# Lithium fail shorted?



## Tesseract (Sep 27, 2008)

DavidDymaxion said:


> Has anyone seen a lithium battery failed shorted?...


We have used both TS and Headway cells and both have fail shorted. The TS cell failures were fairly benign, aside from drastically reduced performance out of the vehicle and constantly causing the Soliton1 to shutdown because of too low a pack voltage whenever the throttle was floored.

The Headway pack consisted of (IIRC) modules of 10 cells in parallel. One or more cells in a particular module failed short and drained the others flat but aside from a few popping their pressure relief burst discs there wasn't any real safety issue. In both cases the cells failed during discharging, not charging, and caused pack voltage to plummet faster than the Soliton1's "minimum pack voltage" limit could protect against leading to repeated shutdowns from undervoltage. This was a big clue that something was wrong, otherwise we might not have noticed!

Anyway, we didn't experience any fires, explosions, etc., but I have to admit I am now somewhat uneasy about putting lots of small cells like the Headways in parallel. More data about they react to extreme abuse is definitely needed; I'd rather not obtain such data from real life EVs...


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## DavidDymaxion (Dec 1, 2008)

Many thanks Tesseract, you can't beat a real life data point like that. I'm surprised losing 3V of pack voltage was enough to trigger a low voltage event -- was the drop more than 3V (maybe indicating significant IR drop) or were the batteries that well balanced and the LV threshold set to a good value?

If one used bus bars (really bus "plates" in many pics I have seen), you could drill a couple of holes near the holes for the terminal bolts, to make narrow copper "bridges" that would act as fuses. The real art would be where and how big for the holes.


Tesseract said:


> We have used both TS and Headway cells and both have fail shorted. The TS cell failures were fairly benign, aside from drastically reduced performance out of the vehicle and constantly causing the Soliton1 to shutdown because of too low a pack voltage whenever the throttle was floored.
> 
> The Headway pack consisted of (IIRC) modules of 10 cells in parallel. One or more cells in a particular module failed short and drained the others flat but aside from a few popping their pressure relief burst discs there wasn't any real safety issue. In both cases the cells failed during discharging, not charging, and caused pack voltage to plummet faster than the Soliton1's "minimum pack voltage" limit could protect against leading to repeated shutdowns from undervoltage. This was a big clue that something was wrong, otherwise we might not have noticed!
> 
> Anyway, we didn't experience any fires, explosions, etc., but I have to admit I am now somewhat uneasy about putting lots of small cells like the Headways in parallel. More data about they react to extreme abuse is definitely needed; I'd rather not obtain such data from real life EVs...


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## Tesseract (Sep 27, 2008)

DavidDymaxion said:


> ...I'm surprised losing 3V of pack voltage was enough to trigger a low voltage event -- was the drop more than 3V (maybe indicating significant IR drop)...


Sorry, I should have clarified that the cells do indeed turn into resistors when they go dead (whether from overdischarge or defective electrolyte, etc..) and it is this dramatic increase in resistance that causes the pack voltage to plummet when you start to pull current from it.



DavidDymaxion said:


> ...to make narrow copper "bridges" that would act as fuses....


Interesting idea, but might reduce safety rather than increase it, since the copper "fuses" might turn into a plasma upon melting. The fuse really needs to be inside the cell, and could be conveniently implemented by simply narrowing one of the internal metal connecting strips.


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## EVfun (Mar 14, 2010)

Tesseract said:


> Interesting idea, but might reduce safety rather than increase it, since the copper "fuses" might turn into a plasma upon melting. The fuse really needs to be inside the cell, and could be conveniently implemented by simply narrowing one of the internal metal connecting strips.


You want to put the fuse inside? The cell contains a flammable solvent electrolyte and by this time the vent has likely opened and air may have had a chance to get inside the cell. I'm not sure I want to strike an arc in there!


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## Tesseract (Sep 27, 2008)

EVfun said:


> You want to put the fuse inside? The cell contains a flammable solvent electrolyte and by this time the vent has likely opened and air may have had a chance to get inside the cell. I'm not sure I want to strike an arc in there!


Yes I want to put a fuse inside each cell, and there are a number of approaches to sidestep the danger of the fuse doing more harm than good.

The fuse could be kept separated from the solvent, even if the cell vented, via a physical barrier of some sort (ie - metal disc separating the actual cell from the terminal). The fusing mechanism could be a soldered joint that melts at a temperature well below the flash/ignition point of the solvent. Finally, the fuse could be embedded in sand which will immediately quench any arcs that might form. Any or all of these could be combined to make a much safer cell without adding much in the way of cost.


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## Nathan219 (May 18, 2010)

If you have fuses that turn into plasma balls you are using the wrong fuses http://www.mersen.com/en/landing-pages/l/mersen-usa.html?bookmark=http%3A%2F%2Fep-us.mersen.com I think we used these and the one we had blow we didn’t even know it had blown, It was just open our pre-charge relay was un plugged or something like that was the cause. These are filled with sand like was mentioned earlier.


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## DavidDymaxion (Dec 1, 2008)

Good point you don't want an arc or sustained plasma near the cell! That and it might wick unnecessary heat towards towards the cells. Encapsulated safe fuses would be better.


Tesseract said:


> Sorry, I should have clarified that the cells do indeed turn into resistors when they go dead (whether from overdischarge or defective electrolyte, etc..) and it is this dramatic increase in resistance that causes the pack voltage to plummet when you start to pull current from it.
> 
> 
> 
> Interesting idea, but might reduce safety rather than increase it, since the copper "fuses" might turn into a plasma upon melting. The fuse really needs to be inside the cell, and could be conveniently implemented by simply narrowing one of the internal metal connecting strips.


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## T1 Terry (Jan 29, 2011)

;246152 said:


> We have used both TS and Headway cells and both have fail shorted. The TS cell failures were fairly benign, aside from drastically reduced performance out of the vehicle and constantly causing the Soliton1 to shutdown because of too low a pack voltage whenever the throttle was floored.
> 
> The Headway pack consisted of (IIRC) modules of 10 cells in parallel. One or more cells in a particular module failed short and drained the others flat but aside from a few popping their pressure relief burst discs there wasn't any real safety issue. In both cases the cells failed during discharging, not charging, and caused pack voltage to plummet faster than the Soliton1's "minimum pack voltage" limit could protect against leading to repeated shutdowns from undervoltage. This was a big clue that something was wrong, otherwise we might not have noticed!
> 
> Anyway, we didn't experience any fires, explosions, etc., but I have to admit I am now somewhat uneasy about putting lots of small cells like the Headways in parallel. More data about they react to extreme abuse is definitely needed; I'd rather not obtain such data from real life EVs...


Thanks for that info Tesseract, I hadn’t even thought about the effect of a cell going dead short. When the TS cell failed did it take out the other cells that were paralleled with it or were they recoverable? I have bought multiple smaller cells to make up the capacity required on the idea that a single smaller cell would be much cheaper to replace than a single large cell but if they all go out with one failing anyway I will need to rethink this strategy.

T1 Terry


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## coryrc (Aug 5, 2008)

DavidDymaxion said:


> Has anyone seen a lithium battery failed shorted?


I have a client who fried cells. I think they were overdischarged. They were Headway cells.

The cells became a dead short and a very low resistance; 100A through a 10Ah cell with no noticeable heating.


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## Tesseract (Sep 27, 2008)

T1 Terry said:


> ...When the TS cell failed did it take out the other cells that were paralleled with it or were they recoverable?...


It was Headway cells that were paralleled, not TS, but that *is* the $64,000 question: did the one (or more) bad cells in a 10p module damage the others. Well, it appears not. Draining the cells to zero is supposed to greatly reduce their cycle life, but so far the cells not actually bad in the module were "recoverable" - i.e., I was able to charge them back up normally. Whether these cells only deliver 300 cycles instead of 3000 or whatever is a much more difficult question to answer (without some sort of automated cell tester, which is on my list of things to do but, well... don't hold your breath).


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## pm_dawn (Sep 14, 2009)

I had a TS 160ah cell go dead short on me.
I do not know why but I guess that it was overdischarged.

I did not measure the resistance after it had gone short but I did not detect it only based on pack voltage. I can add that it was during winter and that normally lowers the pack voltage a bit, especially during load. So I thought all things were normal. Until I used a Cellog8 to check voltage. 

Best Regards
/Per


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## GizmoEV (Nov 28, 2009)

It sounds like you might have been able to detect it if you had a split pack voltage monitor. It is great to know that nothing caught fire. Thanks for reporting.


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## pm_dawn (Sep 14, 2009)

Yes for sure, a split pack monitor would have shown the problem. 

Regards
Per


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## T1 Terry (Jan 29, 2011)

GizmoEV said:


> It sounds like you might have been able to detect it if you had a split pack voltage monitor. It is great to know that nothing caught fire. Thanks for reporting.


 Do you have a link to one of these devices, sounds interesting.

T1 Terry


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## GizmoEV (Nov 28, 2009)

T1 Terry said:


> Do you have a link to one of these devices, sounds interesting.


There is a thread at http://www.diyelectriccar.com/forums/showthread.php/battery-balance-monitoring-system-54845.html where several posted info about it. I also posted some correspondence I had with Lee Heart who designed (the original?) one and posted the schematic on the EVDL at http://www.evdl.org/pages/battbridge.html. I haven't built one yet but I plan on it.


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