# Battery Recovery From Overcharge???



## onegreenev (May 18, 2012)

Its interesting you expected such a capacity loss due to a bit of overcharging. After resting and being below 4 volts I highly doubt you ruined any of the cells. At what amperage was your charger at the end of the charge when you overcharged your cells? What charger are you using?


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## dougingraham (Jul 26, 2011)

ecglasco said:


> Recently I overcharged my Thundersky 200Ah pack. End voltages were varied from 4.6 to 5.2 VDC. No swelling though. However, after resting a while... 3mos. They were all under 4V.
> 
> So I took my friends out for a demo ride... Well when I returned, I noticed that ALL 34 of the cells now read 3.34V +10mv -0mv!!! what gives! I expected alt least a couple to be below 2.5V because of lost capacity. But, none such!
> 
> I cant find research on this. Have they recovered (wishful thinking...)


The only way to tell how much loss of capacity you have is if you measured the capacity before and then measure it again afterwords. If you have cells above 4.35 volts there was some damage. This usually can be seen by swelling of the cells but if the vents released then there wouldn't be any visible damage. The electrolyte starts to break down at 4.35 volts and out gas.

What you may find if you do a careful test is that instead of the original 210AH you might have seen originally in those 200AH cells you now have only 180AH. You might also find an increase in sag under high currents. This might be perfectly acceptable with your driving habits and particular EV.

If it was me I would cycle test every cell. This would tell you if you have any that are particularly poor. Your weakest cell is what limits your overall range. You might want to remove or replace these really weak cells. I would then bottom balance the pack and make sure your charger does not over charge the pack again. For the purposes of protection something like a JLD404 that can open a relay to stop charging if the voltage goes too high due to a miss configured charger would be a reasonable idea.

Best Wishes!


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## onegreenev (May 18, 2012)

> If you have cells above 4.35 volts there was some damage.


If you have cells RESTING at above 4.35 then you can say you have damage.


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## EVfun (Mar 14, 2010)

onegreenev said:


> If you have cells RESTING at above 4.35 then you can say you have damage.


Where is that video from Jay Whitacre again? If you have over 4.35 volts across the electrolyte you have damage. If you have cells resting above 3.40 volts then you have overcharged them with some resulting damage. Lithium cells do not like to be overcharged, but an instance of mild overcharging won't destroy them.


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## ecglasco (Apr 4, 2011)

Hmmnn,

Well, all the info I could find indicated that if the voltage was above 4.2, that the cells were toast and could no longer be used to power a car. Indeed, I see that my range is substantially reduce -- though I havent measured it.
I have Mr. Mitkahov's 10KW charger. It is set with a LiFePO4 charge curve. I didnt record the end of charge current, but it seemed acceptable (below 4A). 
I've considered buying new CALB cells, but it's taking me a year to save up (or at least justify the expense to myself). So if I cant get my old range back (100+ miles)... I wont be satisfied.


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## GerhardRP (Nov 17, 2009)

ecglasco said:


> Recently I overcharged my Thundersky 200Ah pack. End voltages were varied from 4.6 to 5.2 VDC. No swelling though. However, after resting a while... 3mos. They were all under 4V.


I think, three months ago, we would have advised immediately removing at least 10% of the charge after overcharging, because storage at high charge state is damaging.
Gerhard


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## EVfun (Mar 14, 2010)

I've heard a few reports that storing an LiFePO4 cell at very high states of charge causes a decline in capacity that is similar to, or even somewhat greater than, the slow loss from regular use (in my case that seems to be about 1% per year.)


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## golfelectric (May 24, 2012)

I had a similar event early on with my Thundersky pack. They are 90ah.
I was trying to charge with 220v @3.5kw and the charger could not see that some of the cells were overcharging before the total pack voltage was reached. The cells out-gassed and peaked around 4.5. I used some cell shunts to pull them back down to around 3.6v, but they were all over the place voltage wise.
Once the pack was under load and the car moving, all of the cells settled to 3.2-3.3v. Of course that did not solve the fact that some of the cells were more "full" than others. I got some Volt Blochers that let me shunt the cells to 3.6v while charging and switched back to charging with 120v @2.5kw. I hand watched the problem cells and shunted them to match the others.
I had a couple of runaway events later on by not paying attention to the charge cycle. I lost a couple of cells.
Pushing the Lithium cells at a high voltage charge without some fail safe Is asking for trouble. They will turn the corner and overcharge in a matter of seconds, really. Once they pass 4.0 you can watch the voltage meter literally scroll like a run away counter!
I have never been in the "bottom balancing" club, and the idea really wasn't around 5 years ago when I was testing what these cells would do. I found the Elithion BMS when it first came out and added it to my pack.
I now have top balance protection, the charger shuts off if any cell goes over 3.6v and balances the entire pack, at the preset cell voltage. I can see temperature, resistance and each cells voltage, resting and under load. I have a few cells that might still be damaged, but since I can see which ones they are I can plan to replace them. I added 20 more cells this past year and that has taken the stress of the older ones, but again, I can watch all of them separately. 
On my fifth year of top balancing with a BMS. Still doing fine, wouldn't risk it any other way.


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## ecglasco (Apr 4, 2011)

I use the Elithion BMS also. I had just completed the 10KW charger and was anxious to test it... so I didnt have the cut off installed.

Im getting new cells. Those Thunderskys are heavy and scarce now. So far.. everything seems balance +/- 10mv. But Im almost sure that I have some plating going on...


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## golfelectric (May 24, 2012)

How old were your cells? I have had good luck with my Thunderskys, but I don't push them hard. 
Have two local guys that have just put in CALB 100ah cells. One is a 156v the other is 300v. We've put the Elithion in both conversions. The smaller one is doing great, the 300v is nearly on the road with the same 10kw charger. We are making sure the cut off is working and ready before we put the power to that beast!
When I put in the additional, batteries it took a few charge cycles to get every thing back to normal on balance. I would try taking your pack down to say 30% without hurting any cells and do a charge cycle then repeat. I would definitely make sure you set your cut off voltage below where you want to be, at that charge rate those cells are going to be rocking near the top of the curve. 
If you have been charging already, what would you recommend on that charger and voltage settings for the Elithion?


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## onegreenev (May 18, 2012)

Why do you think that?


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## golfelectric (May 24, 2012)

About the charger? Have you watched a lithium cell overcharge? Other than on Jacks web show?
They will run away in seconds! In the time the sensor takes to sees an over voltage, turns off the relay for the charger, the charger voltage drops, you could still see 1 to .5v increase in the cell. It's like a bucket of water pouring on the floor, once it breaks the lip, everything goes on the ground. With a charger putting out that much juice, it's not going to stop dead in its tracks on current. Not sure if they are stopping the current on the front end, or output side. I'm guessing input.
That's the best analogy I can come up with. That's why I like a top balance, all the buckets have the same amount of water.


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