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diy solar

New Bank isnt charging past 3.35 each cell

NewRuins

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Aug 6, 2020
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Oaxaca Mexico
Just made my first LiFePo4 bank to replace old FLA. Its 48V. 16 500ah 3.2V LiFePo4. With the Ant BMS (that will did the video on). Outback Inverter charger and Outback flexmax

So all the batteries were pretty much the same voltage upon arrival 2.285-2.296 and together they were 52.6.
Connected batteries towards the end of the day and they started to charge and saw the voltage rise on the BMS lcd screen.
But wanted to give them a good charge for the first night so ran the generato1r for 3 hours which puts out 25-30 Amps. And BMS showed it charging.
It seamed stuck at 53.4 for with average of about 3.33 per sell.
The BMS shows 25amps coming in and the individual cell voltage seams to jump around a little bit in the 1/100s and 1/1000s of voltage (3.3XX)
But cant seam to get them past 53.5. It showed the battery status at 100% and AH 499.99
The BMS has the basic settings for LiFePo4. Number of batteries to 16 and battery size to 500.

So am i just paranoid that it should have charged more in 3 hours at 25amps? Seamed to hit that cieling and not pass it.
Or
Is the battery just really big? its 48V * 500amp so like 24 kW hours. And will take a lot more to get it charged up?

Tomorrow when the sun comes up i'll have more data and can post the BMS config.
 

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Last edited:
I’ve read that LFePO4 cells are typically shipped at ~50% SOC.

You state 500Ah for a 16S 48V (51.2V) battery, so 50% SOC translates to ~12.8kWh to charge the cells near 100%

3 hours @ 25A being supplied at 51.2V translates to 3.84kWh or ~30% of your batteries full capacity.

So yeah, it’s a really big battery (at least for that 0.05C charger) and you need to plan on at least twice as long to charge it at that rate...
 
I agree... Not full. Just keep going. If you use 10kWh daily, you might want to put your system on a power diet for a day to make sure you can get your battery fully charged (or run the genny).

Since you've changed batteries, have you changed the settings in your FM80 for the desired peak voltage, absorption cut-off criteria and float voltages?
 
set Absorb to 58 (3.65*16(-minus a little to be safe) and time to 1/10th of an hour (6 mins)
The float to like 56 (or something) will check again in the morning.
Couldnt find the Rebulk settings in the Flexmax, but would like to set that
 
Absorption - If you're going for maximum cycle life at the expense of a little capacity (at 24kWh, I'd assume you're good with that). Consider charging to something a little lower than peak, say 3.55V or 56.8V.

Float = 3.35V*16 = 53.6V. You generally don't want to float them above 3.3-3.4V.

Rebulk is in the advanced menu of the FM80. The default is 48V unless you've changed it. I'd set it to 52V. Even if it doesn't rebulk during the day, it should rebulk the next day when the SCC is activated by the sun.

Your 3600W array will put out 3600/58 = 63A at peak voltage

Since you can't feed it the 250A needed for a 0.5C charge, termination criteria are atypical. IMHO, set absorption to 30 minutes or 25A termination.

The above is in absence of cell-specific criteria.
 
I’ve been using the FM80 for DC charging my 20kwh LiFePO4 for the last 7 years.
I use 55.5V bulk, 0.5hour Absorb, 55.3V float, and rebulk at 55.0V
 
I’ve been using the FM80 for DC charging my 20kwh LiFePO4 for the last 7 years.
I use 55.5V bulk, 0.5hour Absorb, 55.3V float, and rebulk at 55.0V

Have you ever measured your peak SoC?
 
OK. So so all day had a constant 30+ amps coming in. Its 5Pm and still some good aftersun sun. 12+KWH for the day.
It did go past that 53.4 that i "felt like" it would go past. Ended the day with 53.9. I guess these batteries were just very very thirsty.
 
Have you ever measured your peak SoC?

The only way to measure peak SOC is to fully discharge the cells which i don’t do

Every year or so i take the cells up to 3.6V and then draw 350ah out of the pack to check it can deliver that without any cell falling below 3V.

I have a 400ah bank, and regularly fall 250ah below my peak charge using the above settings.

My LVD is set to 50V, and this has yet to be triggered.
 
You could conduct the full charge after the other and evaluate the difference.

What do you estimate is your range of utilization in terms of SoC?
 
When I parallel top balanced my first set of four eve 280ah, I was using the 10amp power supply that a lot of people are using. I was thirty something hours into the top balance thinking something was wrong but I wasn’t calculating the ah correctly, I was thinking 280ah but that is at 12volts not 3.6 volts. After realizing this my top balancing taking between 72 and 76 hours made Sense for starting at a 40% soc.
 
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