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Old Jun 21, 2005, 03:01 PM
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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!)
The new kokams will burn like any other Lipo it just takes higher voltage to light them off. The electrolyte is still flammable.

Chuck
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Old Jun 21, 2005, 03:17 PM
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Quote:
Originally Posted by rcelectfly
The new kokams will burn like any other Lipo it just takes higher voltage to light them off. The electrolyte is still flammable.

Chuck
Based on your first hand experience?


Please explain the test pictured here which shows out gassing but no flame..
http://www.rcgroups.com/forums/showp...84&postcount=3


Charles
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Old Jun 21, 2005, 03:19 PM
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"higher voltage"?

Quote:
Originally Posted by rcelectfly
The new kokams will burn like any other Lipo it just takes higher voltage to light them off. The electrolyte is still flammable.

Couple of things:

- What do you mean by "higher voltage"?? It looks like they're putting 12V, at God knows how many amps, through a single cell, you can't get much higher than that!!

- Does anyone have photos, video, etc. of a new Kokam actually burning due to an overchage/short?



I'm always suspicious of unsubstantiated claims...
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Old Jun 21, 2005, 03:47 PM
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Originally Posted by electroman
A major feature of the new Kokam 4th generation HDT cells is that the chemistry and design permit the cells to handle over voltage up to 18.5V/cell without igniting. When the cell does vent, it generates hot gas and smoke, but no flame.
If these cells are only claimed not to be subject to venting with flame when charged at 18.5V per cell or less, then they must be subject to venting with flame when charged at 18.6V per cell or more. Otherwise, why would they not claim that these cells can never vent with flame under any circumstances?

It would take a more thorough technical explanation to fully understand the process. However, the reality is that a single LiPo cell is highly unlikely to ever be exposed to more than 18.5V in any real world RC situation. Therefore, if this is all accurate, these cells could be called virtually fireproof under charging conditions that could reasonably be expected to occur in an RC environment.

This does not address the issue of what sets of circumstances outside of charging could cause them to vent with flame, such as physical damage causing internal shorting, etc.
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Old Jun 21, 2005, 04:11 PM
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Quote:
Originally Posted by everydayflyer
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
I saw that post charles but I wouldn't consider that "promoting". Do you? I think it would be promoted in the RC magazine Ads, on the Kokam vendor sites and especially on the FMADirect website? There must be more to the story.
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Old Jun 21, 2005, 04:21 PM
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Originally Posted by hoppy
I saw that post charles but I wouldn't consider that "promoting". Do you? I think it would be promoted in the RC magazine Ads, on the Kokam vendor sites and especially on the FMADirect website? There must be more to the story.
Well he did chose his wrods with care.
Note the Post Title
Resistance to Li Po ignition.
I read only Model Avaition and RC Reports rags.
I would think there would be a Banner on the FAM Direct site but then perhaps more would try to prove otherwise. The world is full of critics,Lord knows I do my part. I once read that after claiming 2C charge capable cells others experienced vent with flames whiule so charging.
Charles
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Old Jun 21, 2005, 06:39 PM
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Quote:
Originally Posted by meteor
Couple of things:

- What do you mean by "higher voltage"?? It looks like they're putting 12V, at God knows how many amps, through a single cell, you can't get much higher than that!!

- Does anyone have photos, video, etc. of a new Kokam actually burning due to an overchage/short?



I'm always suspicious of unsubstantiated claims...
They will ignite at voltages above 18.5. FMA only claims that they will not ignite below 18.5 volts.

If they would not ignite at all then they would say that intheir advertizing.

Chuck
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Old Jun 21, 2005, 06:50 PM
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Quote:
Originally Posted by rcelectfly
They will ignite at voltages above 18.5. FMA only claims that they will not ignite below 18.5 volts.

If they would not ignite at all then they would say that intheir advertizing.

Chuck
Do you have video or photos of them igniteing at wahtever volts?
It would seem to me that is they vent and do not flame then the gases which are being vented are not flameable. Electromn did not state they would not ignite.Read his post ,read the title.
If they will ignite at 220 volts then that still makes them safer than ones which ignite due to being charge with a charger set one cell to high. I am not a Kokam fan/supporter but fact are facts.The photos show what appears to be much safer LiPos. If the test was fake or you have other proof then I would like to see it.
I guess if you supply enough electrical enery to anything it will melt. An Arc Welder will melt a stell rod. I never had a piece of steel catch on fire while I was welding it.

Charles
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Old Jun 21, 2005, 07:40 PM
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The key question is, what's so special about that 18.5V limit? Why would a vendor claim that one of their cells will not vent with flame when being overcharged at rates up to 18.5V, but not make the same claim at 18.6V and above? What happens at 18.6V that's so different from 18.5V?
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Old Jun 21, 2005, 07:47 PM
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In FMA's defense, I think that they are simply being conservative...


It's plain common sense; if they essentially guarantee that their cells won't burn at 18.5V, it's extremely unlikely that they suddenly burst into flame 1/10V higher!


It would be useful to see what level of abuse is required to get ignition, as it were.

Although this might seem counter-intuitive, it would actually strengthen people's faith in their claims to see a failure, outside of the accepted parameters.



Good stuff!
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Old Jun 21, 2005, 08:09 PM
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Quote:
Originally Posted by Dave Hederich
The key question is, what's so special about that 18.5V limit? Why would a vendor claim that one of their cells will not vent with flame when being overcharged at rates up to 18.5V, but not make the same claim at 18.6V and above? What happens at 18.6V that's so different from 18.5V?
What is the maximum voltage of thier Super Nova Charger?
Perhaps that is why he listed that voltage. I still contend that if the gases vent witout flames then they are much safer than most.


Charles
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Old Jun 21, 2005, 09:46 PM
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Quote:
Originally Posted by everydayflyer
What is the maximum voltage of thier Super Nova Charger?
Perhaps that is why he listed that voltage. I still contend that if the gases vent witout flames then they are much safer than most.


Charles
Nope, that's not it, the SuperNova is Nicad, Nimh, and Pb only, no Lithium.

The maximum cell count for Nicad, Nimh is 25 cells which would peak out at around 37.5 v.

Brad
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Old Jun 21, 2005, 09:53 PM
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Quote:
Originally Posted by bjpaul
Nope, that's not it, the SuperNova is Nicad, Nimh, and Pb only, no Lithium.

The maximum cell count for Nicad, Nimh is 25 cells which would peak out at around 37.5 v.

Brad
OK ,what is the max. allowed with there Li Po Charge Guards.? You know I hate to go to their site ,I get nauseous every time I do.

Does it really matter? 8.4 volts per cell would be charging at twice the actual cell count.If someone is that careless they truely should not be alowed to use LiPos.


Charles
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Old Jun 22, 2005, 07:17 AM
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Quote:
Originally Posted by everydayflyer
I still contend that if the gases vent witout flames then they are much safer than most.
There is no question that if they perform as advertised that they represent a great leap forward in LiPo safety. It's just that the details are really sketchy at this point. For example:

* What is the ignition source that results in the cell possibly venting with flame at charging voltages >18.5V but not <18.5V? Is it that higher charging voltages are required to drive the cell into a thermal runaway condition?

* What exactly is it that ignites in these cells when they do vent with flame at >18.5V charging rates? Is it the gases that vent at lower charging rates that ignite from a source of ignition that may be produced at >18.5V charging rates? If the gases that vent are flammable, how concerned do users have to be about potential ignition of those gases by an external source?

Since these cells are not advertised as 100% safe, it will be important to understand the threshold and mechanism at which they become less safe so that these points can be avoided. So far we have seen a vendor description of how these cells are designed to fail when accidently charged at 18.5V or less. I've seen no vendor description of the failure mode in the unlikely circumstance that they should accidently be charged at >18.5V.
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Old Jun 22, 2005, 07:58 AM
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Well this seems rather pointless. If I play the critic the I am bashing Kokams. If I have something positive to say about theri new cells that to is questioned. This announcement(post) by electroman was posted several months ago. Kokam has a Vendor Forum. I guess those who want to know more should question electroman directly. It is kinda surprising he has not show up here. Perhaps they explode if chared at greater than 18 volts per cell but I do not have a charger capabile of going that high on anything over a 2S packs and since many use a max 4S charger even a 2S pack is well within this limit of SAFETY(?).

Charles
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