New to Life PO4

[Rgulack]

Just installed a new system; 2560 watts solar on a pedestal mount, Victron MPPT 250/100, Victron Quattro 48v 5000/70, Lynx LifePO4 48v/200ah/10KW W/Daly BMS. All the com, bluetooth, and associated software installed. Trying to keep the batteries between 50% and 95% SOC. Tweaking and searching for the most efficient settings and they are numerous. Monitoring batteries with Victron Smart Shunt and Victron Connect software. SOC on Quattro and Smart Shunt never agree. Live in NE Washington, so solar averages 2 kw or less per day this time of the year. Am running the genset about 2 hours per day. When the LED’s on the battery says it is full, the Quattro says 96% and the Smartshunt says around 76%. Haven’t made sense of that yet?

 

[rmaddy]

It's not entirely clear what your question is. Please clarify what you need help with exactly.

 

[Rgulack]

According to the smart shunt SOC is only 76% when the rest of the system says 95% SOC. According to the battery voltage of 55.3 and the chart I found, 76% is close. I probably need to change the parameters on the charger to get 95%?

 

[rmaddy]

55.3V for LiFePO₄ is well over 99% SOC. 76% SOC would be more like 53.0V.

 

[MisterSandals]

Trying to keep the batteries between 50% and 95% SOC.

Why? Longevity?
It sounds like you bought twice as much battery as you need.

According to the battery voltage of 55.3 and the chart I found, 76% is close.

I probably need to change the parameters on the charger to get 95%?

Is there something wrong with your system or are you fussing over numbers and anxious to make changes?

 

[Rgulack]

Great chart !!! All seems to be working correctly. Voltage was 52.92 this morning, about 75%, when I started the gen. Average load overnite was 150 watts. SOC LED’s on battery were down from 6 to 1 with red warning lite blinking. I need to get into the software on the BMS and see what is going on. I have heard that using voltage as the measure of SOC is not that accurate as the curve is so flat ? Will rely on the smartshunt as soon as I get it set correctly. Thanks for the input. ??

 

[Rgulack]

Great chart !!! All seems to be working correctly. Voltage was 52.92 this morning, about 75%, when I started the gen. Average load overnite was 150 watts. SOC LED’s on battery were down from 6 to 1 with red warning lite blinking. I need to get into the software on the BMS and see what is going on. I have heard that using voltage as the measure of SOC is not that accurate as the curve is so flat ? Will rely on the smartshunt as soon as I get it set correctly. Thanks for the input. ??

Also, I really appreciate Y’all’s patience with my slow learning curve ??

 

[Steve_S]

Using the voltage to determine the SOC is the only option with these batteries (All lithium etc).
Accuracy is relative as well,
1) the Shunt has to be a good one (you'd be surprised),
2) the software has to be able to handle accuracy, preferably 3 decimal points, Lithium is Millivolt & Milliohm.
3) the readings are always affected whether charging/discharging or in "storage" mode. See Chart Below for Load/Rest values.

Clarification on what is FULL !
LFP Full Voltage Curve is 2.500-3.650. Full Working Voltage curve is 3.000-3.400 with Nominal being 3.200.
Gross Cell Capacity is rated from 2.50-3.65 BUT the Deliverable capacity (Grade A) should deliver specified AH rating from the Working Voltage.
This is why Grade-A Cells test out on average 10%+ higher than label rating. From 2.50-2.95 & 3.40-3.65 only represents 5-7% of Gross Capacity which more reserve off anyway.
Cells charged to 3.425 and fully saturated (meaning Amps taken drop as IR increases) will still settle (Normal for LFP) and that can be considered 100%. NOTE on Settling, it is quite Normal for LFP to settle as soon as charge ceases, the majority of settling occurs within 1 hour without loads being applied.

BMS & Other monitors accuracy.
Virtually all BMS' and shunt based monitors must go through a full cycle from your designated 0% SOC to your 100% SOC to be accurate for YOUR system setup. For example, my 100% is 3.400Vpc and my 0% is 2.85Vpc (Vpc = Volts per cell). Once everything is discharged to below "my 0%" I then charge to "my 100%" and stop when saturated. At this point the Shunts & BMS Coulomb Counters are starting from my designated point.

Hope this Helps, Good Luck.
Steve_S

 

[MrM1]

Using the voltage to determine the SOC is the only option with these batteries (All lithium etc).
Accuracy is relative as well,
1) the Shunt has to be a good one (you'd be surprised),
2) the software has to be able to handle accuracy, preferably 3 decimal points, Lithium is Millivolt & Milliohm.
3) the readings are always affected whether charging/discharging or in "storage" mode. See Chart Below for Load/Rest values.

Clarification on what is FULL !
LFP Full Voltage Curve is 2.500-3.650. Full Working Voltage curve is 3.000-3.400 with Nominal being 3.200.
Gross Cell Capacity is rated from 2.50-3.65 BUT the Deliverable capacity (Grade A) should deliver specified AH rating from the Working Voltage.
This is why Grade-A Cells test out on average 10%+ higher than label rating. From 2.50-2.95 & 3.40-3.65 only represents 5-7% of Gross Capacity which more reserve off anyway.
Cells charged to 3.425 and fully saturated (meaning Amps taken drop as IR increases) will still settle (Normal for LFP) and that can be considered 100%. NOTE on Settling, it is quite Normal for LFP to settle as soon as charge ceases, the majority of settling occurs within 1 hour without loads being applied.

BMS & Other monitors accuracy.
Virtually all BMS' and shunt based monitors must go through a full cycle from your designated 0% SOC to your 100% SOC to be accurate for YOUR system setup. For example, my 100% is 3.400Vpc and my 0% is 2.85Vpc (Vpc = Volts per cell). Once everything is discharged to below "my 0%" I then charge to "my 100%" and stop when saturated. At this point the Shunts & BMS Coulomb Counters are starting from my designated point.

Hope this Helps, Good Luck.
Steve_S
View attachment 81048

If this info is accurate (and I believe it is) this is one of the best single post explanations of LFP and voltages that I have ever seen.

 

[MrM1]

Cells charged to 3.425 and fully saturated (meaning Amps taken drop as IR increases) will still settle (Normal for LFP) and that can be considered 100%.

What do you consider "Fully Saturated"? How much amp drop relative to voltae and to IR?
- Would that be charging to 3.425 and 0 amps (which would involve a long "hold" at 3.425),
- OR charging to 3.425 and 2% of C (5.6 amps for a 280Ah cell).
- OR some other?

How do arrive at "Fully Saturated"?

 

[upnorthandpersonal]

Trying to keep the batteries between 50% and 95% SOC.

Just putting this out there in case: you don't have to keep them above 50% - that's a lead acid thing. Feel free to do down to 20% or even 10%.

 

[Steve_S]

What do you consider "Fully Saturated"? How much amp drop relative to voltae and to IR?
- Would that be charging to 3.425 and 0 amps (which would involve a long "hold" at 3.425),
- OR charging to 3.425 and 2% of C (5.6 amps for a 280Ah cell).
- OR some other?

How do arrive at "Fully Saturated"?

Saturated as opposed to surface... Again terms get fiddly so lets not fall over that.
If you charge to 3.425 and just stop, that will settle at least 2 times lower, maybe more because that's just to the Voltage Point and no saturation. If you charge the cell and allow amps taken to drop, the lower it drops the more saturated at THAT voltage. More Saturated = Less voltage drop on settling.

Charge Profile PITA, sadly SCC's & Inverter/Chargers etc all do their own thing to a point. It's way too broad to cover simply.
Simply put, EndAmps / TailCurrent is more or less the completion point. A 280AH Battery Packs EndAmps = 14A. (280AH * 0.05 = 14A) which is saturated, more charge can be pushed and that will decrease as IR increases right own to 1A if you want but there is no gain there.
This is where the "To Float or Not to Float" nonesense begins... mostly because many don't get that FLOAT = Constant Voltage VARIABLE CURRENT and Lithium Based Batteries require CC (Constant Current) to get them to 90-95% FULL (pending on cell & chem) and THEN CV to finish the to 100%. IF you Push too high an Amperage as the cells reach above 3.375 +/- that's when runners take off & imbalance deviations happen.

GOTCHA With a Battery Bank with 2+ Packs.
EndAmps/TailCurrent is always based on the Largest Pack in the bank, this is because it will be the last to reach 100% and the last to reach 0%.

 

[Rgulack]

Just putting this out there in case: you don't have to keep them above 50% - that's a lead acid thing. Feel free to do down to 20% or even 10%.

Was told by the Tech at Lynx Battery in Seattle that if I kept the system between 50% and 95% I could expect close to 20 year life span. Does it really make that much difference?

 

[upnorthandpersonal]

You have at least 2500 to 3000 cycles (on new batteries) worst case scenario. That's a full cycle every day for 7 to 8 years. At that point, they don't stop working, they're just at 80% of their rated capacity. At 20 years, you probably have calendar aging that takes over instead of cycle aging. In addition, solar applications are hardly stressful on these cells, with relatively low charge and discharge rates. I use mine for the full capacity because I want to use the capacity I paid for - just like your operating system uses available RAM you paid for (and having RAM sitting idle just wastes money spent on it).

 

[MisterSandals]

Great chart !!!

That was created by Steve_S who has chimed in with more of his wisdom.

I have heard that using voltage as the measure of SOC is not that accurate as the curve is so flat ?

Just look at the chart, a .2 voltage change is the difference between 30% and 80% SoC (i just made that up but you get the idea). Differences in battery packs also make voltage harder to use with charts in mid voltage/SoC.

BUT, on the ends its good enough for me. On a 12.8V battery, if i see 13.0V, its getting low and 13.3V+ its pretty full.
Once you watch your battery for a few weeks you'll get used to watching voltage...you'll see.

 

[Rgulack]

That was created by Steve_S who has chimed in with more of his wisdom.


Just look at the chart, a .2 voltage change is the difference between 30% and 80% SoC (i just made that up but you get the idea). Differences in battery packs also make voltage harder to use with charts in mid voltage/SoC.

BUT, on the ends its good enough for me. On a 12.8V battery, if i see 13.0V, its getting low and 13.3V+ its pretty full.
Once you watch your battery for a few weeks you'll get used to watching voltage...you'll see.

Considering the above, what voltage settings should I be using for bulk and absorb cycles in my Victron MPPT 250/100 and Quattro 48/5000/70 ??

 

[Ampster]

BUT, on the ends its good enough for me. On a 12.8V battery, if i see 13.0V, its getting low and 13.3V+ its pretty full.

Voltage also works for me if I want to use adjectives to describe my SOC. My pack also sometimes gets low and after a day of good solar it is pretty full. My BMS and inverter do not use adjectives. so I have to use numbers like 3.4 volts per cell to tell it when to stop charging. That voltage is when it is pretty full.

 

[rmaddy]

Considering the above, what voltage settings should I be using for bulk and absorb cycles in my Victron MPPT 250/100 and Quattro 48/5000/70 ??

For a 48V LiFePO₄ battery you want the absorption voltage set to 56.8V (56.4V - 57.2V) and the float voltage set to 54.0V (54.0V - 54.4V).

When you setup the SmartShunt, set the "Charged voltage" to be 0.1V less than your absorption voltage setting.

 

[MisterSandals]

Heh, i'm typing a little slower than rmaddy but looks like we're on the same page.

Live in NE Washington, so solar averages 2 kw or less per day this time of the year. Am running the genset about 2 hours per day.

what voltage settings should I be using for bulk and absorb cycles

It sounds like you have a good incentive to squeeze as much out of the batteries as possible because it reduces generator run time (costly, time consuming and annoying).

I'll recommend higher settings than what i use because i am a pretty conservative charger (3.45Vpc absorb, 3.32Vpc float as my cells settle to 3.35Vpc).

I recommend that you try 3.5Vpc or even 3.55Vpc absorb to maximize capacity (though its only marginally more capacity). And since it sounds like you are using these full time with 24/7 loads so float at a higher value like 3.4Vpc. If your cells don't behave this high, you'll have to back of the absorb a bit to keep the BMS from terminating charge.

 

[Steve_S]

@Rgulack there is something that went unmentioned essentially.
Remember that there IS voltage & amperage drop from Solar Controller to Battery & Battery to Inverter. This is where calibrating things to operate correctly and within the required voltages requires a bit of OCD Anality ! (there's a mental picture for ya) LOL.

The SCC is charge only so you have to set that accordingly.
When charging by solar ONLY and NO Inverting being done (so idle BUT running) read the voltage at Batt Terminals, and then at SCC terminals. Adjust your voltage setting on SCC to COMPENSATE for voltage loss across the wires, breakers, fuses etc... The key is WHAT is being seen at the Battery Terminals.
The Inverter again is different because of added voltage sag while operating and that floats relative to load. With a "Normal & Usual" load being inverted, check BATT terminals against the Inverters Terminals. You MUST ensure that when the Inverter sees the "CUT OFF" Voltage that it is correct. If this is off, then for a 48V System you want cutoff Absolutely no lower than 40.0V (2.50Vpc) but 44.0V (2.750Vpc) is safest. But even 1.0V drop would result in cutoff @ 39.0V which is BAD ! Again the correction here is for when the Inverter is discharging the Normal Load. So if you have a 1.0V drop between Inverter & Battery then you would compensate by changing Inverter Parameters to correct for it.

Far too many people forget about the voltage & amperage drop across the wire & attached gear in between, and while it may be 0.5V for one and 1.5V for another it all must be corrected so what is happening at the Battery Terminals is correct. Every single item, like breaker, fuse, connector, shunt etc ALL add to Voltage & Amperage Loss. There are Shunts out there that lose 1.5V just crossing it! Also Fuses can really drop voltage, soem better than others are ALL depending on the Amps the fuse has to handle...

There are links to resources in my signature that will answer most of these questions and more.
Hope it helps, Good Luck.