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Old Jun 20, 2005, 08:09 PM
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Walled Lake, MI, USA
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Quote:
Originally Posted by ozace
I think Hoppy is counting disasters
Hoppy has volunteered a fair amount of his own time to gather links to all of the LiPo catastrophic failures reported on this forum so that people who want to research the issue can go to a single location instead of having to hunt around. It is one of the more valuable safety contributions made on this forum.
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Old Jun 20, 2005, 11:00 PM
BEC
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Auburn, Washington USA
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Peripherally related: I have exactly one crash-damaged LiPoly pack so far - a 2s Kokam 1250 pack (the new 20C type) that had all of two or three flights on it. Due to equipment abuse on my part the plane went straight in and the pack is about half an inch shorter on one corner than it used to be.

I was, shall we say, apprehensive to handle it or transport it for some long time after the crash. It is now almost seven weeks since that crash and the pack has done nothing untoward. I have NOT tried to recharge it or otherwise use it. The last time I checked the voltage it was commesurate with how much it was discharged when I crashed it.....

So, is anyone keeping track of damaged LiPolys that don't go up in flames? I wonder what the proportion of crashed packs to flamed crashed packs is really. Or is there something remarkable about the new HDR Kokams along with their reported high tolerance for overcharge?

Just checked it: 7.77v per Astro Micro Meter (the low range Whatt meter)
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Old Jun 21, 2005, 12:24 AM
Whistling Death
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WA,USA
Joined Jun 2004
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The other day I crashed in hard and damaged one of my kokam packs. One of the cells was ripped open and was emitting that very strong sweet smell. I quickly stuck it in my (lipo bunker) and the next day I checked it and to my surprise it had not swelled or caught fire, voltage was also at 12.1V. Since I was smelling that strong odor wouldn't that mean the cell was punctured, therefore, I would think that the voltage should have been lower. Needless to say, I won't be using that battery anymore.
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Old Jun 21, 2005, 01:02 AM
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Sorry about the plane guys, hope it wasnít one of your AP birds?
I donít think anyone is tracking it yet BEC, but itís good to know your pack didnít flame.
I know Kokam says the HDR's will vent >18.5v but not ignite when charged.
Anything could have an electrical fire from crash damage, but if they donít go off like mini-incendiaries it would be a major improvement.
We may be thinking the same thing, and thatís why I asked what type of pack it was this time.
If I burn my house down charging, that's too bad for me. But my ďEĒ AP flights will remain very limited during harvest time, unless something changes.

Jim
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Old Jun 21, 2005, 01:14 AM
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United States, VA, Fairfax
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was just about to order LiPos. but after reading so many such cases i am gonna stick to NiCd and Nimh till they come up with some non inflammable LiPo. I am too scared of lipos. I used them for 2 years now. now i am gonna stop
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Old Jun 21, 2005, 01:25 AM
Cogito ergo fly!
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Kansas City, MO
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Naw, don't stop. Just be very careful! Ni-Cd's and NiMh's are not totally safe either!

Tom
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Old Jun 21, 2005, 08:40 AM
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Quote:
Originally Posted by IA-Flyer
I know Kokam says the HDR's will vent >18.5v but not ignite when charged.
Jim
Hey Jim,
I read that when they first came out. But I've looked and looked and looked and I can't find that info anywhere. Can you remember where you saw it? Was it recently?

.................................................. ..................................................
OK, I found 1 post on the subject. Nov2004 http://www.rcgroups.com/forums/showp...05&postcount=7
"An individual cell can sustain up to 18.5V without igniting. If, e.g., you had a 4S charge (16.8V) set up and inadvertently put it across one cell, the cell would not ignite, per JJ Hong."

Has anybody verified that claim yet?
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Old Jun 21, 2005, 08:59 AM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Flameless Kokams

Hoppy, I saw the photos months ago but like you do not remember where on RC Groups they were posted,I believe it was in Batteries and Chargers.

I did find this on the FMA site however.
Kokam Super High Discharge LiPo Electric Pack
Part Number: KOK3200-20C-2S-DNS




This 2 cell series pack is composed of Kokam 3200 mAh Super High Discharge (20C / 90%) Lithium Polymer Cells. The KOK3200HC cell is the newest generation of Kokam high discharge cells. The pack includes a DNS connector ideal for interconnection using the DNS series or parallel connector modules available separately. The 3200 has unprecedented current delivery capability in that it can deliver up to 64 amps continuously with the loss of just 10% capacity.

Unlike any other battery chemistry, Lithium batteries are designed for parallel or series/parallel operation. In choosing your configuration, first assemble cells in series to achieve your voltage requirements. Next parallel multiple series packs to increase your capacity. Other than size, there is virtually no limit to the current capabilities of a series/parallel LiPo battery. The more cells you parallel, the more current you can draw from the battery pack. Series/parallel packs are defined by NSXP where N = number of cells in series and X = number of series packs wired in parallel. As an example a 2S3P pack of 2100 mAh high discharge cells would be comprised of 3, two cell series packs wired in parallel. The nominal voltage of this pack would be 7.4V. The total capacity would be 6300 mAh. Running this pack at 20C means it can support 6300 mA x 20 = 126,000 mA or 126A of current.



In order to utilize Kokam LiPo electric packs to their fullest potential, and to prevent the batteries from deep discharge conditions, we recommend the use of a special electronic speed control. New auto-cell detect ESC's are in development and/or in production from FMA Direct. The first in this new series is the FMA Direct SUPER 30 (pn: ASC30) The SUPER 30 is the perfect compliment for LiPo battery packs. Designed with auto-cell detect, the unit will automatically detect the number of cells in a LiPo, NiCd, or NiMH battery pack and set the correct motor cutoff accordingly. In addition, the latest software version enables the selection of a user-programmable, fixed cutoff that can be set at any level. This unit will prevent the undesirable condition of discharging LiPo batteries below 2.5V per cell. Be advised, this condition can prevent the cells from re-charging. Visit the Motor Controllers section of the store for more information.
______________________________________________
The bold letters are my modification.

This is part of the continuing confusion for the LVC for the ones who do not undersatnd the difference in LiPoly cells/ chargers.

Added:
OK here is my good deed for the day.
Photos of Kokam LiPolys that according to electroman will not vent with flames. .



Charles
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Last edited by everydayflyer; Jun 21, 2005 at 09:10 AM. Reason: Aded link.
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Old Jun 21, 2005, 11:34 AM
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Quote:
Originally Posted by hoppy
Hey Jim,
I read that when they first came out. But I've looked and looked and looked and I can't find that info anywhere. Can you remember where you saw it? Was it recently?

.................................................. ..................................................
OK, I found 1 post on the subject. Nov2004 http://www.rcgroups.com/forums/showp...05&postcount=7
"An individual cell can sustain up to 18.5V without igniting. If, e.g., you had a 4S charge (16.8V) set up and inadvertently put it across one cell, the cell would not ignite, per JJ Hong."

Has anybody verified that claim yet?

Hi Hoppy,
Several threads mentioned it in the vendorís forum, but this is the thread that sparked my interest.
http://www.rcgroups.com/forums/showthread.php?t=372784
Itís probably the one Charles was thinking about also.


"Has anybody verified that claim yet?"
I havenít seen any independent tests, but itís defiantly something worth verifying.

Jim
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Old Jun 21, 2005, 12:22 PM
know it all
Miami, Fl
Joined Nov 2003
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it can happen to nimh too, I plugged these in backwards..

Herm

Quote:
Originally Posted by TubaTom99
Naw, don't stop. Just be very careful! Ni-Cd's and NiMh's are not totally safe either!

Tom
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Old Jun 21, 2005, 12:37 PM
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United States, CA, San Diego
Joined Dec 1999
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Quote:
Originally Posted by hermperez
it can happen to nimh too, I plugged these in backwards..

Herm

If you look the wires cooked and shrink melted and smoked but the cells did not burn--unlike lithium poly cells!

Steve
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Old Jun 21, 2005, 12:46 PM
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Ontario, Canada
Joined Nov 2002
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How long will it be before all Li-Poly cells use a non-flammable electrolyte??

If Kokam can do it, why are others not?

Also, is the Kokam electrolyte really non-flammable, or is it more a matter of cell design which resists ignition?


It all seems so obvious, Li-Po's would then just be the same as any other cell when shorted, etc. They just get really hot, and at the worst case, melt things nearby. (as long as they don't reach 451 degrees!)
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Old Jun 21, 2005, 12:53 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
34,834 Posts
Quote:
Originally Posted by meteor
How long will it be before all Li-Poly cells use a non-flammable electrolyte??

If Kokam can do it, why are others not?

Also, is the Kokam electrolyte really non-flammable, or is it more a matter of cell design which resists ignition?


It all seems so obvious, Li-Po's would then just be the same as any other cell when shorted, etc. They just get really hot, and at the worst case, melt things nearby. (as long as they don't reach 451 degrees!)
Well for one thing Kokams are heavy.
If everyone only purchased Kokam LiPolys then other manufatures would have to folow unless it is a patented process and Kokam refuses to sale/share its rights.


Charles
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Old Jun 21, 2005, 01:15 PM
Space Coast USA
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Space Coast
Joined Oct 2000
21,111 Posts
Quote:
Originally Posted by IA-Flyer
Hi Hoppy,
Several threads mentioned it in the vendorís forum, but this is the thread that sparked my interest.
http://www.rcgroups.com/forums/showthread.php?t=372784
Itís probably the one Charles was thinking about also.


"Has anybody verified that claim yet?"
I havenít seen any independent tests, but itís defiantly something worth verifying.

Jim
Thanks Jim,
I hadn't seen that post - attention getting to say the least.

A "fire proof lipo", even at a heavier weight, should attrack a lot of modelers, expecially those sport flyers who don't care about top performance.

So why isn't Kokam promoting these as "fireproof"?
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Old Jun 21, 2005, 01:24 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Quote:
Originally Posted by hoppy
Thanks Jim,
I hadn't seen that post - attention getting to say the least.

A "fire proof lipo", even at a heavier weight, should attrack a lot of modelers, expecially those sport flyers who don't care about top performance.

So why isn't Kokam promoting these as "fireproof"?
Let me try again. I guess you missed the link I provided in my other post.
Electroman posted in responce to this thread months ago.
http://www.rcgroups.com/forums/showthread.php?t=349202


Charles
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