Remote Solar Power Disconnect Switch Installation
Thanks, that's what I'm finding when researching lithium. Seems that high temperatures and long periods held at a high state of charge will make them age faster. Supposedly if you can use them in the 20% - 80% range or even a tighter middle range its best for them. Unlike lead-acid they don't need to be recharged fully, it's easy to do. That got me to thinking its probably not good to have them sitting a full charge on float charge the months that we are on full hookups in the summer.
If boondocking all the time it's not that big of a deal as time spent at full charge won't be as significant
I found one really interesting in-depth article done by a marine mechanic all about LiFePO4 batteries. https://marinehowto.com/lifepo4-batteries-on-boats/
This one section really stood out.
JUST SAY NO TO FLOAT CHARGING
Hardly a day goes by without someone asking if it is okay to float your LiFePO4 batteries. The answer, from me, is still going to be no. Float charging however has different meanings to different segments. In the lead acid world we charge to a high voltage of say 14.7V then drop back to a “float voltage that well exceeds the resting open circuit voltage of say a 13.6V float. This holds the bank at 100% SOC, a desirable feature for lead acid. LFP has no need to be at 100% and the mere act of storing them at 100% has a negative impact on battery life. I break “floating” & LFP down like this;
Float Charging LFP = Holding the cells at a voltage that results in the battery being maintained at 100% SOC continually
LFP Storage Voltage = A voltage that results in the battery being held at a “mid range” SOC or below 100% SOC.
Why do I break it down to “float” and “storage”? Because there is a lot of confusion surrounding this subject and the term float is really a lead acid charging subject. Many folks, who get stuck in a lead acid mind set, want to try and adopt lead acid charging practices to LFP and this can negatively impact cycle life.
Dockside Use: If you’re in a situation where charge equipment can’t be turned off or set to achieve a “mid-range SOC” and would necessitate floating the LFP bank, you can wire in a cross-over lead acid battery to handle dock-side loads. For dock side or unattended uses you ideally want to be able to discharge the LFP to 50-60% SOC and take it off-line. With the LFP bank in storage mode the small lead acid bank & shore charger can run DC system loads.
Alternatively a “storage voltage” can be applied that will allow the battery to slowly discharge to a mid-range SOC and then be held there by the charger. This approach essentially allows the charger to supply the house loads while the battery is comfortably sitting at a more comfortable storage voltage. Of course with this approach, if you lose dock power, you are relying on your BMS to protect the LFP bank where as with a lead acid battery taking dock side duty you lose a $100.00 battery as opposed to a 3K to 15K bank.
STORAGE SOC EXPERIMENT: I recently ended a very expensive experiment regarding storage at 100% SOC. The test duration wound up being 12 1/2 months using four 100Ah CALB cells where they were charged to 100% SOC and then left to sit idle with no connections to a BMS or other parasitic loads. The low temp recorded over the 12 1/2 months was 46°F and the high temp was 87°F and was meant to be a representation of the real wold.
A min/max capture thermometer was used to record the peaks. The cells, prior to letting them sit at 100% SOC for 12 1/2 months, were regularly testing at 101.2 to 101.3 Ah’s of capacity (previous 6 Ah capacity tests) as a 12V nominal bank. After 12 1/2 months the cells were discharged to a cut off voltage of 2.9V for the lowest cell. After 12 1/2 months of doing nothing but sitting there, at 100% SOC, the cells had lost 11.6% of their previous rigorously confirmed Ah capacity. Now imagine if you additionally stressed the cells by continually float charging them. Ouch!!!!
“The cells lost 11.6% of their confirmed capacity just sitting at 100% SOC”
How can these manufacturers suggest that the mere act of storage, at 100% SOC, is bad for the cells, which I have now confirmed is, and then suggest it is okay to float? How can they say “store at 50-60% SOC” yet then give you a “float” voltage? Really?