# BBBBad cel.



## www.3xE.pl (Nov 22, 2008)

Basing on our experience - I don't think it is battery cell. 
It is too simple construction in manufacturing it to make here any mistake. 

I think you have already answered your question. Too high voltage set on charger causes high current charging when batteries are already full. It makes the charging process faster, but balancing works more than it supposed to. If it was exceeding 800mA (shunting current of CM60) you had overcharge for a long time. You wrote that you had 600mA at 162V. In my opinion you should have it already under 158V. Keeping LiFePO4 batteries under 3,6v prolongs its life.

Eventually it could be some BMS overheating (and shut off), BMS mechanical break or internal shortcut...

I am sorry to say that, but the broken cell have to be replaced. I hope it is the first and last one and the others will work for a long time.


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## samwichse (Jan 28, 2012)

Whoops, meant to hit refresh and hit report on your post... it's not spam, really!


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## Coulomb (Apr 22, 2009)

It looks like cell #21 is bulged a little more than the others, too, at least from that photo.


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## www.3xE.pl (Nov 22, 2008)

samwichse said:


> Whoops, meant to hit refresh and hit report on your post... it's not spam, really!


It is no problem  I hope it will not get to forum admins 



Coulomb said:


> It looks like cell #21 is bulged a little more than the others, too, at least from that photo.


It is normal for overcharged cells. Electrolyte is boiling inside. Before safety valve opens, the battery box is swelling.
lou-ace should be happy that he doesn't have li-polys. He would have huge fireworks in his car and garage.


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## dougingraham (Jul 26, 2011)

The broken BMS board would not have shunted that cell causing it to be overcharged. Overcharging would cause loss of capacity in that cell. A deep discharge would cause over discharging of that cell with the possibility of reversal. Cell reversal is pretty much instant death.

So in this case the BMS is pretty much directly responsible for the destruction of a cell.


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## arklan (Dec 10, 2012)

slightly off topic
i notice the battery connectors are copper.. could corosion and the resistance that comes with it, cause any of this?


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## dougingraham (Jul 26, 2011)

arklan said:


> i notice the battery connectors are copper.. could corosion and the resistance that comes with it, cause any of this?


If you have high resistance in a connection you will get lots of heat. With lead acid you often melt the terminal post off the battery. So yes a bad inter cell connection could cause issues during discharge. But much less chance during charge because the currents are so much lower. With a dead bms board you really don't need to look much further.


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## lou-ace (Jul 21, 2009)

great answers guys. yes this cell WAS a little bloated when I removed it. I didn't realize it untill it cooled and shrank. so now I'm concerned about the rest of the pack according to my calculations, I still have cc ( 15 amps) to 152 v this should be 3.53v/cell ( well within the safety margin) and finishing ( .6 amps) to 162.5v. some of the shunts are turning on at switchover ( 152v) that is red/green light. now as finishing continues about 9 cells turn solid red untill finishing voltage is reached,and they are a little warm too, this concerns me. soo does any one know the difference between red/green indicator and solid green? I'm guessing that red/green is a lessor shunt than solid red, ( over volt??), ( no green).??? any thoughts............ knowladge. the EV-power site is impossible to get any info from ( Ive tried to e-mail them but the site refuses to accept any USA phone number that I put in to the "required field). also any thoughts on how to test the removed cell?? It still measures 16.3 mohms, an 3.42v at rest, as do the rest of the "good cells"??


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## lou-ace (Jul 21, 2009)

CC copper bus bars, I used conductive jelly on all of the connections, is that OK?


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## lou-ace (Jul 21, 2009)

To continue: I have noticed that when the shunts are "on" I read a much higher voltage across the terminals, My assumption was that you would read a mush higher voltage because the shunt is on, so how do you tell what the cell is receiving and what is being shunted?????


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## dougingraham (Jul 26, 2011)

lou-ace said:


> also any thoughts on how to test the removed cell?? It still measures 16.3 mohms, an 3.42v at rest, as do the rest of the "good cells"??


If the cell is swelled it is damaged. You could get one of the RC hobby chargers/cyclers (something like a PL6 or an iCharger) and do a cycle test on it. It might still be usable for something but the capacity will be down making it the defining size of your pack. I would not put this one back in your traction pack.

A cell that is resting at 3.42 volts (resting a couple of days) is over charged a little.


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## kennybobby (Aug 10, 2012)

lou-ace said:


> great answers guys. yes this cell WAS a little bloated when I removed it. I didn't realize it untill it cooled and shrank. so now I'm concerned about the rest of the pack according to my calculations, I still have cc ( 15 amps) to 152 v this should be 3.53v/cell ( well within the safety margin) and finishing ( .6 amps) to 162.5v.


Why are you raising your CV phase voltage so high, and your finishing current is too low--60AHr cells should be 3 amps cut-off during CV. It looks to me like you are over-charging.

i don't believe you can 'shunt' all current and if you have voltage across the cell terminals you are still charging. The only way to shunt is to have a lower impedance path than the internal resistance of the cell, otherwise you have a parallel path thru both the shunt FET and the cell, and what does that do?


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## dougingraham (Jul 26, 2011)

lou-ace said:


> To continue: I have noticed that when the shunts are "on" I read a much higher voltage across the terminals, My assumption was that you would read a mush higher voltage because the shunt is on, so how do you tell what the cell is receiving and what is being shunted?????


The reason a particular shunt is turned on is because the voltage across that cell is higher than it should be. Your statement makes it sound like you think the cell voltage is high because the shunt is on. If the charge current is higher than the shunt current the voltage will continue to rise on that cell. Holding a cell at more than somewhere between 3.40 and 3.45 volts for extended periods of time will damage a cell. Shunt balancing arrangements hold some cells that way every time the pack is charged.

If you want to see what the shunt is doing you will have to hook an ammeter between the shunt and the cell. The current that is going into the battery from the charger is the current every cell/shunt sees. The current that the shunt sees can be subtracted from the charger current giving what is left to the shunted cell.


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## sholland (Jan 16, 2012)

kennybobby said:


> Why are you raising your CV phase voltage so high, and your finishing current is too low--60AHr cells should be 3 amps cut-off during CV. It looks to me like you are over-charging.
> 
> i don't believe you can 'shunt' all current and if you have voltage across the cell terminals you are still charging. The only way to shunt is to have a lower impedance path than the internal resistance of the cell, otherwise you have a parallel path thru both the shunt FET and the cell, and what does that do?


What is a good cutoff voltage for CV?


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## kennybobby (Aug 10, 2012)

He's probably okay for 162.5/44 = 3.69vpc, i was thinking it was going much higher, so i was mistaken there. 

But CV trickle charging down to 0.6 amps at that voltage may be an issue. 

Most specs i have seen lately show CC at C/3 Amps up to 3.65, then CV at 3.65 down to C/20 A.


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