Huge lithium degradation

[fnnwizard]

So I set the voltage on the power supply to 14.0 volts, amperage to 5 amps, and confirmed voltage with my Fluke at 13.97 volts. Close enough for government work.

After 24 hours, when I checked on the power supply it was showing 0.14 amps and 14.0 volts.

This is actually not good. You were grossly unbalanced already at 13.70's Volts per your post #39

So driving the pack V to 14V would certainly have bms try to cutoff from cell ovp as the high cell goes >3.70V which will give you very little time to charge the low cell.

That's why I mentioned 13.60V previously. This will allow BMS to work while staying below 3.65V for the high cell.

But, with this much imbalance and 100Ah "cells", it will take too long to fix it with the bms. Your only choice is to individually charge each group of 25p cells with thes leads at opposing ends.


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[Zwy]

How does it draw 0.14A if one cell hit OVP?

The process was started at 13.8V which it was at for a week.

 

[fnnwizard]

How does it draw 0.14A if one cell hit OVP?

The process was started at 13.8V which it was at for a week.

BMS would cut off, but then connects as cell V drops... power supply is always on, so bms essentially cycles the charge on/off/on/off etc throughout the night.

But it could be that cell ovp is 3.80, 3.90, even seen 4.0V. We don't know... but I certainly don't want any of my cells over 3.65V for extended periods of time ever.

 

[Zwy]

BMS would cut off, but then connects as cell V drops... power supply is always on, so bms essentially cycles the charge on/off/on/off etc throughout the night.

Nothing was mentioned about the BMS cutting off charging.

But it could be that cell ovp is 3.80, 3.90, even seen 4.0V. We don't know... but I certainly don't want any of my cells over 3.65V for extended periods of time ever.

You say to charge at 13.65V for an extended time frame. Instead, it was charged at 13.8V for a week. What would be the difference? Nothing.

Keep trying..........

 

[fnnwizard]

Nothing was mentioned about the BMS cutting off charging.

Unless op was there to supervise throughout, he may not know. There is no logger.

You say to charge at 13.65V for an extended time frame. Instead, it was charged at 13.8V for a week. What would be the difference? Nothing.

Keep trying..........

I'm not sure what you are trying to ask. I thought my statements are very clear.

There are a few issues.
1st. Charging to 13.60 V should keep any high cell from going above 3.65V for the OP.
I did not mentioned anything about 13.80V... it may work, depends on cell level V when pack level is there.

Charging to 14V will bring some of his cells over 3.65V.

We do not know what the BMS ovp for cell level is. If it is at 3.9V sure, the charger keeps going, but it is something not to be trying for.

 

[Zwy]

Unless op was there to supervise throughout, he may not know. There is no logger.

One is not needed if charging never stopped.

I'm not sure what you are trying to ask. I thought my statements are very clear.

I understand what you are stating. But if charging never stopped, how did OVP occur?

There are a few issues.
1st. Charging to 13.60 V should keep any high cell from going above 3.65V for the OP.

Pack voltage was already at around 13.8V and it appears it was held there for a week.

I did not mentioned anything about 13.80V... it may work, depends on cell level V when pack level is there.

You didn't mention 13.8V, the OP did. 13.6V doesn't do anything if pack voltage was at 13.8V.

I mentioned in my first post to discharge but I'm not certain that was done.

Charging to 14V will bring some of his cells over 3.65V.

If charging continued after charging for a week at 13.8V, the balance function should have been working. It is possible the balancer may not begin balance until 3.45V.

We do not know what the BMS ovp for cell level is. If it is at 3.9V sure, the charger keeps going, but it is something not to be trying for.

We do not know many things about that BMS and how it is setup. Many here including myself mentioned BMS replacement but OP decided not to. Balance can be achieved by just slow charging with a power supply and allow the BMS time to balance cells. I have not seen anything to cause the alarm you have promoted. I would have preferred discharge, then slowly charging with the power supply but this isn't my battery. If it continued to charge after 13.8V for a week, it most likely isn't hitting OVP.

If OVP is at 3.9V which is possible, then the battery probably is toast. Considering it is a JBD BMS, I would consider that unlikely.

 

[91cavgt]

Keep in mind that this whole battery had been charged to 14.6 volts for the past 2 years….. every day. Any damage caused by over charging cells is already done. A few more days won’t change anything.


Slowly bringing the voltage up from 13.8 where it was at for a week to 14.0 volts at only 5 amps vs 45 amps from my solar system is not going to damage the cells in any measurable way beyond what they may already be damaged.


Now if these were new cells that I had never charged to 14.6 and were unbalanced then it would be a very different situation.

 

[fnnwizard]

I understand what you are stating. But if charging never stopped, how did OVP occur?

I'm saying OVP likely already occured, or at least I hope so, but OP may not be aware of it.

He has stated he charged to 14.6V already. How high do you think cell 2 got with pack V at 14.6v? At 13.86V, it's already at 3.67V.

I'm saying charging to 14V now will guarrantee the high cell will be above 3.65V again, so not a good idea.

 

[740GLE]

Keep in mind that this whole battery had been charged to 14.6 volts for the past 2 years….. every day. Any damage caused by over charging cells is already done. A few more days won’t change anything.

Better statement was a voltage of 14.6 was applied to the battery, who knows if the battery took a charge or went into protection mode.

When it was taking 5a did you ever notice it stop taking current?

Either was it’s good that it was still taking current when you last checked.

Best of luck trying to read the cell voltages and seeing where they sit, remember you want to heck very closely after you disconnect the power supply to get a true reading of how bad they are out of balance.

 

[fnnwizard]

Keep in mind that this whole battery had been charged to 14.6 volts for the past 2 years….. every day. Any damage caused by over charging cells is already done. A few more days won’t change anything.


Slowly bringing the voltage up from 13.8 where it was at for a week to 14.0 volts at only 5 amps vs 45 amps from my solar system is not going to damage the cells in any measurable way beyond what they may already be damaged.


Now if these were new cells that I had never charged to 14.6 and were unbalanced then it would be a very different situation.

Knowing Jiabaida bms, it's likely that cell ovp is 3.650V +- .005V if at default. It is likely your cells are still good and just out of balance.
That bms probably balances at 50-75mA. So it's very easy to get it out of balance.

Considering you charge to 14.6V, any charge rate over .25A (250mA) can be considered too high for the balancer to work effectively.

Again, try to individually charge the cells. You are well 25Ah off, so to try and balance at say 50mA would take 500 hours if you manage to stay between balancing V and any OVP.

 

[91cavgt]

I will be charging each cell individually, hopefully next week. 5 amps should do to 3.65 volts, right?

 

[740GLE]

Anything above 3.5v current isn’t important.

Also seeing you are acting as the BMS a lot can go wrong very quickly. I am cautious and just bring to 3.5v, which after time (you’ll see current fall off) will get the cells to 100%.

 

[fnnwizard]

I will be charging each cell individually, hopefully next week. 5 amps should do to 3.65 volts, right?

As 740 wrote.. 3.50 is a good V to get to. Your current will get very close to zero.

Once all 4 are charged to that level, it's ok to hook back up to the bms. The open cell V is likely around 3.33-3.41 depending how long they have sat.

Now set PS V to say 14V. You should see the cells all get close to 3.5V. You can use this step to verify how good the cells are and how accurate the BMS is, as well as wiring issues wrt the 25P cells bank. The balancing circuitry should now keep the cell V very close. likely within 50mV.

Now you an take V up .100V at a time to 14.4V and see if the bms can keep up. there's really no need to go beyond that.

With 25P cells, it will be hard to maintain a good balance over time, so you should expect to hold the charger at 14V for a good while everytime you charge. The "good while" part can not be quantify since we don't know how well they were made.

You can easily verify with a Vmeter but need 3 decimals and time/history.

 

[91cavgt]

Interesting update.

So I am working outside on our vehicles today doing maintenance. So I’m constantly in and out of the shed walking right past the solar system. So, I raised the voltage of the power supply up to 14.1 volts and noticed that within just a few seconds, the amperage had dropped down to less than 0.1 of an amp. Hmmmm……. So I lowered the voltage, 0.01 of a volt at a time. Each time that I lowered the voltage, the amperage stayed around 0.1 amps on the power supply, until it hit 13.93 volts. Then the amperage kicked up to 2.5 amps. I think the over voltage protection had been working!

So I decided to start over and lower the voltage of the whole pack down to 13.3 volts, and slowly start working back up, but this time at 0.05 volt increments. It will be Tuesday or Wednesday at the earliest before I can devote time to tear this down so I figured this would be good to do.

 

[sunshine_eggo]

Interesting update.

So I am working outside on our vehicles today doing maintenance. So I’m constantly in and out of the shed walking right past the solar system. So, I raised the voltage of the power supply up to 14.1 volts and noticed that within just a few seconds, the amperage had dropped down to less than 0.1 of an amp. Hmmmm……. So I lowered the voltage, 0.01 of a volt at a time. Each time that I lowered the voltage, the amperage stayed around 0.1 amps on the power supply, until it hit 13.93 volts. Then the amperage kicked up to 2.5 amps. I think the over voltage protection had been working!

So I decided to start over and lower the voltage of the whole pack down to 13.3 volts, and slowly start working back up, but this time at 0.05 volt increments. It will be Tuesday or Wednesday at the earliest before I can devote time to tear this down so I figured this would be good to do.

Quit futzing with it. If you're seeing > 13.8V with current flowing, that is evidence of balancing.

 

[91cavgt]

Quit futzing with it. If you're seeing > 13.8V with current flowing, that is evidence of balancing.

If one of the BMSs was in over volt protect, wouldn’t it be a good idea to lower things down in order to try to rectify the over voltage problem, instead of continuing to send current to it? Remember, there are 3 BMSs inside this battery. If one of the BMSs was balancing but at least one of the others was in over volt protect, then it would not be good to keep that BMS in over volt protection.

Or am I completely wrong here?

 

[sunshine_eggo]

If one of the BMSs was in over volt protect, wouldn’t it be a good idea to lower things down in order to try to rectify the over voltage problem, instead of continuing to send current to it?

You did not present evidence of BMS protection. 0.1A was still flowing. When BMS protection occurs, you get 0.000A.

Remember, there are 3 BMSs inside this battery. If one of the BMSs was balancing but at least one of the others was in over volt protect, then it would not be good to keep that BMS in over volt protection.

Maybe, but why in the name of all that is holy would you restart at 13.3V? Hit the battery with a brief load to pull all cells under 3.4V and then resume to some fixed voltage, 13.8-13.9V and just leave it alone.

Even if the BMSs are in protection mode, they should still be balancing, and they will pull the voltage down to the release point. That's likely what you observed when you saw the current jump.

This is where you went wrong:

So I am working outside on our vehicles today doing maintenance. So I’m constantly in and out of the shed walking right past the solar system. So, I raised the voltage of the power supply up to 14.1 volts

It wasn't your recovery efforts afterwards. Find that happy level and just leave it there.

 

[fnnwizard]

If one of the BMSs was in over volt protect, wouldn’t it be a good idea to lower things down in order to try to rectify the over voltage problem, instead of continuing to send current to it? Remember, there are 3 BMSs inside this battery. If one of the BMSs was balancing but at least one of the others was in over volt protect, then it would not be good to keep that BMS in over volt protection.

Or am I completely wrong here?

I take it you have the 3 batteries ( consisting of 4s25P) in parallel.

So the max charged rate at continuous balancing, will be around 150mA into the 3P banks.

It is academic now to charge them this way at this point since it will take you over 500hrs. I am confident you have packs that are over 25Ah imbalance. If that is 25% off, your total capacity would then only be around 50%... which is supported in your discharging test.

Anyway, to fully answer your question, yes, it is best to start low enough to keep all 3 batteries "online".
To do that the math says to start at 13.60V and inch it up.

At >13.860V, the battery 1 had over V on cell #2. It cuts off, so other 2 pulls some current. 100mA charge rate sounds about right if the other 2 are balancing at 50mA.

But again, the math is saying you'll need at least 500hrs to get all the cells to within a 20mV differential so its not practical to continue charging in 4S.

The #1 pack would of course take longer everytime its BMS cuts off.

 

[91cavgt]

I take it you have the 3 batteries ( consisting of 4s25P) in parallel.

So the max charged rate at continuous balancing, will be around 150mA into the 3P banks.

It is academic now to charge them this way at this point since it will take you over 500hrs. I am confident you have packs that are over 25Ah imbalance. If that is 25% off, your total capacity would then only be around 50%... which is supported in your discharging test.

Anyway, to fully answer your question, yes, it is best to start low enough to keep all 3 batteries "online".
To do that the math says to start at 13.60V and inch it up.

At >13.860V, the battery 1 had over V on cell #2. It cuts off, so other 2 pulls some current. 100mA charge rate sounds about right if the other 2 are balancing at 50mA.

But again, the math is saying you'll need at least 500hrs to get all the cells to within a 20mV differential so its not practical to continue charging in 4S.

The #1 pack would of course take longer everytime its BMS cuts off.

There are 3 separate 100 ah batteries inside of the enclosure. Each 100 ah battery consists of 4 100 ah cells that are 25p.

Can a single BMS be in both over voltage protection AND in balance mode at the same time?

 

[sunshine_eggo]

There are 3 separate 100 ah batteries inside of the enclosure. Each 100 ah battery consists of 4 100 ah cells that are 25p.

Can a single BMS be in both over voltage protection AND in balance mode at the same time?

If it's a good BMS, yes. Can you see that a BMS in charge protection mode would also benefit from burning off charge from that high cell?

 

[91cavgt]

If it's a good BMS, yes. Can you see that a BMS in charge protection mode would also benefit from burning off charge from that high cell?

I was under the understanding that a BMS could only be in 1 mode at a time; under volt protection, over volt protection, balance mode, over temp, under temp.

I freely admit that I’m still learning.

 

[sunshine_eggo]

I was under the understanding that a BMS could only be in 1 mode at a time; under volt protection, over volt protection, balance mode, over temp, under temp.

You have listed four protection modes and one balance mode.

I have personally observed multiple JBD BMS balanding while engaging charge protection.

HOWEVER, the "balance only while charging" option was DISABLED (as it always should be). If this was enabled, balance would not occur. This brings us back to:

If it's a good BMS, yes. Can you see that a BMS in charge protection mode would also benefit from burning off charge from that high cell?

If the BMS only balances while charging, it is not a good BMS.

 

[fnnwizard]

There are 3 separate 100 ah batteries inside of the enclosure. Each 100 ah battery consists of 4 100 ah cells that are 25p.

Can a single BMS be in both over voltage protection AND in balance mode at the same time?

As sunshine wrote, the answer is yes... but to further elaborate on this, you still need to charge the low cell. And bms ovp cutoff would not allow this... so essentially adding more time required. The tiny resistor that discharges the hi cells at 50mA per/cell per BMS ( I keep writing 50mA, but it could also be up to 75mA, you'd have to look up the specs on that bms) is what allows you to continuously charge the low cells at 50mA, times 3P packs = 150mA.

BUT, 150mA into a 300Ahr that is likely >60Ahr off, is less than a trickle.

 

[91cavgt]

So what charge rate should I put the cells at? 5 amps? 10 amps? 3.5 volts?

 

[fnnwizard]

So what charge rate should I put the cells at? 5 amps? 10 amps? 3.5 volts?

On the 25P cell level you can go up to .5C = 50A and be fine. But since they have some charge on them, they will naturally absorb less and less as they reach 3.50V. IOW, whatever max your PS can put out up to 50A.

It's best to hook up say to the negative cell at one physical end of the 25P bank, and the positive at the other, furthest end to help mitigate connection resistance.