Charge profiles for LiFePo4 - once and for all!

[mLyhne]

Hi fellas

In short: what's your settings and why?
Please be elaborate and include all settings possible (abs, float, storage, recondition, re-bulk current/voltage, abs/recondition duration/time, etc.)



The longer version:
I know there is a ton of knowledge on this subject out there, but as a result of that I am now confused.
I would very much appreciate if we could try to summon some knowledge and experiences

Will Prowse is recommending abs 14.5, float 13.6 (says nothing about absorbtion time, tail current, re-bulk etc)
Andy from off-grid garage is recommending abs 13.6, float 13.6 and 0.1v offset (re-bulk at 13.5)
Some say that float voltage is supposed to be off completely when using lithium chemistry?
TheWilltoBuild says that it doesn't make sense to charge higher than 3.35 per cell

These different recommendations are vastly different - which is correct for what sort of use?
Feel free to just share your recommended preset and why you choose those settings - perhaps a screen dump to include all the expert settings as well.



My situation:
I have a 460Ah battery (2p4s, 8x230Ah EVE fixated) in my van that I live in.
Most of all it's important for me not to stress the batteries more than needed, but during winter I'd like to charge to almost full capacity, to make it through periods of little sun.

On my victron blue smart 25A I tried setting the absorbtion to a conservative 13.4v, since I hear there is not much power to gain above 3.35v per cell, but this made charging a very lenghthy process, since it almost always goes in absorbtion after short time, and then ends absorbtion after 2h time
I tried raising the voltage to 13.6v while I was fiddling with some settings, which meant that the standart lithium preset of 2h limited absorbtion got reset a few times, and the batteries was kept in absorbtion for maybe 8 hours (+ the initial bulk phase of ish 2 hours), and was still pulling 5A at the time the charger cut off. So I wonder how many Ah the batteries could still charge, if I just let it sit in absorbtion?
After the charger ended the absorbtion phase the voltage in the batteries settled at 13.35. Why did the voltage drop this much?

Some random questions:
What's the difference between longer absorbtion time at lower voltage (13.6), rather than short/no absorbtion time at a higher charge rate (14.5)
Does it hurt lifepo4 batteries to stay in absorbtion for too long, low or high voltage?
Why do some use float and others not?
I turned off float - how does my charger decide
Can you overcharge a lifepo4 battery at a lower voltage (13.6)?.. by leaving it in absorbtion for too long? Or can you only overcharge at a higher voltage (above 14.5)

My system:
BMS: one Daly 150A
Victron smart shunt
Solar charge controller: Lumiax Win-MPPT 20A
Charger: Victron blue smart ip67 25A
DC-DC: Renogy 40A

 

[RCinFLA]

Don't forget about cell balancing time. Requires absorb level charge voltage.

 

[Skypower]

Don't forget about cell balancing time. Requires absorb level charge voltage.

Probably in the case of Lifepo4, absorption should have been named balancing time.

 

[Skypower]

Hi fellas

In short: what's your settings and why?
Please be elaborate and include all settings possible (abs, float, storage, recondition, re-bulk current/voltage, abs/recondition duration/time, etc.)



The longer version:
I know there is a ton of knowledge on this subject out there, but as a result of that I am now confused.
I would very much appreciate if we could try to summon some knowledge and experiences

Will Prowse is recommending abs 14.5, float 13.6 (says nothing about absorbtion time, tail current, re-bulk etc)
Andy from off-grid garage is recommending abs 13.6, float 13.6 and 0.1v offset (re-bulk at 13.5)
Some say that float voltage is supposed to be off completely when using lithium chemistry?
TheWilltoBuild says that it doesn't make sense to charge higher than 3.35 per cell

These different recommendations are vastly different - which is correct for what sort of use?
Feel free to just share your recommended preset and why you choose those settings - perhaps a screen dump to include all the expert settings as well.



My situation:
I have a 460Ah battery (2p4s, 8x230Ah EVE fixated) in my van that I live in.
Most of all it's important for me not to stress the batteries more than needed, but during winter I'd like to charge to almost full capacity, to make it through periods of little sun.

On my victron blue smart 25A I tried setting the absorbtion to a conservative 13.4v, since I hear there is not much power to gain above 3.35v per cell, but this made charging a very lenghthy process, since it almost always goes in absorbtion after short time, and then ends absorbtion after 2h time
I tried raising the voltage to 13.6v while I was fiddling with some settings, which meant that the standart lithium preset of 2h limited absorbtion got reset a few times, and the batteries was kept in absorbtion for maybe 8 hours (+ the initial bulk phase of ish 2 hours), and was still pulling 5A at the time the charger cut off. So I wonder how many Ah the batteries could still charge, if I just let it sit in absorbtion?
After the charger ended the absorbtion phase the voltage in the batteries settled at 13.35. Why did the voltage drop this much?

Some random questions:
What's the difference between longer absorbtion time at lower voltage (13.6), rather than short/no absorbtion time at a higher charge rate (14.5)
Does it hurt lifepo4 batteries to stay in absorbtion for too long, low or high voltage?
Why do some use float and others not?
I turned off float - how does my charger decide
Can you overcharge a lifepo4 battery at a lower voltage (13.6)?.. by leaving it in absorbtion for too long? Or can you only overcharge at a higher voltage (above 14.5)

My system:
BMS: one Daly 150A
Victron smart shunt
Solar charge controller: Lumiax Win-MPPT 20A
Charger: Victron blue smart ip67 25A
DC-DC: Renogy 40A

The best question is, are the cell balanced? If it isn’t great, do the cells get over 3.4 vpc, the earliest where the bms’s balancing should start? How long is it in that range in a charging state (5+ amps the time when Daly’s balance)? A slow continuous charge above balance start voltage gives any balancer more time to do it’s job before it reaches end of charge. A Daly really needs that quality time with only 50mili amp balancing current LOL. If you set end of charge voltage of 14 (3.5 per cell) will give you more time up there. If you don’t need it, set it at 13.75 (3.438 vpc). Your system doesn’t an overly high charge current potential (one source at a time) so it’ll have the slow part if the voltage part is set high enough.

 

[mLyhne]

The best question is, are the cell balanced? If it isn’t great, do the cells get over 3.4 vpc, the earliest where the bms’s balancing should start? How long is it in that range in a charging state (5+ amps the time when Daly’s balance)? A slow continuous charge above balance start voltage gives any balancer more time to do it’s job before it reaches end of charge. A Daly really needs that quality time lol with only 50mili amp. If you set end of charge voltage of 14 (3.5 per cell) will give you more time up there. If you don’t need it, set it at 13.75 (3.438 vpc). Your system doesn’t an overly high charge current potential (one source at a time) so it’ll have the slow part if the voltage part is set high enough.

The cells are balanced and perfectly matched.
I don't know how long it could stay in that charging state (5A). At least 6 hours.

And by 'high enough' you mean at least 13.75 until 14v?

 

[John Frum]

Pretty much everything in my system is a compromise.

I charge to 27.75V with a tail current of 10 amps.
I float at 26.75V.
Because I control an IOTA converter via a raspi, float and boost must be 1 volt difference.

Its my understanding that 26.8V(3.35V per) is a good compromise between high reserve capacity and low stress on my cells.
26.75V was as close as I could tweak the tiny trim potentiometer before I started getting cramps.

My system is a double conversion UPS.
LFP batteries tend to drift out of balance if left floating indefinitely, plus its cheaper for me to charge from mains between 7:00PM and 7:00AM so I start charging at 7PM and after the charge terminates on tail current I float until 7:00AM.
Then I run off of battery while mains power is expensive.
Battery draws down to ~50% DOD leaving ~50% in reserve.
I also have logic to turn on the charger if a cell goes lower than 3.0V or the pack goes below 25.2V.

 

[Browneye]

My comments in blue - what I've learned over the past year after building my solar supported LFP mobile system for a motorhome.
I think you're on the right track. Tweak it till you get what you want.

Hi fellas

In short: what's your settings and why?
Please be elaborate and include all settings possible (abs, float, storage, recondition, re-bulk current/voltage, abs/recondition duration/time, etc.)
Each user is going to have slightly different settings to suit their particular application and usage. Once you grasp the concept, you can tweak yours to get exactly what you want. I could give you my SCC settings, but they may or may not work for your application.

>snip

Will Prowse is recommending abs 14.5, float 13.6 (says nothing about absorbtion time, tail current, re-bulk etc)
Andy from off-grid garage is recommending abs 13.6, float 13.6 and 0.1v offset (re-bulk at 13.5)
Some say that float voltage is supposed to be off completely when using lithium chemistry?
TheWilltoBuild says that it doesn't make sense to charge higher than 3.35 per cell
3.35VPC is considered 100% state of charge for LFP. The only reason to charge higher than that is for a faster charge. A float charge is generally to maintain a charge level, and to support loads while charging, solar or whatever.

>snip

My situation:
I have a 460Ah battery (2p4s, 8x230Ah EVE fixated) in my van that I live in.
Most of all it's important for me not to stress the batteries more than needed, but during winter I'd like to charge to almost full capacity, to make it through periods of little sun.

On my victron blue smart 25A I tried setting the absorbtion to a conservative 13.4v, since I hear there is not much power to gain above 3.35v per cell, but this made charging a very lenghthy process, since it almost always goes in absorbtion after short time, and then ends absorbtion after 2h time
I tried raising the voltage to 13.6v while I was fiddling with some settings, which meant that the standart lithium preset of 2h limited absorbtion got reset a few times, and the batteries was kept in absorbtion for maybe 8 hours (+ the initial bulk phase of ish 2 hours), and was still pulling 5A at the time the charger cut off. So I wonder how many Ah the batteries could still charge, if I just let it sit in absorbtion?
After the charger ended the absorbtion phase the voltage in the batteries settled at 13.35. Why did the voltage drop this much?
13.35 is considered a 'resting state of full charge'. A battery will show a higher voltage while charging, lower while discharging, then settle out when at rest. This is normal.

Some random questions:
What's the difference between longer absorbtion time at lower voltage (13.6), rather than short/no absorbtion time at a higher charge rate (14.5)
Does it hurt lifepo4 batteries to stay in absorbtion for too long, low or high voltage?
Why do some use float and others not?
I turned off float - how does my charger decide
Can you overcharge a lifepo4 battery at a lower voltage (13.6)?.. by leaving it in absorbtion for too long? Or can you only overcharge at a higher voltage (above 14.5)

As OGG has demonstrated, you can charge slower at a lower voltage, or faster at a higher voltage, and still arrive at the same place. The higher voltage allows you to charge at a higher current, as long as you don't exceed your bms high voltage cut off. And again, float at 13.4-13.6 is good for supporting any loads you have while in charge mode. You may or may not need float on a charger - but a good float level for a solar charger is to support loads while you have solar gains without depleting your battery. I spent a lot of time watching charge and discharge on my system and making adjustments, to arrive at the same conclusions he did. I could have save myself some time on that. LOL

Charging at 14.5V is likely to get a cell running up at high knee and your bms shuts off charging to the battery. I use 14.1-14.2 on my charge sources and float at 13.6. My battery maintains a high level while charging in use, and charges up quickly after a night of discharge.

BMS: one Daly 150A
Victron smart shunt
Solar charge controller: Lumiax Win-MPPT 20A
Charger: Victron blue smart ip67 25A
DC-DC: Renogy 40A

Decently good equipment. You shouldn't have any problem maintaining your energy supply.

 

[Skypower]

The cells are balanced and perfectly matched.
I don't know how long it could stay in that charging state (5A). At least 6 hours.

And by 'high enough' you mean at least 13.75 until 14v?

One or the other voltage, the lower one is better if things stay balanced. if you don’t have a balance problem, and this systems been in use a while, don’t change a thing. Sounds good.

 

[Steve_S]

Sadly the terminology is NOT Standardised across companies/brands. This results in some confusion of course.

EndAmps/Tailcurrent is dependent on the equipment being used, some are programmable, others are fixed and some SCC's don't even list it so who knows what it is. I use Midnite Classic SCC with their WizBangJr (their smartshunt) and Midnite has a settable EndAmp which is (Battery AH * 0.05) (100AHx0.05=5A). When the Shunt reads that the battery pack is only taking 5 A charge then it switches to Float Mode. Most Tier-1 Products have an EndAmps/Tailcurrent setting (Victron, Midnite etc)

The Working Voltage range, where all the Amp-hours come from is 3.000-3.400 Volts per cell with the nominal voltage being 3.200 Volts per cell. The "work between 10-90% "shtick" is essentially the 2.500-3.000 (the 0-10% and then the 3.400-3.650 (the 90-100%) zones of the "Allowable Voltage Range" (2.500-3.650) which the cells can work within safely without harm/damage/degradation. Above 3.400Vpc the cells will deviate, some will charge faster (runners) and others will charge slower. When a Manufacturer tests cell capacity it is between 3.000-3.400, NOT from 2.50-3.65.

Not all equipment is the same !
Again, I use Midnite Classic SCC & Samlex EVO Inverter/Charger so I will speak to that.
It bulk charges then flips to Absorb when Target voltage is reached with Constant Current Constant Voltage (perfect world, remember clouds etc will cause DC input to vary through the day).
I allow 45 Minutes for Absorb but most often doesn't last that long because EndAmps is reached before the hour and flips to Float (Constant Voltage Variable Current). From then on whatever the batteries will take, even if it's just 1A will be provided by float WHILE the balance of input services demand. IE If I turn on my Coffee Maker that demands 55A and there is sufficient Solar Power coming in, then float will serve up that 55A and never bother the batteries. If there is not enough Sun, then the shortfall comes off the battery bank and as soon as the demand is over, then Float will top up what was taken and slips back down to "trickle" to the battery bank and servicing loads demanded. Between Mar-Oct I'm usually in float by 13:00 hours on clear days. One hour after being in float, the battery packs are all sitting with an 0.005v Delta most days.

I use JKBMS' w/2A Active Balancing that starts at 3.370 and keeps the cells in balance, so they will take a bit from Float while leveling up (Note I have 5 Packs in the bank for 1190AH/30.4kWh).

My profile and screenshots of the battery packs etc are located in this thread :

Steve_S-Tech: My Final Config for Midnite Classic SCC & JKBMS' w/ Large Bank (works amazingly well) Includes Charge Profile & BMS Config

INTRO: I have debated posting this for a while until I got everything tweaked in and working as best as possible. The End Result is Gobsmackingly Good ! I cannot speak for other SCC and such as each is different & unique in their own ways BUT this may likely be a Good Reference. Civility &...

diysolarforum.com

In Winter, when I occasionally have to use the Samlex EVO Inverter/Charger, I set it to 80A Charge which uses 120V/23A from the generator, while highly programmable it has no EndAmp/Tailcurrent setting as such, it works simply by reading the voltage point programmed for absorb and once reached drops to Float and continues to provide Pass-Through power to satisfy actual demand.

You have a DALY BMS and I would hope a smart one with an app that you can monitor.
- Something simple you can try to see what's going on. Set your charging to 14.4V (3.600Vpc) and observe what the cells do when they get past 13.5V (3.375Vpc) and you will see them start to deviate and the higher you go, the more deviation will occur, quite likely you will have 1 Cell hit 3.650 Cutoff (a runner) and trip HVD. Again, I will remind you that manufacturers target 3.000-3.400 as the working voltage range where cell IR should be quite consistent. Assuming the cells are properly Matched/Batched.

Next test you can do after that is your charging to 13.7V (3.425 Vpc) and again the cell behaviour. As they cross 3.400 +/- a tad, they will start to deviate a bit BUT none will hit HVD (unless you got weak cells). Set Float to 13.6V (3.400Vpc) and let it go. The cells will "naturally settle" and any form of balancing will level them out. Passive burns off excess from a cell, while active transfers from Hi Cell to Lo Cell.

REBULK @ Nominal Voltage Point (aka 50%) 12.8V which is the best compromise before getting below the 50% threshold.

Over the past few years, I have adjusted & added to my configs and even changed my fleet of BMS (at great expense) by removing some Pricey Gear and changing it. I've even done hard Thrash Tests which pushed everything to the "Extreme Limits" to find the edges of what will and will not work. I have the capacity to push 230A Charge and to draw quite a bit more... Great way to find out when a busbar will melt! hahaha

A Side Note: LFP is rated to be able to take 0.5C Rate Charge and it will, the cells WILL Warm up quite a bit and at the same time the cells within a pack taking that WILL deviate a fair bit as well, especially as the cells internal temps will vary. All Cells will behave slightly differently relative to their temperatures and that will show in how fast they charge (take amps) and how they will discharge. IF you have 4 packs on shelves, 1 above the other & so on and each pack is at a different temp they will reflect that. Even 1 degree Celsius between each pack becomes very observable. I had them stacked and saw that daily in winter bottom at 13C, next up 14C, next at 15C and top one at 16C each taking a different amount of charge and outputting different amps.

I hope this helps and do try the tests for yourself to see. Good Luck.

 

[Substrate]

@mLyhne See what you started with only your 2nd message?

Pick a strategy and try it, otherwise this is just fodder to start a 3000+ message thread, that will make you more confused than ever.

Will's advice is sound for your application. He is familiar with your living situation, so there's that. You will get reasonable life if you follow it.

You live in a van, and not in a lab, and trying to achieve lab-perfection, while admirable, means you will never leave the van. Follow Will's advice for now. Just "fiddling around" with settings is counter-productive.

This will also give you valuable time and experience to see if what you read in *other* voluminous threads about the subject is applicable to your situation, or can be ignored - say from those racing or marine, which has different concerns.

 

[mLyhne]

My comments in blue - what I've learned over the past year after building my solar supported LFP mobile system for a motorhome.
I think you're on the right track. Tweak it till you get what you want.

Thank you so much for your elaboration! That's a big help. I will read it through a second time now..

I hope this helps and do try the tests for yourself to see. Good Luck.

It sure does. It's definitely becomes more and more clear that I need to learn more to adjust the battery pack to my needs. But it's helping a lot to have specific numbers from other system, for reference. So thank you!

 

[ianganderton]

Here’s a link to my charging profiles and a lot of info I’ve collated

My Build Questions - Camper Van 480W Solar 12V 200Ah LifePo4

All loads off the charge controller? You need your feed directly off the battery or lynx, The max load will be within the 40A its rated for and I'm trying to keep cables as short as possible while oversizing them where possible too. By having them of the load terminals my understanding is it...

diysolarforum.com

 

[mLyhne]

You live in a van, and not in a lab, and trying to achieve lab-perfection, while admirable, means you will never leave the van. Follow Will's advice for now. Just "fiddling around" with settings is counter-productive.

While his advice might be sound, others who seem to know a lot about this battery chemistry say very different things.
I think that Will's recommended settings are not elaborate and specific enough in terms of the behavior of charge controllers. Take for instance the standard 2 hour limit of absorbtion time setting - I guess in case of using Will's settings a 2 hour absorbtion time will bring the batteries to a higher state of charge than I wish? I'm guessing. Shouldn't absorbtion time be significantly shorter, if at all, in that case then? Or lower the voltage from 14.5 to maybe 13.6 and extent the absorbtion time to some hours. Will doesn't cover that in this post, but I'm curious to learn which might fit my needs the best, and just following Will's recommendations does not seem like a well informed decision atm. But thanks to people replying to my specific questions I'm a few steps closer to understanding

 

[time2roll]

What's the difference between longer absorbtion time at lower voltage (13.6), rather than short/no absorbtion time at a higher charge rate (14.5)
Does it hurt lifepo4 batteries to stay in absorbtion for too long, low or high voltage?
Why do some use float and others not?
I turned off float - how does my charger decide
Can you overcharge a lifepo4 battery at a lower voltage (13.6)?.. by leaving it in absorbtion for too long? Or can you only overcharge at a higher voltage (above 14.5)

You can press it a bit more than 13.6 without going 14.5 volts. Consider 13.8 to 14.0
Full time use at 13.8 for a few hours and 13.5 float is fine for daily cycling on solar.
If charging above maybe 13.8 I would use float so the voltage is not held at near max all day.
13.6 on solar all day is fine. May not get all the capacity if it is short charged and no harm in that. If more capacity is needed it is better to get an additional battery vs managing that last 5% to 10% to get through the night.

 

[Substrate]

I think that Will's recommended settings are not elaborate and specific enough in terms of the behavior of charge controllers.

While I can't speak for Will, I will say what I *perceive*.

That's because most people just want numbers that work. And his recommendations take into account the fact that many people are using drop-in's, where fixed-value non-user-adjustable things like balance-resistor triggers can be very low (bad) or very high depending on manufacturer. For the average user, getting those to work means using a 14.5v cv, rather than something lower. They really don't care about absolute long-term performance. Most don't even own a voltmeter.

Take for instance the standard 2 hour limit of absorbtion time setting - I guess in case of using Will's settings a 2 hour absorbtion time will bring the batteries to a higher state of charge than I wish? I'm guessing.

Long hours of absorb are not good - but when you take into account a highly variable solar-powered conditions, and when most people want to charge fully, (likely most of the reader demographic) that will get them there when there could be very overcast or cloudy skies. But if you want to get more specific, then limit your absorb to when current trails to .05C. But if it's already overcast, you may be at .05C tail current well before you are fully charged and pull the plug prematurely. This assumes you are monitoring for that condition. Does your SCC purchase have those kinds of smarts?

Some people don't believe in tail-current and charge to zero amps. That's bad, because the voltage you see when you exceed .05C tail current, is *mostly* now driven by secondary reactions, not any sort of recharge (lithium movement) activity.

Or lower the voltage from 14.5 to maybe 13.6 and extent the absorbtion time to some hours.

This has already been covered extensively in other threads. But what you seek is possibly a personal 300+ message thread covering all this ground again, and maybe playing off Will vs Andy. Choose your guru.

What I'm saying is that for the vast majority of people that "just want the numbers", especially with drop-in's, Will's advice is sound for the most part.

If you want to follow Andy's advice, especially since you have what appears to be DIY, and really want to fine-tune, then by all means go that route.

Put it this way - If my unskilled neighbor bought a drop-in, I'd be more than happy to give him a copy of Will's advice and not worry about it. If I asked him to watch Andy's advice, and he had a programmable bms-app, without any background, I'd find the system tweaked out of operation, and I'd be the 24/7 on-call support guy.

 

[toms]

Charge at maximum of 1C (0.5C if you have cheap cells) until the first cell reaches 3.50V.

Lower charge current to 1A/cell while balancing cells until all cells have reached 3.50V (depending greatly on BMS capabilities)

Reduce Voltage to 3.40V, hold at this level if loads are present - otherwise terminate charging.

At no time go outside the 0° - 35°C temperature range.

 

[mLyhne]

Thanks to everyone for helping out.
I've got a better understanding of how it all works, and have found settings that seem to work for now.
With these settings i've tested the capacity to be 450Ah (460 should be full capacity), so I definitely don't feel any need to charge at a higher voltage than 13.8 (when the batteries settle after charging they reach 13.4 for the pack - 3.35 per cell)

I've set my victron charger to
Absorbtion: 13.8
Float: 13.4
Storage: 13.4 (I don't see how I need this setting, but it cannot be turned off)
Absorbtion time: max 1h

SCC:
CVT (charging target voltage): 13.8
CVR (charging recovery voltage): 13.4

BMS:
LVD: 12v

Thanks guys!