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Old Jul 30, 2009, 01:55 PM
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Data
WHAT LIPO - Independent Lipo Tests

COMPARISON OF 4 x 20C and 4 x 30C RATED 3S 2200 LIPO PACKS

There have been several long threads about the relative merits of various lipos and most of the contributions are based on modeller’s experiences. Inevitably much of the contribution to such threads must be subjective, however well intended. It was suggested some time ago that I should run objective tests on lipo packs from several different makers and compare the results.
I am an active modeller, but completely independent and receive no payment from anyone.
The 3S 2200 pack format was chosen as the most popular type and eight different packs have been tested in two groups of four. One group is for 20C rated packs and the other for 30C rated packs.

To avoid attacks from various quarters I am not putting my opinions in the report, just specifying how the tests were carried out and publishing results that were obtained. The reader should, from the notes below, decide on what he considers the most important criteria on choosing a pack and compare the results obtained in the tables from the various packs.


NOTES ON RESULTS.

Trying to choose a pack just by asking other modellers or seeing a model fly is impossible because there are too many variables such as model weight, motor, prop, ESC programming, temperature etc. Add our individual prejudices and brand loyalty and, as Basil said in Fawlty Towers, “You might as well ask the cat”. In these tests the packs are all discharged at maximum rated current down to 3.00V/cell under identical conditions.
This full rated constant current discharge that the packs are subjected to is more severe than they are likely to see in practice, but it is a consistent, flat-field measurement of the pack’s ability to deliver their claimed performance. They are only subjected to the max rated load conditions specified by the manufacturer, starting from a fixed ambient temperature of 25 deg.centigrade.
The pack voltage and temperature is measured at 15secs, at the 50% nominal discharge point and at the end of discharge. The pack ESR (Effective Series Resistance) is measured at 25deg. and the total Ah and Watt.hrs delivered by the pack are both recorded.

(1) PACK VOLTAGE – The higher this is at any point, the better, as it means the motor will deliver more power. If the ESR is high then the initial voltage on load (say at 15Secs) will be lower, and this will continue throughout the discharge, but at a reducing level as the internal heat dissipated in the pack will reduce the ESR and the voltage drop due to it.
(2) TEMPERATURE – High temperature is the killer of a pack, but it is very difficult to quantify Life v Temperature in an equation. It is not linear and a small increase in temperature is likely to shorten life considerably, particularly near the higher limits.
Electrolytic capacitors, which are electrochemical devices not unlike rechargeable cells, show a halving of their projected life for every 10deg.cent. rise in temperature.
If you are looking for a long life pack, then look for low temperatures.
The surface temperature rise over the discharge is quoted at the end of the results. I have made a nominal 55deg. rise the maximum I consider acceptable, equating to a max. surface temperature of 80deg. starting from an initial figure of 25deg. Even this figure is only a guess and may be much too generous, as the internal cell temperature will be higher, but cannot be easily measured. There are other factors affecting pack life, such as QC and electrochemistry of the pack but I have no way to quantify them.
(3) ESR - The voltage drop of a pack and the heat generated in the pack due to load current is a direct function of ESR and we should be looking for the lowest value. It is very temperature dependant and the very different figures shown at 25deg. tend to converge at higher temperatures.
(4) Ah – The Amp.hrs delivered by a pack is compared with its rated capacity and quoted as a percentage. The manufacturers figure will be at 1C so at full rated current anything over 90% is acceptable.
(5) Wh – Watt.hours is a true measure of stored energy delivered by the pack. A lower voltage under load will reduce this figure. Note that the packs with lower voltages deliver lower W.h figures.


GENERAL

I carry out the testing with an open mind and operate on a flat playing field, but I only test one sample of each pack and therefore cannot account for production spread. There must inevitably be some tolerance in all the parameters of each pack but the poorer performing will always say that their sample must have come from a bad batch; it is a standard excuse I have heard several times.

The above testing only demonstrates the ability of the packs to deliver their stored energy. It would be nice to compare pack life which many users are interested in, but that would involve running 100 or more cycle tests on each pack. I have access to the necessary equipment but not the inclination to carry out such testing due to the time and effort involved in such an exercise. As a short cut to the likely life of a pack I would suggest that temperature rise is the best indicator to look at.

I should make it clear that the above only tests the performance of the packs, there may be quality aspects of which I have no knowledge which may affect the life of the packs apart from the damaging aspect of excess temperature rise. If there is not then the old adage “You get what you pay for” definitely does not apply to lipo packs.

Having said all the above and despite their safety problems, lipos really are a fantastically efficient energy storage device, having tremendous power delivery/weight ratios and have transformed electric flight over the past year or so. Electric helicopters and 3D flying were unthinkable a few years back, whereas now they are commonplace.

SEE ATTACHMENTS FOR RESULTS TABLES

Wayne Giles

PS Sorry for second post - intended to class as DATA first time
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Last edited by Wayne Giles; Jul 30, 2009 at 02:24 PM. Reason: Should be classed as DATA
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Old Jul 30, 2009, 03:06 PM
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Thanks Wayne - very good data. There are some superb price/performance lipos available presently!

Ron
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Old Jul 30, 2009, 05:03 PM
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thanks for the testing!
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Old Jul 30, 2009, 07:22 PM
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Yes, thanks for doing these tests.
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Old Aug 02, 2009, 10:58 PM
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Are you going to test other packs? I'm surprised this thread hasn't gotten more attention since the results are shall we say, eye opening.
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Old Aug 03, 2009, 10:18 AM
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Hoppy,

Have done several other tests, but the problem is cost of the packs as I am not inclined to buy new packs I don't need just to post a test, when, as you accurately say, the results are often ignored/overlooked. Most manufacturers will not supply packs as they don't want to see independent results published - you can see why from the above results!!!
Bob Smith, who wrote much in the UK, was invited by a major UK magazine to write two articles on Lipo life and he did all the work and submitted the results, but the articles were suppressed by commercial interests. You can still however find these results at http://www.geocities.com/gbobs7/INDEX.HTM Look at "ART1" and "ART2". I wondered about repeating and updating the excercise but it is a lot of work, as I only do it as a hobby.
If you dig around sensibly you can find out the truth; the extra money for expensive packs is generally spent on adverts and publicity, so it does not improve the pack!
An agent in the UK sells the best performing pack in my 20C tests and says they are "suitable for light to medium use". He also sells Hyperion and Thunderpopwer at double the price. I sent him test results but he just did not want to know. Perhaps the facts are not convenient for him!

Wayne
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Old Aug 03, 2009, 10:50 AM
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Those are really valuable test results. The trouble with the subjective info gleaned off line is the incredible variation in knowledge and field testing being carried out.
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Old Aug 03, 2009, 11:11 AM
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Interesting tests... You will always have some variation in packs, but you can hardly test 10 each (Kokam 2100 and Graupner 2100 are identical cells in Bob's test, results - abit over 3 and almost 5% loss over 100 cycles. Still confirms that Kokam cells last many cycles....) Hopefully there's more to come...
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Old Aug 03, 2009, 02:43 PM
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Thank you for doing the testing and making the results available.
It makes interesting reading.

My contribution ? I use LoongMax lipos and am satisfied with them. Over 30 cycles on some of them and interested to see how long they last. Still going well at the moment.

I have downloaded the articles that were mentioned in one of the replies and now have some reading to do.
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Old Aug 03, 2009, 08:03 PM
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Quote:
Originally Posted by hoppy
Are you going to test other packs? I'm surprised this thread hasn't gotten more attention since the results are shall we say, eye opening.
I find it hilarious

It hasn't got more attention because those that are using the cheap packs already knew this. As for the TP or FP fanboy's or should I say sponsored by the over priced lipo's are staying away because they don't want it to be on the front page
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Old Aug 03, 2009, 08:26 PM
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I thought so!

Wayne, thank you very much for your time and effort! After a year of using all of the Hobby King lipo brands I suspected as much. I had been getting ripped off for the previous 3 years on the high priced "name brands". Most value conscious lipo users have discovered the quality and savings involved at HK. I wonder what the so called "experts" in this battery section are going to say! Should get interesting!
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Old Aug 04, 2009, 05:52 AM
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Quote:
Originally Posted by chribrian
I find it hilarious

It hasn't got more attention because those that are using the cheap packs already knew this. As for the TP or FP fanboy's or should I say sponsored by the over priced lipo's are staying away because they don't want it to be on the front page

Where's Charles??????????????????????????????????????????? ???????????
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Old Aug 04, 2009, 06:01 AM
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The potential disadvantage of cheap lipos is Quality Control problems, but in discharge performance terms some of the very best are the cheapest.
I have heard of a case of a reversed power connector which can be exciting and that was on a Chinese pack, but that is not to say it does not happen on expensive packs. Obviously I have no way of quantifying this.
One noticeable improvement over the last year has been the closing of the gap between claimed and actual "C" ratings. Two or three years ago it was laughable, packs claiming 20C would not safely deliver 8 - 10C. Now most will at least survive a full rated discharge although the final temperatures are dangerously high and damaging the pack and some are starting to puff.
There are still some exceptions; I recently had to abandon a 20C run on a "30C" rated pack because it was smoking! I believe this was mainly due to completely inadequate terminations at the connections to the cells.
Whoever started this wild overclaiming of C ratings has caused many modellers a lot of expensive problems.
If supporters of the poorly perfoming types respond, they will probably try to discredit the results. The usual one is:-

"If you subject the same pack to 5 tests, you will get 5 different results!"

Answer is, "No you won't!" - In a recent comparison test (not the above), two differenet make packs were so close in performance that I suspected that they were the same cells, despite the supplier's denial. So I stripped the packs down and sure enough they were the same cells, interconnected with the same coded PCB. This proves how repeatable the testing is and also suggests that there is not a wide manufacturing tolerance.

Wayne
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Old Aug 04, 2009, 08:37 PM
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Bump
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Old Aug 05, 2009, 03:48 PM
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Wimh,

Sorry I'm late but not convinced that the Graupner 2100 and Kokam2100 packs that Bob tested are the same cells. There is a significant difference in weight, which could be packaging, but the "C" ratings are different as well.
There is definitely a lot of "badge engineering" goes on in lipos (see my last post) but the differing results may be because they are different cells.
Because of the fact that some "makers" will use more than one manufacturers' cell, it is dangerous to assume that if an XYZ 3S2200 20C pack is good, that an XYZ 5S3700 25C will be equally good.

Wayne
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