Strange issue with 48V LiFePO4 system

[acecard]

49.4V = 3.08 Volts per cell in a standard 16S Build. This is the Bottom of the Working Voltage Range (3.000-3.400). If 1 cell happened to go below LVD (Low Volt Disconnect) setting which from what you describe seems to be 3.000. that would cause an LVD.

You stated you do not have a SmartBMS, sorry to say but that was a Mistake, especially for a DIY Battery Pack, you do need the ability to view the status of what the cells are doing and to be able to set parameters for your use case.

While the normal Working Voltage Range is just 0.400 it is very narrow BUT the cells can and should be allowed to drop to 2.700Vpc with a cutoff / Shutdown @ 2.600 Vpc. This is for surge handling that creates a sag... IE when a fridge starts it's surge will pull the voltage down for a few seconds and if that trips over the LVD line the BMS will shutdown. Most Smart BMS' can be programmed for a Delay to prevent a surge from triggering an LVD state.

The ability to monitor the cells also will help resolve issues if something is wrong with the cells because you see the voltage of each cell for troubleshooting. If you have a loose connection or a weak cell etc you can identify it and check it out.

Your operating Range is 48.0V-54.4 (working voltage range)
EndAmps/Tailcurrent for charging is 14A which is the point that Absorb switches to Float to finish off the battery pack to 100%.

Suggested BMS Settings for a Smart BMS: (most have similar programmable settings)
Cell Overvolt Protection 3.600
Cell Overvolt Release 3.500
Cell Undervolt Protection 2.700
Cell Undervolt Release 2.750
Power Off @ 2.600 (never get to 2.500, and this allows a simple restart)
* Charge Over Current Protection Delay (time in seconds) 30
* Charge Over Current Protection Release (time in seconds) 60
* Discharge Over Current Protection Delay (time in seconds) 200 (to allow for a device surge that causes a sag that drops below LVD setting)
* Discharge Over Current Protection Release (time in seconds) 60

THERE IS A NASTY GOTCHA LURKING HERE TOO !
Voltage Drop between Actual Battery & Inverter/Charger & SCC (if separate).
There is ALWAYS a voltage drop due to the wires, lugs/terminals, switches, fuses & breakers "Ces't la vie".
Once fully charged take a GOOD DMM/DVOM and measure the Actual Voltage @ the Battery Terminals, the SCC, the Inverter/Charger. The "Battery Rules" not the other devices !

EXAMPLE: IF the Battery terminals are @ 54.4 and you see the Inverter terminals showing 54.0 +/- the SCC may show 54.6 +/-. That differential has to be addressed so you correct & compensate for that in your Device Settings. If you want the Inverter to cutoff @ 44.8, then to should be 44.8 @ the battery as well, if NOT Corrected it will cutoff @ 45.2. Similar applies to the SCC for Charging, if you want it to charge to 54.4 @ Battery then you have to set that correction (IF it does not have a Voltage Compensation setting, Most Tier-1 SCC's do have that facility) then you do it in the charging settings by reducing the charge voltage by 0.2.
* A Typically an SCC will see higher voltages as it is the incoming source prior to derating & loss.
* An Inverter will see a lower voltage as it IS derated from batt to inverter.

A Good SmartBMS with Active Balancing (2A or 3A for a 280AH Pack) General rule is 1A Balance power per 100AH is the best solution. I would highly recommend a JKBMS B2A20S20P with 2A Active Balancing, 200A Capacity, Bluetooth & RS485 with the extra Add-on LCD Screen with power switch. NB: the BMS itself ships with an On/Off Switch but the wire is only 5" long.

One vendor for example:

45.94US $ 29% OFF|Jk Bms 1a 2a 5a Balance Current 8s 12s 13s 14s 16s 17s 20s 24s Smart Jk Bms 60a 80a 100a 150a 200a 600a Lifepo4 Li-ion Battery - Battery Accessories & Charger Accessories - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

Wow, thanks for the comprehensive answer! In my case it seems that the display on my inverter (which is also my SCC) is reading higher than what is happening at my battery. E.g. my inverter was reading 52.9V which correlates to about 70ish%, but my battery was reading 52.6V, which is more like 50%! Due to this, I think that the battery isn't even fully charging because the inverter thinks it's charged but it's not.

If I were to install a smart BMS with active balancing, would that negate the requirement for me to top balance?

 

[acecard]

No top balance here. All cells were at 3.105. Assembled and JKbms has cell delta at .001.

1.) order a JKbms and install.
2.) Get a victron smart shunt and install.

The colder nights might make the electric water heater run more. Clouds might make it charge less. Sun angle would do the same.

Ok so the shunt would give me accurate readings of the battery operating parameters rather than using the inverter display, which I'm just finding out is very inaccurate!!

 

[labeeman]

wouldn't a 3kW solar system produce 3kW even if it only had an hour's worth of sunlight??

Only if they were pointed toward the sun NOT at an angle to the sun and I suspect they are mounted Flat which will in your area give you not even half of that.

 

[Steve_S]

For a "48V" System 3.450 Volts per cell is 100% @ 55.2V and just above the Working Voltage Range which is 3.000-3.400 (48V (3.000Vpc) - 54.4V (3.400Vpc).

Like all Battery Cells regardless of chemistry, there is an Allowable Range & Working Range.
LFP Allowable is 2.500-3.650Vpc which is the "Safe Zone" where no harm comes to the cells BUT is not intended to be pushed into.
LFP Working Range is 3.000-3.400 which is where you rated AH comes from. By charging to 3.450Vpc and saturating the cells to that point, they will settle to 3.400 quickly after Charging stops. You gain NOTHING by charging above that as they will settle to working range, it IS the chemistry ! NB, WHY do you think they use 3.200Vpc as NOMINAL (which is 50% SOC btw) It is the midpoint of the Working Voltage.

You often hear the Wives Tale of work between 10-90%. The bottom 10 is 2.500-2.90o. The top 10% is 3.450-3.560
This uses the full allowable range -10% Top & Bottom is an old safety measure that became a common wives tale.

NOTE ALSO that quite often (most time) that once you charge above 3.450 you will get runner cells that hit HVD before others and trip cutoff. This also works similarly when voltages are below 2.850 typically, one or more cells will bottom out fast resulting in an LVD cutoff.

There IS history on this, when the Chinese Co's started to make LFP and document + Chinglish translate it was not correct and that is where this originated.

 

[acecard]

For a "48V" System 3.450 Volts per cell is 100% @ 55.2V and just above the Working Voltage Range which is 3.000-3.400 (48V (3.000Vpc) - 54.4V (3.400Vpc).

Like all Battery Cells regardless of chemistry, there is an Allowable Range & Working Range.
LFP Allowable is 2.500-3.650Vpc which is the "Safe Zone" where no harm comes to the cells BUT is not intended to be pushed into.
LFP Working Range is 3.000-3.400 which is where you rated AH comes from. By charging to 3.450Vpc and saturating the cells to that point, they will settle to 3.400 quickly after Charging stops. You gain NOTHING by charging above that as they will settle to working range, it IS the chemistry ! NB, WHY do you think they use 3.200Vpc as NOMINAL (which is 50% SOC btw) It is the midpoint of the Working Voltage.

You often hear the Wives Tale of work between 10-90%. The bottom 10 is 2.500-2.90o. The top 10% is 3.450-3.560
This uses the full allowable range -10% Top & Bottom is an old safety measure that became a common wives tale.

NOTE ALSO that quite often (most time) that once you charge above 3.450 you will get runner cells that hit HVD before others and trip cutoff. This also works similarly when voltages are below 2.850 typically, one or more cells will bottom out fast resulting in an LVD cutoff.

There IS history on this, when the Chinese Co's started to make LFP and document + Chinglish translate it was not correct and that is where this originated.

Ok so anything below 2.5V would damage a cell? The reason I ask is that I just had a repeat of what happened the other day, so I checked the individual cell voltages and they were at 3V, apart from one which was at 2.2V!!! I thought the BMS was supposed to protect against it going so low?!!!

 

[timselectric]

It should have.
Double check the settings.

 

[acecard]

Ok, I'm going to order a new Smart BMS anyway and do away with this one. Does this mean that this cell is now damaged and I need to replace it?
Also, if I install a JKBMS with active balancing, I'm guessing I won't need to bother top balancing?

 

[labeeman]

It should have.
Double check the settings.

He has said he does not have a smart BMS and does not have a way to check them.

 

[Steve_S]

Correct below 2.500Vpc is NOT Good if left long BUT it's not a panic ! I had a different brand BMS Crap Out BIG and before I knew it the cells in the pack were all at 1.75 +/- Vpc. So I had to do the 2 day ecovery provess, they've been fine since.

I believe the default cutoff for low voltage that shuts down is 2.600Vpc for JK but that is preset in the Settings Screen.
BTW the "Default" settings for LFP that are provided are BUNK because a few parameters are NOT for LFP like Cutoff charge @ -20C Should be 0C And charge start should be 5C Temps.

* DUMB BMS' are an unknown quatity and some are really awful ! It was a DumbBMS that brought my cells down to the 1.70's. Not even sure is was for LFP actually... I killed it with a Sledgehammer ! (litterally)

Below is for JK-BMS Smart BMS with active balancing.
Check your settings against this:

<---- IMPORTANT shuts down the BMS




<--- Adjust for your pack, 0.5C Rate




<--- Adjust for 1C of your pack & BMS Handling capability








<--- The MAX Temp LFP can handle

<--- This and below is OK for charge
<<-- as above

<<-- as above

<--- STOP charging at 0C

<--- START Charging at 5C

 

[labeeman]

Does this mean that this cell is now damaged and I need to replace it?

I do not think it is damaged yet. A BMS with take some time to balance the pack if you have a power supply that can be set to the other cell voltage you can charge that cell to that voltage and speed up the balancing.

 

[timselectric]

Ok, I'm going to order a new Smart BMS anyway and do away with this one. Does this mean that this cell is now damaged and I need to replace it?

Maybe not. If it didn't happen fast, or under high load.

Ok, I'm going to order a new Smart BMS anyway and do away with this one. Does this mean that this cell is now damaged and I need to replace it?
Also, if I install a JKBMS with active balancing, I'm guessing I won't need to bother top balancing?

The JK will take care of it. But, I would keep an eye on that cell.

 

[acecard]

Correct below 2.500Vpc is NOT Good if left long BUT it's not a panic ! I had a different brand BMS Crap Out BIG and before I knew it the cells in the pack were all at 1.75 +/- Vpc. So I had to do the 2 day ecovery provess, they've been fine since.

I believe the default cutoff for low voltage that shuts down is 2.600Vpc for JK but that is preset in the Settings Screen.
BTW the "Default" settings for LFP that are provided are BUNK because a few parameters are NOT for LFP like Cutoff charge @ -20C Should be 0C And charge start should be 5C Temps.

* DUMB BMS' are an unknown quatity and some are really awful ! It was a DumbBMS that brought my cells down to the 1.70's. Not even sure is was for LFP actually... I killed it with a Sledgehammer ! (litterally)

Below is for JK-BMS Smart BMS with active balancing.
Check your settings against this:

<---- IMPORTANT shuts down the BMS




<--- Adjust for your pack, 0.5C Rate




<--- Adjust for 1C of your pack & BMS Handling capability








<--- The MAX Temp LFP can handle

<--- This and below is OK for charge
<<-- as above

<<-- as above

<--- STOP charging at 0C

<--- START Charging at 5C

1.75v! Wow! What is involved in the 2 day recovery process?

 

[acecard]

Thanks for all your help guys, here is the plan of attack......

I will get a JK BMS installed on there, as well as a Victron shunt so that I can accurately monitor the battery. The next thing to do after that will be to adjust my charge controller charging parameters to account for the differential at the battery vs. what the charge controller thinks so that the right charging parameters are set according to what the battery actually needs rather than what the controller thinks it needs. It is also very clear that solar generation is much more of an issue than I initially thought. My unit tells me that overall, my solar generation over the month of October is 35kWh, which is an average of 1.34kWh a day, from a 3kW system, and today, for example, I generated nothing! I know that the solar is wired up OK because there was one point yesterday that the sun was actually out (briefly!), and at that point, my charge controller was showing PV array generation of 280ish volts (total array voltage is 320V in optimal conditions, so 280V at that point yesterday seems to make sense). So clearly, the next thing is to sort out some kind of RV-friendly back up for the solar, maybe some kind of small genny that I can use just to keep the battery topped up. I will post this up as a separate thread in the "RV mounted system" part of the forum.

 

[Steve_S]

1.75v! Wow! What is involved in the 2 day recovery process?

Recovery Instructions:
Charge each LOW cell, one at a time, starting at 3.000V and around 10A and let it slowly take the charge till it cuts off. Rinse repeat for each cell. They should all take it BUT BE GENTLE & POLITE ! Once they all get to 3.000 then parallel the cells and top them in INCREMENTS, I would suggest 0.100V increments. Yes slow, painful, TEDIOUS but if you want to recover them....
-
They technically can recover IF they were not frozen or cooked while in a state of discharge, if they have, then do one cell at a time and in a safe box in case it pops & leaks. IF you are lucky, they will recover and maybe you've only lost a percentage of capacity. IF they recover to at least 3.400Vpc, I would run at least 3 good cycles through them (charge/discharge) and then capacity test each cell to ensure the packs integrity, because even if One Cell goes wonky, it will affect the whole pack, as the lowest common denominator rules.
-
Once you get the cells up to 3.650 (I would stick to 3.600 myself) and fully saturated (meaning taking <2A) and stop charge current. The cells WILL SETTLE which is perfectly normal & expected behaviour. They will likely drop to about 3.500 from 3.600 within 1 hour or so, give or take a bit. They will usually continue to settle till around the 3.400-3.450 mark where it will slow considerably as the LFP Working Voltage range is 3.000-3.400.
-
Once this is done, I would setup the pack temporarily with the BMS and discharge the battery pack to cutoff, then recharge through the BMS till it reaches full at a respectable Amperage. 100AH Cell can typically take a Max of 0.5C or 50A charge rate. 20-40A Charge rate would be as high as I would go "for now" while determining their condition.
-
When charging at a higher amperage the cells heat up (normal & expected) and the higher the amps the warmer they get. With ESS cells @ 0.5C it's never crazy ! EV Grade Cells @ 5C Charge Rate = another matter ok. We are dealing with ESS cells here, so staying "in context". You will want to check the cells during Higher Amp charging feel the sides etc, they should be consistent / constant... a Hot Spot = Warning Flag ! You WILL NOT GET THAT with Lo Amp Charging, it has to be at least 0.25C and the temps should be notable within 1/2 hour or so. Be diligent & watchful !

This was done with 8x AoyouPower Used EV Cells.

 

[acecard]

Recovery Instructions:
Charge each LOW cell, one at a time, starting at 3.000V and around 10A and let it slowly take the charge till it cuts off. Rinse repeat for each cell. They should all take it BUT BE GENTLE & POLITE ! Once they all get to 3.000 then parallel the cells and top them in INCREMENTS, I would suggest 0.100V increments. Yes slow, painful, TEDIOUS but if you want to recover them....
-
They technically can recover IF they were not frozen or cooked while in a state of discharge, if they have, then do one cell at a time and in a safe box in case it pops & leaks. IF you are lucky, they will recover and maybe you've only lost a percentage of capacity. IF they recover to at least 3.400Vpc, I would run at least 3 good cycles through them (charge/discharge) and then capacity test each cell to ensure the packs integrity, because even if One Cell goes wonky, it will affect the whole pack, as the lowest common denominator rules.
-
Once you get the cells up to 3.650 (I would stick to 3.600 myself) and fully saturated (meaning taking <2A) and stop charge current. The cells WILL SETTLE which is perfectly normal & expected behaviour. They will likely drop to about 3.500 from 3.600 within 1 hour or so, give or take a bit. They will usually continue to settle till around the 3.400-3.450 mark where it will slow considerably as the LFP Working Voltage range is 3.000-3.400.
-
Once this is done, I would setup the pack temporarily with the BMS and discharge the battery pack to cutoff, then recharge through the BMS till it reaches full at a respectable Amperage. 100AH Cell can typically take a Max of 0.5C or 50A charge rate. 20-40A Charge rate would be as high as I would go "for now" while determining their condition.
-
When charging at a higher amperage the cells heat up (normal & expected) and the higher the amps the warmer they get. With ESS cells @ 0.5C it's never crazy ! EV Grade Cells @ 5C Charge Rate = another matter ok. We are dealing with ESS cells here, so staying "in context". You will want to check the cells during Higher Amp charging feel the sides etc, they should be consistent / constant... a Hot Spot = Warning Flag ! You WILL NOT GET THAT with Lo Amp Charging, it has to be at least 0.25C and the temps should be notable within 1/2 hour or so. Be diligent & watchful !

This was done with 8x AoyouPower Used EV Cells.

Wow, that really is a process! Thanks for detailing it for me.

 

[740GLE]

One thing that may help people in providing guidance is first stating each make and model of the equipment you have in your system.

It sounds like you have an AIO growatt type unit with an unknown BMS.

That AIO should allow you to charge the battery from shore power at 20-30A and fully top up the cells so you don’t have to worry about low PV generation. Then you’ll just have to track usages vs production and possibly re top up next time you’re on shore power.

Just my two cents reading through the discussions.

 

[acecard]

For a "48V" System 3.450 Volts per cell is 100% @ 55.2V and just above the Working Voltage Range which is 3.000-3.400 (48V (3.000Vpc) - 54.4V (3.400Vpc).

Like all Battery Cells regardless of chemistry, there is an Allowable Range & Working Range.
LFP Allowable is 2.500-3.650Vpc which is the "Safe Zone" where no harm comes to the cells BUT is not intended to be pushed into.
LFP Working Range is 3.000-3.400 which is where you rated AH comes from. By charging to 3.450Vpc and saturating the cells to that point, they will settle to 3.400 quickly after Charging stops. You gain NOTHING by charging above that as they will settle to working range, it IS the chemistry ! NB, WHY do you think they use 3.200Vpc as NOMINAL (which is 50% SOC btw) It is the midpoint of the Working Voltage.

You often hear the Wives Tale of work between 10-90%. The bottom 10 is 2.500-2.90o. The top 10% is 3.450-3.560
This uses the full allowable range -10% Top & Bottom is an old safety measure that became a common wives tale.

NOTE ALSO that quite often (most time) that once you charge above 3.450 you will get runner cells that hit HVD before others and trip cutoff. This also works similarly when voltages are below 2.850 typically, one or more cells will bottom out fast resulting in an LVD cutoff.

I have been playing with the settings on my charge controller and am a little confused. I plugged the batteries into mains power to charge them to full capacity over night. I set the bulk charge voltage to 56.7v and floating charge to 54.3v (this accounts for about 0.3v differential between the controller readings and the actually battery readings). I think I may have got this wrong and not quite understanding float vs. bulk charge. When I woke up this morning, the unit has stopped charging and the battery voltage was 54.3. So I turned off the mains charging and the batteries pretty quickly dropped down to 53.3v, this happened withing 10mins. Is this normal?

 

[Steve_S]

I have been playing with the settings on my charge controller and am a little confused. I plugged the batteries into mains power to charge them to full capacity over night. I set the bulk charge voltage to 56.7v and floating charge to 54.3v (this accounts for about 0.3v differential between the controller readings and the actually battery readings). I think I may have got this wrong and not quite understanding float vs. bulk charge. When I woke up this morning, the unit has stopped charging and the battery voltage was 54.3. So I turned off the mains charging and the batteries pretty quickly dropped down to 53.3v, this happened withing 10mins. Is this normal?

LFP will always settle post-charge. This is normal & natural for this chemistry and is similar to what happens with FLA in fact.
It is NOT unusual to see 1V +/- a bit drop as soon as incoming power stops.
54.3V (3.393Vpc) is fine as working range is to 3.400.
56.7 (3.543Vpc) Bulk is a tad much and may likely cause runner cells to HVD.
* Max Suggested:
56.4V (3.525Vpc) would be better for Bulk (max really) then Float at 55.6V (3.475) PENDING on Cell Grade, you could even float to 56.0V (3.500).

Constant Current Bulk Charge Stage: In the first stage, known as the Bulk Charge Stage, the charger delivers a constant, maximum charging current that can be safely handled as specified by the battery manufacturer. The value of the Bulk Charge Current depends upon the total Ampere Hour (Ah) capacity of the battery or bank of batteries. A battery should never be charged at a very high charging current as a very high rate of charging will not return the full 100% capacity. The Bulk Charge Stage restores about 75% of the battery's capacity. * INFO As the Bulk Charge Stage is a constant current stage, the charger does not control the voltage and the voltage seen at the output terminals of the charger will be the actual battery voltage.

Constant Voltage Absorption Stage: During the Absorption Stage, the charger changes from constant current to constant voltage charging. The charging voltage is held constant to ensure that the battery is further charged to its full capacity without overcharging. The Absorption Stage feeds up to an additional 40% of the capacity which adds up to a total charge capacity of around 115% to take care of around 15% loss of charging efficiency. As the output voltage of the charger is held constant, the battery absorbs the charge slowly and the current reduces gradually. The time the charger is held in the Absorption Stage before it transitions to the next Float Stage is determined in one or more of the following conditions:

• By a fixed timer (e.g. 4 to 8 Hours). This may result in overcharging of almost fully charged batteries.
• When the charge current drops to the specified threshold: Switching over to the Float Stage when the charge current drops below a certain threshold (e.g. 10% of the charger Bulk Charge Current). This may result in overcharging and locking in the Absorption Stage if the battery is feeding an external load that has a value > the specified threshold.

Constant Voltage Float Stage: The Float Stage is a maintenance stage in which the output voltage is reduced to a constant lower level, typically to maintain the battery's charge and also, to compensate for self-discharge. Self-discharge of the electrical Ampere Hour (Ah) capacity that is lost when the battery is not being charged and there is no load connected to it. i.e. sits idle in storage. Self-discharge is caused by electrochemical processes within the battery and is equivalent to the application of a small electrical load. Self-discharge increases with an increase in temperature. Self-discharge of the battery under long-term storage will create conditions equivalent to undercharging.

Hope it helps, Good Luck
Steve

 

[acecard]

LFP will always settle post-charge. This is normal & natural for this chemistry and is similar to what happens with FLA in fact.
It is NOT unusual to see 1V +/- a bit drop as soon as incoming power stops.
54.3V (3.393Vpc) is fine as working range is to 3.400.
56.7 (3.543Vpc) Bulk is a tad much and may likely cause runner cells to HVD.
* Max Suggested:
56.4V (3.525Vpc) would be better for Bulk (max really) then Float at 55.6V (3.475) PENDING on Cell Grade, you could even float to 56.0V (3.500).

Constant Current Bulk Charge Stage: In the first stage, known as the Bulk Charge Stage, the charger delivers a constant, maximum charging current that can be safely handled as specified by the battery manufacturer. The value of the Bulk Charge Current depends upon the total Ampere Hour (Ah) capacity of the battery or bank of batteries. A battery should never be charged at a very high charging current as a very high rate of charging will not return the full 100% capacity. The Bulk Charge Stage restores about 75% of the battery's capacity. * INFO As the Bulk Charge Stage is a constant current stage, the charger does not control the voltage and the voltage seen at the output terminals of the charger will be the actual battery voltage.

Constant Voltage Absorption Stage: During the Absorption Stage, the charger changes from constant current to constant voltage charging. The charging voltage is held constant to ensure that the battery is further charged to its full capacity without overcharging. The Absorption Stage feeds up to an additional 40% of the capacity which adds up to a total charge capacity of around 115% to take care of around 15% loss of charging efficiency. As the output voltage of the charger is held constant, the battery absorbs the charge slowly and the current reduces gradually. The time the charger is held in the Absorption Stage before it transitions to the next Float Stage is determined in one or more of the following conditions:

• By a fixed timer (e.g. 4 to 8 Hours). This may result in overcharging of almost fully charged batteries.
• When the charge current drops to the specified threshold: Switching over to the Float Stage when the charge current drops below a certain threshold (e.g. 10% of the charger Bulk Charge Current). This may result in overcharging and locking in the Absorption Stage if the battery is feeding an external load that has a value > the specified threshold.

Constant Voltage Float Stage: The Float Stage is a maintenance stage in which the output voltage is reduced to a constant lower level, typically to maintain the battery's charge and also, to compensate for self-discharge. Self-discharge of the electrical Ampere Hour (Ah) capacity that is lost when the battery is not being charged and there is no load connected to it. i.e. sits idle in storage. Self-discharge is caused by electrochemical processes within the battery and is equivalent to the application of a small electrical load. Self-discharge increases with an increase in temperature. Self-discharge of the battery under long-term storage will create conditions equivalent to undercharging.

Hope it helps, Good Luck
Steve

Thanks so much for the response. One last thing, the 56.7V bulk was to compensate for the 0.3V differential between what the controller display shows and what I actually see at the battery terminals. So that should correlate to 56.4V at the battery, which you suggest is good for bulk. So for float I will up it to 55.9V, which should be 55.6V at the battery. Is my logic correct here?!

 

[Steve_S]

Thanks so much for the response. One last thing, the 56.7V bulk was to compensate for the 0.3V differential between what the controller display shows and what I actually see at the battery terminals. So that should correlate to 56.4V at the battery, which you suggest is good for bulk. So for float I will up it to 55.9V, which should be 55.6V at the battery. Is my logic correct here?!

Yes that should hit the "Sweet Spot". It's sad that so much gear out there do not have "Offset Settings" to correct for voltage differentials due to line loss & resistance for BOTH cases of Charge vs Discharge. Tier-1 Product do often have that but not much else, it's a real "pisser" cause it is not hard to add. If using FLA it really makes no difference as it is Brute Force Tech but any Lithium Based system Millivolts & Milliohms count... Even Sensing Shunts have to be at least 2 Decimal Accurate, but 3 decimal place accurate would be best and manufacturers ar "just Now Getting it".

Funny part is I even got into an Argument with the head engineers of High Cost Tier-1 Products with them saying "1 Decimal Accuracy is Fine and we've always done it like that for 15+ years" Damned Lead Heads !!! Fine for Lead but NOT for Lithium, Example that LFP is technically at 0% SOC @ 2.900Vpc and 100% SOC @ 3.400 Vpc. THAT IS 0.500V for the whole AH Range ! so they did some quick internal tests to realize they were wrong, Never admitting it of course but all of a sudden Firmware & Software changes appear for 2 decimal accuracy. Gee Golly, Wonder Why. As a retired IT Hardware/Software Engineer I know about the detail devil that lurks in the tech...

 

[acecard]

Yes that should hit the "Sweet Spot". It's sad that so much gear out there do not have "Offset Settings" to correct for voltage differentials due to line loss & resistance for BOTH cases of Charge vs Discharge. Tier-1 Product do often have that but not much else, it's a real "pisser" cause it is not hard to add. If using FLA it really makes no difference as it is Brute Force Tech but any Lithium Based system Millivolts & Milliohms count... Even Sensing Shunts have to be at least 2 Decimal Accurate, but 3 decimal place accurate would be best and manufacturers ar "just Now Getting it".

Funny part is I even got into an Argument with the head engineers of High Cost Tier-1 Products with them saying "1 Decimal Accuracy is Fine and we've always done it like that for 15+ years" Damned Lead Heads !!! Fine for Lead but NOT for Lithium, Example that LFP is technically at 0% SOC @ 2.900Vpc and 100% SOC @ 3.400 Vpc. THAT IS 0.500V for the whole AH Range ! so they did some quick internal tests to realize they were wrong, Never admitting it of course but all of a sudden Firmware & Software changes appear for 2 decimal accuracy. Gee Golly, Wonder Why. As a retired IT Hardware/Software Engineer I know about the detail devil that lurks in the tech...

Thanks again! It does seem strange not to have this functionality. Things don't seem to have quite caught up with lithium batteries yet!!

 

[Steve_S]

Thanks again! It does seem strange not to have this functionality. Things don't seem to have quite caught up with lithium batteries yet!!

TBH my system is "Dated" and many products were not available here in Canada at the time I started my adventure. IF I was building today I would go all Victron (No AIO) and Low Frequency still. but I am now heavily invested into my gear and essentially stuck on the path, the only thing to be added in now that my battery bank 1300AH / 33kWh I will have to add another Midnite Classic SCC a 150, and another solar array. The Classics were designed for FLA primarily so there is a requirement to KLUDGE them for Lithium Based, their new product lines are Li Ready but I cannot integrate them in with the old...

 

[acecard]

TBH my system is "Dated" and many products were not available here in Canada at the time I started my adventure. IF I was building today I would go all Victron (No AIO) and Low Frequency still. but I am now heavily invested into my gear and essentially stuck on the path, the only thing to be added in now that my battery bank 1300AH / 33kWh I will have to add another Midnite Classic SCC a 150, and another solar array. The Classics were designed for FLA primarily so there is a requirement to KLUDGE them for Lithium Based, their new product lines are Li Ready but I cannot integrate them in with the old...

That's the thing, once you go too far down a path you kinda need to continue! I've been monitoring my system over the last couple of weeks and noticing that my battery bank doesn't seem to settle at 54.4V after charging, but rather around the 53.1V. Is it possible to increase this, or is there something fundamentally wrong?

Also, been looking into BMS function a little bit more. I've ordered a JKBMS but I was looking at a Daly BMS on the following links:

Daly 4S 10A~250A 12V LiFePO4 BMS Common Port with Balance

Professional high current wiring design &workmanship, thus can withstand the shock of high current high. The appearance is sealed by injection molding process to improve moisture-proof and oxidation-proof components and prolong the service life of the products. Dust proof, shockproof...

www.gobelpower.com

BMS of LiFePO4 Battery - Sunon Battery

For all lithium-ion batteries, BMS is a must-have, why? Li-ion battery is sensitive to high voltage, low voltage, and high current. It will lead to crystallization inside the battery, then lower the internal capacity, or even that a severe crystallization will stab through the electrode film...

sunonbattery.com

Both say that the over-discharge cut-out happens at 2.2V, which is what mine seems to do, but I thought that was too low?

 

[Steve_S]

54.4V = 3.400Vpc. Set Bulk/Absorb to 55.6V (3.475) but No Higher than 56.0V (3.500). Give Absorb 1 hour to run. Float at 0.1 V below your absorb. Absorb + Float will allow the cells to "Saturate" and properly fill, not just a surface charge at target voltage. You'll see that as the Amps Taken drop and eventually the battery will go into "rest" mode at which point Float will carry the demand. *!* Depends on your location, sun-hours and overall generation capacity.

- no comment on Daly... ugh.

With the JK, the BMS can be set to shutdown @ 2.600, Under Volt Protection @ 2.700 with Under Volt Recovery @ 2.750 to allow for voltage sag from a surge demand @ low voltage.

 

[Ampster]

my battery bank doesn't seem to settle at 54.4V after charging, but rather around the 53.1V. Is it possible to increase this, or is there something fundamentally wrong?

53.1 is 3.32 per cell which is what some LFP cells settle at. That may be a normal resting voltage versus 3.4 volts per cell. 3.45 vpc is where I terminate charging.