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.
In my humble opinion, all the manufacturer ratings are 'guidelines' or relative comparisons at best, and total bunk in other cases.
I use a battery analyzer to put a constant 100 or 150W load on the battery and plot voltage (and energy) for each pack. The results don't always match expectations, but should directly equate to hover time. I really like constant-power, since it accounts for the decreasing voltage under load and over time, as do our copters.
For example, my Turnigy 6000 mAh 3S pack was not worth the extra money and doesn't live up to its label. The Zippy 3S were 5000mAh and performed just as well.
One thing to also consider is the voltage curve with higher discharge batteries. I like to run higher C batteries on all my aircrafts as it keeps a more consistent voltage output and doesn't get "soft" towards the end of the flight. I wouldn't go less than 30C on my aircrafts and for my 3D planes I don't go less then 45c.
Just my 2cents
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!
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