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Sudden battery discharge


Sudden discharge of LiFePO4

FAQ: “Sudden” battery discharge

I have bought a several of LFP cells and made the pack with them to replace the lead-acid battery in my houseboat. The LFP battery was working great and it gives much more capacity than the lead acid. However after several weeks of usage, I came back after the weekend and I found out that the battery is completely discharged. Why this happen?

Please note that unlike the lead acid batteries, the LFP batteries will be completely damaged if you discharge them bellow the minimal voltage (usually >2.5V per cell, or bellow 10V for 12V battery). This may happen if you have some equipment that takes the power from the battery continually. Maybe you simply forget some light or some equipment „on“, and after few days the battery is deeply discharged and damaged forever.

The example:  12V 90AH battery is connected to houseboat with alarm. This alarm takes only 5W of power (12V 0.4A). If the battery has 70% charge, the alarm will discharge the battery in about 150 hours, that is 6 days. If you have some equipment with higher power consumption, the discharge will be much faster, even perhaps less than one day.

In order to prevent this kind of „mistaken“ discharge, we strongly suggest to monitor the battery (or the cells) to see the voltage of the pack. We also suggest using the protection devices to give warning when the battery is getting low. Also when leaving for a longer period of time, please be sure to disconnect the battery from the load completely with some mechanical switch or circuit breaker.

The suggested equipment:  the CellLog to monitor the voltage (and give the alarm), BM1 – battery monitor, or the Akumon - 12V LFP battery management board.

Concerning the “self-discharge”: due to the chemistry of the LFP cells, the internal discharge of the cells is very low, less then 3% in a month. The LFP cells are internally very stable and it would be a very unusual situation if the cell would discharge by itself in some way. It is virtually impossible that several cells in one battery would discharge at the same time. The reality shows that majority of these “discharge” failures are due to the negligence of the battery user.

If the LFP cells or the battery were deeply discharged, there is no way to restore them back to proper function.



23.Jun 2018
 
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