar MPPT 75/10 Charger for a 12.0 V battery, while choosing the Smart Lithium battery preset, set o 14.20 volts?

Even the float voltage is set at 13.50 volts which is also higher than the recommended max voltage of 12.60 volts.

Will these settings not damage the LiFePo4 battery?

Thank you,

Martin

battery chargingLithium Batterysmart solar charging behaviourbatterylife
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4 Answers
Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

@Martin Haemmerli

A 12V LiFePO4 battery consist of 4 cells. A LiFePO4 cell has a nominal voltage of 3.2V which makes it a nominal voltage of 12.8V for a 12V battery.

No one will ever charge the cells up to 4.20V. That's borderline and not recommended to do because everything beyond will damage the cell.

The Li-ion (not to be confused with Lithium Ion cells) preset included in the MPPT is a suggestion and based on a Victron Lithium Smart 12.8V battery. This is a very conservative and safe setting which should work also for 3rd party 12V LiFePO4 batteries (still need to follow manufacturer recommendation). However, you can always tweak the settings and make them a user preset, according to your own preferences.

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lalluyn avatar image
lalluyn answered ·

Hello,

I always define the max cell voltage at 3.6v, so 14,4v for 12V battery.

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jeanmarie avatar image
jeanmarie answered ·

Yes if you look at any voltage chart for LFP cells, you can see that the maximum ever accepted by this technology is 3,65V.

You should never ever goes higher than this (14.6V) in a 4S battery.

And 12.8V correspond to 3.2V/cell which means, roughly, SOC=20%

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ commented ·
12.8V corresponds to the nominal voltage (you may want to check the definition for nominal voltage on google), which has nothing to do with state of charge.
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martin-haemmerli answered ·

Thank you very much for your professional and quick support!

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