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Old Jun 22, 2005, 03:44 PM
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Now Charles, just wanted to give you a chance to let those that have not been on ezone for years to know some relevent history....

As I have said before, I have not been a big fan of Kokam, but 3C Lipo's might be interesting if true, AND they have a good cycle life with a 3C charge.

Brad
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Old Jun 22, 2005, 03:52 PM
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Quote:
Originally Posted by bjpaul
Now Charles, just wanted to give you a chance to let those that have not been on ezone for years to know some relevent history....

As I have said before, I have not been a big fan of Kokam, but 3C Lipo's might be interesting if true, AND they have a good cycle life with a 3C charge.

Brad
Understood and I agree however I think I will wait for Thunder Power to release there line of fast charge LiPolys.I seem to get along with Charlie much better.
I have seen a few of the new Kokams in use at one of the local club field where I am a member and they do indeed charge in 20 minutes. I have enoghh LiPolys and aircraft that I tire of flying befor I run out of something to fly. Besides I have six LiPoly chargers and a 5 pack charging setup for my AF 109 meaning that I can charge 10 packs at a time. I guess if I used $600 plus LiPo packs being able to charge quicker would be a savings but you still have to wait for them to cool befor charging and so there you go.

Charles
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Old Jun 22, 2005, 04:03 PM
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RCgroupers,
this drift has been interesting.....but not always fruitful. If Kokam does have a non-flame 4th gen cell, then it should be rather straightforward (but expensive) activity to get UL approval for the fire protection part.

My "guess" about 18.5 volts/cell is that is the max at FMA/Kokam that they could test the unit on conventional chargers. Putting some diodes on a full-wave bridge to the AC lines would not be considered a good battery charger. If the electrolyte is not flammable at room temperature, then that should be easy to test with the UL flammability tests. The Sony LiPoly were not flammable by tests I made when I started in LiPoly testing....however, they were practically useless for r/c plane applications. The magic of high discharge is in the electrolyte and the plate layout.

TEST FOR INTERNAL SHORTS: as this thread began, the question was asked how to know if a crashed cell was set to go "vent and flame" at a later time. I do not have a complete answer, but let me tell you what I have observed in some destructive tests.

1) put a sensitive DMM on the cell. Set it to A/C volts
2) bend the "crap" out of the cell
3) observe the reading. It will change strongly as you deform the cell
4) if a "micro short" has been created, there will be an increase and decrease in cell potential as the short "burns out" or "grows". This is reflected in changes to the DC potential and shows up as an AC signal.

So for a damaged pack, put on the DDM on AC and see if there is a signal. If there is a signal that lasts more than a few seconds, you have "micro short" activity going on. Get that pack to the "safety ground" and leave it alone. Only if it shows zero AC volts for a couple of days would I consider recharging and testing it.....and then watch it like a hawk.

NOTE: I am still on a path to complete R.D. Blakelee's testing of the Ammo Cans as a holder for LiPoly. I have just been short on funds to buy a 1,000 PSI transducer (they are a couple $100 bucks a shot). Anybody know where a couple could be picked up cheaply? I would be very interested in knowing how much pressure a "vent and flame" LiPoly can present to a closed container. I dare say that closed containers are what most of us use to keep our "stash" of 10-20 LiPoly's that we use. Mark's 10s2p pack is a stark reminder that we have to assume that the battery can go up at any moment.
Crazy Ted -- trying to keep the lip on battery charging.
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Old Jun 22, 2005, 04:56 PM
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Quote:
Originally Posted by tjcooper
My "guess" about 18.5 volts/cell is that is the max at FMA/Kokam that they could test the unit on conventional chargers.
A variable voltage/current power supply makes a perfectly good charger for LiPo cells, and you can get one that does way more than 18.5V pretty cheap. I can't imagine that a big company like Kokam would be constrained to 18.5V for lack of an adequate charger.
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Old Jun 22, 2005, 06:30 PM
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Quote:
Originally Posted by Dave Hederich
A variable voltage/current power supply makes a perfectly good charger for LiPo cells, and you can get one that does way more than 18.5V pretty cheap. I can't imagine that a big company like Kokam would be constrained to 18.5V for lack of an adequate charger.

This is how I read it.
If you charge a cell that starts at <4.2v it will puff & vent (without flame) as it (the cell voltage, not the charge voltage) approaches or exceeds 18.5v.
Kokam used a 12v(?) car battery in the link Charles gave so the charge voltage should have been over 13v(?) when the circuit was open.
What happens after 18.5v shouldn’t be an issue. Because after it puffs and vents it’s no longer a battery, just a shorted or open circuit lump of wasted money.
Most true lipo chargers would safely shut down if they sense an open or closed circuit.
Now, if you hit the post-vent lump with a high amp, high voltage burst “after” it has safely vented and goes to 0 volts, who knows what would happen?


Jim
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Old Jun 23, 2005, 07:46 AM
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Jim, interesting interpretation. Electroman has just responded in the thread on the Kokam forum that breakdown of the electrolyte in these cells is postponed to 18.5V versus about 6.5 V for other LiPos.
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Old Jun 23, 2005, 07:58 AM
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Interesting statement from that reply of electroman's:
"The resultant "hot spot" may be hot enough to ignite the finely powdered lithium and thermal runaway commences and can only be stopped by starving the fire of oxygen."

New chemistry I guess.
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Old Jun 23, 2005, 08:12 AM
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There is a bit of salesmenship in all of us but this is the kind of statement which I find very misleading.

http://www.rcgroups.com/forums/showp...14&postcount=2

Fourth paragraph:

Quote from electromans post:

The attached data from recent independent tests in the UK is revealing of this issue. If, e.g., a KOK 200/15C cell is run continuously at 20 amps, cell temperature reaches 131 Deg F. Competing cells can not be run safely at 20 amps and will be damaged at anything above about temn amps even though rated at 10C by the vendor.
____________________________________________
___

I guess that electromann left a 0 out and meant 2000 versus 200 however the statement suggests / implies that other 2000 cells are not capable of 20 amp. continuious output without damage. and that in addation they are only capable of 5C (10A) continuious output without being damaged.
It would be interesting to read his difination of being damaged as I know for a fact that I have tested many Thunder Power LiPoly cells at 10C and greated without any damage that I can tell. I have flown them at greater than 5C many flights witout any apperat damage. I have also used and tested E Techs ,PolyQuest , iRatesTanics and Apogee at greater than 5C without damage.

Now it could be that by competing cells he means some of the Generic low price wonders which show up every few days.

Charles
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Old Jun 23, 2005, 10:12 AM
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I always assume a certain percentage of each vendor message is marketing, and try to filter that out and look for the data that's most relevant to me. I think a discussion that's purely focused on how and why these new cells react differently from other cells in different scenarios would be quite interesting. But there's a tendency for these types of discussions to range far and wide and not stay focused.
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Old Jun 23, 2005, 10:20 AM
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Quote:
Originally Posted by Dave Hederich
I always assume a certain percentage of each vendor message is marketing, and try to filter that out and look for the data that's most relevant to me. I think a discussion that's purely focused on how and why these new cells react differently from other cells in different scenarios would be quite interesting. But there's a tendency for these types of discussions to range far and wide and not stay focused.
Agreeded however some use smoke and mirrors ( charts which few could understand) ,more so than most.
I agree on that point as well but it would appear that electroman does not wish to let the cat out of the bag so unless or until users can provide indenpendant data I guess we will just have to wait.


Charles
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Old Jun 23, 2005, 01:53 PM
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Quote:
Originally Posted by Dave Hederich
Jim, interesting interpretation. Electroman has just responded in the thread on the Kokam forum that breakdown of the electrolyte in these cells is postponed to 18.5V versus about 6.5 V for other LiPos.
Quote:
Originally Posted by electroman
A reminder to all: the Kokam 4th Gen HDR cells do not ignite and burn the way older cells do. THey can handle up to 18.5V over charge without igniting. When you do over charge, they still swell and can vent, but do not flame.
Yes, the answer was more confusing than the question about the confusing previous answer.
In a strange kind of way, it answered the question.
lipo's contain "finely powdered lithium", and metallic lithium will burn.


But my question still remains.
Can the cells vent (with flame) when using a normal lipo charger, that would shut down when it sees an open or closed circuit?
The quote above leads me to believe they cannot.

Jim

PS.
My interest is in finding a more crash resistant lipo anyway.
I can control my charges.
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Old Jun 23, 2005, 02:27 PM
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See my comments/questions in the Kokam group. Li-Ion/Li-Po's never contain metallic lithium...


You can get trace amounts of metallic lithium by a "plating" action on the carbon (or other material) cathode during an overcharge.

This tiny amount of metallic Lithium could provide the "spark", but it is certainly not the cause of the big fireballs we all love!


Fun!
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Old Jun 23, 2005, 07:49 PM
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Quote:
Originally Posted by sneu
New "Kookem Pyro Light 400,000 BTU" Lithiums!

Here is a picture from this today at our field after a crash of a helicopter. 20 minuters later this started.

Steve
Hi Steve,

that small fire looks not so dangerous as the "italian land mines" from last year.
;-)

Best Regards,

Ulf
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Old Jun 23, 2005, 10:58 PM
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Quote:
Originally Posted by tjcooper
...NOTE: I am still on a path to complete R.D. Blakelee's testing of the Ammo Cans as a holder for LiPoly. I have just been short on funds to buy a 1,000 PSI transducer (they are a couple $100 bucks a shot). Anybody know where a couple could be picked up cheaply? ...

http://rocky.digikey.com/scripts/Pro...&M=13C1000PA4K
http://rocky.digikey.com/WebLib/Sens...C%20Series.pdf
http://dkc3.digikey.com/PDF/T052/1505.pdf
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Old Jun 24, 2005, 12:07 AM
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Competing cells

Quote:
Originally Posted by everydayflyer
There is a bit of salesmenship in all of us but this is the kind of statement which I find very misleading.

http://www.rcgroups.com/forums/showp...14&postcount=2

Fourth paragraph:

Quote from electromans post:

The attached data from recent independent tests in the UK is revealing of this issue. If, e.g., a KOK 200/15C cell is run continuously at 20 amps, cell temperature reaches 131 Deg F. Competing cells can not be run safely at 20 amps and will be damaged at anything above about temn amps even though rated at 10C by the vendor.
____________________________________________
___

I guess that electromann left a 0 out and meant 2000 versus 200 however the statement suggests / implies that other 2000 cells are not capable of 20 amp. continuious output without damage. and that in addation they are only capable of 5C (10A) continuious output without being damaged.
It would be interesting to read his difination of being damaged as I know for a fact that I have tested many Thunder Power LiPoly cells at 10C and greated without any damage that I can tell. I have flown them at greater than 5C many flights witout any apperat damage. I have also used and tested E Techs ,PolyQuest , iRatesTanics and Apogee at greater than 5C without damage.

Now it could be that by competing cells he means some of the Generic low price wonders which show up every few days.

Charles
Yes, Charles, my 71 year old fingers make a typo once in a while at midnight and after, but I can always rely on you to catch them, can't I? I did proofread your post, but don't have time to correct the myriad typos. Let's be very clear about that data you are referring to in my post. It is attached and comes right straight out of the files from www.trextuning.com. I believe you can read the names of those cells tested, either from the chart or from Trex reports. Every one of them comes from Asia. Read the very professionally done reports; they say the same thing in narrative. Stopping a test when the cell reaches 90 Deg C is just common sense. You can plot it yourself. Yes, you are right, you can pop a TP to 10C momentarily, but if you run continuously at 10C=21 amps as in the subject tests, the cell get hot enough to create damage and cycle life will be very short. At the same time, you can pop a KOK 2000/15C to 40 amps for no more than 3 sec without harm. Facts and real, independent data are meaningful; data from an independent source.

Objective test data shows that running LI Pos, even Kokams, at temperaturs above the operating limit line shortens cycle life to as little as 25 cycles as is being reported periodically. Our objective is to help everyone be successful with Li Pos and it is self evident that keeping the packs cooled and keeping the load within a safe operating range is important to that success. Just today, as part of our on-going quest to make Li Pos as safe and practical as can be done, it has been confirmed by running cells water cooled that it is over-temperature that comes from poor cooling and/or cell overload that shortens cycle life. KOK 3200 cells were run in continuos runs at 64 amps for 250 cycles when so cooled. Running those same cells uncooled at 64 amps continuously cause temperature rise to over 150 Deg F and shortens cycle life.

Your lack of objectivity is evident in your slanderous statement that relating those facts is misleading salesmanship. What is misleading and unfair is making unsubstantiated claims about running those cell at 10C and ignoring that they get so hot you can't touch them. Isn't it interesting that running them in a professional lab with professional people and professional equipment shows results so different from your subjective assessment? It is the facts you left out that really matter because they may lead an innocent newbie to make a mistake.
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