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Old Jun 24, 2005, 01:40 AM
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Toronto (Don Mills), Canada
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Interesting stuff on the TREXTuning site.
The TP pack tested was a 4S 2000, vs a 3S Kokam.
The TP is still lighter by 5 grams. At 10C The TP had 40% higher energy density ( WH/kg). The TP pack had a delta T of 50 degrees C, vs 31 degrees C for the Kokam.
It could be argued that one reason that the TP runs hotter is that it's lower mass results in a larger temperature change for a given amount of energy absorbed ( CMdeltaT).
The Kokam pack also has about 20% more surface area which would help in the dissipation of heat.
Pat MacKenzie
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Old Jun 24, 2005, 04:06 AM
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IA-Flyer's Avatar
United States
Joined Nov 2003
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Quote:
Originally Posted by electroman
<snip>
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.
<end snip>
Hi Fred,

I have a secondary question.
It’s not related to fire resistance, but the storage and use of the new stronger cells.
Specifically answer #4 (in the reply to meteor, in your forum) about the state change that can happen when LiCo 02 is stored discharged.
Some of us have been using a higher cutoff voltage (3.2-3.3v), to leave some capacity remaining at the end of a flight in an attempt to extend lipo life, and avoid the area of temptation below the knee.
Personally, I try to operate them between 3.7 & 4.2v OCV.

What is Kokam’s suggestion for the best short-term, and long-term storage “voltage” for the new formula?


Thanks
Jim
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Old Jun 24, 2005, 08:17 AM
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Haralson County GA. USA
Joined Oct 2004
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Quote:
Originally Posted by electroman


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.
I was an innocent LiPoly Newbie last June when I was mislead by the statement that Kokams were the Gold Standard and wasted money purchasing over $400 worth of overweight,underporforming packs.

My cells /packs ran in flight 10C or any other C do not get above 128F to the best of my knowledge. I have always stated that running discharge test on LiPolys without cooling was not advisible or practicle. There is cooling air available during flight and would not be wise to not use it. I ran CBA Test on some cells without cooling which did reach 160F but I could still touch them in fact I could hold them without any problems.

It would be interesting to see how many Tanic,Apogee,E Tec,Thunder Power,DuraLite ,LiPoly users you could get to agree that non of the Packs they use are capable of being used above 5C without damage, as you stated in your statement.

Newbie seeking help with Kokams

Changed to Tanic and problems solved..

Charles
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Last edited by everydayflyer; Jun 24, 2005 at 08:26 AM.
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Old Jun 24, 2005, 09:31 AM
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sneu's Avatar
United States, CA, San Diego
Joined Dec 1999
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Quote:
Originally Posted by Ulf Herder
Hi Steve,

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

Best Regards,

Ulf

The " land mines" were quite the thing! The fire from these cells was much "hotter" Did you see the "american welders" in York? That was nearly as nice as the Italian one!


Steve
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Old Jun 24, 2005, 09:38 AM
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I was going to list all the summaries but it's getting very long and it's easier to just go to the trextuning site and read them
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Old Jun 24, 2005, 10:43 AM
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USA, FL, Apopka
Joined Dec 2000
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I went to the T-REx site http://www.trextuning.com/ and read through the tests and found them to be very informing. My observations are:

1.) We need to pay better attention to airflow cooling of our packs especially now that it is summer.

2.) No manufacturer seems to be taking into consideration the heating of middle cells in our packs.

3.) The Gen 4 Kokam cells handle temperature rise very well but have a weight penalty.

4.) The TP ProLites are very light but will have a heat problem if not well cooled by airflow.

5.) Polyquest is somewhere in between the TP ProLites and the Gen4 Kokams and is a very good alternative.

6.) Wow, what happened with the Tanics?

The tests by Mark Hopkins seem to be very professionally done and to be what many of us have been begging for, an independent tester that could perform the tests under labratory conditions. I have bookmarked his site and plan to refer to it often.

Brad
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Old Jun 24, 2005, 02:06 PM
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Walled Lake, MI, USA
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The fact that lighter weight LiPos have more of a problem with heat than heavier weight cells may only be applicable in this single comparison, or it may be preliminary evidence of a general trend. The truth should come out as more evidence is gathered.

Previously, heavier LiPo cells have been considered inferior to lighter cells in every way. In fact, it is possible that heavier cells may have internal components that provide undocumented and yet-to-be-measured benefits. Simplistic measurements of complex systems often produce misleading results. It's possible when all the facts are known that there may be good reasons for many people to choose the heavier of two LiPo cell options. But this will require understanding all aspects of LiPo performance rather than just a few.
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Old Jun 24, 2005, 04:57 PM
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Gaithersburg, MD, USA
Joined Jun 2000
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Cut off

Quote:
Originally Posted by IA-Flyer
Hi Fred,

I have a secondary question.
It’s not related to fire resistance, but the storage and use of the new stronger cells.
Specifically answer #4 (in the reply to meteor, in your forum) about the state change that can happen when LiCo 02 is stored discharged.
Some of us have been using a higher cutoff voltage (3.2-3.3v), to leave some capacity remaining at the end of a flight in an attempt to extend lipo life, and avoid the area of temptation below the knee.
Personally, I try to operate them between 3.7 & 4.2v OCV.

What is Kokam’s suggestion for the best short-term, and long-term storage “voltage” for the new formula?


Thanks
Jim
Jim,
You will find the answer to your question at

http://www.rcgroups.com/forums/forum...ysprune=&f=220

under Li Po Cut-off and storage where it will not slide off the page in a few hours.
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Old Jun 24, 2005, 05:11 PM
Space Coast USA
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http://www.batteryuniversity.com/parttwo-34.htm
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