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Old Aug 12, 2004, 08:10 AM
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Kit, it's obvious from reading the wording of your messages that you don't care much for the RC Groups rules pertaining to keeping this forum a place for courteous discussion and treating other users with respect at all times. That's fine. Those of us who don't find much value in your commentary can simply ignore you, and the moderators will eventually give you an attitude adjustment to bring you in compliance with the forum rules supported by the rest of the posters in this thread.

A more productive alternative would be for you to edit the snide little remarks out of your own messages before a moderator does it for you. Those who contribute good data on this forum are generally valued and respected. If you have good information to contribute, you could earn the respect of others by presenting it in a way that does not show disrespect for others.
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Old Aug 12, 2004, 08:25 AM
Rhinebeck CD-99,00,01,02
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New Bern, NC
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Rd

Only reason for the 22 slug is to expose the innards to the salt water. The only thing exposed now is the snipped off wire ends, and that isn't very much exposure. Thanks, I'll get out the salt and make up a strong solution and let them sit for a few days under water. Then I will test to see if they are in fact dead. If so, in the trash they go. Thanks for the assistance. Tom
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Old Aug 12, 2004, 08:31 AM
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You're welcome, Tom.

- RD
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Old Aug 12, 2004, 08:38 AM
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Quote:
Originally Posted by flieslikeabeagl

I just measured my Kokam 1500 mAh 2S1P cells at roughly 3.6cm x 1cm x 7.3 cm, for a volume of roughly 26 cubic centimeters. This cell weighs 73 gm on my digital scale. Put those two numbers together, and the cells specific gravity works out to roughly 2.8 gm/cc, which is to say, 2.8 times denser than water.
These cells would have to puff out to almost three times their volume before they would float in water. -Flieslikeabeagle
Good thinking!

Check out this picture - http://www.rcgroups.com/forums/attac...hmentid=136292

Those cells look like they could be 3X larger than the unswelled one.

(FWIW, The density of the dead sea is 1.16g/ml.)
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Old Aug 12, 2004, 09:22 AM
Good Better Best quest.
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Think ill just keep my old crock pot and a bucket of sand handy it doesn't evaporate,and the dogs wont drink it , and no one else will be bothered carrying it away.
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Old Aug 12, 2004, 11:10 AM
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This is the third time I've heard of a LiPo pack being blown up on an Astro 109 charger. In one case a 3 cell 1500 Kokam pack was hooked to the charger, but the voltage was 8.4 volts, so the charger recognized it as a 2 cell pack, but it put in a little charge anyway. The pack was disconnected, then reconnected, and since it was over 9 volts at this point, it was recognized it as a 3 cell pack, and it began charging. The pack burned within a half hour, all but one cell. Apparently one cell was shorted, so it was in fact a 2 cell pack. Why would the Astro 109 put some charge into the pack if it was recognized as a 2 cell pack that was fully charged?
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Old Aug 12, 2004, 02:41 PM
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Sunnyvale Ca
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return to thread topic!

Flyers,
we need to return to thread topic. The thing we are trying to discover is how/why Lipoly could flame up when put into a vat of salt water.

I am still hoping that FREEFLYER and THOMASJOEHNK will return to this thread and fill in the missing pieces of information I requested. We really do need as much information on this as possible.

OBSERVATIONS: the resistance between two wires in a vat of salt is a difficult thing to compute. There are a semi-infinite set of virtual wires going through the salt water to each of the leads (of copper?) thrust into the water. I know that in a 1 cubic foot fishtank full of salt water, I measured something like 0.035 ohms between two copper plates about 1 inch square separated by a distance of 6 inches. I could light up a 60watt light bulb using 120VAC with no problem at all. So the resistance is pretty low if you really saturate the water. A few handfuls of salt in a 2 gallon pale should give you around 1-2 ohms of resistance to 1/4" wide strips of Cu space by roughly 1 inch (all of these are SWAGs). So you can discharge the Lipoly in a pale of water with no problem at all.

I really don't feel that the chargers are to blame in these cases. Something has happened in the cell and shorting is starting to occur in a way that promotes stronger shorting which goes to thermal runaway. History of the cell use and charging, and an autopsy, are about the only way we can know for sure what happened (can you imagine CSI doing a segment on how a man murdered his business partner by using thermal runaway Lipoly cells in the trunk of his car over the gas tank? LOL).

Anyway, I am very interested to see if a cell can "flame" in a waterbath. I feel it will be very difficult for me to try and reproduce this event. But it is definitely worth a try. FREEFLYER, can you estimate how hot the pack was when you thrust it in the water? Was it so hot that you were getting a mirage of heat around the surface of the pack? Any clues would be very helpful.

I have found that the metal tubes around the cells can really help control the fireball when a pack goes thermal. I hope many of you will consider using this method to transport and charge your packs. The firesafe is great for a few packs, but I can assure you that if one pack goes, they will all go.....one after the other. More than 5 packs in a firesafe could possibly cause the fireball to leak out of the safe. Only testing will tell for sure.

Anyway, back to thread topic and lets drop all the snide comments. We have a lot of work to do.
Crazy Ted -- a battery junkie
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Old Aug 12, 2004, 03:42 PM
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CT,
As you have stated, a strong salt solution is a very good conductor. Once while heating a salt solution on a hot plate in the lab, the beaker broke and some of the solution ran into the 110V electrical outlet. 5' Flames shot out of the outlet and scared everyone out of their shoes.

In regards to the lipo, consider that if the lipo ruptured in the salt bath, a lot of contact area would be available and massive shorting could occur.

I remember some videos that showed the packs growing quite large prior to bursting. As I recall, they were probably well over the 3X volume increase needed to float the cells. The pack could have sunk, continued to balloon, rose to the surface, vented and ignited. Too many variables to track down I'm afraid.

But I do have a suggestion for a test.
The question is: Will a bucket of sand poured on a smoking LiPo contain the reaction. Will it stop the vapors from igniting?

In regards to the multiple cell burning scenario in a firebox, I still have strong
feelings that the limited amount of oxygen in the box will inhibit even the burning of the first cell. Didn't someone do some fire tests in a container? Maybe it was a ceramic jar.....
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Old Aug 12, 2004, 04:06 PM
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Quote:
Originally Posted by hoppy
Didn't someone do some fire tests in a container? Maybe it was a ceramic jar.....
Were you thinking about this thread on charging in a firesafe box ?
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Old Aug 12, 2004, 04:11 PM
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I decided to try the coffee cup test. I tried different concentrations of salt including saturated, and the lowest resistance I saw using two copper electrodes that had about 3 square inches submerged was about 350 ohms. Anyone else try it?
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Old Aug 12, 2004, 05:13 PM
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Sunnyvale Ca
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coffee cup science

Dan,
how close together were these 3 in square conductors in the coffee cup?
I normally get resistances on the order of a few ohms when I use 3 x 3" square copper plates separated by a inch or so. Something sounds wrong with this experiment.

RD,
if you look at my barbeque of a LiPoly and some of the other tests, they have at least trippled in size before they ruptured. Both others probably only got to just 3 times size before venting. There is a good video on the sticky page that shows the LiPoly get so big that it "flips over" because it has become like a tennis ball before it ignites. I would guess that it is easy for a thermalling LiPoly to get swollen enough to float, but I have never tried to measure it -- and I really don't want to spend the time to find out. I am interested only in seeing if fire will come from it when it is under salt water.

I have read a thread where the person put a swelling pack into a vat of plain water when it began to swell up and that stopped any further expansion. The pack did not rupture when it got put in water.

I am afraid that that is what I will find when I do this experiment. The cooling effect of the water will stop the electrolyte from out gassing. So this is why I think I have to get the pack "very hot" before I put it in the salt water solution. Any comments on how to judge where thermal runaway has gone beyond the point of no return?

Oh, I have videos of sand going on the venting Lipoly. It did not stop the flame but it cut down on the fireball by a huge amount. If you had 20x sand for the size of the pack, I think you could stop the fireball from being seen. But the smoke and gas/schrapnel will still make its way out.

Crazy Ted
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Old Aug 12, 2004, 05:59 PM
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I used a small (12 oz) coffee cup, so I couldn't get the electrodes very far apart. I tried everything from almost touching to as far apart as I could get them, and the lowest resistance I ever saw was about 350 ohms. The conductors were 3 square inches (1" x 3") not 3" square (3" x 3").

Dan
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Old Aug 12, 2004, 07:10 PM
kit
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USA
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Quote:
Originally Posted by hoppy
So what you're saying is that you don't have any idea and it was just a WAG...LOL
Looking forward to hearing hoppy's WAG explanation of your resistance measurement Dan. This should be good! Well,......maybe not.
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Old Aug 12, 2004, 08:03 PM
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I would travel to Sunnyvale (and take my own meter) to see two 1" plates submerged in salt water 6" apart show a resistance of .035 ohms.
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Old Aug 12, 2004, 08:14 PM
kit
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USA
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LOL

No need, even though you're relatively new here, I'd say you already have a pretty good idea about who the bs (baloney samwitch...or...bologna sandwich) posters are. Thanks for actually doing the salt water test. It wasn't that hard was it? Maybe even hoxxx ...others could do it.
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