Sunsynk lithium battery management

[sybawoods]

I have a 5Kw inverter, 10.65Kw battery - both Sunsynk -connected to 10 x 550W panels. I run my battery on quite an aggressive (I think! compared to most others I speak to) cycle to maximize savings and make the most use of solar generation. So far, no issues, and electricity savings has been massive. The batteries run as low as 15% overnight - and generally anywhere from 50% to 80% during the day. I will obviously change settings when load-shedding is more active. About once or twice a week this time of the year, depending on sun and load, it will get to 100%. I'm wondering if there's any good practice to maximise battery health? Am I degrading the battery performance by using it in this way? e.g. is it ideal to keep it between say 30%-70%? Should I aim to get it to 100% every-day? Or does it not really matter with Lithium?

 

[Tomtomtom]

e.g. is it ideal to keep it between say 30%-70%?

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

Should I aim to get it to 100% every-day?

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.

 

[leon.davibe]

I have a 5Kw inverter, 10.65Kw battery - both Sunsynk -connected to 10 x 550W panels. I run my battery on quite an aggressive (I think! compared to most others I speak to) cycle to maximize savings and make the most use of solar generation. So far, no issues, and electricity savings has been massive. The batteries run as low as 15% overnight - and generally anywhere from 50% to 80% during the day. I will obviously change settings when load-shedding is more active. About once or twice a week this time of the year, depending on sun and load, it will get to 100%. I'm wondering if there's any good practice to maximise battery health? Am I degrading the battery performance by using it in this way? e.g. is it ideal to keep it between say 30%-70%? Should I aim to get it to 100% every-day? Or does it not really matter with Lithium?

If you don't get to 100% regularly
You could set it a tad higher

Cause the soc does drift
And thus you may cycle deeper than 15% without knowing it

Yes balancing only happens when cells are 3.45v normally 51.75(15s 48v) and 55.2(16s 51.2v)

And since most bms's have pathetic balance current if you get enough drift you can cause faster degradation to certain cells and since the battery is only as good as the weakest cell

I would avoid cycling to deep if you can't see individual cell voltages ie if they are still balanced at 15% soc then its fine imo if you don't go there too regularly i would not do daily

 

[wingnut771]

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.

Isn’t this intermediate charge thing more for NMC chemistry? LFP doesn’t really care which is why EV manufacturers say to charge LFP to 100% but only 80% for NMC.

 

[wingnut771]

I have a 5Kw inverter, 10.65Kw battery - both Sunsynk -connected to 10 x 550W panels. I run my battery on quite an aggressive (I think! compared to most others I speak to) cycle to maximize savings and make the most use of solar generation. So far, no issues, and electricity savings has been massive. The batteries run as low as 15% overnight - and generally anywhere from 50% to 80% during the day. I will obviously change settings when load-shedding is more active. About once or twice a week this time of the year, depending on sun and load, it will get to 100%. I'm wondering if there's any good practice to maximise battery health? Am I degrading the battery performance by using it in this way? e.g. is it ideal to keep it between say 30%-70%? Should I aim to get it to 100% every-day? Or does it not really matter with Lithium?

I don’t see any issue with this strategy. Maybe up it to 20% to give you some buffer for emergencies. It’s mainly the low socs (below 10%) that are heavy on battery health.

 

[SauRoNZA]

Can you actually use that last 15%?

I know I can't and hence mine is setup to 25% to account for load shedding.

Since you aren't getting to 100% at all I would definitely raise it.

 

[wingnut771]

Can you actually use that last 15%?

I know I can't and hence mine is setup to 25% to account for load shedding.

Since you aren't getting to 100% at all I would definitely raise it.

He did say:

I have a 5Kw inverter, 10.65Kw battery - both Sunsynk -connected to 10 x 550W panels. I run my battery on quite an aggressive (I think! compared to most others I speak to) cycle to maximize savings and make the most use of solar generation. So far, no issues, and electricity savings has been massive. The batteries run as low as 15% overnight - and generally anywhere from 50% to 80% during the day. I will obviously change settings when load-shedding is more active. About once or twice a week this time of the year, depending on sun and load, it will get to 100%. I'm wondering if there's any good practice to maximise battery health? Am I degrading the battery performance by using it in this way? e.g. is it ideal to keep it between say 30%-70%? Should I aim to get it to 100% every-day? Or does it not really matter with Lithium?

 

[chrisc]

I prefer to not discharge the battery beyond 50%. This increases the life, and at R25k a pop, you want to maximise your investment

Mine always get to 100% every day. The primary purpose of the system is not saving electricity, but having no load-shedding. However, we use between 3 and 4 units a day now

Output program:

Solar & battery only from 09h00 to 18h00
Thereafter utility if solar power insufficient

Charging program:

Solar first and utility if no solar available

It is a Kodak OG7.2. Whole house except geyser and stove
Separate Geyserwise ECO system with 2 PV panels

 

[wingnut771]

I prefer to not discharge the battery beyond 50%. This increases the life, and at R25k a pop, you want to maximise your investment

Mine always get to 100% every day

Your investment will last 15 years with full cycles. With half cycles it lasts 30 years. We will have invented zero point energy generator by then or your R25k investment will cost R5k to replace.

 

[Tomtomtom]

It is a Kodak OG7.2. Whole house except geyser and stove
Separate Geyserwise ECO system with 2 PV panels

Off topic but I find it insane you have to have two separate systems for this. It's redundant.

Inverters sold here need to start including a geyser output, rated separately from their inverter output (e.g. 8 kW AC + 3 kW DC) because it's just a question of diverting DC battery charger MPPT output. You would do this when the batteries have reached top of charge, basically sending their charge current to a geyser element instead.

 

[Greglsh]

Off topic but I find it insane you have to have two separate systems for this. It's redundant.

Inverters sold here need to start including a geyser output, rated separately from their inverter output (e.g. 8 kW AC + 3 kW DC) because it's just a question of diverting DC battery charger MPPT output. You would do this when the batteries have reached top of charge, basically sending their charge current to a geyser element instead.

Is this not what the SunSynk (and Deye) use the Aux port for, you can connect your geyser to this port and control how it works according to the soc of the battery

 

[Tomtomtom]

Is this not what the SunSynk (and Deye) use the Aux port for, you can connect your geyser to this port and control how it works according to the soc of the battery

No, the aux port is another AC output. So it competes with other loads for the inverter's total power.

But it's just a waste putting a geyser on an AC inverter. It's a simple resistive load, it only needs DC, it could draw directly from the panels, but they are more efficient with an MPPT. That's what Geyserwise is. But there just so happens to be (at least) one MPPT in the inverter too, for charging the batteries. And it is idle when the batteries are full. It should be possible to redirect that power to a geyser element. Then you could have your full rated AC output *plus* MPPT current going to your geyser.

 

[SauRoNZA]

I prefer to not discharge the battery beyond 50%. This increases the life, and at R25k a pop, you want to maximise your investment

To me not using the whole battery is not maximising your investment.

 

[leon.davibe]

I prefer to not discharge the battery beyond 50%. This increases the life, and at R25k a pop, you want to maximise your investment

Mine always get to 100% every day. The primary purpose of the system is not saving electricity, but having no load-shedding. However, we use between 3 and 4 units a day now

Output program:

Solar & battery only from 09h00 to 18h00
Thereafter utility if solar power insufficient

Charging program:

Solar first and utility if no solar available

It is a Kodak OG7.2. Whole house except geyser and stove
Separate Geyserwise ECO system with 2 PV panels

Yea the 50% makes sense with lead acid

But with lifepo4 not so much
ie iver the 15years it will last cycling it down yo 20%

And The energy saved between that 50-20% will be equal to the cost of the battery at current rates

ie 1.5kwh saved per day on a 5kwh battery

1.5kwh x 365 x 15=extra 8212kwh saved over 15years at current rates of almost R3=24k

But power won't stay at R3 a unit

So not cycling battery deep if you can is penny wise and pound foolish imo

 

[sybawoods]

Can you actually use that last 15%?

I know I can't and hence mine is setup to 25% to account for load shedding.

Since you aren't getting to 100% at all I would definitely raise it.

I haven't tried, but I guess theoretically, yes. Will need to check. I just felt that 15% was the lowest I'd be prepared to go. It's a balancing act obviously, but my objective tends more towards saving electricity cost (rather than loadshedding relief) so I do have this nagging feeling that I'm wasting 15% of potential solar energy everyday.

 

[sybawoods]

To me not using the whole battery is not maximising your investment.

This. For me too. But I guess everyone has different objectives depending on household needs.

 

[wingnut771]

I haven't tried, but I guess theoretically, yes. Will need to check. I just felt that 15% was the lowest I'd be prepared to go. It's a balancing act obviously, but my objective tends more towards saving electricity cost (rather than loadshedding relief) so I do have this nagging feeling that I'm wasting 15% of potential solar energy everyday.

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

 

[SauRoNZA]

I haven't tried, but I guess theoretically, yes. Will need to check. I just felt that 15% was the lowest I'd be prepared to go. It's a balancing act obviously, but my objective tends more towards saving electricity cost (rather than loadshedding relief) so I do have this nagging feeling that I'm wasting 15% of potential solar energy everyday.

I ask purely because mine actually cuts out when it goes below 15% and the battery’s own BMS protects itself from further use as that would mean warranty claims and extreme degredation.

Hence why mine is set to 25% so I have the buffer for Load Shedding of around 2kWh / 10%.

During these times where Load Shedding seems to be at bay somewhat I’ll lower it to 20%.

 

[leon.davibe]

This. For me too. But I guess everyone has different objectives depending on household needs.

Imo i would recommend cycling down to 20%

Not so keen on daily cycling down to 0%

Once in a while not the end of the world

It opens up your battery to much quicker degradation

ie you cyt battery life expectancy to almost a 1/3 in cycling down to 0% soc

And imo (salt) drift happens more drastic right at the bottom
And with most bms's having pathetic balance currents ,too much drift may put you in a downward spiral where one cell allways gets abused and then being weakest link drags down the whole battery amd the bms being unable to balance cells

i bought a second hand battery that was abused like this

None of the cells were in balance even after giving it 3months and even adding extra balance sessions by doing slight discharge forcing a charge cycle again

Eventually i opened it up manually balanced it

And now the bms can keep 14 of the cells in balance all except the abused/bad cell

The balance stays ok on this battery if i cycle it fown to 20-25%soc

every time i cycle it down to 0% the balance drifts and i have to manually adjust the weakest cell

Hence why i feel 0% is a bad idea for batteries especially on cheaper batteries where cell matching may be sub par

 

[leon.davibe]

I ask purely because mine actually cuts out when it goes below 15% and the battery’s own BMS protects itself from further use as that would mean warranty claims and extreme degredation.

Hence why mine is set to 25% so I have the buffer for Load Shedding of around 2kWh / 10%.

During these times where Load Shedding seems to be at bay somewhat I’ll lower it to 20%.

Yea i think some batteries forces a reserve for warrantee purposes

ie those offering long warrantee often do and those that don't only care for capacity not caring to cycle deep knowing the battery will likely fail after the short warrantee window has expired

Have heard some installers say that some warrantees are subject to not cycling under 20%

Take the life batteries it is printed on them ie 4/5 4kwh usable 5kwh total
Or 8/10