LiFePo4 battery setup questions

[T1 Terry]

There is no such thing as perfect energy storage, there will always be losses. The losses when the battery is in new condition are so small it is in the watts in v watts out, not Ah in v Ah out. Because the charging voltage is higher tha the discharging voltage, the watts in will always be more than the watts out, but as far as Ah lost, that's 138Wh per Ah, and the loss is that small I'm thinking it would take a weeks worth of deep cycling including the max low voltage and max high voltage each cycle. As the batteries age……I don’t know, it really depends how hard they have been treated.
So, set the Peukert’s factor to zero, there is more chance of the shunt module not being finely enough calibrated creating an error than capacity loss. Something like 5,000 full cycles for a 20% loss, and the cell capacity is always greater than the advertised capacity so even after 5,000 full cycles you could still effectively have 90% capacity left.

T1 Terry

[goboatingnow]

Originally Posted by roetter

Great idea to use individual cell level for HVC and LVC. For some reason it slipped my mind. The Junsi looks like a toy, but I have good hope that they will be quite reliable. Have to use two of the, though. One for high and one for low voltage cut off.

You can't do it any other way , using the bank voltage is useless , equipment that monitors current or bank voltage do not provide enough protection or detection for LV or HV events.


Dave

[Moonos]

Great thread!

Finally I am understanding the requirements for managing lifepo4 systems.

It looks pretty easy as long as you have good monitoring and controlling of all variables.