Do I have defective eve Cell(s) ...Please help

[Brearz]

Except you're assuming you're at 80% SOC. You very well may not be. How do you know?

Why do you rarely ever see that voltage? You should be regularly hitting that when charging to full. Unless you're saying you almost never see full charge? If that's the case, you need more solar power (because your solar/battery balance is battery heavy so it can't quite make it to the top), or if that just isn't possible, maybe you should bottom balance if you're going to spend most of your time between empty and 80%.

As it stands right now it appears your individual cell SOC is all over the place. A balancer active below the upper knee can make things worse partially because nothing is 100% efficient. If it is constantly running, it is constantly adding an extra draw to the cells.

I rarely see full charge as the EV is plugged in daily and discharges fully. It will take what I have. If it leave it to charge fully for say 2 days it knocks off when its still sunny and sun is wasted.

 

[SparkyJJO]

Well that's part of your problem, you really do need to fully charge (and waste some sun) every so often to let the batteries balance out.

 

[Brearz]

Hi there,consider taking everything in parts and start doing a manual balancing....this doesn't have to be a high voltage i.e. 3.6V,important is,that they are all equally balanced.If you do that one by one and write down the capacities,you'll find there already some answers....Guessing and moving around cells and then having maybe a poor active balancer won't get you far....Automatic balancing needs to be only done at the end of the charging time....Those battery banks ideally should last tenth's of years,maybe 20-if treated well...so we might invest some time to propperly install them....Anyway once everything is sorted it should look a bit like this....

Yes i'm considering a full strip down and capacity test of each cell then charging each to 3.65V unless I have some duff cells then i'll swap them out. I am switching to a JK BMS away from Daly. Is that photo from a JK? Do you have the same photo when the cells are fully discharged - say 3.0V?

 

[frankrudis65]

Yes i'm considering a full strip down and capacity test of each cell then charging each to 3.65V unless I have some duff cells then i'll swap them out. I am switching to a JK BMS away from Daly. Is that photo from a JK? Do you have the same photo when the cells are fully discharged - say 3.0V?

Yes it's a JK bms NOT the inverter version,as there seems to be too many problems.I haven't had the chance to discharge them so far but I'll do that and send the data....I am happy so far with the balancing of the bms,also jumps in with all the security settings,i.e. over voltage,over temp,and so on...Stripping down gives you all the answers you are hoping for....unfortunately this involves some time

 

[Brearz]

Yes it's a JK bms NOT the inverter version,as there seems to be too many problems.I haven't had the chance to discharge them so far but I'll do that and send the data....I am happy so far with the balancing of the bms,also jumps in with all the security settings,i.e. over voltage,over temp,and so on...Stripping down gives you all the answers you are hoping for....unfortunately this involves some time

A job for Winter ! Thanks

 

[frankrudis65]

@Brearz : avoid going too far up with your charge 3.65V is the absolut maximum and could already damage your cells....I go to a max of 3.42V per cell(17S) and rather have more cells or mor banks in parallel.The lifetime of lifepo4 cells gets almost doubled if you keep them between 3.00V and 3.45V. In this case you avoid overheating,mechanical stress.There's NO gain to go over 3.45V per cell other then pushing them to their far limit!
Best regards Frank

 

[Brearz]

Ok Thankyou . I have also seen suggestions of absorbing at 3.35V for an hour say to get more energy in without high voltage ?

 

[SparkyJJO]

3.35V won't get you very far, that's somewhere in the middle of the very flat SOC "curve." 3.45V is a good point for a regular basis full charge as at that point you know you're at the top without going to the tippy top.

 

[frankrudis65]

Ok Thankyou . I have also seen suggestions of absorbing at 3.35V for an hour say to get more energy in without high voltage ?

Absolutely wright,be careful even with your float charge:Lifepo4 cells need to be charged and then stop,nothing else.Like your mobile phone:it gets charged and once the charge is complete it stops charging.....A float charge is to be set as low as poss,maybe even down to 51V.Depends how much capacity you'll have together....If you keep the soc between 40% and 75/80% you can't go wrong......Frank

 

[TomC4306]

Absolutely wright,be careful even with your float charge:Lifepo4 cells need to be charged and then stop,nothing else.Like your mobile phone:it gets charged and once the charge is complete it stops charging.....A float charge is to be set as low as poss,maybe even down to 51V.Depends how much capacity you'll have together....If you keep the soc between 40% and 75/80% you can't go wrong......Frank

Completely disagree.
Cell phone batteries are a different chemistry and behave differently.
If you charge lifepo4 above 3.45 volts per cell hold it there for an hour and then disconnect everything and sit them on the shelf after 2 weeks they will settle to 3.35.
This is where you should set your float charge. 3.35 or 3.375.
That way, once your batteries are charged your solar charge controller can run your loads and maintain the battery at 100%.
If you set float to 51 volts, you will charge to full by 1:00 p.m., and then from 1pm to sunset you will be discharging your battery. There is no reason to do this.
Also, there is no voltage that you can set in your solar charge controller to stop charging at 75 or 80%. The state of charge to voltage curve is very flat.

 

[AntronX]

I am quoting the Growatt output from their server into my phone. To quote their description - "Charged and discharged". I am interpreting this as the amount of energy (Sunshine) the growatt charger has pushed into the batteries from the panels to the amount the batteries have provided into the Tesla charger. (Not EV).

Charge / discharge shows DC energy flowing in and out of battery. My theory (not verified) Growatt has a constant load of somewhere under 60 watts which BMS does not detect and reports as zero. This makes discharge amount appear less than it actually is and calculates artificially low battery efficiency number. In my (friends) case it's 88%.

 

[kommando]

If you keep the soc between 40% and 75/80% you can't go wrong.

I think that's the exact behaviour that go this bunch of cells into the state they are in. You have to periodically get to 3.45V and gets the cells balanced or the bank will drift over months. Does not need to be daily or weekly, once a month will be fine. My 2 banks have spent 3 weeks well below 80% and last week I finally got some sun, they came up in V to 3.45 and then spent an hour being balanced back from a delta of 0.027V to less than 0.008V.

 

[frankrudis65]

Completely disagree.
Cell phone batteries are a different chemistry and behave differently.
If you charge lifepo4 above 3.45 volts per cell hold it there for an hour and then disconnect everything and sit them on the shelf after 2 weeks they will settle to 3.35.
This is where you should set your float charge. 3.35 or 3.375.
That way, once your batteries are charged your solar charge controller can run your loads and maintain the battery at 100%.
If you set float to 51 volts, you will charge to full by 1:00 p.m., and then from 1pm to sunset you will be discharging your battery. There is no reason to do this.
Also, there is no voltage that you can set in your solar charge controller to stop charging at 75 or 80%. The state of charge to voltage curve is very flat.

If you need to keep your batteries charged constantly on full charge you might have done something wrong with your calculations in regards of capacity in the first place.I for myself,and everyone needs to decide that for themselves, quite happily charge and then have them dicharged.As I said if you haven't got enaugh capacity then your goal would be to have them charged as long as possible....Not quite sure if this would help to get the most(in regards of lifetime) out of them.Frank

 

[frankrudis65]

charge and discharge cut-off voltage: the usable and nominal capacity and thereby the definition of the SOC are dependent on the set operating voltage limits of a cell ,i.e the charge and discharge cut-off voltage.A high charge cut-off voltage can lead to over-delithiation of the cathode material and thereby accelerate structural disordering on the cathode.Furthermore,over-lithiation of the anode can lead to lithium plating and dendrite formation.Low discharge cut-off voltages can lead to corrosion of the anode's collector.The operating voltage window should therefore be set such that the cells deliver a high nominal capacity while retaining high cycle life..ore then double the cycle life at a 20% reduction in usable capacity can be expected by limiting the manufacturer's recommended safe discharge and charge cut-off voltage from 2.5V,3.65V to 2.9/3.0V ,3.45V for a commercial Lifepo4 graphite cell.Decreasing the charge cut-off voltage from 3.65 to 3.45V cathode aging effects can be reduced.Increasing the discharge cut-off voltage from 2.5V to 3.0 V ,reduced anode aging,which was attributed to less volume change of the graphite anode.
I hope this makes it finally clear why and how to treat your cells decently ....Frank

 

[frankrudis65]

Floating LFP is a complex subject and depends on your need to come up with some capacity you wish for,and agreeing to reduce life span of your batteries .The bottom line is ,to avoid floating LFP banks if you can .Remember that holding float charge at a higher level keeps your SOC level at a high rate and sometimes for a long period .These batteries prefer to sit on a lower SOC maybe even down to 50/60% and not 90%.We don't know the mechanical and temperature stress holding those batteries on a high float voltage,once charged,additional current will damage the battery.Reducing this risk should be everyone's goal by for ex. oversizing the capacity of banks,or even adding cells.A 17S is not so uncommon anymore,and for one or two cells more,reducing charge and discharge cut-offs and in consequence keeping your cells cool gives you very little to argue for,considering the long lifespan you'll achieve like this.Best regards,Frank

 

[frankrudis65]

I think that's the exact behaviour that go this bunch of cells into the state they are in. You have to periodically get to 3.45V and gets the cells balanced or the bank will drift over months. Does not need to be daily or weekly, once a month will be fine. My 2 banks have spent 3 weeks well below 80% and last week I finally got some sun, they came up in V to 3.45 and then spent an hour being balanced back from a delta of 0.027V to less than 0.008V.

yes,fine agree....But we need to keep in mind tbat balancing keeps you out of trouble while for ex. charging at the highet end,the bms won't stop (passing) charging because one of the cells has already reached the full charge parameter .What it doesn't do and can't do is to cure cells drifting appart because of slight differences of build,chemisyry,aging aso...So to a cirtain degree you'll have always a "little" cell drift and that's nothing to worry about

 

[Brearz]

Charge / discharge shows DC energy flowing in and out of battery. My theory (not verified) Growatt has a constant load of somewhere under 60 watts which BMS does not detect and reports as zero. This makes discharge amount appear less than it actually is and calculates artificially low battery efficiency number. In my (friends) case it's 88%.
View attachment 245755

Not sure about the BMS not registering zero (My BMS is not plugged into the Growatt)but I believe the Growatt is power hungry when at idle which will account for some of the difference. Maybe these numbers are published somewhere for the inverter. I see your friends numbers are better than mine 88% vs c. 80%. The difference maybe the poor Balance/Capacity of my cells. I'd be happier with 88%. Thanks for sharing the data i'm learning

 

[HughF]

Completely disagree.
Cell phone batteries are a different chemistry and behave differently.
If you charge lifepo4 above 3.45 volts per cell hold it there for an hour and then disconnect everything and sit them on the shelf after 2 weeks they will settle to 3.35.
This is where you should set your float charge. 3.35 or 3.375.
That way, once your batteries are charged your solar charge controller can run your loads and maintain the battery at 100%.
If you set float to 51 volts, you will charge to full by 1:00 p.m., and then from 1pm to sunset you will be discharging your battery. There is no reason to do this.
Also, there is no voltage that you can set in your solar charge controller to stop charging at 75 or 80%. The state of charge to voltage curve is very flat.

This…. Float needs to be set so the solar will carry the loads once the batteries are full.

 

[Brearz]

charge and discharge cut-off voltage: the usable and nominal capacity and thereby the definition of the SOC are dependent on the set operating voltage limits of a cell ,i.e the charge and discharge cut-off voltage.A high charge cut-off voltage can lead to over-delithiation of the cathode material and thereby accelerate structural disordering on the cathode.Furthermore,over-lithiation of the anode can lead to lithium plating and dendrite formation.Low discharge cut-off voltages can lead to corrosion of the anode's collector.The operating voltage window should therefore be set such that the cells deliver a high nominal capacity while retaining high cycle life..ore then double the cycle life at a 20% reduction in usable capacity can be expected by limiting the manufacturer's recommended safe discharge and charge cut-off voltage from 2.5V,3.65V to 2.9/3.0V ,3.45V for a commercial Lifepo4 graphite cell.Decreasing the charge cut-off voltage from 3.65 to 3.45V cathode aging effects can be reduced.Increasing the discharge cut-off voltage from 2.5V to 3.0 V ,reduced anode aging,which was attributed to less volume change of the graphite anode.
I hope this makes it finally clear why and how to treat your cells decently ....Frank

Thanks again Frank (and others) I am going to revisit the charger high and low cut off voltages based on these numbers- 3.0V ,3.45V. and review how I can float at 3.35V.

I'll let the high charge develop so the balancer can do its job of balancing at high SOC. 3.45V. and not steel the power daily for the Tesla. might need to loose some Sun to achieve balance. Hopefully this will get them more balanced or its a total strip down and balance / capacity test-swap out.

I'd like to see a balance photo at 2.9/3.0 V of someone else's nicely top balanced battery so I can compare with my Docan EVE cells to understand if the imbalance I am seeing just before cut off is typical (Capacity variation). Not interested in seeing the top balanced numbers of top balanced cells.

Where I have seen videos on U tube of top balanced cells being discharged, 600mV imbalance is typical. (immediately prior to BMS cut off)..not charger.

 

[frankrudis65]

Thanks again Frank (and others) I am going to revisit the charger high and low cut off voltages based on these numbers- 3.0V ,3.45V. and review how I can float at 3.35V.

I'll let the high charge develop so the balancer can do its job of balancing at high SOC. 3.45V. and not steel the power daily for the Tesla. might need to loose some Sun to achieve balance. Hopefully this will get them more balanced or its a total strip down and balance / capacity test-swap out.

I'd like to see a balance photo at 2.9/3.0 V of someone else's nicely top balanced battery so I can compare with my Docan EVE cells to understand if the imbalance I am seeing just before cut off is typical (Capacity variation). Not interested in seeing the top balanced numbers of top balanced cells.

Where I have seen videos on U tube of top balanced cells being discharged, 600mV imbalance is typical. (immediately prior to BMS cut off)..not charger.

I looked up at ca. 3.2V,17s the imbalance was between 4 and 7 mv....I'll give you some Screenshots ,once i go more down,maybe for testing purposes .....Frank

 

[TomC4306]

Floating LFP is a complex

No, it really isn't.
You're not floating the cells you're allowing the solar charge controller to stay alive so that it can power loads while maintaining 100% SOC at a reduced voltage. (The voltage at which the cells naturally settle to anyway at 100% state of charge)
And then the sun goes down and everything slides over to the battery.

 

[Brearz]

No, it really isn't.
You're not floating the cells you're allowing the solar charge controller to stay alive so that it can power loads while maintaining 100% SOC at a reduced voltage. (The voltage at which the cells naturally settle to anyway at 100% state of charge)
And then the sun goes down and everything slides over to the battery.

TomC in your opinion would it be reasonable to charge to 3.45V then float at 3.35V and kick in the balance current at 3.35V (for say max 2 hrs?) . For me if I could balance for a few hours every 2-3 days at "high V" I'd be able to move closer to a balanced battery?

 

[SeaGal]

would it be reasonable to charge to 3.45V then float at 3.35V and kick in the balance current at 3.35V

... we already suggested balancing below 3.4V is not going to help and will probably make things worse - see posts #17 and #18

 

[TomC4306]

TomC in your opinion would it be reasonable to charge to 3.45V then float at 3.35V and kick in the balance current at 3.35V (for say max 2 hrs?) . For me if I could balance for a few hours every 2-3 days at "high V" I'd be able to move closer to a balanced battery?

Charge to 3.45 and hold there for Max 2 hours while balancing, then reduce voltage to 335

 

[frankrudis65]

No, it really isn't.
You're not floating the cells you're allowing the solar charge controller to stay alive so that it can power loads while maintaining 100% SOC at a reduced voltage. (The voltage at which the cells naturally settle to anyway at 100% state of charge)
And then the sun goes down and everything slides over to the battery.

My inverter devides the energy needed for loads regardless of the float settings.Battery power during a "normal" day with enaugh sunshine gets hardly used in a well designed system.When the batteries are fully charged and drop slightly before settling to a constant voltage they would,if not touched ,loose -what about 3%SOC in a month,that means 0.1% in 24 hrs and even less from fully charged to about sunset....Why on earth do you want to keep them on 90% SOC or maybe more with the risk of heating up on a hot summers day? I haven't tried this and I'm not going to fo this.Of course if you haven't got a well balanced system which provides you with the energy you need during the day,you might have to come up with some need to push things to the limit.....It certainly won't help the lifespan of your equipment.Float was purely designed for lead acid based storage as they need to be hold at a certain level,lifepo4 thanks god ,they don't need that anymore