Dead cell on my 7s 5ah Zippy pack...What do I do?

[rg12]

Yesterday I have charged about 4ah into that cell that dropped to about 1.5v and it got to about 4v
then I stopped, went to sleep, woke up 4 hours later and it's back down to 1.5v (during charge it was
warm the whole time so I guess it discharged itself through heat dissipation)

Anyway...It's the 3rd cell of my 7s pack.

Is there a way to remove it without tearing and bending the other cells killing them also?
I have once seen someone on YouTube trying to take a part the cells from each other and he ended up
killing a few healthy cells because they have bent due to the strong glue...

Also, Is it safe having my pack laying around with one cell in it at 1.5v?
I'm afraid of it deciding to set itself on fire due to all the LiPo horror stories I've heard...

btw, until I get a new cell that fits and actually get to fix this...What will happen if I will run the pack at 6s?
My pack consists of 6 Zippy 7s 5000mah that are connected 3x2 (2 sets of 3 in series that are paralleled)
so I get a 21s pack that is 10ah.
Now one of the 7s will become 6s but the question is what will happen at discharge? is it going to throw
the other 5 7s packs off balance?
* I will charge each 7s pack separately so I won't overcharge the 6s to a 7s voltage.
* Don't got no BMS.


Roy

 

[dogman dan]

If you are real careful, you can get that cell out of the middle, but I would not bother myself.

You can discharge it to about 2.8v, so almost zero energy remains in it. Then cut the tabs to take it out of the series circuit. Then solder a jumper wire, to reconnect the remaining 6 cells.

Now you have a 6s pack at least. You'll have to also re work the balance plug, to a 6s plug. Or add a 7th cell to the end of the pack.

 

[rg12]

Did just that...I found a very helpful guide on youtube about how to separate these suckers easy!
You take a piece of thin plastic (I used a ruler) and you put some paint thinner on it and you slide it
in and every few cm you put some more thinner on it with a towel soaked with the thinner.
Soldered a jumper wire and didn't bother to mess with the balance plug as I already ordered a 2s 5000mah pack
so I can add the missing cell later and even have an extra one laying around...

One question, How do you think my pack will discharge while riding with my pack having five 7s and one 6s in it?
Do you think that all five 7s packs will be the same voltage after riding?
I have three 7s on one side of the bike and on the other side two 7s and one 6s and each of the sides are in series
and I take both sides and parallel them to get my 10ah.
Do you think the two 7s that are on the side with the 6s will end up different voltage than the three 7s on the other side?

 

[Simonvtr]

Did just that...I found a very helpful guide on youtube about how to separate these suckers easy!
You take a piece of thin plastic (I used a ruler) and you put some paint thinner on it and you slide it
in and every few cm you put some more thinner on it with a towel soaked with the thinner.
Soldered a jumper wire and didn't bother to mess with the balance plug as I already ordered a 2s 5000mah pack
so I can add the missing cell later and even have an extra one laying around...

One question, How do you think my pack will discharge while riding with my pack having five 7s and one 6s in it?
Do you think that all five 7s packs will be the same voltage after riding?
I have three 7s on one side of the bike and on the other side two 7s and one 6s and each of the sides are in series
and I take both sides and parallel them to get my 10ah.
Do you think the two 7s that are on the side with the 6s will end up different voltage than the three 7s on the other side?

If you run them in series then it wont matter as long as all the packs are rated the same (same ah rating). Instead of having 7s x3 = 21s (21x4.2v = 88.2) now you have 7sx2 + 6s = 20s (20sx4.2 = 84volts). If you run them in parallel then that is a whole different story.

 

[rg12]

They are both in series and paralleled...
Original pack was two sets of 3 7s packs in series and both sets of 3 7s in series are then paralleled to
make the two 21s 5ah packs into one 21s 10ah.

Now one of the 3 7s on one "side" is a 6s so it complicates my calculation since there is the paralleled thing...

 

[rg12]

Ok I just tested the bike with this setup and something is weird...

Went out for a spin with the bike with battery at full charge (all 7s topped and the 6s topped to 6s voltage separately).

Went back home and one side that has the three 7s packs in series had these voltages 28.1v 28.1v 28.1
BUT the other side with the 6s in between the two 7s looks like this 28.1v 26.2v (the 6s) 26.6v

Seems like the 6s that was 25.2v full from the charger got charged by the pack next to it that instead of being
28.1v dropped sharply to 26.6v

So now I'm discharging the 6s to a safe voltage since each cell right now is about 4.37v(!)

So I guess my bike is paralyzed until I get my pour cell back

 

[nutnspecial]

Yes, either that or remove 1s from the other side of the parallel. Can't parallel different voltages, or one charges the other- B careful with them lipos, specially under or overcharged!

 

[Gregory]

Yes, either that or remove 1s from the other side of the parallel. Can't parallel different voltages, or one charges the other- B careful with them lipos, specially under or overcharged!

Agreed. You've been fortunate twice now, the initial charge with a dead cell and then parallelling 20S to 21S.

Seriously look at where and how you are treating this pack in the future, charge in a safe place, store in a fireproof area etc, especially the 20S cells. For my own peace of mind I would retire the 20S cells, and run 21S 5Ah for now.

 

[rg12]

Man what a mess 1 cell can make...
I don't wanna tear up another one of my beautiful 7s packs...I will just wait for the new cells to arrive
although that can take a while...

I guess I will ride 20s 5ah and when they run out I will switch to the 21s 5ah...
Sounds decent for the situation that I'm in...

 

[dogman dan]

You can temporarily relocate the red wire on one 7s pack, then parallel it with the 6s.

Never parallel 6s with 7s. For a little while, that greatly overcharged the 6s. Ok if you rode off immediately. I mean instantly. If you did not, you just ruined your 6s pack with an overcharge. In about 5 min, your 6s pack reached 4.5v per cell. Now they are ruined. The voltage would have equalized, sending about 2 v more into the 6s pack, and leaving the rest in the 7s pack, till the voltage of both packs was equal.

But if you rode immediately, then they would have sagged 2v, and then only ever seen about 4.3v, while the other pack was more like 4v under load.


Did I miss something in the first post? Did the other 6 cells get overcharged before you re worked the pack? If they got over 4.3v, then they are trash. Seriously, not worth keeping on the property, unless you have a place to keep them that is super duper fire proof.

If they are toast, discharge them to at least 2v or less, then chuck em in the recycle.

 

[rg12]

The 6s got overcharged only when I connected them in parallel with the 7s.
I connected them that way and went right out for a 5m ride with lots of full throttle.
When I went back home I checked the voltages first thing and when I realized that the paralleling with the 7s
caused the overcharge of the 6s I put it in my Accucell8 to discharge to 24v (from the 26.2v that it was overcharged to).
and now I have learned my lesson and am going to run it like I wrote above until my precious cell comes in the mail.

* I don't wanna resolder the red wire of a 7s pack to make it 6s since that requires alot of tearing apart of the zippy case
and it will never be neat and sealed again... my pour 7s had to be amputated so young...

 

[izeman]

it's always bad to read those stories and it frightens me every time to read what noobs do to batteries. the results can be seen on local news
but the good thing is, that you came here to ask. you maybe should have asked earlier and NOT try solving that by yourself.
and because you asked, i will try to give as much information as needed so you hopefully won't repeat the same mistake again.

as you said you have all 7s packs. when you put 3 of them in series you make one 21s pack. so far so good. then you do the same with the 3 other packs and get the second 21s pack. both packs (if charged equally to the same state-of-charge (SOC)) have the same voltage. you can put them in parallel. there will be no current flow between them.
BUT i will give you a more extreme example of what you did: take a 7s pack with about 25V and a SINGLE cell of about 4V and put them in parallel. what will happen? they both will try to reach the same voltage. and this is just impossible. the 7s pack will try to become 4V which is completely DEAD and the 1s pack will try to become 25V which is completely super-overcharged. and the whole process will happen SO FAST that your thick battery wires will get super hot, maybe melt (depending on AWG) and your single cell will blow up like a balloon, then start to release it's built up gas, and then go up in a fire ball. it's that easy. fun to watch if done on purpose in a fire place, but nothing you want to do with the battery on your bike.

doing the same with a 7s and a 6s battery, or in your case with a 21s and a 20s pack is not so extreme, but will still lead to some serious issues. if put in parallel when empty, not much will happen. but if you charge them to full voltage which is 88.2V for the 21s or 4.2V per cell, your 20s string will also be at 88.2V BUT with 4.41V per cell which is HIGHLY OVERCHARGED. cells will puff, and may catch fire. if you release this overcharge immediately (as you probably did) they may have survived. but you can't look inside, and you don't know if you did some irreversible damage to them.

so if your cells are still ok, which is hard to say from a distance i would recommend not to use the pack. maybe just use the 21s pack and baby it. it's no capable of such high amps as the 21s2p pack and the bike will only have half range. if this is something you can live with you're fine. if not i would wait until you have the spare cell and repair the pack.

as you already found out: thinner and an old credit card is the easiest way to pry those cells apart. very slowly, very gently. and the replace the broken cell. as already mentioned: slowly discharge your battery to sub 3.0V (but slowly and not really much lower), so in case you short two cell during the repair not much will happen. an uncharged cell can not provide any current, and it will not explode, as there is no energy left.

i hope i could help and you can save your pack

 

[rg12]

Thanks for the detailed reply

As I said above, I will run it 5ah 20s and when run out I will switch to the 5ah 21s and live like
this until the new cells come in the mail.

I don't think I did any damage to the 6s since it was charged to 26.2v for only about 15 minutes
WHILE I was riding pretty hard with lots of full throttle.

Came back home, realized what I did wrong and immediately discharged the 6s pack to safe zone.

Checked today and it keeps charge and all is good...Even if the worst happens which I'm pretty sure
did not, I will just get a new 7s which isn't that bad like replacing the whole 21s.

Thanks alot,
Roy

 

[dogman dan]

That 6s pack is still a huge risk. Keep that sucker outside from now on.

I'm burn your house down with mom inside serious about this. Really.

I have some stuff like that around too, I keep it outside, charge it outside. I use them to run my mower, after doing whatever is needed to make them 6s or 7s for "24v" If they flame my mower, I can just flip the mower over. They'll dump right out, and I can watch em burn in the yard.

 

[MrDude_1]

for $4 you can get a smoke alarm with battery. I would put one near wherever it is you keep these packs.

 

[izeman]

if a 21s2p goes up in flames a smoke detector is nice to have, but you won't be able to kill the fire. better keep the batteries outside.

 

[dogman dan]

One more time,,,,

Never store or charge RC lipo batteries in a place you would not build a fire.

Personally, that's my fireplace. But I do keep the damper closed, so a fire will still smoke the crap out of my house. I have added a smoke alarm close by, there is a door 2 feet away, and outside that door is a flat blade shovel. The lipo is inside a metal box.

My plan, if possible, is get out of the house first by a window if the hall is too smoky. Then run around the house, and if the door is not hot, take a deep breath, and get that box out the door using the shovel. The max size of each lipo battery is 48v 10 ah. Small enough to flip out the door by the shovel. Other packs will be fine, in their separate metal boxes. No 48v 30 ah monsters in my house or garage.

The first line of defense is, as always. NO dinged packs inside. NO over charged packs inside. NO over discharged packs inside. NO stinking packs inside.

All the suspect stuff is outside, kept dry in an old refrigerator.

 

[izeman]

That may work if you are in a moderate climate zone without freezing. It goes down to -20c here. Not a good temperature to store batteries.

 

[MrDude_1]

Personally, that's my fireplace. But I do keep the damper closed, so a fire will still smoke the crap out of my house.

Thats why I said smoke alarm. I keep my scooter and lipo in a safe area of the garage. nothing but concrete around it, and its by the door... but I add a smoke alarm above it. to catch it as early as possible.

 

[999zip999]

This story is the recipe for a major lipo fire.