craigav
Senior Member
Just FYI. While this battery is a 50ah rated battery, the amp hours are down to just above 80% now (or 40~45) which isn't bad for a ~10 year old LifePo4. The chart here is for a different AH (amp hour) battery than most RV'rs would have however, it is a common chart pattern for all LifePo4's I have tested including 100AH batteries and is useful for my point regarding voltages.
If you notice the blue line is the voltage and red is the current (both charge and discharge current) and the battery starts out just above 14.35 volts (voltage legend is on the left and current on the right) and within about one minute of 5A discharge the voltage is 13.1 volts. If I was to not have discharged the battery for a few days the starting (resting) voltage would be around 13.5V (+or-.1) but this test started with a fresh charge that stopped at 14.4v
You can see based on the time legend (bottom) that just past 8 hours the voltage was ~11.9v so 8 hours times 5 amps of discharge tells me this battery has 40 amp hours capacity (slightly more if I take it down to 11 volts).
The charge section is what I wanted to share more though as many believe that you must have a LifePo4 converter (or solar controller) to bring the battery up to 14.4 volts in order to fully charge a LifePo4. In reality though you can see where I marked 13.8 volts (recorded at the battery, not at the charger) and for all practical purposes the battery is at 100% state of charge (soc) at 13.8 volts and while my settings were set to reach 14.4 volts, if I had the setting to taper the current at 13.8 then the same AH charge would have been reached anyway (within minutes in this case).
What I am demonstrating here is that even with 13.8 volt charge a LifePo4 will reach a 100% charge in about the same time and a 13.6 volt charge will also take the battery to 100% but with a little more time. When you read most LifePo4 battery manufacture's guidance, they commonly state to charge the battery to 14.4 volts however if they don't state it (they should) you are to stop charging and disconnect the charger as a LifePo4 shouldn't be maintained at 14.4 continuously (for the longest life) or even above its 100% soc resting voltage (again commonly 13.4~13.6v) however maintaining the LifePo4 at 13.8 is still better than maintaining it at 14.4v.
The best float voltage would be just at or below the 100% soc resting voltage so around 13.4v to 13.6v which would maintain a 100% charged battery to stay at 100%. Which gets me to the right end of the chart where I pull 10 amps for 1.5 hours (15 amp hours) before storing the battery. (remember this is a ~50ah battery at 80% capacity so drawing down 15ah leaves it around 25AH left or ~ 50% of its 50ah rating. Also for another point, I like to bring the battery to 14.4v but for only brief periods of time such as when testing as that helps balance the individual cells inside. I suggest that once a year at 14.4v would be enough to maintain the balance, perhaps even every couple of years.
Last thought, a conventional RV converter depending on its charge profile may not be optimal for a LifePo4 but it certainly may be more optimal than some RV converters that attempt to maintain the battery at 14.4 volts. ~CA
If there are any requests, I can create a similar chart in the near future from a 100AH LifePo4, nothing really changes though just that the discharge and recharge time increases to double that of a 50ah LifePo4.
If you notice the blue line is the voltage and red is the current (both charge and discharge current) and the battery starts out just above 14.35 volts (voltage legend is on the left and current on the right) and within about one minute of 5A discharge the voltage is 13.1 volts. If I was to not have discharged the battery for a few days the starting (resting) voltage would be around 13.5V (+or-.1) but this test started with a fresh charge that stopped at 14.4v
You can see based on the time legend (bottom) that just past 8 hours the voltage was ~11.9v so 8 hours times 5 amps of discharge tells me this battery has 40 amp hours capacity (slightly more if I take it down to 11 volts).
The charge section is what I wanted to share more though as many believe that you must have a LifePo4 converter (or solar controller) to bring the battery up to 14.4 volts in order to fully charge a LifePo4. In reality though you can see where I marked 13.8 volts (recorded at the battery, not at the charger) and for all practical purposes the battery is at 100% state of charge (soc) at 13.8 volts and while my settings were set to reach 14.4 volts, if I had the setting to taper the current at 13.8 then the same AH charge would have been reached anyway (within minutes in this case).
What I am demonstrating here is that even with 13.8 volt charge a LifePo4 will reach a 100% charge in about the same time and a 13.6 volt charge will also take the battery to 100% but with a little more time. When you read most LifePo4 battery manufacture's guidance, they commonly state to charge the battery to 14.4 volts however if they don't state it (they should) you are to stop charging and disconnect the charger as a LifePo4 shouldn't be maintained at 14.4 continuously (for the longest life) or even above its 100% soc resting voltage (again commonly 13.4~13.6v) however maintaining the LifePo4 at 13.8 is still better than maintaining it at 14.4v.
The best float voltage would be just at or below the 100% soc resting voltage so around 13.4v to 13.6v which would maintain a 100% charged battery to stay at 100%. Which gets me to the right end of the chart where I pull 10 amps for 1.5 hours (15 amp hours) before storing the battery. (remember this is a ~50ah battery at 80% capacity so drawing down 15ah leaves it around 25AH left or ~ 50% of its 50ah rating. Also for another point, I like to bring the battery to 14.4v but for only brief periods of time such as when testing as that helps balance the individual cells inside. I suggest that once a year at 14.4v would be enough to maintain the balance, perhaps even every couple of years.
Last thought, a conventional RV converter depending on its charge profile may not be optimal for a LifePo4 but it certainly may be more optimal than some RV converters that attempt to maintain the battery at 14.4 volts. ~CA
If there are any requests, I can create a similar chart in the near future from a 100AH LifePo4, nothing really changes though just that the discharge and recharge time increases to double that of a 50ah LifePo4.
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