LiPo Surgery Time!

[LI-ghtcycle]

I have a Turnigy Nano Tech 4x LiPo pack that I got around 2009, and it finally has a dead cell.

I have been running 18s 2p, and I am thinking I should be able to just trade out the weakest cell out of another 4s pack and continue on with 17s 2p.

Anything special I have to do other than remove the bad cell(s) and charge this pack as a 3s?

Thanks!

 

[amberwolf]

That should be it, although you don't need to physically remove the cell, which risks damage to adjacent cells.

A method that some people have used is to:

Discharge just that cell down to zero volts, slowly, then bridge across it's contacts with wire heavy enough to carry the current (or several smaller pieces, or just solder if you really have to).

Move the balance wires (starting with that cell, and not the ones more negative than it) over by one, so the one that was on it is now shifted up toward the postive by one cell, and that cells' is now up one, etc.

If the cell puffs up during discharge I suppose you could prick it and seal it up, but that has it's own risks over time.

 

[LI-ghtcycle]

Hmmm I really am not following your terminology AW, I am really unfamiliar with how these cells are put together, my first Q is how do I identify the bad cell?

Last night while charging, I noticed this particular pack kept giving me a "charge no balancer" error on my Hyperion even though the balancing plug was installed, and the voltage was low enough because of the bad cell that it was recognizing it as a 3 instead of 4 cell pack (I was able to manually correct this) however, now it is even much lower than last night, as the balance readings showed the bad cell at 3.6v while the rest of the pack was closer to 4.1, and the weird part is the voltage of the bad cell started getting lower ... now it shows as around 2V, and it got pretty warm last night so I stopped charging it.

Any hope of saving this cell or is that just too risky? It hasn't puffed up or anything, I have removed the shrink wrap and some of the tape around the balance leads, and there is no apparent damage I can see (no evidence of over-heated wires or discoloration of anything).

I can take some pics if that will help?

Thanks again!

 

[amberwolf]

Well, given all that, I'd say the first thing to do is read all the other LiPo repair threads to get a better idea before you get in there and do anything, to reduce any risk of fire from damage to the cells. Maybe start with the LiPo sticky thread in the battery section.

There's more than I have time to post right now to tell you about it.


I'd also strongly recommend storing that pack outside in a metal box until you can do something with it.



Which terminology specifically?

 

[motomech]

When I have by-passed bad cells, it was because I had a dud cell when the brick was new or fairly new. Or when I damaged a cell.
In your case, your Lipo is old and while it is not time that shortens service life, in all those years it must have gone though many cycles. Since one cell is going bad, I think you can expect the rest to follow soon.
I.M.O., 6 or 7 year old Lipo isn't worth messing with.

 

[LI-ghtcycle]

Thx AW!

I have been checking on some of those threads, and I think I found a solution!

I am now charging at VERY low current, normally I would do 12A now 0.5A and the low cell is recovering! 8)

I know it will never be as good as new, but in the last few minutes I got it to come up above 3V and climbing steadily, maybe I will just have to charge this particularly pack at 6A or less in the end.

I'm getting away from LiPos these days, so if I can get this pack to recover enough to get another year or so while I save-up for a 18650 pack, that will be more than enough.

I think I will probably not attempt "surgery" after all, too much risk for my blood lol!

If it comes down to it, I will just run 14s and "suffer" at regular bicycle speeds instead of charging uphill at 28 MPH. :wink:

 

[amberwolf]

I am now charging at VERY low current, normally I would do 12A now 0.5A and the low cell is recovering! 8)

Sinnce it dropped ini voltage during charging, I think you're asking for a fire. Something is wrong inside that cell.

might not happen now, at low current, but could happen at regular charge current, or once it reaches a certain SOC, or during discharge, or even while it's just sitting there.

Fire risk is too great.

 

[LI-ghtcycle]

When I have by-passed bad cells, it was because I had a dud cell when the brick was new or fairly new. Or when I damaged a cell.
In your case, your Lipo is old and while it is not time that shortens service life, in all those years it must have gone though many cycles. Since one cell is going bad, I think you can expect the rest to follow soon.
I.M.O., 6 or 7 year old Lipo isn't worth messing with.

Agreed!

I am not against LiPo, but today's 18650's are more attractive to me in that I need higher capacity than just a few bricks of LiPo would supply, so I am just using what I have on hand for now.

Hopefully it gets me through the summer, if not, I can find room to stuff a large LiFePo4 pack in their place, just will have to do it on a rear rack or some such for the bike I am currently riding (E-Zilla Cruiser) until I can afford a larger 18650 pack.

 

[millzy555]

Just throw it in the bin. Its not worth the hassle for $40-50 a pop. I had one cell fall off the face of the earth....i couldnt even get it to register via the balance taps or a multimeter. Currently sitting in a bucket of salt water

 

[LI-ghtcycle]

Probably best advice millzy555, I have however got this cell back up to 3.65 currently, and it's not heating up!

I also found a good deal on a 72V pack from Luna, realized I had the cash and pulled the trigger! 8)

I will post a link up shortly!

 

[LI-ghtcycle]

Yeah, I have eliminated this pack for now, currently it is sitting in a fire resistant bag in a place where it shouldn't hurt anything if worst case happens, what is the best way to dispose of it? I'm just going to write off the entire pack at this point as I don't really have a desire to "play with fire" (pun in tended )

 

[motomech]

I think volatility is a function of battery potential and you need not worry much about combustion.
You could always poke a hole in a pouch and see how bright it's glowing inside :lol:
It seems many folks here drain the battery down to zero, soak it in saltwater and dispose in the house-hold garbage.
I just drain it and toss it.
I do clip off the leads to possibly use again, especially the balance laeds.

 

[LI-ghtcycle]

Ok, I have found this post by Ypedal and that along with a couple other videos linked to his, has made this a very simple process:

https://endless-sphere.com/forums/viewtopic.php?f=14&t=26219&hilit=lipo+repair

I have the typical outside cell that has gone bad, and in my case, being on the negative lead, it's pretty straightforward.

Nanotechs don't have circuitboard so it's just a matter of de-soldering & removing the neg lead along with it's corresponding balance tap, cutting tabs (I will just abandon the bad cell in-place as it has self-discharged to nearly zero over the last week or so.

I have only heard it mentioned briefly, but is there a special solder I need for the tabs?

*Edit* later in that same thread it is mentioned you do NOT need special solder.

Thanks!

 

[motomech]

Yes, I have done that.
I just leave the bad out-side pouch there and move the the main lead in-board making a 6S brick a 5S.

 

[LI-ghtcycle]

Yes, I have done that.
I just leave the bad out-side pouch there and move the the main lead in-board making a 6S brick a 5S.

Kewl, I have even seen where you can trim the balance lead connector, I unfortunately butchered mine, so I will probably bum one from the local hobby store now that I have converted to a 3s (they usually have dead packs that they have to dispose of hehe)

But I think it will be an idea battery pack for my Magic Shine headlight!

I still have a headlight in the mail .. planning on using the bezel and using the Magic Shine to light it so it still has a "retro motorcycle" look to it. 8)