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Storing LiFePO4s for the winter

PeterBC

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Nov 4, 2020
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I'm planning my first install on my boat soon. It will spend 6-9 months idle in European winter etc. Ive chosen the Electrodacus for my BMS. I am concerned that Daican doesnt not believe it harmful to keep the batteries at 100% over winter. There does not seem to be a easy way to get it to reduce to less than say 70%. Picking a lower highvoltage disconnect (eg 3.4V ? 3.3 ? ) doesnt seem that safe or accurate to pick a lower SoC setting. Ideally I'd like a 'storage mode' where it only charges if SoC is say 30% and stops at 70%. Its not easy or accurate I think to try and pick voltages for these SoC levels. From readings I've done I am of the belief that storage at 100% (and keeping it there every day all day) is not ideal, and can affect life span in cycles , and/or capacity. (Not disastrously, but enough to warrant not doing it).

An alternative is to switch over to some basic Lead Acids for winter storage and change my Victron Quattro profile to suit them, and disconnect the LiFePO4 , including the BMS.. That would also solve any possible low temp charging issues (which I can put thermistors into the SBMS0 of course).

Comments ?
 
Science agrees with you. Lead Acid love to stay at 100%, LiFePO4s degrade there (as Peter knows, this post was moved from https://diysolarforum.com/threads/soc-degradation-of-lifepo4.13215/#post-147521 so his specific case could be discussed).

There's also @Inq720's thread What is a cycle and how many of micro-cycles can I get? that reveals LiFePO4 have a memory effect, that is you get stuck at the memory voltage (and lose capacity) if you don't occasionally fully charge your battery to wipe out the memory effect. So, lowering your max voltage on your BMS and leaving it there for a long time (years?) is also bad for your batteries.

But in this case, if the batteries aren't being used over winter, why not just disconnect them? They don't self-deplete like lead acid will, so unplugging them over winter and doing nothing should be fine.
 
Thanks svetz for moving my post here..

I am considering disconnecting the batteries (and BMS) over winter. But I do need some 24V systems for safety (eg auto bilge pump). Also I prefer to monitor a security camera and weather station to know my boat (a 100 yo barge in France/BE/NL) is still floating (and has power). I am considering reconnecting some Lead Acids for winter , connected to my Quattro (reprogrammed from LiFePo4 friendly voltages to a std Gel profile)
and also my solar and/or shore power. But thats yet another configuration and winterisation/dewinterisation task of many to add to the list.

The purist in me wishes my smart BMS system could do this for me. I did read 'somewhere' that one BMS detects that after x days of no significant load drawn from the batteries it would go to 'storage' mode and maintain a lower SoC (I think 70% ?). Of course getting to that SoC could be a challenge if no loads present. Lets assume I could manually get there by disabling charging the last few days of the 'season' , and perhaps even manually telling my BMS to go to 'storage' mode. Given shore power and solar may be available, what should storage mode look like ?
Allow drop to 30% SOC, and then charge to 60% , then repeat ?

I think I will have to disconnect my batteries in the short term, until I see a smarter BMS or changes to my Electrodacus software. My initial discussions with Dacian show he does not believe it a problem to keep them at 100% over winter if I'm on shore power. I fear he is more thinking of home solar systems with regular loads and charging, not a 'hibernating' situation common with Boats.
 
From the Lishen 272AH Data Sheet.. (the batteries I have on order)..


5.4 Storage and Usage
a) For any short time storage (in one month), cell should be in a clean and dry area
(humidity ≤65% RH) and at -30℃ ~+45℃ at 20~40%SOC .
b) For any long time storage (in 6 month), cell should be in a clean and dry area(humidity
≤65% RH) and at -20℃ ~+35℃ at 20~40%SOC.
 
Hopefully someone can recommend a device to augment/replace your BMS that handles programmable high voltage cutoffs that's cheaper/easier than having a second set of lead acid batteries. Seems like a microcontroller relay to disconnect the solar when the battery voltage hits your max or the temperature is too low would do it (or possibly use excess solar to warm the batteries up). You could possibly share notes with Inq720 who may be planning on building something similar that also eliminates issues from micro-cycles.
 
One soln suggested is to set the Victron devices to a float voltage of 26.2 V , which is 3.275V/cell.. I hadnt thought about using the Victron charge profiles to deliberately 'override' the SBMS0's desire to charge till HVD. (3.55V) every day all day if Shorepower or solar present. 3.275V is about 50-60% SoC I understand. The negative of this mode would be that it would never recalibrate SoC in the SBSM0 , but it shouldnt matter as maintaining 3.275 is a lot safer than 95 -100% for 9 months (3.55V/cell). Once season begins reset the Float /Absorbption Voltages to something like 28.4v (3.55/cell) and we should charge almost full again and reset the SoC on the SBMS0.
 
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