Lithium ion battery packs dangerous and shoddy manufacturing

[akis]

I have bought and been using a number of 6 cell lithium battery packs for a while now and they have all developed one bad cell which drops to below 3V and loses its charge on its own right after charging. They are all 3000-3700mAh and discharging was at a low 0.3-0.4C and charging at around 0.4-0.5C.

Because there were a few with the same fault and were unuseable anyway, I opened them up to take a peek inside, especially as it was always the 6th cell that went first (the one attached to the positive terminal).

I am not yet sure why the 6th cell was the first one (and only, many times) to develop a fault. But what I saw horrified me. The packs are made from thin (4mm), flat, rectangular cells packed together with the conductors for each cell sticking out at the top and pressed together to form a chain - 6 cells in series.

There are rubber spacers in between the conductors so as to prevent any short circuits but they are placed haphazardly and are not strong enough to prevent the bent conductors from making conduct! A moderate push and the rubber spacer collapses and allows the conductors to touch.

In addition the soldering was done so badly that there were plenty of solder balls and debris littering the conductor area and in the attached photo you can see a trail of solder debris almost short circuiting two cells together!

Terrible and shoddy making in two brands, Zippy and Turnigy alike.

And then they wonder why lithium batteries blow up "on their own"....

[nfmax]

The Curse Of Cheapness!

[Audioguru]

Zippy and Turnigy are Chinese Lithium rechargeable batteries sold by Hobby King. Some work and some don't but they are very cheap. The company seems to be missing some quality control.

[amyk]

I am not yet sure why the 6th cell was the first one (and only, many times) to develop a fault.

How are you charging them? It sounds like a balance problem.

As for the cell connections, I'm surprised they seem to be soldering the tabs; it's usually highly recommended to spot-weld instead, and any good pack manufacturer should have spot-welding equipment.

[akis]

If you look closely you will see that the tabs have been pressed together, spot welded maybe. The wires attached to the tabs have been soldered on, Because of the heat conductivity, you need a very hefty soldering iron to make the connections especially on the thick + and - terminals, which even at 350C (or more) I was unable to take off. Heat travels up the wire to make it impossible to hold with bare hands well before the solder on the tab has even melted enough to allow the wire to be removed. Based on that I believe they have used very strong, mains powered (no transformers) old style soldering guns with very thick and imprecise tips and add an amount of carelessness and you get the result in the photo.

It is a terrible battery pack an accident waiting to happen. I wonder have they not read the news how many lithium batteries blow up on their own and why they are not allowed on planes.

As far as charging goes I always have used a balanced charger, there is something else that causes one cell to collapse. I do not have a proper battery monitor, and cannot tell if one cell has gone below 3.5V or 3.0V ot whatever.

[nfmax]

It is possible that overheating of the 'end' cell during soldering of the anode connection wire may be why this cell position consistently fails first. This is a terrible poduct - an accident waiting to happen!

[akis]

It is possible that overheating of the 'end' cell during soldering of the anode connection wire may be why this cell position consistently fails first. This is a terrible poduct - an accident waiting to happen!

Ahh yes! Because the other end cells also fails occasionally one one or two packs (I have 14 packs in total)! I was wondering about this and it makes sense! Thank you, it all makes sense!

[wraper]

I am not yet sure why the 6th cell was the first one (and only, many times) to develop a fault.

How are you charging them? It sounds like a balance problem.

As for the cell connections, I'm surprised they seem to be soldering the tabs; it's usually highly recommended to spot-weld instead, and any good pack manufacturer should have spot-welding equipment.

Why would you spot weld wires? Smartphone battery tabs are soldered to internal PCBs as well. Spot weld must be used for connecting tabs directly to individual elements in the batteries, like 18650. There is no need to spot weld thin tabs together, as they provide enough of  heat resistance to not damage the battery. BTW it seems that tabs are spot weld or pressed together, and only wires are soldered on top of them.

[AmmoJammo]

Assembly looks fine to me...

[Siwastaja]

It looks like the tabs are properly ultrasonic welded together. If done right, soldering the wires is good enough although not the best practice. The solder quality looks pretty decent as long as there is some strain relief on the wires, and as long as the heat to the cell internals was managed during the manufacturing to acceptable levels.

They have used several layers of different types of insulating tapes, which is a good sign, but it's impossible to say whether the insulation is good enough or not from this single image. I can't see anything critically wrong that would ring the alarm bells. Fusing the sense/balance wires would be a great thing to do, but no one in that market segment is doing that anyway. The insulation and the solder connections probably don't like taking direct hits, but the pouch cells themselves do not either; these packs leave the mechanical protection to the end user (who often deliberately ignores the issue and takes the risk, trying to handle them as carefully as possible) and everybody knows this.

[akis]

Your comments are weird. Do you work for the company?

The insulating tapes sit on top of the tabs and do nothing to prevent the tabs from accidentally shorting. This is left to the rubber spacers to prevent. There is no insulating tape between yellow and black for example.

In the photo we have the worst possible soldering I have ever seen with solder debris trailing between the two tabs on the surface of a squashed rubber spacer that needs only a small pressure to collapse completely and fuse the two tabs (and fireworks).

But just looking at the soldering debris left over and forming a path between yellow and black is enough to QC fail this battery pack at an instant.

[Siwastaja]

Well, as you have removed or at least moved around some of the insulation, it's impossible to say from a single photograph whether it was originally good or not. That's why I only could say that using several types of insulation is a good sign, but a good sign doesn't equal good end result. But only you have the knowledge how it was put together before the destructive teardown, so we need to trust your analysis, which would require taking you seriously first, which is a bit difficult to do for the following reasons:

- As this is the worst soldering you have ever seen, that clearly means this is one of the first electric or electronic products you have ever opened -- you don't need to do too many teardowns to find actually horrible solder job, namely cold joints, or joints that have not flown properly at all due to oxidized surfaces. Very typical in low-cost Chinese products, but you have clearly not seen it. (For example, a Chinese hot air station I examined connected the Protective Earth wire with a cold solder joint from a single strand, they had managed to do a solder work that had tens of ohms of resistance! I call that a special ability!)

- And, yes, you got me there! Of course I work for some random no-name Chinese battery manufacturer ! Are you kidding me

You know, you post something, I analyze it just for fun. I use whatever information is available. Not much was this time. I'm not your feelgood circlejerk robot, so I skip your analysis and do my own, I don't exist to confirm your bias. I didn't draw any conclusions about the quality, and will not, because not enough data is available for that. I can always guess that most likely, the quality is horrible shit and the product is dangerous, as you say; that would be fairly typical in this product segment.

But on the surface, based on that teardown photo, it looks like any other Chinese RC battery, some are more dangerous than others, and I have seen some that are a lot worse, namely soldered series connections instead of welded; and really bad solder job.

[akis]

Your observations were all spot on. Your assumptions also spot on. Except you failed to notice and/or comment on the foremost issue which is a ton of junk left behind after soldering, forming a dangerous short circuit path, clearly visible, not disguised as a cold joint, and all that during a procedure where separating the tabs is of paramount importance for whichever technician worked on it and whichever QC person that looked at it (if anyone at all).

It's like someone showing you a car with a bullet ridden windscreen and you are commenting on a flat tyre

This reminds me of the ancient Microsoft joke which I will not type here, it has a million variations, but here it is for your amusement
http://alunthomasevans.blogspot.co.uk/2007/10/old-microsoft-joke.html

[Siwastaja]

You know, telling people that their contributions are totally worthless is a great way to ensure that you get even fewer contributions in the future.

[AmmoJammo]

Your comments are weird. Do you work for the company?

Do you work for the companies opposition?

The assembly may not be fantastic, but its perfectly acceptable... if you're worried about it catching on fire, don't use it in an environment where it may suffer an impact.

[wraper]

Except you failed to notice and/or comment on the foremost issue which is a ton of junk left behind after soldering, forming a dangerous short circuit path, clearly visible, not disguised as a cold joint, and all that during a procedure where separating the tabs is of paramount importance for whichever technician worked on it and whichever QC person that looked at it (if anyone at all).

I clearly see debris left, I don't see any of it that could possibly create a short.

[nfmax]

The 'any old shit will do' school of engineering are out in force today, I see...

[Whales]

Rubber?  Pah!  The ones I dismantled used cardboard and tape: