With most things in life it depends. In other words the assumptions on use will determine whether a "float" charge will hurt. For example if your inverter is on and powering loads it cannot hurt a Lithium battery to have some of that draw offset by a low Amperage constant voltage. On the otherhand, unattended Lithium batteries with no load can be damaged long term by continuosly applying even a small current while they are fully charged.Can someone give a definitive answer if you should turn off float stage in charge controller for LiFePO4 cells?
Battleborn cell packs are 30 cylindrical cells per pack. 4 packs per 12v battery. Top balancing of 12v battery with the BB BMS is passive per 'cell pack' balancing, not per cell in each pack balancing. Top balancing starts at 14v + for a 12v BB battery.The Rabbit hole... shoot the rabbit & eat it.
In the context of Lithium Float is Constant Voltage Variable Current. I USE FLOAT - It Works and I'll explain with a pinch of Curmudgeon.
Bulk Charge or CC get's you to 95% of your TARGET Voltage, in my case 27.0V (3.375Vpc), the ABSORB takes it to 28.2 (3.525Vpc) for a MAX of 1 hour or until EndAmps (Tail-Current) of 14A is reached.
Then float kicks in at 27.9 and starts to decrease Amps as the packs take it, while this is occurring the cells are a bit Deviated after the 28.2V so the balancing is underway as well as the cells themselves settling post charge*, while Floating the deviations decrease as all cells level up as the lower charge cells are taking more than the higher ones within the pack, This IS observable.
* Post-charge LFP will always settle if not provided with power, depending on "saturation" (depth of charge at voltage) that settling can be significant.
-- Typically by 12-13:00 hours I am in FLOAT, Amps decrease from 14A as the packs top off & balance out, By 14-15:00 batteries are in "storage Mode" (BMS function) and float is servicing whatever demands my Inverter has, even if I start the Coffee Maker that pulls 50A, if the panels can provide it, the batts won't be touched.
-- IF the batts are pulled from, the SCC flips back to Bulk and tops off again and returns to Float when done, this actually is fairly quick.
NOTE: I use Chargery BMS, with Passive Balancing (only ON during Charge) above 3.30V and allowing for 30mv differential. All my Production Packs also have a QNBBM-8S Active Balancer.
A LAST POINT because it is a PEEVE (being extremely polite OK)
A FOOL charges to 3.65Vpc every day ! An IDIOT keeps charging above Working range {3.50} (THAT is where you are aging / hurting cells) and that means TOPPING OFF to <2A Taken ... ie Charging and Floating to 3.500Vpc 28.0 & <2A.
But BattleBorn Says ! Those are Grade A+++ Matched & Balanced Premium Cells which they test the crap out of. Even they say you can Goto 29.2 (3.650Vpc) but they recommend 28.4 (3.550Vpc) And forget what Chinese Battery Packers say, they want to sell more, so burn em up and buy more... "Consume & Spend".
Hope that helps, Good Luck.
PS: I came from Lead World, am familiar with LEADisms.. Humbug ! Not entirely applicable in context.
I was not aware of any significant difference in charging parameters within the same chemistry. Your examples support that they all use the same voltage for discharge cuttoff and maximum charge voltage. As far as Float is concerned it is my opinion that it is more about the use case and not the physical form factor of the cells. For example, for many years I used Headway LFP cylindrical cells then evolved to Winston and Thundersky LFP primatic cells for an EV and a stationary pack.I think to be correct when comparing charging parameters, consideration should be given to whether the battery calls are cylindrical or prismatic. Including battery float voltage spec/usage. consideration.
I wonder why the CALAB 100ah prysmatic cell data sheet states: Recommended SOC usage Windon - SOC 10%-90% ?I was not aware of any significant difference in charging parameters within the same chemistry. Your examples support that they all use the same voltage for discharge cuttoff and maximum charge voltage. As far as Float is concerned it is my opinion that it is more about the use case and not the physical form factor of the cells. For example, for many years I used Headway LFP cylindrical cells then evolved to Winston and Thundersky LFP primatic cells for an EV and a stationary pac
Why do some prismatic cells require compression by the manufacturer ? Cylindrical cells do not require compression, they are each in a steel case that will not expand. What causes the prismatic cells to expand. What does that expansion do to the structure of the cell elements ?I was not aware of any significant difference in charging parameters within the same chemistry. Your examples support that they all use the same voltage for discharge cuttoff and maximum charge voltage. As far as Float is concerned it is my opinion that it is more about the use case and not the physical form factor of the cells. For example, for many years I used Headway LFP cylindrical cells then evolved to Winston and Thundersky LFP primatic cells for an EV and a stationary pack.
Strictly speaking, I don’t believe this is correct. In a series string, all cells ‘take’ exactly the same charge current during float (and at any phase of the charging process).The Rabbit hole... shoot the rabbit & eat it.
In the context of Lithium Float is Constant Voltage Variable Current. I USE FLOAT - It Works and I'll explain with a pinch of Curmudgeon.
Bulk Charge or CC get's you to 95% of your TARGET Voltage, in my case 27.0V (3.375Vpc), the ABSORB takes it to 28.2 (3.525Vpc) for a MAX of 1 hour or until EndAmps (Tail-Current) of 14A is reached.
Then float kicks in at 27.9 and starts to decrease Amps as the packs take it, while this is occurring the cells are a bit Deviated after the 28.2V so the balancing is underway as well as the cells themselves settling post charge*, while Floating the deviations decrease as all cells level up as the lower charge cells are taking more than the higher ones within the pack, This IS observable.
* Post-charge LFP will always settle if not provided with power, depending on "saturation" (depth of charge at voltage) that settling can be significant.
-- Typically by 12-13:00 hours I am in FLOAT, Amps decrease from 14A as the packs top off & balance out, By 14-15:00 batteries are in "storage Mode" (BMS function) and float is servicing whatever demands my Inverter has, even if I start the Coffee Maker that pulls 50A, if the panels can provide it, the batts won't be touched.
-- IF the batts are pulled from, the SCC flips back to Bulk and tops off again and returns to Float when done, this actually is fairly quick.
NOTE: I use Chargery BMS, with Passive Balancing (only ON during Charge) above 3.30V and allowing for 30mv differential. All my Production Packs also have a QNBBM-8S Active Balancer.
A LAST POINT because it is a PEEVE (being extremely polite OK)
A FOOL charges to 3.65Vpc every day ! An IDIOT keeps charging above Working range {3.50} (THAT is where you are aging / hurting cells) and that means TOPPING OFF to <2A Taken ... ie Charging and Floating to 3.500Vpc 28.0 & <2A.
But BattleBorn Says ! Those are Grade A+++ Matched & Balanced Premium Cells which they test the crap out of. Even they say you can Goto 29.2 (3.650Vpc) but they recommend 28.4 (3.550Vpc) And forget what Chinese Battery Packers say, they want to sell more, so burn em up and buy more... "Consume & Spend".
Because the cases are not able withstand the normal swelling of ingredients like cylindrical cells can.Why do some prismatic cells require compression by the manufacturer ?
When I set battery float at 13.60v (cell float 3.40v), after a Bulk and absorb (absorb time 10 minutes) of 14.1 v, my cylindrical cell 12v battery settles at 13.60 v (the float setting). The SCC settles at 13.60 v, 0.60 a. The battery settles at 13.60v 0.00a. The SCC suppliess the 0.60 amp parasitic load to my system. If I turn the inverter on, with no ac load, the dc load on the system is 3.60 a at 13.60 v. Thats 0.60 a parasitic and 3.00 a to inverter idle at no ac power out. The battery sits at 3.60 v, 0.00 a. If the SCC powered float voltage is not able to keep up with the system load (clouds, shade, more load current), the voltage will drop 0.10 v for more than one minute and the SCC will go into Bulk charge mode and repeat the solar charge cycle (less absorb duration). 13.60 v at 0.25C load is 100% SOC, at zero current load is 99% SOC. Perfect for maintaing max solar energy in BB battery on sunny days. The battery sits at nearly 100% SOC ready for the night or a few cloudy days in the future.Any time you take LiFePO4 into either voltage knee you reduce its lifespan.
If you set “float” on a charge controller to 3.4V, your charger will be at zero amps without taking your cell into its high voltage knee.
It is my understanding that during charging to 100% SOC of a prysmatic battery the litthium Ions attach to the Cathode. The ions are rather large and over time can cause cracking in the cathode if cell expansion is allower. You do not have this phenomina with cylindrical cells. The swelling contributes to less battery longevity in prysmatic cells.Because the cases are not able withstand the normal swelling of ingredients like cylindrical cells can.
The Lithium ions also attach to the Cathode in a cylindrical cell. The only difference between a prismatic and cylindrical cell is the form factor not the chemistry. Some prismatics use a jelly roll configuration shaped into more or less a rectangle and others use a series of individual anode and cathode sheets. A cylindrical cell is a circular jelly roll. I don't have a link to a white paper but a Google search can probably get you links to various types of cell construction.It is my understanding that during charging to 100% SOC of a prysmatic battery the litthium Ions attach to the Cathode.
Got it. I read somewhere that in Prismatic cells the cathodes expand as large lithium ions attach to them. Thus the swelling of prysmatic cells. But no swelling can occur in cylindrical cells. This causes cracking of the cathode material over time in prismatic cells. Thus a need to compress prysmatic cells. This process reduces the life of prysmatic cells. I think thats why the CALB data sheet mentions using the battery cell in the 90%-10% SOC range (to extend their life). I do not see this on a cylindrical cell data sheet I viewed. If I'm wrong here please straighten me out. If you have a link to a white paper that discusses this phenomina, please post a link.The Lithium ions also attach to the Cathode in a cylindrical cell. The only difference between a prismatic and cylindrical cell is the form factor not the chemistry. Some prismatics use a jelly roll configuration shaped into more or less a rectangle and others use a series of individual anode and cathode sheets. A cylindrical cell is a circular jelly roll. I don't have a link to a white paper but a Google search can probably get you links to various types of cell construction.
*checks my own discharge curve*I just noticed that 13.60v (3.40v per cell pack) is up pretty high on the charge/discharge knee.
Do you have a link? I do not doubt that it said that. However physics says the same Lithium attachment has to take place in any similar Lithium chemistry. By its shape, a cylindrical cell is in compression automatically and prevents the impact of that expansion just like compressing prismatics does.I read somewhere that in Prismatic cells the cathodes expand as large lithium ions attach to them.
I'm sorry, I do not have the link. Was in hope that someone elese hear understood the same thing and might have some link to more info.Do you have a link? I do not doubt that it said that. However physics says the same Lithium attachment has to take place in any similar Lithium chemistry. By its shape, a cylindrical cell is in compression automatically and prevents the impact of that expansion just like compressing prismatics does.