Need help with LTO battery charging

Tmadsen

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Jun 30, 2022
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I have an off grid cabin that uses solar power and I am upgrading to LTO batteries. LTO is a best choice for my cabin. I am seeking some advice on what settings to use on my charge controller as i am very new to LTO and i have not yet been able to feel confident about my settings. I have not yet upgraded and installed the LTO cells but here is what i plan to do.... 24v system. my inverter will operate at 18-32 volts. installing 72 yinlong 40ah cells in 12s6p configuration. I have a Daly LTO 12s 200a 4th gen. BMS (2.65v power balancing). I currently have a 600watt array (with ability to add more). My charge controller is a Renogy commander 60a .


my charge controller has a user select setting available (since it does not have predefined LTO settings) and these are the adjustable parameters....

high voltage disconnect
charging limit voltage
over voltage reconnect
equalization voltage
boost voltage
float voltage
boost return voltage
low voltage reconnect
under voltage recover
under voltage warning
low voltage disconnect
discharge limit voltage

the above parameters can be set at 9v-17v ( x 2 for my 24 volt system)

equalization duration ( 0-180 minutes)
boost duration (10-180 minutes)

i am looking for advice on what to use and maybe some reasoning why. I do not need to have use of 100% battery capacity, I would prefer to have access to less capacity in exchange for better care and condition of the batteries.

thank you in advance
 
2.3V nominal cell voltage

usually 5S is used for 12.0V nominal, similar to lead GEL setpoints

12S is too high for 24Vnom

10S or could go to 11S for 24V


full charge of 2.6V is gentlest for optimal longevity

max I would go is 2.75 - 2.80Vpc, stressful

No Absorption / CV time is needed, just "Charge TO and Stop"

100% SoC is maybe ~2.55V resting?
after isolating for a few hours

...

Will quickly drop to 2.5V start of discharge, 2.4something under heavy load

2.1V per cell as the LVC for all C-rates, bit lower is OK for normal House, sub-C rates

Use 2.0V for very high rates
lowest 1.8Vpc (9.0V) LVC under load

2.0 is good as **rested** 0% SoC

1.5V is truly dead flat, will shorten lifespan
 
john61ct said:
2.3V nominal cell voltage

usually 5S is used for 12.0V nominal, similar to lead GEL setpoints

12S is too high for 24Vnom

10S or could go to 11S for 24V


full charge of 2.6V is gentlest for optimal longevity

max I would go is 2.75 - 2.80Vpc, stressful

No Absorption / CV time is needed, just "Charge TO and Stop"

100% SoC is maybe ~2.55V resting?
after isolating for a few hours

...

Will quickly drop to 2.5V start of discharge, 2.4something under heavy load

2.1V per cell as the LVC for all C-rates, bit lower is OK for normal House, sub-C rates

Use 2.0V for very high rates
lowest 1.8Vpc (9.0V) LVC under load

2.0 is good as **rested** 0% SoC

1.5V is truly dead flat, will shorten lifespan


Thank you for your reply . I am aware of the "nominal" battery voltages . And 12s is fine for my needs and my equipment .

I am also aware that LTO ideally should be charged at CC to a set voltage than CV until a current drop to pre determined amount and then STOP charging . But thank you for reminding me .

What I really need help with is understanding how to set my charge controller ( or any solar charge controller for that matter ) to do that . I listed the adjustable settings and I just don't see a " charge to and stop" setting .

Do you know what values to set the settings I listed at to achieve this ?

Do you know of a solar charge controller that will ?

Again I really appreciate the help and info . I have a pretty good understanding of how LTO batteries should be charged . but there aren't any LTO solar charge controller a out there yet (that I can find anyways ). . sure there are some that say they are LTO compatable but if you look at their charging parameters they charge basically the same as other lithium chemistries only at a different voltage . There is no options to charge to and stop as you put it . So unless someone can direct me to a proper LTO solar charge controller I am looking for suggestions on what voltages to set the setting I listed for me controller at to achieve the best possible charging parameters for LTO .

For example ... I can turn off equalization no problem , but my charger as with most all solar chargers can not turn off float . I must set a value for boost and a value for float.

I am hoping someone out there using LTO with a solar charger can share what they are doing and how they are doing it
 
Tmadsen said:
LTO ideally should be charged at CC to a set voltage than CV until a current drop to pre determined amount and then STOP charging
You misunderstood.

Read again:
john61ct said:
No Absorption / CV time is needed, just "Charge TO and Stop"
Means CC only.

> There is no options to charge to and stop as you put it

So a HVC circuit shutting off the SC, or at the panels can handle that, so long as the charge source is set a little higher than the setpoint cutoff of say 26V.

Ideally less than the max voltage on the data sheet - 2.80Vpc?

It will be much simpler if you keep your system / pack voltage within the "normal 24V" charging range, around 27-29V

The output range of normal 24Vnom solar controllers is your limiting factor.

11S will do that, but 10S gives more flexibility.

> 12s is fine for my needs and my equipment .

Are you saying you cannot do 10S or 11S? Why not?

...

"Boost" should mean CC stage, often the term is used incorrectly by charge source and battery vendors.

CV = "Absorption", some vendors let you set that to just a few minutes if it can't be disabled.

Lithium should not be Floated at all.

By using HVC as above, CC becomes the only stage used.
 
"So a HVC circuit shutting off the SC, or at the panels can handle that, so long as the charge source is set a little higher than the setpoint cutoff of say 26V"

by HVC i am assuming you mean a high voltage contactor, i had thought about that, is there such a thing as a programmable one that would cut in and out at the voltages i need ? if you are aware of one please include a link. is there no way to buy a solar charge controller capable of doing this itself ? (i am not aware of one)

"It will be much simpler if you keep your system / pack voltage within the "normal 24V" charging range, around 27-29V The output range of normal 24Vnom solar controllers is your limiting factor. "

can you explain why it is simpler? my solar controller outputs are from 18v to 34v . I obviously don't know what all charge controllers output are but i am big fan of Renogy and this is this range for all of their controllers, Victron solar controllers have a wider range but i don't remember exactly what it is.

"Are you saying you cannot do 10S or 11S? Why not?"

there is no why not, my equipment runs from 18v-32v , nominally 12s = 27.6 and 11s = 25.3 , both 11s and 12s will work fine, I chose 12s for several reasons, but this is off topic and not what i really need help with.

"You misunderstood. "

I may have, i do not have a data sheet that gives exact charging parameters for these cells. DO you have one or can you find one and share it with me ? either way... we do agree they should be charged at a CC and to certain point and then stopped. i wish i knew how to make my solar controller do this, do you know how ?

""Boost" should mean CC stage, often the term is used incorrectly by charge source and battery vendors."

this was very helpfull and the type of help i am looking for ... thank you

"CV = "Absorption", some vendors let you set that to just a few minutes if it can't be disabled. "

no "absorption" option in my controller, just boost float and equalize, i can limit boost to 10-180 minutes, equalize i can limit to 0 and will obviously.

"Lithium should not be Floated at all. "

this really baffles me . if lithium should not be floated then why does every major solar charge controller manufacturer use a float voltage on their lithium solar charge controllers. Victron, Renogy, and Outback just to name a few. i think this has to do with it being a solar application and not a bench charge, when using solar there is almost always a load on the system even while charging.

what would really be helpful is if you could please give direct answers to the actual setting i have to work with..
let me ask you to help me this way... if you had to use my charge controller to charge your LTO batteries what voltages would you set each and every of the following settings at ...... (basically my original question) ... they can all be set from 18v-32v but they have to be set, they cannot be turned off or set to anything other than 18v-32v .... and you must obey the following rules....

Rule 1: High Volt Disconnect > Charging limit voltage ≥ Equalization voltage ≥ Boost
voltage ≥ Float voltage > Boost return voltage;
Rule 2: High Volt Disconnect > Over Voltage Reconnect;
Rule 3: Charging Limit Voltage > Low voltage reconnect > Low voltage disconnect;
Rule 4: Charging Limit Voltage > Under voltage recover > Under voltage warning;
Rule 5: Boost return voltage > Low voltage reconnect;


high voltage disconnect
charging limit voltage
over voltage reconnect
boost voltage
float voltage
boost return voltage
low voltage reconnect
under voltage recover
under voltage warning
low voltage disconnect
discharge limit voltage


thank you again
 
john61ct said:
No Absorption / CV time is needed, just "Charge TO and Stop"
Well that makes them difficult to use in a solar application. For LFP you can do CC/CV and while in both modes the solar charge controller effectively powers the load, which is what you want while the sun's out. Sounds like for LTO you can't do that, and will be banging on and off all day, running off the battery much of the time (rather than solar) even during the day.
 
JackFlorey said:
john61ct said:
No Absorption / CV time is needed, just "Charge TO and Stop"
Well that makes them difficult to use in a solar application. For LFP you can do CC/CV and while in both modes the solar charge controller effectively powers the load, which is what you want while the sun's out. Sounds like for LTO you can't do that, and will be banging on and off all day, running off the battery much of the time (rather than solar) even during the day.

this is true, but for some applications like mine these batteries are not just perfect but they are a life saver, unfortunately because they are so expensive not many use them for solar so there isn't any real dedicated solar charger support. however, ever person i have found (online and offline) that has used them for solar is floating them without any negative affects (that they have made others aware of). these batteries are designed for electric vehicles... charge hard and fast and then discharge so i believe the reccomendations for "charge to and stop" are based on that application. I have not found a single incident or reported test that floating causes any negative results. obviously that depends on floating at a proper amount based on each and every setup. but i am not wanting to debate if they should or should not be floated, mine WILL be float charged because thats what all solar charge controllers do.

I was only really looking for suggestions on what to put my setting at for these batteries, i am a little confused on what these setting actually mean. for example, should i set my high voltage disconnect at 2.7v per cell or 2.8v per cell and what are the pros and cons of each of these voltages ? and wtf is charge limiting voltage ? Is this what others call absorption voltage ? what should i set my charge limit voltage at and why ? what exactly is over voltage reconnect ? is that the voltage the controller will reconnect to the battery after disconnecting because it reached the high voltage limit? what exactly is boost return voltage ? is that the voltage the SCC should switch from float to boost voltage after the battery has been drained while floating ? and WTF is low voltage recover ? i think i might understand low voltage disconnect and low voltage reconnect but seriously i have no clue what low voltage recover is or what i should set it at. is low voltage recover some voltage the controller will charge at after a low voltage reconnect but prior to a boost voltage.


i think probably the proper answers are simpler with LTO batteries but i was hoping someone who was an expert with LTO solar charger setting would confirm. this is where i currently and thinking on going with these setting, please chime in if you have a suggestion or a reason i should make a change ....

high voltage disconnect 2.75v per cell
charging limit voltage 2.65v per cell
over voltage reconnect 2.5v per cell
boost voltage 2.5v per cell
float voltage 2.35v per cell
boost return voltage 2.0v per cell
low voltage reconnect ?
under voltage recover ?
under voltage warning ?
low voltage disconnect ?
discharge limit voltage ?

let me discuss my reason for not guessing what values to use for the low voltage settings, these settings are designed to prevent all other battery chemistries from being drained to far and too low because it will damage the batteries. BUT LTO are different and all tests and specs and recomendations clearly state that draining these batteries completely dead and even leaving them in a dead does not negatively affect the battery in any way.( this is one of the reason i am using this battery although i wont get into that ). One test in particular discharged these batteries to .8 volts and left them there for 1 year, then charged them at 10c to full charge and the batteries lost zero capacity. if this is true should I even worry about setting these setting too low ?

and again seriously someone please tell me wtf is under voltage recover ?

yes i have sent these questions to Renogy but i get generic unhelpfull answers that really don't explain anything like " we would refer you to the included manual to understand and properly set these parameters" lol
 
" under voltage recover ? " I look at it as like a bag of sand (battery) , Fill the bag of sand with water (watts) = full battery.

Poke a hole in it ( size of hole = flow rate ( velocity is volts, the volume is watts) ) let it drain water ( so the sand does not come out ), .

Look at the level of the water in the bag as it empties , seal the hole up and watch the level rise, back up a little (voltage).

The capillary action of the water to the sand take some time to work its way down to the bottom.

When the battery is full there is a excess of power until that last little bit because of the resistance of the battery (Example - capillary action) . When turning off the usage,the volts go up. This is " under voltage recovery ".
How many volts it goes up depends on the internal resistance and the charge- discharge curve chemistry of the battery.
That last little bit is not worth going after.

JimJr
 
high voltage disconnect 2.75v per cell Ok
charging limit voltage 2.65v per cell Ok
over voltage reconnect 2.5v per cell Ok
boost voltage 2.5v per cell Turn off , Not needed
float voltage 2.35v per cell 2.4v 90% charge , Been using for car start batteries for years
boost return voltage 2.0v per cell Turn off , Not needed
charging limit voltage 2.65v per cell 2.5v 90-95% charged , Any more the voltage goes up fast
over voltage reconnect 2.5v per cell Ok
boost return voltage 2.0v per cell Turn off
low voltage reconnect ? 2.3v
under voltage recover ? 2.3v You do not want the inverter to start back up with a 10-20% capacity , because the the
load will draw the volts back down and cycle on and off
under voltage warning ? 1.9v This is under load ,@10% left- Most inverters will disconnect at @ 1.8v -- 11v
low voltage disconnect ? 1.5v This is under load , Most inverters will disconnect at @ 1.8v -- 11v
discharge limit voltage ? 1.5v This is under load , Most inverters will disconnect at @ 1.8v -- 11v

Lto's will start gassing about 3v and blow their cork about 3.7v, even with that I charge one 40ah accidentally to 4v . I let it cool
off and resealed it with silicone and discharged it and tested it with a charge - discharged and only lost 3ah of capacity. still working good!. :)

JimJr
 
Chinglish is the problem, Renogy will have no clue, they do not make anything, and even the Chinese speaking customers would not be given access to the staff that might know, ad they certainly do not speak English well.

Maybe find and post a sample profile for li-ion or LFP and we can reverse engineer the meanings.

Or buy a better SC!

There is no "damage" from floating at a low SoC voltage, only reduced lifespan lost cycles at the back end.

Same with sitting at Full in general, the higher percentage of total shelf time that is done the greater the "damage".

Same with going low voltage.

All depends how you define that subjective term.

There is no difference between LTO, LFP or other LI types wrt these wear factors in principle, just different specific numbers per chemistry.

Remember industry pays for the research, conclusions that go against the vendor interests are not rested, not even investigated!

HVC for longevity is 2.6V

2.7+V would be stressful, shorten lifespan.

2.55V isolated at rest is 100% Full

...

over voltage reconnect

means after HVC, so lower, charging resumes

> voltage the controller will reconnect to the battery after disconnecting because it reached the high voltage limit

exactly

you got the others right too I think

You can test / confirm using an adjustable PSU

> an expert with LTO solar charger setting

No such thing, SC design is for lead only, never seen one handle LI properly, all their algos and setpoints will harm longevity.

Put in external HVC LVC etc controls yourself if you want optimal, treat the SC output like a dumb PSU.

At the low end, 2.1V per cell as the LVC for all C-rates, bit lower is OK for normal House usage, sub-C rates

Use 2.0V for very high rates
lowest 1.8Vpc (9.0V) LVC under load

2.0V is good as **isolated at rest** 0% SoC

1.5V is truly dead flat, will shorten lifespan
 
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