Hello,
In continuation of selecting the best motor for my X8 (Octo coaxial) build for video/photography (see post here : http://www.diydrones.com/group/arducopterusergroup/forum/topics/tiger-motors-propellers-combinations-for-an-heavy-lift-octocopter),
I must now compare and select the best battery in 6S votlage. I collected some information on various web site to compile a comparison for three categories of 6S batteries based on capacity : 5000 mah, 6000 mah and 8000 mah. I intend to fly with two packs in parallel, so I did not care to analyze bigger capacities like 10.000 mah , also because they are hard to find in these common brands : Zippy, turnigy nanotech and Kypom (i limited the comparison to these three brands because they can be found quite easily online in Europe and in the US, thanks to the Hobbyking web site, the onlylipo.com web site and the altigator.com web site, etc).
I defined five criteria as follows:
-price (in euro)
-weight (in grams)
-power density 1 (capacity in mah divided by total weight of battery). Higher is better. You get more capacity per gram.
-power density 2 (capacity in mah divided by total price in euro). Higher is better. You get more capacity per euro.
-Compacity. This is the biggest dimension of the battery in mm. Smaller is better. I chose only to compare on the biggest dimension because this is the constraint of my craft (battery holders are max 170 mm long in my design)
And the winners are :
-In the 5000 mah category : Zippy 30 C. It is best on 3/5 of the criteria and second best on 2/5 of the others in an unsignificant manner.
-In the 6000 mah category : Zippy 30C (again). It is best on 4/5 ot the criteria and second best on 1/5 of the others in an unsignificant manner.
-In the 8000 mah category : guess what... Zippy 30C (again again). It is best on 3/5 of the criteria and second best on 2/5 of the others.
Unless Zippy batteries are bad quality, Zippy seems to be a great battery. I would like people who have experienced Zippy batteries to give here in this post their testimonials about their quality and durability ?
Replies
Found a LIPO battery with potentially 40% more gravametric energy density.
Most all battery makers use long rectangular shapes for each cell. Thus each cell has to be wrapped in foil making the containment of the LiPo extremely heavy. I've been searching for someone that makes a cubic LiPo. Found one that comes close producing potentially 40% better results.
Kayo makes a 2300 mAh battery TRS804260 that is their most cubic shape. You have to connect the cells in a series, but so what. That's easy. Each cell weighs 42.3 grams for a gravametric energy density that exceeds 200 mWh/g (versus Turnigy Nano's best at 145).
If you are interested, contact Mike Sang at mikesang80@gmail.com
I haven't had a chance to test the battery but see no reason why it won't perform. I apologize for not being jack on the spot on these tests but got side tracked working a higher priority multi-copter project. I have many promising batteries and a battery tested all waiting to be used and tested. But none are more promising than this particular Kayo.
Conditioning a LIPO:
did something unusual. read the directions :-) The Venom battery actually came with instructions (in 5 languages, none of which were Chinese). That was impressive. Here are the interesting parts:
o may require 12 or more charge/discharge cycles to reach full potential
o during break-in time, keep discharge rate to less than 7C (explained this way)
- where C = battery pack mah/1000
- so a 3000 mah battery should not be discharge greater than 21 amps
- so on a 30C battery, during break-in do not exceed 7C! [how many of us have bloated batteries because we didn't know that]
o never discharge greater than mfg discharge rate (explained this way)
- where Rate = battery pack mah/1000 x C rating
- so a 3000 mah 30C battery should not be discharged (after it is broken in) greater than 90 amps
Battery temperature is critical (gives a wide range of charge and discharge temps so no issues there) but:
- store between 40F to 80F (4C to 26C)
- if cold outside warm the pack first to 100F (37C) [found that interesting]
There you go. Now if I can just find the lingerie store without asking for directions :-v
Estimating Amp Discharge Rate
To create a fair test, one needs to calculate the discharge rate of the ship per different battery load combinations. For example, if it carries 15000 mAh of batteries, that could be two 7500, three 5000, four 3700, or five 3000 mAh batteries. So when testing these batteries to see which is the most optimal, the discharge rate is going to change based on total amps divided by the number of batteries.
The following chart shows how total amps is calculated for the X2 Black Momba.
So when testing the 5000 mah batteries, the discharge rate will be set to 26.1 amps x 11.1 volts / 3 batteries = 96 watts. For the 3000 mAh batteries, the discharge rate will be set to 26.1 x 11.1 / 5 = 58 watts.
My 4000 turnigy's are crap - 30 cycles at 1C balanced (every time, without exception), and they're more circular than square.
I hava some 100c maxamps, and they are lasting much better. Even landing at 3.6v (idle) my 10900mAh still takes 9500, so should exceed the stated capacity easily. Mind you, at $400 you would expect it to be good...
The Venum just arrived. Sure enough, it's design is more cubic, minimizing heavy Al skin surface area for the amount of LiPo chemical containment. It is even lighter than advertised (550g) and came in at 541.6 grams. Looks promising but only the test will tell.
Waiting for a few more batteries and the discharger before the tests begin.
AGA Batteries - If LIPO is LIPO then the only way to improve it is to:
o make the battery more cubic so the surface area is less (since a significant portion of weight is the Al skin and wrap)
o make the wiring lighter (shorter thus thinner connections)
AGA might do the first. The battery might be more cubic. I'm think one should be added to the test.
I have a 5Ah 4S Zippy compact which now after about 40 cycles is down to about 2.6Ah and puffs well 15% while discharging. When it cools down, it unpuffs, but I'm still not impressed. The bat is retired now and probably will find itself at the end of our 100m outdoor range for some target practice soon...
I've detroyed 2 2200mAh Turnigy batteries, and the 1 Nanotech 2200mAh just keeps rocking. nanotechs seem to last for more cycles,
If you want to decide which is the best brand to go for, buy comaprable batteries and then do comparitive tests for voltage sag, power cycles etc... It would be interesting to see the results.
At college some students did aome testing of AA batteries to see the difference in brands, and the surprise was that not only the brand, Duracell in this case, last the longest, but ones made in Belgium where best!
@Eric, about the C rating I did my selection based on the max amps I need which is less than 100 amps. Therefore even a 25C at 5000 mah would be enough. Since I plan to fly with two batteries in parallel, I am OK. Actually, taking lower C batteries will save not only on price but also on weight,therefore extending my flight duration.
@Forrest, the data comes from web sites. I only tested nanotech 4500 mah at 4S. I also tested a kypom 6600 mah at 4S.
Nice to see your table, it shows also zippy batteries as quite good.
We really need to testbench some of those! I am going to buy two 6S for a start. Still hesitating between 5000 and 5800 man.
Here is my data. Caution. Most of the data is taken from seller sites. My first experience with Zippy was that they were off by 12 grams (heavier) so don't know if they are inaccurate of not weighing the wire/plug. Also, capacities are only approximations and would need to be actually tested. The weight savings column is relative to the Turnigy Nano Tech 3S 3000 mAh. This was done in the early stages of preliminary design to gestimate the relative performance of 2S versus more cells (which only 2S proved to be an issue). 3S and up was all about the same.
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