Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Intro:
BMS SoC and system SoC readings are always a source of great debate and even great argument(s).
This Posting addresses MANY of the issues not considered, nor weighed and delves into the Important MInutia which can & often does create confusion & misunderstandings that result falling into the Proverbial "Rabbit Hole".
This is the Simple Straight up FACTS, just like what "Gravity" is and how it works.
This is not a discussion or Debate Thread for argument, postulation, theorization or conjecture.
The 2 Proceeding thread slots are reserved for additions if/as required.
As part of my final closures here, I am Posting & Relabelling several other of my "Tech Posts" to "SteveS-Tech:" for easier location and for Library Purposes to make critical & key information available Easily & Quickly for Everyone. This is expected to take me at least 2-3 weeks. Please bear with it until complete. I do have other Very Important priorities that take precedence. Thank You for your patience & understanding.[/]
Update timeline: now in 3rd week of critical care in hospital - so timeline stretching. Aug.9.2022.
Speaking only to LFP Tech.
The "Full Voltage Range" is from 2.500-3.650 volts per cell but this is NOT the actual Working Range !
The "Working Voltage Range" IS 3.000-3.400 volts per cell. That is the 100% range that provides the Actual Amp Hours deliverable. Remember the "Cliff Fall" from 2.900-2.500 and of course the "Cliff Climb" from 3.425-3.650" which are both steep and that are the edges. This is why Cell Voltage Nominal Voltage is 3.200 volts per cell and not something else. It is a Very Tight Spec while other chemistries are somewhat more broad depending on their specifics.
JKBMS like most all other " Smart-BMS' " this must be set into your Configuration as the defaults are broader & designed to prevent general failures / damage to the device. Where you set your Over & Under voltage, Cutoffs always affects that, as that is what is used to determine where the SOC state is in reality and is the base fr those calculations.
To attain 100% SOC, it is best to charge cells no higher than 3.425Vpc and cutoff at 2.900Vpc. This provides for the "Natural" settling of the LFP Chemistry (as expected) while maintaining equilibrium across the cells. For LFP primary charge to "90-95%" (pending on maker & their particular chemistry mix) is reached by CC - Constant Current (Bulk/Absorb) and finishing to 100% by CV - Constant Voltage Variable Current (FLOAT) which reduces amperage as the battery/cells saturate to their set Voltage.
Quality Solar Charge Controllers, Chargers (Inverter or other) make use of TailCurrent / EndAmps to determine when to STOP Bulk/Absorb and ending Float. This is Calculated as, Example: (100Ah x 0.05 = 5A) or 10A for 200Ah. which is the point of Saturation to X Voltage for LFP. Simply consider this as the Depth of Cell/Battery Charge.
Temps / placement - SOC+
With a Battery Bank containing 2 or more Battery Packs always select the "Lowest AmpHour" battery within the Bank to achieve this SMOOTHLY and without running the risk of "runners" or other side issues. Placement within a Bank is also important ! Very Few understand this subtlety which is quite important. Sounds weird but it is what it is. Place the Larger Capacity Batteries FIRST in-line and then the Lower Capacity Batteries at the End of the bank. IE: 280Ah + 280Ah then 200Ah + 200Ah for a total of 960Ah Total. Yes like a "chain" in sequence. The "Common DC Bus" provided by a bank does level this up for both Charging & Discharging.
Lastly, a Hugely Debated "pile of twaddle" like the proverbial wive's tales that never go away is why do Battery Packs vary within a Bank. The answer is extremely simple actually !
- Assume that Ambient Temp is 25C/77F measured @ 3'/0.91m height.
- IF all battery packs within the bank are at "that" height, the temperature equilibrium is the same. Therefore this does not affect Charge/Discharge of packs within the said Bank.
- IF the Battery Packs (like within a Rack) are at different elevations, every battery will have a slightly different Temperature which can and will affect Charge/Discharge Rates per Battery ! This is most notable when ambient temps vary more. Remember, Temp @ Ground Level is not the Temp @ 4'/1.21m nor at 8'/2.43m, unless you have a completely "Conditioned" space that is at equilibrium.
- Even 1C/1.8F - 2C/3.6F CAN make a difference, most especially during Low or High temps outside of the Nominal 25C/77F temps. The wider the Temp Difference is between "packs" DOES affect the charge/discharge rates across a Stacked Bank of batteries. THIS IS OBSERVABLE ! It can be minimal which self-corrects BUT it can be broad by several degrees depending on your "facility" and that is harder to compensate for & does affect rates.
! - * - ! The above also Assumes that ALL Battery Packs within a Bank are using identically configuration with the Same BMS' wire lengths (sense etc) Temp Sensor locations etc. Variances within will present various differences that must be considered when assembling your system.
(*General Note
Context for DOD & SOC with LFP.
In this Context, DOD is the measure of Cell/Battery Charge Saturation Level which is the Depth of Charge within the Cells.
SOC is relative to Actual Working Voltages and NOT the Allowable Voltage Range for LFP Cells.
As there are no "Standards" across Manufacturers for Naming Conventions of various functions/capabilities the Terminology does indeed vary from Top Tier-1 to Value Grade equipment, therefore this is more difficult depending on the grade/level of equipment you are using. Therefore I am using the most common terminology for Tier-1 equipment Semantics can really be a Pain in the Kaboose !
I hope this Helps & Clarifies several small issues that can create longer view issues Encountered.
Steve
.
BMS SoC and system SoC readings are always a source of great debate and even great argument(s).
This Posting addresses MANY of the issues not considered, nor weighed and delves into the Important MInutia which can & often does create confusion & misunderstandings that result falling into the Proverbial "Rabbit Hole".
This is the Simple Straight up FACTS, just like what "Gravity" is and how it works.
This is not a discussion or Debate Thread for argument, postulation, theorization or conjecture.
The 2 Proceeding thread slots are reserved for additions if/as required.
As part of my final closures here, I am Posting & Relabelling several other of my "Tech Posts" to "SteveS-Tech:" for easier location and for Library Purposes to make critical & key information available Easily & Quickly for Everyone. This is expected to take me at least 2-3 weeks. Please bear with it until complete. I do have other Very Important priorities that take precedence. Thank You for your patience & understanding.[/]
Update timeline: now in 3rd week of critical care in hospital - so timeline stretching. Aug.9.2022.
Speaking only to LFP Tech.
The "Full Voltage Range" is from 2.500-3.650 volts per cell but this is NOT the actual Working Range !
The "Working Voltage Range" IS 3.000-3.400 volts per cell. That is the 100% range that provides the Actual Amp Hours deliverable. Remember the "Cliff Fall" from 2.900-2.500 and of course the "Cliff Climb" from 3.425-3.650" which are both steep and that are the edges. This is why Cell Voltage Nominal Voltage is 3.200 volts per cell and not something else. It is a Very Tight Spec while other chemistries are somewhat more broad depending on their specifics.
JKBMS like most all other " Smart-BMS' " this must be set into your Configuration as the defaults are broader & designed to prevent general failures / damage to the device. Where you set your Over & Under voltage, Cutoffs always affects that, as that is what is used to determine where the SOC state is in reality and is the base fr those calculations.
To attain 100% SOC, it is best to charge cells no higher than 3.425Vpc and cutoff at 2.900Vpc. This provides for the "Natural" settling of the LFP Chemistry (as expected) while maintaining equilibrium across the cells. For LFP primary charge to "90-95%" (pending on maker & their particular chemistry mix) is reached by CC - Constant Current (Bulk/Absorb) and finishing to 100% by CV - Constant Voltage Variable Current (FLOAT) which reduces amperage as the battery/cells saturate to their set Voltage.
Quality Solar Charge Controllers, Chargers (Inverter or other) make use of TailCurrent / EndAmps to determine when to STOP Bulk/Absorb and ending Float. This is Calculated as, Example: (100Ah x 0.05 = 5A) or 10A for 200Ah. which is the point of Saturation to X Voltage for LFP. Simply consider this as the Depth of Cell/Battery Charge.
Temps / placement - SOC+
With a Battery Bank containing 2 or more Battery Packs always select the "Lowest AmpHour" battery within the Bank to achieve this SMOOTHLY and without running the risk of "runners" or other side issues. Placement within a Bank is also important ! Very Few understand this subtlety which is quite important. Sounds weird but it is what it is. Place the Larger Capacity Batteries FIRST in-line and then the Lower Capacity Batteries at the End of the bank. IE: 280Ah + 280Ah then 200Ah + 200Ah for a total of 960Ah Total. Yes like a "chain" in sequence. The "Common DC Bus" provided by a bank does level this up for both Charging & Discharging.
Lastly, a Hugely Debated "pile of twaddle" like the proverbial wive's tales that never go away is why do Battery Packs vary within a Bank. The answer is extremely simple actually !
- Assume that Ambient Temp is 25C/77F measured @ 3'/0.91m height.
- IF all battery packs within the bank are at "that" height, the temperature equilibrium is the same. Therefore this does not affect Charge/Discharge of packs within the said Bank.
- IF the Battery Packs (like within a Rack) are at different elevations, every battery will have a slightly different Temperature which can and will affect Charge/Discharge Rates per Battery ! This is most notable when ambient temps vary more. Remember, Temp @ Ground Level is not the Temp @ 4'/1.21m nor at 8'/2.43m, unless you have a completely "Conditioned" space that is at equilibrium.
- Even 1C/1.8F - 2C/3.6F CAN make a difference, most especially during Low or High temps outside of the Nominal 25C/77F temps. The wider the Temp Difference is between "packs" DOES affect the charge/discharge rates across a Stacked Bank of batteries. THIS IS OBSERVABLE ! It can be minimal which self-corrects BUT it can be broad by several degrees depending on your "facility" and that is harder to compensate for & does affect rates.
! - * - ! The above also Assumes that ALL Battery Packs within a Bank are using identically configuration with the Same BMS' wire lengths (sense etc) Temp Sensor locations etc. Variances within will present various differences that must be considered when assembling your system.
(*General Note
Context for DOD & SOC with LFP.
In this Context, DOD is the measure of Cell/Battery Charge Saturation Level which is the Depth of Charge within the Cells.
SOC is relative to Actual Working Voltages and NOT the Allowable Voltage Range for LFP Cells.
As there are no "Standards" across Manufacturers for Naming Conventions of various functions/capabilities the Terminology does indeed vary from Top Tier-1 to Value Grade equipment, therefore this is more difficult depending on the grade/level of equipment you are using. Therefore I am using the most common terminology for Tier-1 equipment Semantics can really be a Pain in the Kaboose !
I hope this Helps & Clarifies several small issues that can create longer view issues Encountered.
Steve
.
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