LiFePO4 issue?

[GeoffL]

Hi All,
I Recently switched to a hybrid system by removing one of my 110Ah wet lead-acid batteries and replacing it with a 100Ah LFP from Alpha Batteries (clicky product link). I have 200W of solar on the roof (2 x 100W in series) with a Victron SmartSolar 75/15 controller. I've tried a few of the charge profiles, but the controller switches to float prematurely and I have to switch profiles and then switch back to get it back on absorption. The controller is set 14.6V absorption and 13.8V float. At 13.8V, the LFP battery stops charging and goes to standby mode. Also the LFP battery log shows lots of "COV" events (I don't know what that means) and a corresponding "Restored" event for all except the last "COV". According to Alpha's blurb, the battery is supposed to have "Victron Communication", but I'm not sure what that means and how to access it! There doesn't seem any obvious way to get the battery and the controller talking to each other!
I'm not sure whether any of this should be of concern because the system seems to work fine (albeit with me having to force the system back onto absorption) and the LFP hasn't dropped below 80% since initially fully charge.
I'd be grateful for words of wisdom ...
Thanks, Geoff

 

[wildebus]

Chances are the errors are due to voltage being too high. I would lower the charge voltage to maybe 14.3V.

The Victron comms would be with a Cerbo GX or similar. it won't talk to a Victron MPPT.

 

[GeoffL]

Thanks, David. FWIW the instructions that were supplied with the LFP said to charge at between 14.2 and 14.6V. It also specifies a minimum charge current of 10A ... which I'll never achieve; not with just 200W of solar and cable resistance keeping alternator current below 5A. The charge current is considerably higher at 14.6V than at 14.4, but I've dropped the charge voltage to 14.4V... but I still don't know what "COV" means (charge over voltage?)

 

[GeoffL]

Re. "COV" ... the app says, "Fully charge or discharge can recalibrate SOC", so "COV" might be something like "Calibration on voltage"? I really don't know and couldn't find anything in the (fairly comprehensive) manual about either the log that the app makes available, "COV", or even "calibrate".

 

[wildebus]

Thanks, David. FWIW the instructions that were supplied with the LFP said to charge at between 14.2 and 14.6V. It also specifies a minimum charge current of 10A ... which I'll never achieve; not with just 200W of solar and cable resistance keeping alternator current below 5A. The charge current is considerably higher at 14.6V than at 14.4, but I've dropped the charge voltage to 14.4V... but I still don't know what "COV" means (charge over voltage?)

I am not sure what COV stands for - Charge over Voltage sounds a very plausible meaning.
just for extra info ... the reason why you can get a charge error even if the voltage is under the maximum quoted is that the maximum quoted is based on the maximum voltage allowed of each cell. If the cells are not in perfect balance (and they rarely are), then you will hit the maximum voltage of an individual cell before you get the maximum overall voltage.

FWIW, I have similar batteries to you - 2 Lithiums are from Alpha and are heated 'Polarmax' models in a Hybrid configuration (3 x Lead Acid, 3 x Lithium) and I cut charge voltage to the Lithiums at 14.19V which is fully charged. The charger then continues to provide a charge to the Lead.
I would have said lower to 14.2V for you except that would not give the lead the full charge it needs. 14.4V is a reasonable compromise.

 

[Robmac]

Coefficient of Variation apparently.

 

[r4dent]

I Recently switched to a hybrid system by removing one of my 110Ah wet lead-acid batteries and replacing it with a 100Ah LFP f

Can you confirm what leisure battery bank you now have please.

 

[Robmac]

This is what AI says about it, maybe a red Herring - means nothing to me!

AI Overview


In the context of lithium-ion batteries, "COV" refers to the Coefficient of Variation, a statistical measure of the dispersion of data within a dataset. Specifically, in lithium-ion battery coating, COV indicates the consistency or uniformity of the coating process. A lower COV value signifies better coating uniformity.

Elaboration:

• Coefficient of Variation (COV):
  This is calculated as the standard deviation divided by the mean, expressed as a percentage.
• Lithium-ion Battery Coating:
  COV is used to assess the consistency of the coating applied to the battery's electrodes.
• Coating Uniformity:
  A lower COV value indicates a more consistent and uniform coating, meaning there's less variation in the coating's thickness or density across the battery.
• Importance:
  A uniform coating is crucial for battery performance, as it affects cell capacity, energy density, and overall battery lifespan.

 

[Robmac]

AI Overview


To address battery capacity variations (which is related to the coefficient of variation), you need to balance the cells within a battery pack or system. This involves ensuring all cells are at the same level of charge, typically by distributing excess charge from high-capacity cells to low-capacity cells.

Methods for Balancing Battery Cells:

1. 1. Cell Balancing Circuits:
   • These circuits are used in series-connected battery packs (like in electric vehicles or energy storage systems) to equalize the voltage and capacity of individual cells.
   • They work by diverting charge from overcharged cells to undercharged cells, using bypass diodes, FETs, or other components.
2. 2. BMS (Battery Management System):
   • A BMS monitors and controls the charging and discharging process of a battery pack, including cell balancing.
   • It can implement various cell balancing techniques, such as bypass, passive, or active balancing.
3. 3. Active Balancing:
   • This method actively shunts (bypass) excess charge from cells with higher voltages or higher capacity to cells with lower voltages or lower capacity.
   • It's more efficient than passive balancing but requires more complex circuitry.
4. 4. Passive Balancing:
   • This method uses resistors or bypass diodes to allow excess charge to flow from cells with higher voltages to cells with lower voltages.
   • It's simpler than active balancing but less efficient.
     

Addressing Capacity Variation Issues:

1. 1. Proper Charging:
   • Follow the recommended charging procedures for your battery type (e.g., lead-acid, lithium-ion).
     
     
   • Avoid deep discharging, as it can lead to sulfation in lead-acid batteries and degradation in lithium-ion batteries.
     
2. 2. Storage:
   • Store batteries at the recommended temperature and charge level to minimize degradation.
     
     
   • Avoid leaving batteries in a discharged state for extended periods.
     
3. 3. Calibration:
   • Battery calibration (e.g., in smartphones) can help re-train the battery management system to accurately track the remaining capacity.
     
4. 4. Monitoring and Maintenance:
   • Regularly monitor battery voltage, capacity, and temperature.
     
     
   • Replace batteries when they reach the end of their lifespan or show signs of degradation.
     

 

[trevskoda]

Thanks, David. FWIW the instructions that were supplied with the LFP said to charge at between 14.2 and 14.6V. It also specifies a minimum charge current of 10A ... which I'll never achieve; not with just 200W of solar and cable resistance keeping alternator current below 5A. The charge current is considerably higher at 14.6V than at 14.4, but I've dropped the charge voltage to 14.4V... but I still don't know what "COV" means (charge over voltage?)

Wire in parallel and devide 14.6 into 200 gives about 13 amps top

 

[marchie]

Re. "COV" ... the app says, "Fully charge or discharge can recalibrate SOC", so "COV" might be something like "Calibration on voltage"? I really don't know and couldn't find anything in the (fairly comprehensive) manual about either the log that the app makes available, "COV", or even "calibrate".

COV = Cell Over Voltage, one or more cells being too high. I had this problem in Spain in erly March, with Cell 4 roaring away which caused the Solar charging to cease, although Cells 1-3 were still quite low, resulting in Bulk Charging ceasing at around 13.3v. Solution was to buy a Victron IP64 Charger, amend the max Cell Voltage limits, and do a Top Down Balancing exercise over almost 3 weeks, initially at 14.0v and finally at 14.2v when we returned to Scotland. Lithium hits 14,23v regular as clockwork now before dropping back to 13.5v Float

Steve

 

[Robmac]

COV = Cell Over Voltage, one or more cells being too high. I had this problem in Spain in erly March, with Cell 4 roaring away which caused the Solar charging to cease, although Cells 1-3 were still quite low, resulting in Bulk Charging ceasing at around 13.3v. Solution was to buy a Victron IP64 Charger, amend the max Cell Voltage limits, and do a Top Down Balancing exercise over almost 3 weeks, initially at 14.0v and finally at 14.2v when we returned to Scotland. Lithium hits 14,23v regular as clockwork now before dropping back to 13.5v Float

Steve

That seems to tie in with the AI summary Steve. Although their definition of the abbreviation COV is different the cell balancing recommendation seems to agree with your solution so sounds a good path to follow.

You would think the BMS would handle this though?

 

[trevskoda]

Now i know why im sticking to old type batteries.

 

[Robmac]

Now i know why im sticking to old type batteries.

I don't think problems with Lithiums are common Trev. Mine have a 10 year warranty on them.

 

[GeoffL]

Can you confirm what leisure battery bank you now have please.

I now have a 110Ah wet lead/acid battery in parallel with a 100Ah LiFePO4.

FWIW, I have similar batteries to you - 2 Lithiums are from Alpha and are heated 'Polarmax' models in a Hybrid configuration (3 x Lead Acid, 3 x Lithium) and I cut charge voltage to the Lithiums at 14.19V which is fully charged. The charger then continues to provide a charge to the Lead.
I would have said lower to 14.2V for you except that would not give the lead the full charge it needs. 14.4V is a reasonable compromise.

Thanks for that. I've re-set the absorption voltage to 14.4V and not seen a logged COV since (but it's early days!) That said, the LFP hasn't achieved a 100% SOC either -- but that's probably not a bad thing...

COV = Cell Over Voltage, one or more cells being too high. I had this problem in Spain in erly March, with Cell 4 roaring away which caused the Solar charging to cease, although Cells 1-3 were still quite low, resulting in Bulk Charging ceasing at around 13.3v. Solution was to buy a Victron IP64 Charger, amend the max Cell Voltage limits, and do a Top Down Balancing exercise over almost 3 weeks, initially at 14.0v and finally at 14.2v when we returned to Scotland. Lithium hits 14,23v regular as clockwork now before dropping back to 13.5v Float

Steve

Thinking about this, it makes sense as that's just the BMS stopping charging when the battery is at 100% SOC. So, it seems it might be an error, but it's just the BMS doing what I'm relying on it to do by default. Seems weird, though...

My MPPT has an equalization option, but it's set by default at 16.2V and I'm not sure whether that's the same thing as cell balancing. Typically, the cells have a differential of less than 0.005V except at very high SOC, when it can get at large as 0.1V -- high enough, as @wildebus mentioned, to put the highest cell into an 'over-voltage' state. I'm planning to buy a mains charger at some time to take the battery back home to rebalance. However, I suspect I won't need to do that until next year.

Thanks to all for the help.

 

[marchie]

I now have a 110Ah wet lead/acid battery in parallel with a 100Ah LiFePO4.


Thanks for that. I've re-set the absorption voltage to 14.4V and not seen a logged COV since (but it's early days!) That said, the LFP hasn't achieved a 100% SOC either -- but that's probably not a bad thing...


Thinking about this, it makes sense as that's just the BMS stopping charging when the battery is at 100% SOC. So, it seems it might be an error, but it's just the BMS doing what I'm relying on it to do by default. Seems weird, though...

My MPPT has an equalization option, but it's set by default at 16.2V and I'm not sure whether that's the same thing as cell balancing. Typically, the cells have a differential of less than 0.005V except at very high SOC, when it can get at large as 0.1V -- high enough, as @wildebus mentioned, to put the highest cell into an 'over-voltage' state. I'm planning to buy a mains charger at some time to take the battery back home to rebalance. However, I suspect I won't need to do that until next year.

Thanks to all for the help.

Roamer recommended the Victron IP64 Bluetooth 10 amp Charger, because it is powerful enough to be a useul 'normal'/standby Charger, but it has the capability to make the minute adjustments to Cell levels, even when my battery was showing 229.70Ah charge [230Ah capacity] to achieve the Top Down Balance. It is the equivalent of playing Freecell with only 1 spare place to swap cards around! 1 week with an overall 14.0v ceiling, then a further week at 14.2v [in practice it took another 2+ weeks at the higher SOC to get things back in line. Roamer conirmed that the screeshots I sent and my non-tech reports on progress were consistent with the problem having been solved. It does need a 13 or 16 amp socket conneection for the Top Down to work, because it needs a 24/7 power supply for the rebalance to work [had to leave heating on to stop cold nights killing the charging!]

Steve

 

[merl]

Geoff. Depending on which BMS was used in your battery the balance current that's drawn from the strongest cell can often be tiny, it therefore takes ages to drag that cell down to a similar level to the lowest cell in the pack, this problem is often exaserbated by the fact that a lot of BMSs only provide cell balancing while the battery is actually being charged or even worse being charged above a set current. (maybe this is the 10A figure that you mentioned?)
Take a look at the BMS settings and see if there's a 'balance' setting page where you can set the charge current when balancing commences and set this as low as possible, ideally there'll be an option to make balancing happen continuously or ALWAYS, so the cells will balance constantly.

 

[wildebus]

I now have a 110Ah wet lead/acid battery in parallel with a 100Ah LiFePO4.


Thanks for that. I've re-set the absorption voltage to 14.4V and not seen a logged COV since (but it's early days!) That said, the LFP hasn't achieved a 100% SOC either -- but that's probably not a bad thing...


Thinking about this, it makes sense as that's just the BMS stopping charging when the battery is at 100% SOC. So, it seems it might be an error, but it's just the BMS doing what I'm relying on it to do by default. Seems weird, though...

My MPPT has an equalization option, but it's set by default at 16.2V and I'm not sure whether that's the same thing as cell balancing.

NEVER use the equalization option with Lithium. If it say a Victron SmartSolar, when you select the Lithium profile that is disabled. Also if a Victron disable the low temp disable feature as well for your setup.

Typically, the cells have a differential of less than 0.005V except at very high SOC, when it can get at large as 0.1V -- high enough, as @wildebus mentioned, to put the highest cell into an 'over-voltage' state. I'm planning to buy a mains charger at some time to take the battery back home to rebalance. However, I suspect I won't need to do that until next year.

Thanks to all for the help.

I honestly would not bother. A decent Lithium battery is balanced as needed prior to shipment and will do the neccessary self-balancing with no user-interaction.
I just had a look at my Polarmax batteries to see the cell voltages (batteries are at around 78% SOC)

The only time I see any significant variance between cells is in times of high charge or discharge, which is what I would expect. When the batteries are pretty idle, the BMS will (or at least should) do some gentle equalization.

 

[marchie]

That seems to tie in with the AI summary Steve. Although their definition of the abbreviation COV is different the cell balancing recommendation seems to agree with your solution so sounds a good path to follow.

You would think the BMS would handle this though?

I *think*, Rob, that the BMS takes an overall view, rather than looking at the individual cell levels; however, the Roamer Smart 4th [?] Generation BMS has active Cell Balancing built in [mine is the previous generation, so lacks this sophisticaton, and at only 16 months old, I can't justify binning it, having paid just north of £1,000 in the January 2024 sale! The irony is that the Roamer reports cell levels to 3 decimal places, whereas the KS Energy predecessor only reported to 2 decimal places, so, whilst Roamer made me panic with 3.311 to 3.328v, KS would have have shown 3 cells at 3.31v and one at 3.32/3.33v, and I would have lived in blissful ignorance until the much cruder BMS copped a strop and the battery went into a coma that may or may not have been possible to wake from ... 'See a problem' spend £££ to solve it, create another problem that causes angst and costs ££££ to resolve' seems the way of the world at present; but then I had the DPF Sensor failure to distract me from BMS problems ...

Steve

 

[wildebus]

I *think*, Rob, that the BMS takes an overall view, rather than looking at the individual cell levels; however, the Roamer Smart 4th [?] Generation BMS has active Cell Balancing built in [mine is the previous generation, so lacks this sophisticaton, and at only 16 months old, I can't justify binning it, having paid just north of £1,000 in the January 2024 sale! The irony is that the Roamer reports cell levels to 3 decimal places, whereas the KS Energy predecessor only reported to 2 decimal places, so, whilst Roamer made me panic with 3.311 to 3.328v, KS would have have shown 3 cells at 3.31v and one at 3.32/3.33v, and I would have lived in blissful ignorance until the much cruder BMS copped a strop and the battery went into a coma that may or may not have been possible to wake from ... 'See a problem' spend £££ to solve it, create another problem that causes angst and costs ££££ to resolve' seems the way of the world at present; but then I had the DPF Sensor failure to distract me from BMS problems ...

Steve

If you had a Lithium battery without a bluetooth BMS you would be relaxing in blissful ignorance from the very start.

It reminds me of the early days of Lithium adoption when there was a group of people adament that you couldn't parallel- connect Lithium Batteries with Bluetooth BMSes but ones with 'dumb' BMSes you could - all based on the fact that they could actually see differences in the those batteries but just assumed the cells in the dumb batteries were all aligned as they had no evidence otherwise