What constitutes a Lipo Dud?

[mauimart]

I just received, from the USA warehouse, a set of six 5Ah/6S/20C Turnigy Lipo packs and, not unexpectedly, it looks like I may have a couple of dud cells.

Pack 1 (s/n *3629855) data:

Pack 1 cell voltages upon unboxing:
cell voltage
1. 3.849
2. 3.850
3. 3.855
4. 3.784 *-possible stinker
5. 3.851
6. 3.854

I charged the pack (using the iCharger 208b) to 4.15V/cell @ 1A. I was able to put in 2.516Ah in 3h45min. Unfortunately I lost the charge curve data as I forgot to plug in my laptop and it died prior to saving the log file. Anyway, it took the alomost 4 hours as it was trying to get cell 4 to catch up with the others. I then did a 0.8A (max of my 208b) discharge to 3.7V/cell. The discharge curve is shown below. I would have to guess that this cell 4 is a dud. It's a tenth of a volt out from the others under a very small load (.16C) and from the graph you can see it starting to go 'over the cliff' at about 3.68V.

View attachment Pack1discharge.pdf

Pack 6 (s/n *3629818) data:

Pack 6 cell voltages upon unboxing:
cell voltage
1. 3.849
2. 3.853
3. 3.851
4. 3.851
5. 3.849
6. 3.805 *-possible stinker

In this pack cell 6 arrived .045V below the others. I charged this pack to 4.15V/cell @ 1A and after 4h37min I put 2.839Ah into the pack. It basically took an hour longer to balance than pack 1. Below is the charge curve.

View attachment Pack6charge.pdf

I then performed a discharge @ 0.8A and there was no indication that cell 6 had a problem. I have yet to charge this pack again to see how long it takes to balance. Here is the discharge curve.

View attachment 3629818discharge1.pdf

For reference the other 4 packs took about 2.5 hours and about 2.15Ah during their initial charge out of the box. I have not done any discharge cycles on them yet. Also there is no evidence of puffing on any of the 6 packs. My thoughts so far:

Pack 1, cell 4 is a dud
Pack 6, cell 6 might be ok

I am going to do a few more cycles and then I'll be contacting Hobby King.

Martin

 

[neptronix]

Pack 1 may not be a dud - it looks like you did not fully balance charge it before charging.

Fully balance charge, then discharge from 4.18-4.2v until a cell in the the pack hits 3.3v.
If you get a cell that dives towards 3.3v prematurely, then you got a dud.

It could be that this pack just wasn't charged right.


Now for Pack 6.. i think this also needs the full balance treatment, but the charge curve shows that the cell in blue is way off. This could be that a cell with a different C rating could have been stuck in the pack, thus it charges at a different rate.

The bizarre discharge curve here on pack 6 is really odd too.
I have owned 28 lipo packs, fully discharged them, and never saw anything that weird!! Usually one cell acts up.. but not to that extent.

IMHO the real dud test is when you discharge down to 3.3v ( i go down to 3.0v ) to see what the capacity of the pack really is. If you have a really weak cell in there, it's only gonna get worse over time.

1 pack out of 13 zippy lipos produced this dud. My definition of a dud is a little stricter than most though. I like my packs to go a hundred cycles before worrying about balance. The above Zippy would cause the entire pack to need occasional monitoring. Screw that - i set aside packs like this for use as magicshine batteries, or cell replacements for the other packs down the road.

 

[mauimart]

I just finished charging packs 1 and 6.

View attachment Pack1charge2.pdf

It appears that cell 4 is playing nice now.

View attachment Pack6charge2.pdf

I will try a deeper discharge as suggested and see what happens.
Thanks.
Martin

 

[dogman dan]

I wouldn't call anything a dud just yet. If after 3-4 cycles you have one that stays .1v different, then you do have a dud.

A dud would also tend to not hold a charge too. So balance the pack, sit overnight, and if one cell drops more than the others, it's working on being a dud. Might still be quite usable for 100 cycles or maybe even more. But not a good pack to include in a big package to be bulk charged without lvc hvc boards.

A real dud you know right away. puffs within 10 cycles. That's a stinker. Or arrives at 2. something v.

 

[Ykick]

You don't seem to have anything too drastic going on within your bricks. When you understand how these "bleed off" balance chargers work you'll see it's hard for a slightly under voltage cell to ever get caught up to higher voltage cells in a brick.

One method to treat this condition is charge the lowest cell individually through the balance leads. Keep it under 2 amps (wire size) and use 1S settings, bump the cell until it's resting a little above the other cells in the brick at the end of top charge cycle. Put it back in service and cycle it a few times, see if it stabilizes.

Sometimes, it's just a matter of getting a consistently low cell topped off enough so that it has similar capacity to other cells in the series string of bricks/pack. Most "bleed balance" setups rarely allow that to happen since the low cell never has a chance to get as full as the other cells. Sorta weird to call 'em "balance chargers", eh? LOL...

 

[dogman dan]

Actually, the one that can't catch up may be the one with higher capacity. Filling up first is the sign of a low capacity cell.

Graphing the discharge of course tells all.

 

[Ykick]

Actually, the one that can't catch up may be the one with higher capacity. Filling up first is the sign of a low capacity cell.

Graphing the discharge of course tells all.

True, true and true.

My point is that bleed balance doesn't always balance cells fairly. Sometimes my bricks need a little manual intervention to level things out.

 

[mvly]

Just FYI, I got one of my Nanotech like this:

10s4.5Ah:
3.74
3.74
3.74
3.73
3.73
3.74
3.71 <-----
3.74
3.74
3.73

And now the 3.71 is a dud even after around 10 balance charges. The one cell self-discharge very quickly. The others are fine. I suspect your pack one is a dud. It will charge fine and maybe be good if you charge and use quickly, but if you leave it in storage, it will self-dicharge very quickly.

Good luck with your pack.

So far all the battery I ordered:
8 x 37V5Ah
6 x 37V4.5Ah
6 x 14.1V4.5Ah

Out of all my nanotechs, only the one 1 37V4.5Ah had problems. The other batteries are spot on now during charge and are very balance down to 3.6V. After that it goes wack very quickly.

 

[dogman dan]

Arriving low could be because it was undercharged due to higher capacity. Same for being last to fill.

But not holding a charge is usually a symptom of low capacity. Not having a great graphing charger, I just look for cells that were charged yesterday, but today have lost .1v more than the others.

 

[Allex]

I have 4 10S5Ah Nano-tech
One pack is a bit odd.

One cell is always 0.03V under when charging.
After balancing them all to 4.18 and letting cells rest overnight the cell drops to 4.14

Whe then riding down to 3.7V all cells are even, even the "bad" one. When I start the charge to 4.18 the same cell lags behind with 4.14.
These packs are new, around 15 cycles.
What do you think it could be?

 

[dogman dan]

That cell is a bit of a dud I'd say. It doesn't hold a charge as good as the others, dropping .04v overnight when the others don't.

Two futures are possible. One is your runt cell will behave about like that for many many cycles, and quite likely after quite a few cycles the rest of the pack will begin to behave about the same. Charge, then they will drop .03 to .05v overnight. That's about how my older packs are behaving. Some loss of capacity, but they are all about the same still, and balance to .03 or .04 of each other.

The other possibility is the runt cell is a true dud, and will soon show even worse unbalance and capacity loss. You'll know which if it starts changing in the next 20 cycles or so.

Right now it seems to bottom balance, because the discharge curve is a bit flatter at 3.7v. Take em to 3.6 or lower and I bet some of that difference shows up again.

 

[Allex]

Maybe I will try to run that pack down to 3.0 with a graph...

 

[dogman dan]

If it doesn't show any difference by 3.5v, I'd just ignore it for now. .04 off is still pretty much not worth worrying about for now. Just keep an eye on it every few cycles till you see how it settles in.