Sunsynk lithium battery management

[leon.davibe]

What do the specs say? Technically, LFP can go to 0%, in doing that it will still last 15+ years.

As far as i have it 20% soc often 5-6k cycles

And down to 2k cycles if 0% cycled

Or this is what some lifepo4 spec sheets say

Now naturally once in a while isn't the same as daily

So i aim for 20% daily and don't care if i do hit 0 a handful of times

Have only done about max 5 0% cycles

 

[wingnut771]

As far as i have it 20% soc often 5-6k cycles

And down to 2k cycles if 0% cycled

Or this is what some lifepo4 spec sheets say

Now naturally once in a while isn't the same as daily

So i aim for 20% daily and don't care if i do hit 0 a handful of times

Have only done about max 5 0% cycles

I was asking about the sunsynk specs.

 

[sybawoods]

I was asking about the sunsynk specs.

 

[sybawoods]

Bottom section of the Maintenace requirements refers to “Over Discharge” as 90% DOD, so I guess 20% is probably a safe floor limit?

 

[wingnut771]

View attachment 1698621

45.6V is quite a conservative cutoff voltage so they are not going all the way to 0% SOC. LFP @ 0% SOC is 40V.

They recommend going down to 20% SOC.

So, it looks like you are already maximising your investment. I wouldn't change a thing.

 

[leon.davibe]

I was asking about the sunsynk specs.

This 20% 0% cycles count difference are seen in most lithium batteries

Except the new sodium they claim 0% soc degradation does not apply

Lots of salt naturally

This is how hubble gets higher cycle count on its nmc based 48/51v can't recall what its voltage is

Essentially it is being used in this 20-? band

So that when you see 0% the cells are actually over 20%soc
And the same at full though i think it comes closer at the upper side of the soc

Hence why i think full charge is less detrimental vs running flat

Since they avoid that part with a bigger margin

 

[sybawoods]

View attachment 1698639
45.6V is quite a conservative cutoff voltage so they are not going all the way to 0% SOC. LFP @ 0% SOC is 40V.
View attachment 1698641
They recommend going down to 20% SOC.

So, it looks like you are already maximising your investment. I wouldn't change a thing.

Thanks and thanks everyone for the guidance. I’m setting it to 20% until load-shedding makes an appearance again.

 

[leon.davibe]

Yes, lithium gives the longest cycle (and shelf) life if it's kept in the intermediate charge range, like 30-70%.



It won't help cycle life to fully charge them, but there are reasons to go to 100% now and then e.g. to balance the cells and recalibrate the SoC indication. Not sure what interval would be best though.

It depends on how accurate the bms counts current

I have a jkbms on diy battery and a shoto

And both of them drifts enough in a day that i try and go to full every day (small battery bank) if i had a bigger bank i would maybe do less frequent if i did not have to go to 20% soc to maximise solar panels i have

Most of the drift happens in that scenario where solar is close to meeting load ie low amps in and out of battery

When i had no solar ie only battery backup i had very little drift

So in trying to maximise savings have been caught off guard by bad weather/shedding/power outage

And have a shutdown when i believe there to still be some juice in the battery according yo SOC anyway

Hence why i think this whole 20-80 battery life extension hack

May do more damage that what it supposedly can gain