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LFP Batteries below 20 percent?

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wpns

Solar Joules are catch and release
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I was talking to SS tech support about some other issues (Generator Dry Contacts) and I mentioned that I had set the "Generator" to come on at 10 percent and turn off at 50 percent, and he said that would be really bad for the batteries, that maybe 15% was as low as he would go, but 20% was really the lowest I should allow my PowerPro WallMount OutDoor batteries to get.

Does that make any sense? I mean, I don't _want_ to go down to 0% because that's approaching the limit of margin of error, and they might give up at 1% and then I'm toast, but why can't I cycle my LFP batteries 0-100% once a day for "only" 5,000 cycles for a 14 year lifespan instead of getting 8,000 cycles at 80% for a 22 year lifespan?

As per the other discussions, they don't actually warranty cycles, or total MWHR or anything but a 10-year pro-rated function warranty, and if I'm still around in 10 years and they are still in business, then the batteries have paid for themselves, and the new thing will be out anyway. I mean, I paid $700+ per battery for that last 20%, why can't I use it?
 
Just a bad idea. It can be done once in a while by accident, but to do it on purpose day in and day out seems like you think you are short on battery capacity and should just add another battery.

The once in a while IMO would be because it was a cloudy day and the generator won't start, so the full capacity is used before the sun is up.
 
Lithium-ion batteries, including LFP, have minimized calendar degradation when stored at 0%. In fact 0% is actually the ideal resting SOC as long as there's no vampire drain that overdischarges it to less than -10% or so. Since the PowerPro has a hard low voltage DC cutoff by the BMS at 44.8V = 2.8V per cell, there's not really any risk. 2.8V is above true 0% SOC = 2.5V standard definition of LFP anyways.
 
I get less confident in my BMS's SOC calculation below 30%. If it's wrong and a cell dips early that should drag the SOC down and set off the 10% trigger anyway, but I think it increases the likelihood of unexpected behavior due to SOC errors to dip that low intentionally.

My charger kicks on at 50% and off at 55%. But, that's all I need to leave room for my solar excess. If I needed more I would go lower.
 
olivinelife said:
Lithium-ion batteries, including LFP, have minimized calendar degradation when stored at 0%. In fact 0% is actually the ideal resting SOC
Click to expand...

Do you have a reference for that, because that's not what the generally accepted literature says. Typically LFP is stored at 30% to 50% SoC.
 
olivinelife said:
Lithium-ion batteries, including LFP, have minimized calendar degradation when stored at 0%. In fact 0% is actually the ideal resting SOC as long as there's no vampire drain that overdischarges it to less than -10% or so. Since the PowerPro has a hard low voltage DC cutoff by the BMS at 44.8V = 2.8V per cell, there's not really any risk. 2.8V is above true 0% SOC = 2.5V standard definition of LFP anyways.
Click to expand...

This was false, at least with regard to "long term storage" of recent LFP cells from some manufacturers (including EVE and CALB). For reference, I attach a attach a snaphot of adjacent (and conflicting) EVE "recommendations" for MB31 cells.

In section 4.9, they recommend maintaining SOC within a narrow range (30-40%), during "storage". But in section 4.9, they allow a lower minimum value (15%) if the cell is cycled (charge/discharge) at least once every 3 months. They recommend against storage exceeding 6 months. That lower minimum might be new with the MB31 cells. I think that the minimum of for the LF280K models (V2 and V3) was 30%.
 

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A more serious concern for the wpns (the original poster author) might be the limited ability of cells to safely accept high charge current at extreme states of charge. Even when a cell can handle a maximum charge current of 0.5 C, this needs to be reduced when temperatures are "extreme". But that rate also needs to be reduced at extremely low or high valuies of SOC.

That is the main reason why I red-line my own cells at about 14% minimum, cutting off further discharge automatically. (In bad situations, I can still re-enable "emergency use" in spite of low SOC.) My charge systems (RV "Converter" and Solar SCCs) do not make power adjustments for low or high SOC, and neither do my JK BMS units. I also limit my maximum charge voltage to 3.500 Volts (rather than 3.650 Volts) to avoid "pushing to hard" when the cells are already about 99% full.

Instead of using "100%", I generally limit my use to 85% - unless I need to go into that 14% reserve under unusual circumstances.
 
https://iopscience.iop.org/article/10.1149/2.0411609jes/meta
1720023443319.png

1720023509573.png

These are calendar degradation tests w/ long-term storage of many months. It is true that all lithium batteries have self-discharge during the course of long-term storage, and that there could be practical problems with storing close to 0%, especially if your whole system has unstoppable idle drain. There is no permanent damage risk with storing actual cells at 0% SOC until they are discharged to about -10%.

Regardless, OP is not asking about long-term storage. It is completely fine to cycle 100-0% if you are going to charge it back up again soon. There practical problems to operating close to 0% if you are running your house or EV on it, but it will not permanently damage the battery. Home blackout, phone dying, or getting stranded on the highway is really bad for you - the human user. That's why manufacturers do not "recommend" keeping your battery at 0% all the time.
 
Oke
Yes a lipo4 can do 0 to 100%>
But if you like to kill your bms after some years .

If you stay in the 10-95% the bms will last longer to use.
Special if the battery is close seal model .
If its diy battery than you can always swap easy the bms.

My battery come from Victron (Victron sell my battery for 2e option than Victron own battery)
And even Victron tell do not use a 100% .
 
rickst29 said:
A more serious concern for the wpns (the original poster author) might be the limited ability of cells to safely accept high charge current at extreme states of charge. Even when a cell can handle a maximum charge current of 0.5 C, this needs to be reduced when temperatures are "extreme". But that rate also needs to be reduced at extremely low or high valuies of SOC.
Click to expand...
Good point, but my two 18Kpv inverters have never made more than about 20KW total, my 6 batteries are never less than 60 degrees F, and looks like my maximum charge rate would be 0.25C.
And I'm not planning on running down to zero, but the SS tech seemed to think that setting my 'turn on the generator' setting of 10% was way too low and would ruin my batteries.
 
olivinelife said:
Lithium-ion batteries, including LFP, have minimized calendar degradation when stored at 0%. In fact 0% is actually the ideal resting SOC as long as there's no vampire drain that overdischarges it to less than -10% or so. Since the PowerPro has a hard low voltage DC cutoff by the BMS at 44.8V = 2.8V per cell, there's not really any risk. 2.8V is above true 0% SOC = 2.5V standard definition of LFP anyways.
Click to expand...
Where did you get this info from? I'm not sure this is correct.
At 0% you are risking the cells going too low.
When that happens, you could get to a point where irreversible damage could happen to the cells and they won't be able to charge up again.

Just look at any respectable LFP manufacturers datasheet, they all have some self-discharge! Although alot less than most other battery chemistries, but they still have it.

This is the reason most LFP sellers will ship batteries with at least 30% SOC. 30% to 70% SOC is recommended for long term storage of LFP.
 
meetyg said:
Where did you get this info from? I'm not sure this is correct.
At 0% you are risking the cells going too low.
When that happens, you could get to a point where irreversible damage could happen to the cells and they won't be able to charge up again.
Click to expand...

There have been many studies on over-discharge and what the true threshold for permanent damage is.
dx.doi.org

Influence of over-discharge on the lifetime and performance of LiFePO4/graphite batteries

In this study, the degradation of a LiFePO4/graphite battery under an over-discharge process and its effect on further cycling stability are investigated. Batteries are over-discharged to 1.5, 1.0, 0.5 or 0.0 V and then cycled 110 times under over-discharge conditions. The batteries...
dx.doi.org dx.doi.org
zheng2016.png

Also https://www.nature.com/articles/srep30248 for NCM cells.

As you can see there's no damage at 2.0V, so the 2.8V cutoff on the PowerPro is more than safe enough, providing that it will charged back up again soon. (I'm not sure about the idle power draw from the internal BMS, but the cells should be very closely matched). You might be surprised to learn that 3.6V (or 4.2V for non-LFP) is not the true physical/chemical 100%, and that you can actually charge them up even higher. However above 100% the battery can be permanently damaged and can be unsafe. The same rationale goes for below 0%. The 100-0% range is established by engineers and manufacturers as the usable range/capacity without undue amounts of degradation.

A lot of people have carryover knowledge from Lead-Acid where you shouldn't discharge below 50%, or old Nickel batteries which can develop memory effects.
 
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wpns said:
And I'm not planning on running down to zero, but the SS tech seemed to think that setting my 'turn on the generator' setting of 10% was way too low and would ruin my batteries.
Click to expand...
10% is too low because if you have BMS drift then it may suddenly jump from say 15% to 0% SOC and the generator won't have time to be activated. This would not damage the batteries, but would damage your happiness.

If you mitigate BMS drift by frequently charging to 100% or always starting from 100% then it's not a big deal. Or if your use case tolerates surprise shutdown and you're not purely relying on the batteries.
 
olivinelife said:
If you mitigate BMS drift by frequently charging to 100% or always starting from 100% then it's not a big deal.
Click to expand...
Indeed, it might go 3-4 days without hitting 100% but so far we’ve had 2 days in a row without a full charge. 🤷‍♂️. Never going to be a week
 
That's still pretty good for recalibration. Mine goes weeks without hitting 100% and it seems to run into an SOC correction after 2-3 weeks.
 
olivinelife said:
Lithium-ion batteries, including LFP, have minimized calendar degradation when stored at 0%. In fact 0% is actually the ideal resting SOC as long as there's no vampire drain that overdischarges it to less than -10% or so. Since the PowerPro has a hard low voltage DC cutoff by the BMS at 44.8V = 2.8V per cell, there's not really any risk. 2.8V is above true 0% SOC = 2.5V standard definition of LFP anyways.
Click to expand...
Actually, this is wrong. You can't store Li-Ion batteries at 0%, as this will damage them. Typical shipping SoC and storage is 20-25%
You can take LiFePO4 batteries to 0% temporarily, but best to not go below 20%. 30%-80% for best cycle life for either types of batteries.
 
wpns said:
Good thing we’re not using those old-school lead-acid batteries that you were only supposed to use half the capacity of. 🙈
Click to expand...
Lead battery for Solar systeem can do 60% use .
Still it can only handel max of 1200 cycle

If you use and abuse it go even lower.

So really lipo4 have the best cycle use.

Attach file is a lead battery.
 

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ShirBlackspots said:
Actually, this is wrong. You can't store Li-Ion batteries at 0%, as this will damage them. Typical shipping SoC and storage is 20-25%
You can take LiFePO4 batteries to 0% temporarily, but best to not go below 20%.
Click to expand...

Agree.

ShirBlackspots said:
30%-80% for best cycle life for either types of batteries.
Click to expand...

Disagree.

LFP is atypical of other lithiums in that charges to 100% are far less stressful than with NCM/NCA, etc.

The challenges of successfully targeting 80% as a peak charge are not worth the limited life gains of reduced SoC charges. Many have demonstrated near zero degradation after 5 years by still charging to 100% but limiting it to 3.45V/cell and allowing a longer absorption period (full charge, but at lower voltage and lower current).
 
Suijkerbuijk said:
Lead battery for Solar systeem can do 60% use .
Still it can only handel max of 1200 cycle

If you use and abuse it go even lower.

So really lipo4 have the best cycle use.

Attach file is a lead battery.
Click to expand...
You missed the part where shirblackspots said for best results use LFP 30-80 percent (aka 50 percent of capacity)
 
wpns said:
You missed the part where shirblackspots said for best results use LFP 30-80 percent (aka 50 percent of capacity)
Click to expand...

I have here on cell see attach files .
Its tell you.

Recommended SOC Us age Windom SOC:10%~90%
 

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  • EVE-LF280-3.2V-280Ah-LiFePO4-Battery.pdf
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