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Old Sep 18, 2003, 01:43 PM
Just an average RC'er
Jim McPherson's Avatar
Laurel, Maryland USA
Joined Aug 2000
4,291 Posts
Don't puncture balloned lipos!

Well, I just balloned a lipo pack. I have no idea how it happend, I had the right cell count and have never had these batteries in a crash. I was charging them and they balloned up pretty big. I had read that a good way to ensure your saftey when this happens was to puncture the cell and put it in salt water to neutralize the chemicals inside.... so I decided to do that. I got the salt water togther, then took a very sharp knife and went to ever so slightly puncture the case. I knew the gas would escape so I was ready for it. HOWEVER what I was not ready for was the violent expolsion that took place when I ruptured the outer case. Remember DNA's video? Yeah, just like that except more directional. The whole side of the cell blew open and flames 2 feet long rushed out of the entire length of the cell. Fortunatly it died down pretty quickly and before it burnt anything I was able pick the pack up by the wires and put it in the salt water. But this was really an eye opener to me.. This was a very small cell, less than 500 mAh. The amount of flame was incredible, I've never seen anything like that before except for an acetelyn (sp) torch. I have a new respect for Lipos and will treat them more carefully.

-Jim
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Old Sep 18, 2003, 01:52 PM
Micro Hydro Racer
Trent Hare's Avatar
Rocklin, Ca. USA
Joined May 2001
136 Posts
HOLY MOLY...
That's a bit scarry

- another sentence to be added to the warning label -
"um.. don't be pokin puffy cells"
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Old Sep 18, 2003, 02:01 PM
now that's a wattmeter...
simingx's Avatar
Singapore
Joined May 2002
1,136 Posts
Could be the chemicals reacting with the oxygen in air.
I see a new use for these cells now... Put your puffed up cells in a contraption of sorts, have a servo poke them and voila you have an instant rocket.
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Old Sep 18, 2003, 02:58 PM
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Joined Dec 2002
428 Posts
Jim,

Thanks for the post.

There are alot of reports of very volatile Li-po experiences, but beyond adding to the number of reported incidents (which is important info), there is most often no apparent analysis that may point to the cause.

It is very possible that these cells sometimes "just blow", but it may be more likely that we are using them in a way that strikes us a normal and safe, but may in fact be leading to these sorts of incidents.

So if you don't mind me asking:

Can you add anything on the history of the pack?

# of cycles?

charge / discharge rates typically used

How was the pack built? Cell , configuration, package (shrink?)

Any visible results of handling or other external stress in the past?

I don't mean to interrogate here, but you seem like a very analytical guy and can possibly add to the (pretty alarming) report of the extreme failure of the cell(s).

Thanks,

Chris
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Old Sep 18, 2003, 03:29 PM
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Joined Jan 2002
6,587 Posts
Jim, thanks for the heads-up.

It's tough to take a chance you'll malign somebody, but it sure seems like charger malfunction should be suspected (internal failure, whatever).

Can you tell us what charger you're using, so we can be on our guard?

- RD
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Old Sep 18, 2003, 04:09 PM
AMA 148796
Where it Rains
Joined Jul 2002
1,058 Posts
Once again - flames from a LiPo pack, from a very careful and experienced eflyer. This time we can't lay it on shrink wrapping the cells, shorting power leads, poor charging procedures, inexperience, or leprechauns. Jim was following "accepted" procedures.

"flames 2 feet long rushed out of the side of the cell"

Somebody is going to be seriously hurt.

Guys, it isn't worth it.

Ken
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Old Sep 18, 2003, 04:15 PM
Just an average RC'er
Jim McPherson's Avatar
Laurel, Maryland USA
Joined Aug 2000
4,291 Posts
Ok more info:

I was using a Ginzel Spectra, which I use almost everyday to charge lipos of all makes and sizes. It has the newest lipo software and requires you to validate the cell count before it starts charging. Note that it has never blown up any cell except that of this particular brand (killed 2 packs now)... which I won't mention until I get more info. I really don't think it was the charger.

I had about 10 cycles on the pack, I was using it under the recommend discharge levels set by the manufacturer. I was charging right at the maximum charge level suggested by the manufacturer. This charge rate may have been to high, this is my current theory for failure as the last pack ballooned while charging at this same rate.

The pack had a small amount of heat shrink, but not enough to put any real pressure on the pack, it was open on the sides where it ruptured. The pack was a factory built pack. It had never been in a crash or abused in anyway. I kept it very safe as I respected it as a hazard.

Closer inspection looks like only once cell balloned heavily, the other did ballon but no where near what the other did. I guess there could have been some unbalance, but I don't think that was the cause.

I'm just thankful that nothing flamable was nearby or my house would have burnt. This was a BIG flame, much bigger than I though possible.

-Jim
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Old Sep 18, 2003, 04:35 PM
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William A's Avatar
Tacoma,WA USA
Joined Jun 2001
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The LHS has a ballooned pack sitting on a shelf behind the counter for show-n-tell.

Me thinks I'll call them.
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Old Sep 18, 2003, 04:56 PM
Senior Member
Finland
Joined Feb 2001
584 Posts
Quote:
Originally posted by Jim McPherson
I guess there could have been some unbalance, but I don't think that was the cause.

Why not?

To me it sounds the most probable reason. Did you ever balance them? Have you been using them down to 3V? Or taking a lot of Cīs? Was there a possibility for asymmetric cooling/warming in flight? All that would make the unbalance worse.

It would be very interesting to hear which lipo brand is using flammable solvents.

Yes itīs very much worth to use them. Just not without regular balancing.
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Old Sep 18, 2003, 05:04 PM
Just an average RC'er
Jim McPherson's Avatar
Laurel, Maryland USA
Joined Aug 2000
4,291 Posts
At 10 cycles I never thought balancing was needed. That's why I'm hesitant to say that was the problem. I think the reason they blew was the factor of heat and rupture. A cool, ballooned cell will probably not be so violent. My pack was hot off the charger when I punctured it.

I have never taken the pack belon 3.2 volts per cell, but had been discharging at extremely high discharge rates. But again, it was well within recommendations by the manufacturer.

Who knows??? I'm going out to buy one of the fireproof safes now. I really thought it overkill before this afternoon, now I don't.

-Jim
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Old Sep 18, 2003, 05:06 PM
Registered User
Walled Lake, MI, USA
Joined Feb 2000
11,182 Posts
>> I was charging right at the maximum charge level suggested by the manufacturer. This charge rate may have been too high, this is my current theory for failure as the last pack ballooned while charging at this same rate.

Jim, this is the first thought that struck me. There has been discussion of LiPo charging at greater than 1C. Some people have successfully done this. I've debated in my mind if it's really worth the risk. Your experience convinces me that, at least for the time being, it might be best if everyone sticka with 1C for LiPo charging.

The issue of the violent reaction of the cell to being punctured is another issue altogether. My understanding has been that this is the proper way to prepare LiPos for their salt water bath prior to disposal. There must be some kind of variable here that has not occurred in similar situations. For instance, I recall Electroman warning about sticking a sharp object too far into a LiPo cell and causing a short.

We're getting a lot of clues from all of these various incidents. But I don't think anyone has been able to add up all the clues and figure out what exactly is happening in the cases of violent failures that is not happening in the cases of "soft" failures. It only reinforces the fact that the use of Li-poly for e-flight is "experimental" rather than a proven technology.

No one should be using these cells unless they fully understand this, and are prepared to take the safeguards required when using experimental technologies.

EDIT: I see now where you said your cell was hot off the charger when you punctured it. I can't recall of Electroman had mentioned letting a ballooned cell sit for awhile before puncturing. In any case, we now know that puncturing a LiPo hot off the charger is not a good thing to do!
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Old Sep 18, 2003, 05:10 PM
Just an average RC'er
Jim McPherson's Avatar
Laurel, Maryland USA
Joined Aug 2000
4,291 Posts
What's even stranger is that the rupture where the flames shot out are on the other side of the pack. I punctured the cell on one of the flat sides in about the middle. Right after that the side of the cell opened up and the flames shot out. The very very small hole I made is still there, and just as small.

-Jim
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Old Sep 18, 2003, 05:21 PM
characters welcome!
Mark Wood's Avatar
United States, CA, Bear Valley Springs
Joined Feb 2000
26,457 Posts
I'll stick to high-end NiMh, thanks.

mw
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Old Sep 18, 2003, 05:28 PM
Registered User
Walled Lake, MI, USA
Joined Feb 2000
11,182 Posts
Jim, we just don't know enough about this to fully understand it. It's possible that the entry of cool air into the hot pack contributed to a failure that was already in the process of happening. Or it could be a complete coincidence of timing that the failing cell happened to let loose just as you were puncturing the covering on the other side.

We just all have to keep reading and trying to understand all of the details about all of these incidents, keep discussing them and keep trying to work together to figure out exactly what's happening.
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Old Sep 18, 2003, 05:37 PM
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Arthur Knowles's Avatar
Fallbrook, CA
Joined Oct 1998
1,113 Posts
Hey Guys,

Keep in mind that Jim punctured these cells HOC. Everything I have seen about damaged Lipos suggests that you wait at least 20 minutes, or more, to verify that the damaged pack will not self ignite before doing anything else.

I would not recommend taking a balloned pack HOC and doing anything with it until it cooled.
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