Quote:
Originally Posted by Joe Parklane
Question for the Board on dealing with LFP04 banks when at the dock in storage?trickle charge, a no no. I have Victron Multiplus 3000 set and a custom BMS. Unfortunately, I had these bank on storage mode float for several months prior to learning of the possible damage to the batteries CALB 180 ah 4X4 PS with micro boards on each super cell communicating with the BMS which can separate the bank via a solenoid should a HVC or LVC event occur. Currently my very conservative charging profile is controlled thru assistants that forces absorb voltage charging to float when voltage increases to 13.8/3.50vpc volts, float is set at 13.4/3.35vpc and current at 60 amps.. Currently after reach a full charge (90%) at the force to float point, I turn off charging.
Now the question:
I spoke with a Victron Tech in Maine that recommended setting the float voltage at or below the resting voltage for my bank i.e 13.1 This would result in no "real" charging until battery voltage fell to or below that point at which time the batteries would accept charging until forced to float again. This should keep the SOC of charge low enough to prevent damage to the by trickle charging albeit repeated shallow discharging and recharge well below 100% SOC. If cruising I would set the fLoat back to 13.4.
Thoughts as to this method to automatically prevent damage if not cruising?
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I recently ended a very expensive
experiment regarding storage SOC & LFP. The cells were 100Ah CALB SE's. I conducted this test because there was scant data on prismatic cells and
storage SOC in terms of real world scenarios.
The test
duration wound up being 12 1/2 months (intended to be 12 months but forgot about them) using four 100Ah CALB cells where they were charged to 100% SOC and then left to sit idle. The cells were wired in series, with no connections to a BMS or other parasitic loads. Just bare cells, at 100% SOC, sitting on the bench in my shop.
The low temp recorded over the 12 1/2 months was 46F and the high temp was 87F. This was meant to be a representation of the
real wold. Obviously if temps were consistently higher, the scientific data we have shows this, I would have expected to see even more capacity loss. A min/max capture thermometer was used to
record the peaks.
The cells, prior to letting them sit idle at 100% SOC for 12 1/2 months, were regularly & extremely consistently testing at 101.2 to 101.3 Ah's of capacity, over the previous six capacity tests, when tested for Ah capacity as a 12V nominal bank. These cells were used as the control or "gold standard" for the Practical Sailor AGM PSOC/sulfation testing.
After 12 1/2 months the cells were discharged to a cut off voltage of 2.9V for the lowest cell (my normal cut off for a capacity test). The Ah's delivered were recorded. They were then fully recharged and capacity tested four more times.
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. Remember this is just sitting there at full charge with no float....
Imagine if you additionally stressed the cells by continually
float charging them....
FWIW our LFP house bank is in storage at this moment and sitting at 50% SOC stored in our garage which runs about 40F - 60F during the off season (unless I have the heat on). Those cells are 2009 vintage and have lost nowhere near what the CALB cells lost in just 12 months of storage.
Our house bank is still delivering an Ah capacity well in excess of their rated 400Ah capacity when discharged at 0.075C or 3.75X our normal house discharge rate to 2.9VPC. The cells have never, ever been floated, never ever spent any appreciable time at 100% SOC and never regularly charged above 3.5VPC.
If we continue to tread LiFePo4, like it is lead acid, we are not doing ourselves any favors.
Best course of action for LFP is to charge then discharge and store at 50-60% SOC when not in use.
https://youtu.be/fGBmEh72UlY
These cells have:
--Never been floated, they get charged, then discharged
--Only
absorbed to a net 8A > 10A of tail current at 13.8V -14.0V
--Not charged above 14.0V unless for testing purposes (I now have a few other banks for that)
--Max charge rate at approx .3C
--Stored at 50% SOC when not being used or cycled
--Stored in 40-60F +/- temps when not being used or cycled
--Only very rarely exceeded 80F
--Highest voltage they have ever seen was 3.8VPC while top balancing initially.