Hi all,

I've just helped my in-laws on a farm to install a "UPS" system (Growatt SPF5000-ES and 2x Pylontech US3000C batteries) for 3 essential circuits in their house.  No solar as yet, as their primary goal was to keep office on for 12 hours without having to start the generator...   ESKOM sometimes is down as well, being a relatively rural area.

So, now I'm considering which option is better to extend the life of the batteries:

a) Keep the inverter in SUB mode, which means 100% capacity of battery when ESKOM goes dark, and potentially once a week switch to SBU to have the batteries "drain" to 50% (or some other level), to at least "work" a bit, or

b) Keep the inverter in SBU mode, changing to "utility source" when reaching 50% (some marging of safety if ESKOM goes dark when batteries are on 55%!) and back to "battery mode" at 95%, and potentially once a week switching to SUB mode to get to 100% to NOT build up memory or otherwise damage the battery (if that can even happen on these type batteries)?

The above two scenarios are what I thought would be the most likely options to "best" run the (what is essentially a big) "UPS" system.  Any thoughts or best practice guidance would be highly appreciated, as I've tried Google, and could not find any definitive guide on "optimal usage" of these large Li-ion batteries.

 

 

 

Here is the illustration of scenario B above...

Here are my thoughts, after further research, including links to key words used:

• https://www.google.com/search?q=pylontech+prolong+lifespan+cycle+soc
• https://www.google.com/search?q=extend+lithium-ion+battery+lifetime+pylontech

 

Results from further research is noted beneath each referenced URL.

• One should "Charge them up to 100% regularly (at least once a week) and keep them at that level for an hour or two to do some balancing."     I've not managed to find ANY other reference site that says this is best practice however!   Potentially the Pylontechs even do some "own balancing" when above 90% SOC, I'll write to Pylontech and hope for a response on the "regularly charge to 100% to balance" recommendation.

 

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

• The LOWER the DOD is, the MORE cycles you'll get out of your batteries.  (Table 1)
• "Cycling in mid-state-of-charge would have best longevity."   --> in other words, pick your own SOC levels and swop between SUB (bottom end) and SBU (top end) and keep cycling!
• Cycling between 75% and 65% prolongs cycle count dramatically  (Figure 3  https://batteryuniversity.com/img/content/DST-cycles-web2.jpg)

 

https://www.youtube.com/watch?v=Yf9N9zBgyB8

• It is NOT advisable to charge the battery to 100%, as it degrades battery life  --> https://www.youtube.com/watch?v=Yf9N9zBgyB8&t=225s
• Best SOC cycle range is close to 50% --> https://www.youtube.com/watch?v=Yf9N9zBgyB8&t=318s

 

https://www.4x4community.co.za/forum/showthread.php/331255-Lithium-Battery-Life-Expectancy?p=4415198#post4415198

• "Ideally, your li battery should be charged to 90% max and discharged to 80% DoD (20% SOC) to prolong it's lifespan.  That's the "perfect " charge / discharge limits..(as per battery university)"   -->  could not find a confirmation on the batteryuniversity.com site to confirm the 20% SOC "low" level, but the 90% "high" level seems in order 

 

https://www.electronicdesign.com/markets/mobile/article/21190344/proper-care-extends-liion-battery-life and https://news.umich.edu/tips-for-extending-the-lifetime-of-lithium-ion-batteries/

• "Using only 20% or 30% of the battery capacity before recharging will extend cycle life considerably."
• "Avoid charging to 100% capacity"

 

My setting that I'm using now on the "UPS" will therefore be to cycle between 65% SOC and 85% SOC, until such time as I've heard from Pylontech whether it is necessary/advisable to bring the SOC up to 100% at all. 

I'd welcome any further thoughts or critique.

Hi there! 

Just stumbled upon this - as I am keen on trying to balance between keeping enough charge to see out load shedding, and maintaining a healthy battery long term!

Did you get a reply from Pylontech?

Thanks!

Pete

Nope, no reply from Pylontech.