Just finished installing an on-grid MP2 120v/12v system with a 300ah LiFePO4 battery bank. My smart shunt is showing 0 amps at a float voltage of 13.8 as recommended by the battery manufacturer. I’ve been reading that it is not recommended to leave the batteries on float for extended periods and wondering if I should run the batteries down to about 75% SOC then disconnect the system for extended periods when the sump pump won’t be required? I could then reconnect the system when the pump might be required. Any feedback from those of you only using your equipment seasonally and storage off-season? Do you leave your batteries on float during the months that you’re using the equipment relatively often? I haven’t seen a way to keep the MP2 to abandon the float charging for LiFePO4 batteries.
I wonder where??
Lithium batteries can be left on float for extended periods, provided the float voltage is not too high. Typically for LiFePO4 cells, the max cell voltage is 3.65, giving 14.6V max charge voltage.
13.8V gives 3.45 V/cell which is ok. If you have really extended periods of float, this can be reduced to 13.6V, or 3.4V/cell. The higher the float voltage, the higher the rate of corrosion internally, leading to decreased lifetime. Lithiums also have a finite energy throughput, so cycling them daily also can reduce lifetime. This depends on the depth of discharge, and other battery specific parameters.
Thank you Mike. I just set the MP2 config to match the battery manufacturers spec at 14.6 charge and 13.8 float. The MP2 quickly adjusts the current during bulk/absorption and to zero at float according to the smart shunt. So I’m thinking that for extended periods when I know I won’t be using the sump pump (dead of winter for example) I could shut down the battery system (checking it every few months) and wake it back up in the Spring. Seems a lot of folks have similar questions on float/storage scenarios. Thanks again for your reponse.
Ok, but for winter storage, battery and inverter need to be stored in a cool, dry environment, battery can be safely left disconnected for 3 - 6 months, periodic checking, recharge if terminal voltage <12V. Batteries don’t like very low temps. 20-23C is good.
Thanks Mike! Appreciate your feedback.