Charge Profile Settings - What do you run?

[Mrdanielmh]

Im trying to gather data around how people have their charge profiles set for different charging sources. There is such vast information out there, and i think itd be good to get real world examples.

I suggest copying the following and putting your information in!

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Charging Source: EG: Solar MPPT/B2B/Battery Charger
Charging Source Max Amps:
Float Voltage:
Absorb Voltage:
Absorb Time:
Experience: EG, SOC information, other noteable comments

If im missing some parameters let me know! Lets gather some real world for LifePo4 charging profiles!

 

[Frosty]

I'll follow this thread and contribute when I can, there's so much contradicting information out there I'm also a little lost so it'll be good to hear some feedback from some more experienced users.

 

[sharpey]

Agreed. After a back and forth email with Dacian from the SolarBMS project, I'm not sure what I should set my Solar Charge Controller (SCC) EPEVER Tracer 3210AN at. Since the BMS will be cycling the SCC, perhaps I just want to put out bulk current/amps all the time?

 

[Reed Cole]

I'm certainly not an expert but my charge controller has a lithium charge profile that is simply Bulk - 14.4v. Seems to be working fine with my two 100ah Battleborns.

 

[Frosty]

I'm certainly not an expert but my charge controller has a lithium charge profile that is simply Bulk - 14.4v. Seems to be working fine with my two 100ah Battleborns.

What SOC do you cycle your batteries to and from? I have a 400ah sinopoly diy lifepo4 battery that I'd like to cycle from 10% - 90% and I'm trying to find a definitive answer on what the charge profile would be for this.

 

[Steve_S]

for LiFePO4 24V system: (÷2 for 12V) or (X2 for 48V)

Bulk Voltage: 28V - 29.2V
* Absorption Voltage *: 28V - 29.2V Absorption Time 0-15 min
* Float Voltage *: 26.6V - 27.6V
* Equalize *: OFF or as short time possible @ float voltage
* not necessary
VOLTAGE CUTOFFS Low Voltage: 22V High Voltage: 29.2V

from https://www.mobile-solarpower.com/design-your-own-12v-lifepo4-system.html
Recommended Charge Profile:
12V LiFePO4 Battery w/ BMS:

• Absorption: 14.5V
• Float: 13.6V
• Inverter Cut-off: 10.7V-12V (depending on size of load and voltage drop etc)

24V LiFePO4 Battery w/ BMS

• Absorption: 29V
• Float: 27.2V
• Inverter Cut-off: 21.4V-24V

48V LiFePO4 Battery w/ BMS

• Absorption: 58V
• Float: 54.4V
• Inverter Cut-off: 42.8V-48V

Individual 3.2V LiFePO4 Raw Cell (for individual cell capacity testing)

• Absorption: 3.625V
• Float: 3.4V
• Low voltage disconnect for capacity testing: 2.5V

If you are using a BMS and wish to manually cycle up to 90% SOC:

1. Do a discharge capacity test with a shunt. Record capacity in watt hours.
2. Charge slowly up to 90% SOC (take capacity Wh figure and multiple by .9), and while charging, record the voltage right when it hits 90% SOC
3. Set the absorption for all chargers in system to the voltage you recorded in step 2

5,000+ Charge Cycle Absorption Recommendation
If you want your LiFePO4 cells to last a long time, you can set your absorption to Victron's custom LiFePO4 charge profile recommendation:

• 12V Battery: 14.1V
• 24V Battery: 28.2V
• 48V Battery: 56.4V

You can pull full capacity with the absorption figures above, but the charge rate will be reduced at high SOC.

 

[Sojourner1]

Charging Source: Solar_Magnum PT100, max 80a (.16c)
Charging Source: Magnum Inverter/ Charger, max 125a (.25c)
Absorb Voltage:14.1v (3.52 vpc)
Absorb Time: 10 minutes the least it can be set for, 6 minutes is usual amount of time it lasts.
Float Voltage: 13.6v (3.4 vpc)
BMS
Inverter LVD: 12.0v
Cell LVD: 2.8v (30 sec delay)
Cell HVD: 3.8v (3 sec delay)
Temperature: 32°F (30 sec delay), 150°f (30 sec delay)

April 2016 systems been on 24/ 7/ 365 with these settings.

 

[MisterSandals]

I'll play!
A lot of this is experimental. I am trying to find out what "charge to 90%" means in terms of charge voltage. According to the popular chart below (yea, i know voltage is not an accurate measure), 90% should be around 13.35v. So inching my way down, taking notes and trying to learn something. I am still seeing everybody charging to 100% and claiming to want to charge to 90%.

Charging Source: Solar MPPT, Morningstar Tristar MPPT 45
Charging Source Max Amps: throttled to 20a
Float Voltage: 13.2
Absorb Voltage: x
Absorb Time: 0
Bulk Voltage: 13.8v (max charge)
Experience: charge to 3.45, they quickly settle to 3.35, float 3.3
Battery: 8x 206ah LiFePO4 2P4S no BMS

Charging Source: Solar MPPT, Victron 100/30
Charging Source Max Amps: 8 (temp experimental setting)
Float Voltage: 13.2
Absorb Voltage: x
Absorb Time: 0
Bulk Voltage: 13.6v (max charge) (temp experimental setting)
Experience: charge to 3.45, they quickly settle to 3.35, float 3.3
Battery: 4x 206ah LiFePO4 4S, Testing 8A separate port Daly BMS

 

[Mrdanielmh]

This is awesome, keep them coming!

 

[Reed Cole]

What SOC do you cycle your batteries to and from? I have a 400ah sinopoly diy lifepo4 battery that I'd like to cycle from 10% - 90% and I'm trying to find a definitive answer on what the charge profile would be for this.

I just use the electricity my system provides and don't worry about it too much since everything seems to he working fine without any fuss. It took me thirty seconds to setup my controller and Battleborn says you can use all 100% of their batteries.

I only recently added the second battery and the solar to my van so I still need to get a fridge and find some other ways to use some electricity and find a good balance of taking advantage of most of the electricity I can generate while still having some reserve for poor sunlight conditions.

 

[Ped]

Bulk - 14.7v (14.6v @ terminal)
Float - 14.5v
Bulk time - 180

 

[MisterSandals]

Bulk - 14.7v (14.6v @ terminal)
Float - 14.5v
Bulk time - 180

Does this mean you charge in bulk mode (which i understand as max charge amps) until you get to 14.7v or 180 minutes, whichever is reached first?

Then after it reaches the bulk charge limit(s), it stops charging. When and if the battery discharges to 14.5v, the SCC goes into float mode and holds it at 14.5v?

 

[Ped]

Thats what the controller is supposed to do, yes. Rarely ever see it go into float though. I believe anytine the fridge kicks on it trips bulk mode by pulling voltage down momentarily. Either way it tapers amps to zero once im around 97%...but still calls it bulk. Who knows, thats the controller program.

 

[Ped]

Dp

 

[tictag]

@Mrdanielmh, respectfully I don't agree with the premise of your query. Lithium-ion battery technology charging requirements are well established based on a fuck-ton a lot of science and product development since the early 70's. This isn't new, nor does it change much. Yes, some battery manufacturers tweak their formula so the battery manufacturer's guidelines should always be authoritative but @Steve_S has already stated what the 'science' says in his post above (another good resource comparing different Lithium-ion chemistry is here), the rest is just gravy and described in your battery manufacturer's datasheet.

Float - 14.5v

A float voltage of 14.5V will damage your battery.

A lot of this is experimental. I am trying to find out what "charge to 90%" means in terms of charge voltage. According to the popular chart below (yea, i know voltage is not an accurate measure), 90% should be around 13.35v.

You cannot just use a charge voltage to in any way determine the charge state of a Lithium-ion battery. The only way to do this accurately would be with a coulomb counter. Let's take an example to illustrate my point: charge a 100AH LifePO4 cell to 3.65V, take it off charge then do a capacity test. Will you get 100AH? Absolutely not. Is this battery 100% charged? Not even close. Now take that same cell and charge to 3.65V and leave it there until the charge current has dropped to around C/100A i.e. 1A. Now is it 100% charged? Yes. A battery is only fully charged when it has completed its CC/CV cycle.

Could you make a table where you charge to ever decreasing voltages, wait until completion of the CC/CV cycle then do a capacity test and map charge voltage to capacity? Yes. Has anybody done this? Don't know. Would it be different for every cell and for every battery? Probably.

My guess is that you'd be looking at 10ths of volts between 10s of SoC percentage points e.g. 3.65V maps-to 100%, 3.60V maps-to 90%, 3.55V maps to 80% etc. Just a guess based on the impossibly flat charge/discharge curve of Lithium-ion technology.

Happy to be proven wrong.

Edit: Corrected typo.

 

[tictag]

p.s. And remember that even for lead-acid, where terminal voltage is a reasonable anolog of SoC, the terminal voltage was at its resting state e.g. many hours (days?) after removal of the battery from the charger. The only way to accurately determine SoC was with a hydrometer.

The terminal voltage of a fully charged and rested LiFePO4 cell is around 3.3V and an almost fully discharged cell is around 3.0V. That voltage differentiation is well outside the accuracy range of most consumer-level multi-meters. So even if you could, I would only trust a DVM capable of accurately reporting thousandths of a volt.

 

[gnubie]

I have a Victron SCC myself and largely use the lifepo4 preset, ie, charge, including 'absorption'* stage to 28.4v then let it drop back to 'float*' 27.0v. If I pull a fair bit of power out of the battery once it is has reached 'float' it'll pull it back up to 28.4 and then immediately drop back to 27.0v. My setup can't separate charge current from load current so the Victron is set to use time based 'absorption', 15 mins is sufficient for my setup, the preset default is 2 hours.

Accuracy of a lot of cheaper SCCs is pretty bad. I'm testing a couple of Renogy SCCs (SRNE OEM) and they are both .2 volts out. MakeSkyBlue is worse, and varies from unit to unit to boot.

*let's not go there, these are legacy terms only

 

[tictag]

I have a Victron SCC myself and largely use the lifepo4 preset,

Victron SCCs are brilliant I can't remember what they call it but they have a dynamic charge profile that depends on the time spent in Bulk i.e. quick discharge = quick charge cycle, so the battery ends up less stressed overall (i.e. reduced time spent at the Absorption voltage).

 

[Ped]

A float voltage of 14.5V will damage your battery.

It would if left 24/7 such as shore power. It seldom gets to float much of the year and when it does, its less than 2-3hrs a day at very low current.

 

[MisterSandals]

My guess is that you'd be looking at 10ths of volts between 10s of SoC percentage points e.g. 3.65V maps-to 100%, 3.60V maps-to 90%, 3.55V maps to 80% etc.

and...

The terminal voltage of a fully charged and rested LiFePO4 cell is around 3.3V

Thanks for the posts above. I concur with what you said, particularly the terminal voltage while charging.

The two quotes just above, are the crux of what i am conflicted about: 3.6v maps to 90% ... and fully charged and rested 3.3v.

If i charge to 3.6v or 90%, letting it rest and settle down to 3.3v is fully charged?

(I am NOT trying to play with words, i am trying to merge what i see as 2 descriptions of the same idea. And make sense of it in terms of how to charge to 90%)