One dead lipo cell. Is my pack ruined? :(

[DesignerDan]

I have a 2S 2P turnigy lipo pack. (Four 5000mah packs) I've used it on my bike a couple times now and everything was fine. I ALWAYS balance charge and never over discharge the pack. Well today I charged it up to 90% and rode my ebike to the store and back. I made it back home with 9% left. Well it turns out all the cells were at 3.65 volts but one (two actually because it was paralleled with another) was at 0.07 volts I checked the balance leads and they all had good connections so I know the cell is actually 0.07 volts. I assume there's nothing I can do about this, right? This sucks, $100 lipo pack with only like four cycles on it is ruined. I do I need to actually be monitoring each and every cell WHILE I'm riding to prevent this from happening again? It seems very odd how that one stupid cell somehow completely discharged its self when all the others still have a good charge

 

[dogman dan]

Well, you are now the proud owner of a 9s lipo pack, instead of a 10s lipo pack. Too bad you rode a bit too far, on a pack you weren't entirely sure of yet. Apparently one cell in one pack is no good, and went bad on you.

To start with, take apart the two packs, and see if you still have less than 2.7v on one cell. Maybe you get lucky, and one pack snaps back ok. Double check stuff, maybe you just have a disconnected balance wire or something. Peel the top of the pack away, and take voltmeter readings right from the solder.

If it really is two cells ruined, I see two logical options. Pack surgery to make two 4s packs that work. or, pack surgery to replace one cell on one pack with a good cell from the other, plus buy one new pack. I'd go with buy one new pack, and try to fix the other myself, especially if the bad one is on the end.

Once you have a set of packs that you can trust, say 10 cycles from now, then you can just monitor the whole pack voltage for all but the very longest of rides.

 

[liveforphysics]

Methods made a device to prevent this exact sort of problem. It's clever, reliable, and lightweight. Which is way nicer, safer, and cheaper than buying new packs on a regular basis and waiting for shipping etc.

 

[dogman dan]

One issue with the wonderfully light and cheap 4 brick packs, is that they really don't have a ton of wh in them.

Like all 10ah 36v packs, a bit short range for my needs, and apparently yours too. Might consider buying 3 new packs. Or slowing down for the long rides.

 

[neptronix]

You spent $100 on a single lipo pack? what do you get, the upper end nanotech?

Welcome to why i buy cheap 5S/6S 20C packs. $40 or $50 is the most you're gonna lose.
If you have a dead cell on the edge of one of the packs, they are not too hard to replace actually.

Expect 10%-15% of your hobbyking RC Lipo packs to be duds and always have a spare handy.

 

[DesignerDan]

I had four 6s 5000mah 20C turnigy batteries. I soldered two and two so I have two 10Ah 6s packs. Since one stupid cell went bad it took down TWO packs. And since they were 50 dollars each, that's a 100 dollar loss I'll try separating the two dead packs and see if maybe on of them will come back to life. Then I will only have to buy one new pack.

And liveforphysics, what device are you talking about?

 

[DesignerDan]

oh and its cell number 4 that's dead. SO it's sandwiched between other cells so pack surgery will be a bit more difficult. :/

 

[Ypedal]

http://ypedal.com/Lipo/repair.htm

20 some minutes of video to show how i went about my repairs...it's not for everyone.. dont even try it unless you are the handy type with plenty of tools and lots of tinkering experience and risk taking... no warnings when you get it wrong, it's all business...

It is " possible " sometimes to bring back cells to life as long as they have not puffed and vented.... but that means ++ to the paragraph above.. involves tapping into the ballance leads to pump 1 amp or so and zap it back to life with regulated power..

 

[Grizzlybear]

This is why I love LIFEPO4 especially A123

eventually you will all think likewise.

 

[liveforphysics]

This is why I love LIFEPO4 especially A123

eventually you will all think likewise.

Because LiFePO4 is somehow magically protected from being over-discharged?

Seems to me, if the guy had spent the same money, or dedicated the same space and resources on the bike to LiFePO4, he would have the exact same problem, but only be halfway back from the store when it happened.

 

[Grizzlybear]

This is why I love LIFEPO4 especially A123

eventually you will all think likewise.

Because LiFePO4 is somehow magically protected from being over-discharged?

Seems to me, if the guy had spent the same money, or dedicated the same space and resources on the bike to LiFePO4, he would have the exact same problem, but only be halfway back from the store when it happened.

Rubbish, when are people on this forum going to realise that LIFEPO4 is without doubt the best battery for ebikes?

 

[liveforphysics]

Rubbish?

Tell me what an unprotected A123 pack would have done differently in his situation???

Cost him more, stored less energy, weighed more, been more complex to build, and would have fallen to 0v faster perhaps?

 

[Grizzlybear]

Rubbish?

Tell me what an unprotected A123 pack would have done differently in his situation???

Cost him more, stored less energy, weighed more, been more complex to build, and would have fallen to 0v faster perhaps?

The A123 pack would have a BMS that actually works, plus the battery itself would last many times longer, weight is not an issue, Cellman will make you a pack if you do not have the skill yourself, oh I forgot ...it will not kill you!!

 

[DesignerDan]

No need to fight over which chemistry is better. Does anyone have any recommendations on what I should do once I get the new batteries? Should I have cell monitors on every single cell and monitor them for like the first 10 cycles? And if all is well I will be safe to just use the total pack voltage as a gauge for how much power I have left?

 

[Grizzlybear]

No need to fight over which chemistry is better. Does anyone have any recommendations on what I should do once I get the new batteries? Should I have cell monitors on every single cell and monitor them for like the first 10 cycles? And if all is well I will be safe to just use the total pack voltage as a gauge for how much power I have left?

As long as you buy LIFEPO4 you will have no worries, don't fall into the LIPO trap, enjoy your bike and don't be a slave to your battery pack!!

 

[DesignerDan]

Well then could you link me to a good LIFEPO4 pack equivalent to my 12S 10Ah Lipo pack? I spent $200 on my lipo pack.

 

[Grizzlybear]

Well then could you link me to a good LIFEPO4 pack equivalent to my 12S 10Ah Lipo pack? I spent $200 on my lipo pack.

Cellman is the man, invest a bit more money in a better chemistry and you will save in the long term big time. I have 4 year old LIFEPO4 (Ping battery) still performing like new, I have A123 batteries which I have abused with no problems, please listen to me, I know

 

[Ricky_nz]

Cellman is the man, invest a bit more money in a better chemistry and you will save in the long term big time. I have 4 year old LIFEPO4 (Ping battery) still performing like new, I have A123 batteries which I have abused with no problems, please listen to me, I know

You can destroy a LiFePo4 battery really quick due to just one broken wire or a dry joint in the BMS and because you trust the BMS implicitly you will never know until the battery is toast!. Just because you haven't had a problem dosen't mean others havent.
BMS repairs seem to be quite common in the cheaper ones.

 

[Ypedal]

I went looking on youtube for the Tim the tool man taylor " whoa whoa whoa.. back the truck up " video .. but.. could not find it.

Grizzlydude.. i dont know what you think you know.. but i guarantee you if you over-dicharge any chemistry you will do some damage. I have personally killed Lifepo4, LiMn, LiCo, Nimh, Nicad, SLA, cells both on purpose and accidentally, have repaired new and old packs of all the above, and have yet to see it all, but i've seen plenty.

a weak cell happens, sometimes it's not bad enough that it remains usable, sometimes it's bad enough to quit working, sometimes they vent liquid, sometimes they vent smoke, sometimes you get ooze and sometimes crystals.. on rare occasions sometimes you get fire.. but no matter the chemistry they can all do it.

I've also drained Lipo and Lifepo4 cells to 0v and recovered them..

it's not as black and white as you like to make it seem.

 

[DesignerDan]

I think I'll stick with lipo. I'll just make sure to have enough battery monitors for every cell. That way I can physically make sure none of them ever run below 3 volts. It just seems safer than relying on some PCB or BMS to do that job.

 

[SamTexas]

I've also drained Lipo and Lifepo4 cells to 0v and recovered them..

I too have drained LiPo (18650 LiCoO2, NOT RC LiPo) down to 0 just to satisfy my curiosity. Then I was able to charge the cell back up to full capacity. That cell is part of my Ebike pack. I pay special attention to that cell group and nothing bad has happened yet. That was about 30 charging cycles ago.

 

[Sunder]

I bought 4 x 6S packs from Hobby King, and 1 cell has gone bad in two packs each. They're not puffy, but they sag early, and their voltage spikes early during charge

I've bought another 6S pack, and I'm going to sacrifice it for cells to replace the dud cells before they get worse. One is on cell 1 which should be easy, one is on cell 5 which will be much harder.

I'm then going to use the 4 spare cells to turn my 6s into 7s cells.

I'm not sure when the parts will arrive, but if it's this weekend, I'll let you know how hard it is.

 

[Grizzlybear]

Exceptions to the rule are easy to find if you look hard enough, there will be bad LIFEPO4 batteries out there, but generally LIFEPO4 is buy far the better option compared to LIPO, You know it to be true.

Buy a good quality one suitable for your application, they don't take much to look after, and they will last for years, it's as simple as that.

My ones are lasting longer that the bikes!

 

[neptronix]

Just remember to not go further than the cliff..
If you're gonna run packs paralleled at the cell level, test all packs for dud cells before paralleling them ( so that 1 bad pack does not spoil the other, leaving you with 2 dead packs )

 

[mud2005]

damn cliff! I have 6S 6AH nano tech packs and they hit the cliff at only 5AH. doesn't bother me a bit though I will still use and love lipo batts until something better comes along. grizz, give it a rest 2 each his own