# Need help with Lifepo4 cell possible damage



## dimitri (May 16, 2008)

Most likely cells are damaged if they had less than 2V resting voltage. They might hold a little charge or none at all, you won't know until you try to put a load on those cells.

Obviously you confirmed the voltage with voltmeter, right? Because Paktrakr sometimes can glitch and report bogus data, but sounds like that is not your case.

So, how did this happen? What is your cell size? How many cycles did you put them thru? How much current were you pulling during heavy acceleration? Any BMS installed on cells? They either got drained slowly by some small parasitic current or drained fast by driving to 100% DOD.

Sorry to hear about your trouble, please share as much detail as possible so others can learn from it.


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## willitwork (Apr 9, 2008)

dimitri said:


> Most likely cells are damaged if they had less than 2V resting voltage. They might hold a little charge or none at all, you won't know until you try to put a load on those cells.
> 
> Obviously you confirmed the voltage with voltmeter, right? Because Paktrakr sometimes can glitch and report bogus data, but sounds like that is not your case.
> 
> ...


 
Yes, voltage was confirmed with volt meter, the cell size is 3.2v lifepo4. 
Hah, this is the biggest kick, I have yet to get the vehicle moving, I have a little more work before I can try it out... but I had all cells on the charger. I have the BEQ1 BMS on all cells. And no problem was 'reported' by BMS on the charging cycle.
So since the cells were never really drained, and they were on the maint. charge I dont see how all of a sudden two can go bad.


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## dimitri (May 16, 2008)

Which addresses did these cells have on Paktrakr remote? Is it Paktrakr 800 model for LiFePo4 cells? Each Paktrakr remote feeds itself from first 3 cells. Its theoretically possible that Paktrakr remote could drain first 3 cells, but it would take a very long time without charging the pack on regular basis. Is it possible Paktrakr remote is defective and drains more than it should? Maybe you wired it wrong? You can measure the current via multimeter between cell and Paktrakr wire which goes to that cell, it should be less than 10 mA on Blue wire ( 3rd cell on remote ) and less than 1 mA on other wires.

Was Zivan working as expected? Bulk phase with fans running high and red LED for few hours, then flashing red and less fan noise, then yellow and quiet, then green? Did you check each cell voltage after first charge and after first couple of runs to ensure all cells are balanced? Did any cells swell up at all?


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## dimitri (May 16, 2008)

willitwork said:


> Yes, voltage was confirmed with volt meter, the cell size is 3.2v lifepo4.
> Hah, this is the biggest kick, I have yet to get the vehicle moving, I have a little more work before I can try it out... but I had all cells on the charger. I have the BEQ1 BMS on all cells. And no problem was 'reported' by BMS on the charging cycle.
> So since the cells were never really drained, and they were on the maint. charge I dont see how all of a sudden two can go bad.


There is a good chance than BMS modules drained your cells. Best way to confirm is to measure current between cell and BMS module while connected to a good cell. Should be much less than 50 mA on a good module. Check modules which were on drained cells and check all others and compare their current levels.

There is no such thing as maintenance charge for LiFePo4, they have very little self discharge, so there is no sense of leaving them on the charger.

I know its sounds stupid, but did you verify correct polarity of BMS modules on those cells?


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## willitwork (Apr 9, 2008)

dimitri said:


> Which addresses did these cells have on Paktrakr remote? Is it Paktrakr 800 model for LiFePo4 cells? Each Paktrakr remote feeds itself from first 3 cells. Its theoretically possible that Paktrakr remote could drain first 3 cells, but it would take a very long time without charging the pack on regular basis. Is it possible Paktrakr remote is defective and drains more than it should? Maybe you wired it wrong? You can measure the current via multimeter between cell and Paktrakr wire which goes to that cell, it should be less than 10 mA on Blue wire ( 3rd cell on remote ) and less than 1 mA on other wires.
> 
> Was Zivan working as expected? Bulk phase with fans running high and red LED for few hours, then flashing red and less fan noise, then yellow and quiet, then green? Did you check each cell voltage after first charge and after first couple of runs to ensure all cells are balanced? Did any cells swell up at all?


 
Actually, 
I think you just answered my question. The cells which were drained were indeed part of the first three of the paktrakr 800. And I think I know how the cells were drained, I had to send the Zivan back for reprogramming which took close to a month, so for that time period there was no 'trickle' charge on it. When I got the charger back, it did go through all phases sucessfully. I bet, based on the charge curve, I reached the max, then went to maint., but those first few cells were too far out of balance.
(Dont know why the other 2 remotes did not also drain the first few cells)

So now that I think I found the cause, do you think I can bring up the charge in the 'drained cells and put them back in??? One cell is charged up, so it may be holding the charge.

But thanks... I believe the paktrakr drain and no trickle charge is what caused the problem.
Thanks!!!


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## willitwork (Apr 9, 2008)

dimitri said:


> There is no such thing as maintenance charge for LiFePo4, they have very little self discharge, so there is no sense of leaving them on the charger.


 
And thanks for setting me straight on the 'no maint.' charge for lifepo4. I always thought the green light on the zivan meant it was maintaining the charge. I just looked that book and green light means charge finished. So it does seem like I can just unplug it. 
But... If I am not at the point where I am driving the car, should I turn on the heater to bring total pack charge down, then re-plug the charge so it will fully charge the pack regularly???, otherwise the pak trakr will do the same thing... What do people do in this situation.
thanks again


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## dimitri (May 16, 2008)

willitwork said:


> And thanks for setting me straight on the 'no maint.' charge for lifepo4. I always thought the green light on the zivan meant it was maintaining the charge. I just looked that book and green light means charge finished. So it does seem like I can just unplug it.
> But... If I am not at the point where I am driving the car, should I turn on the heater to bring total pack charge down, then re-plug the charge so it will fully charge the pack regularly???, otherwise the pak trakr will do the same thing... What do people do in this situation.
> thanks again


I bet it was the remote next to display unit, right? Remote next to display drains twice as much since it powers the display, while other remotes only power themselves. 

You never answered what your cell size is, 100AH, 160AH , etc. This would determine how long it would take to drain the cells.

During normal daily use with balancing BMS this issue would not come up since balancers will equalize the charging current and compensate for small amount of charge taken by Paktrakr. Your result makes perfect sense, unfortunately, you should not have anything connected to cells if they are sitting for a month without a charger at hand.

Yes, you can drain a little using the heater, then charge again, repeat until all cells are balanced since you have shunts on all cells it should work. Take note of LEDs on BMS modules, see if some start shunting much sooner than others, there should only be few minutes between first cell starting to shunt and the rest. Also, no cells should shunt while charger is is bulk phase ( solid RED ), which would indicate significant imbalance.

Those cells are most likely dead or lost chunk of capacity, which would make them smallest in your pack and define your range, so you probably don't want to use them. Maybe you got lucky, try to charge them, then put back into the pack and run the heater for a while, closely watching voltage on those cells. Take a note how much current is being used by the heater and how long it takes for those cells to go under 3.0V. This will let you calculate their capacity by multiplying current and time.


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## willitwork (Apr 9, 2008)

dimitri said:


> I bet it was the remote next to display unit, right? Remote next to display drains twice as much since it powers the display, while other remotes only power themselves.
> 
> You never answered what your cell size is, 100AH, 160AH , etc. This would determine how long it would take to drain the cells.
> 
> .


yes, it was the unit next to the display. I have the 100ah cells.
I'll try the heater test and see what happens
thanks again


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## dimitri (May 16, 2008)

willitwork said:


> yes, it was the unit next to the display. I have the 100ah cells.
> I'll try the heater test and see what happens
> thanks again


Yes, it would take about a month to drain 100AH cell via 0.1A current, which is approximately what first remote drains since it powers display as well.

You only mentioned 2 cells, but I bet that 3rd cell on that remote is very close to being empty as well, don't forget to charge it.

In fact, first 3 cells on each remote are now likely severely imbalanced. 

Here is what I would do.

1. Charge those 2 cells individually to get them above 3.2V and any other cell that is below 3.2V.
2. Once all cells are above 3.2V, charge them as a pack, but pay attention to balancers, if some start shunting while in bulk phase, turn off the charger and wait till shunting stops. Repeat until no cell is shunting during bulk phase. Shunting during bulk phase may cause overcharge since shunts can't sink bulk current.
3. Once you pass bulk phase let them all shunt as they go until charger stops, take a note of which cells never started shunting.
4. Top those cells which did not shunt with single cell charger to bring them all to full charge.

Once balanced and used regularly you won't see much imbalance from Paktrakr. You will only see surface charge disappear quicker on first 3 cells on each remote, but the moment you start driving, they all line up.


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## dimitri (May 16, 2008)

willitwork said:


> And no problem was 'reported' by BMS on the charging cycle.


Your BMS is just a shunt, it doesn't actually report anything, it only prevents overcharge of individual cells if charger is still running when first cells reach shunting voltage.

If you had LVC it would alert you when cells dropped below LVC level, but even that depends on which BMS you'd use, some aren't reporting LVC when car is turned off.

This is not a sales pitch in any way, but MiniBMS would never let this happen, since buzzer would alert you when first cell dipped under LVC. Of course it also depends on how well you charge your 12V battery, since the car was not drivable yet, if 12V battery would die as well, then BMS would lose power too.

I just know that someone will read this and say, look at the guy with BMS and still killing cells, it must be BMS fault  , but of course it all depends on what your BMS is designed to do and under what conditions.

On a good note, assuming your garage was relatively cold during that month when cells were drained, its possible that damage was minimal since LFP cells can dip much lower at cold temps without damage. So, I bet if they were closer to 2V they might just recover. However, I would watch those cells closely when accelerating to make sure they don't sag too deep compared to others.

I hope you won't be running 300 amps too often with 100AH cells.


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## willitwork (Apr 9, 2008)

Can't say thanks enough... and I appreciate the quick response before I did something I wasnt supposed to.


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