Charging LiFeP04 battery banks.

I am a newbee and want to take care of my 3 newly created 280ah 16s batteries. I have two questions. (1) I have read that it is best to cycle between 20% and 80%. Also that allowing your inverter to communicate and run the show is better for the battery. My growatt inverter however has preset charging voltage of 57.6 volts when communicating which is very high. So which way do I go?
Question (2). My battery is quite large for my simple house and I only use about 10% of it overnight. So the idea of cycling down to 20% becomes a project. So what are the ramifications of operating between 80 - 90% daily and occasionally deeper on cloudy weeks? Thanks for guidance.

Dominican Ken said:

I am a newbee and want to take care of my 3 newly created 280ah 16s batteries. I have two questions. (1) I have read that it is best to cycle between 20% and 80%. Also that allowing your inverter to communicate and run the show is better for the battery. My growatt inverter however has preset charging voltage of 57.6 volts when communicating which is very high. So which way do I go?
Question (2). My battery is quite large for my simple house and I only use about 10% of it overnight. So the idea of cycling down to 20% becomes a project. So what are the ramifications of operating between 80 - 90% daily and occasionally deeper on cloudy weeks? Thanks for guidance.

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No, just cycle all the way down to 20% or even 10% and charged to the max (safer would be 55.2v top)?

The most important part. Does your 43Kwh lithium batteries have Li BMS communication with the Growatt inverter? By the way, you never mention your 43kwh battery model.

Lifepo4 has calendar aging issue only. Most of the time, it will die from aging rather than cycling. So, you better off utilize all those charging cycles rather than letting it dies from old age.

This issue of battery charging between 20% and 80% keeps coming up. Has this somehow become the #1 google search result, from what source? Its like saying if you never drive faster than 50 MPH your engine will last longer due to less stress. While it may be true to some degree, its impractical and a bit ridiculous.

With this battery chemistry, Voltage vs. State of Charge is very flat (doesn't change much) through most of the usable capacity. This why we recommend setting BMS balancing to start only when the first cell reaches 3.4V. If the battery is only charged to 80% balancing would never take place.

57.6V is too high, 56.0V is 3.5V per cell and will charge to 95+% without driving up the voltage too high which can cause Over Voltage Protection Disconnects.

Many forum members were unsatisfied with the results of closed loop BMS-Inverter communication and have gone back to simple Voltage controls. Reason being, the BMS usually has preset values that get transferred to the inverter and the user no longer has the ability to change charge and discharge settings.

So are you suggesting I simply don't start charging the batteries until 20% or 10.

Dominican Ken said:

So are you suggesting I simply don't start charging the batteries until 20% or 10.

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No, we mean you can just use all of the battery capacity down to last 10%.
If you worry about high battery charging voltage, just charge it at 55.2v (16s configuration, 3.45v for each cell).
At 3.45v, the cell is around 95% charged.

Thanks for your help.

Dominican Ken said:

Thanks for your help.

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Sorry I am not being very clear. My battery capacity is large compared to my daily usage. Say I charge to 95% today. Over night The SOC will drop to 85% and the day begins and charges back to 95%. Some weeks will be cloudy and my charge will drop to 30 to 40%. But mostly it's operating in the 10% range.
I don't know if this is good or bad for battery life. Thanks for your consideration. Ken

Dominican Ken said:

Sorry I am not being very clear. My battery capacity is large compared to my daily usage. Say I charge to 95% today. Over night The SOC will drop to 85% and the day begins and charges back to 95%. Some weeks will be cloudy and my charge will drop to 30 to 40%. But mostly it's operating in the 10% range.
I don't know if this is good or bad for battery life. Thanks for your consideration. Ken

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1 cycle means full capacity usage 280ah.

10% of 280ah = 28ah..........you just used 1/10 of your 1 cycle............

Lifepo4 generally have more than 2500 cycles before the usable capacity drop to 90%.
Calculate how long the cell gonna last?

AshleyL said:

No, we mean you can just use all of the battery capacity down to last 10%.
If you worry about high battery charging voltage, just charge it at 55.2v (16s configuration, 3.45v for each cell).
At 3.45v, the cell is around 95% charged.

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Sorry to be a slow student but I want to understand. 3.45v is about 95% charged.....? What am I missing if I use the attached chart.
Again thanks for your help.

Dominican Ken said:

Sorry to be a slow student but I want to understand. 3.45v is about 95% charged.....? What am I missing if I use the attached chart.
Again thanks for your help.

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To make the story short, charge 16s cell to 55.2v (3.45v) at CV-CC until the current taper to 6 or 7A and consider the battery pack fully charged.

1 hour of absorption phase at lower voltage is less stressful for the cells. Then you can just float the cells at 3.35v each or 53.6v for overall pack.

Only need to ensure all cells are reaching 3.45v at same time (hence the need for active balancer that only trigger at 3.45v and above)

Thanks for you time and guidance.