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Old Aug 11, 2004, 06:51 PM
tjcooper is offline
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Sunnyvale Ca
Joined Jun 2002
1,019 Posts
what happens when you go on vacation????

LiPoly users,

I go on vacation for 1.5 weeks and the battery world falls apart. Just what is going on here?

FREEFLYER: just so I can be sure: the ballooned pack was under salt water for about 30 seconds before you saw flame (what color?) coming out of the pack? And the black/gray soot came out also and rose to the surface?

I am really amazed. I think there is like 1-2 grams of Li in the 3S1P pack and would be amazed if .5 gram of it were pure Li if it got plated out of the LiCo mixture. This really sounds like an experiment I will have to attempt to replicated (which Mr. Murphy will almost assuredly guarentee that I will not be able to reproduce). I know that Li burns in the presence of O2, but would it burn under water? Maybe there is enough O2 in the electrolyte to complete the reaction.

By the way, I think you did all the right things. I would have used sand instead of H20, but water is far more preferrable to nothing at all. And your quick thinking to put all that together in the short time is really commendable. Most of the flyers I know what be thinking: "How can I save those expensive Dean's Ultra plugs before the pack goes?" Just imagine what that would have looked like if you have a 6S3C pack on your hands.

SO HERE IS THE EXPERIMENT:
I will find a 3S1P pack and put it in a ziplock bag. I will RTV the test leads to the sack and get as much air out of the sack as possible (otherwise I will be charging under water). I will weight the pack down to be sure it will go into at least 6" of water. I will use an old fish tank (with fish removed) to hold the water. I will do my usual "overvoltage" setup to cause it to go thermal. I think I will overcharge it outside the water to get the pack hot (like 80 deg C), then I will put it in the H20. I fear the water will cool the reaction and stop thermal runaway, but who knows. It will be very interesting to see if it "burns" underwater. Anyone see any problems with this setup?

RCGUY01:
remember that all pioneers wear "arrow shirts". Those of us who tried Lipoly early are pioneers. Most of us try to use kevlar under those "arrow shirts" to give us some protection from the Indians, but you can never be sure. I don't think that LiPoly is for a first time flyer. I think you have to have at least a year of NiMh under your belt. This helps keep the Lipoly out of early crash situations also. But I think you have to RELIGIOUSLY do the safety things. I get sloppy sometimes and have been lucky. But now I charge in the pyrex pans and am starting to use the metal tubes to separate packs. I am hoping the new chemistry will come to market soon and make this a safer place for all of us. I have only one NiMh any more (for a Zagi) and all the others are LiPoly. I could not fly the little planes if it were not for LiPoly. So it is a question of risks and rewards. And I really like the rewards.

SHARKSTOOTH:
most of the problems are "pilot error", but there are cases where the LiPoly have "gone south" all by themselves. So even more care must be taken. When I was a kid, I used to take my father's 30-06 shells apart to make rocket fuel.....every once in a while, the bullet would go off while I was removing the slug.....you have to say out of the projected path! The same is true for LiPoly: hope for the best, plan for the worst. Get those sand bags beside your charging station. Charge only a few at a time. Always feel for heat or something strange every 10-15 minutes. Don't leave the area but for a few seconds at a time. Transport in safe containers. I am willing to go through all these constraints to get the rewards.

THOMASJOEHNK:
could you please describe how long each cell "burned" before the next cell in the pack went thermal? We have had one case here of a large pack go up and I am trying to estimate how long the entire pack can make a "fireball" that puts everything around it in danger. Please describe everything you can about the pack and its changes before the first outbreak of fire. Thanks.

GENERAL:
I am "gravitating" towards the direction advocated by RD Blakeslee. We need to charge parallel and reconnect serial. This seems to have the least problems....aside from having big connection blocks to put the batteries back together in the xSyP configuration. But at a minimum, I think checking the individual cell balance every 5-10 charges is the "right thing to do". I am making up a pair of multimeter clip leads to do this now. very sharp pins soldered to aligator clips seem like the right way to go. I will let you know how this works over the long term.

I would say that cell imbalance because of overdischarge will turn out to be the "Lord Valdemore"(Harry Potter reference) of the problems with Lipoly swelling.

I took a MSW and a SMK-like EPP plane with me in my motorhome while on vacation. I flew in Portland and Seattle on my trip. I used my Triton to charge my Lipoly while I was driving. I charged inside my big metal tube with a nomex sock over the end. It sat on the driver's console while charging and I could feel it every 5 minutes to see if it were hot. I kept thinking about how I would "eject" it if it went thermal. My best solution was to grab the tube, yank the banana plugs free from the Triton, and chuck the assembly out the driver's window. Can you imagine the look on the semi-truck driver's face to see a flaming Lipoly firmly attached to his radiator as he whizes past me? OK, so I will have to do a "hook shot" and chuck the assembly over the motorhome onto the passenger's side. It would be the "environmentally friendly" thing to do.
Crazy Ted -- living up to his name
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