The article outlines the Tattu vs
Graphene lipo battery
testing procedures we used to come up with our results and presents the
raw data gathered. Be sure to check out the actual results in our
comparison article which will be released next week!
Graphene lipo battery Background
After Bonka announced that they were entering the "graphene" market
behind Turnigy, I knew I wanted to do a comparison test pitting
"graphene" batteries against each other and their predecessors. After
contacting several battery manufacturers, I learned that pretty much
everyone was poised to introduce a new range of battery packs, most of
which are labeled "graphene". I was excited about the prospect of
comparing these "graphene" packs in total against a top-contender of the
"last generation" of batteries.
What is the Graphene?
A little background on graphene. First of all - what it is is a sheet
of carbon atoms, aligned in a 2-dimensional crystalline pattern. When
it's synthesis and handling is perfected, it could feasibly be used in
the electrodes of the battery to thin the chemical layers that make up
the battery and significantly improve both capacity and power. There is
also research going into what is called "lithium sulfur" batteries,
which use graphene as an integral component to make similar leaps in
performance over traditional lithium batteries.
One thing is certain, though - these batteries do have something
different going on with them. As you will soon see, they all have
performance figures that are eerily similar to each other, and all
differ from the "older" style LiPo I threw into the test.
The battery Tests
I performed 3 tests on these sets of batteries, outlined below.
20A Constant Discharge Test
The first test was a constant discharge to 12.8V indicated (3.2V/cell
under load). The intent of this test was mainly to see the capacity of
each battery. The load I selected was 20A - which is very close to my
average flight load when I am not racing. I hooked the battery up to my
load cell, a volt meter and my data recorder and let the battery
discharge until the voltmeter read 12.8V. I chose 12.8V because it is
well into the sharp voltage drop off point of every battery in this test
but not so low as to seriously damage the batteries - they all jumped
back up to 3.5-3.6V / cell when the load was released. After the
batteries were done with the test, they were set aside for 30 seconds
and then had their temperature measured. After that, I measured the
balance of the pack, recording the voltage difference between the lowest
cell and the top cell. Generally, when battery cells are mismatched, it
is because they have a slightly different capacity than their mates -
since this test is all about totally discharging the battery it is a
perfect time to check that. Finally, the batteries were charged back up
to full and the amount of charge put back into them was recorded.
40A Stress Test
The second test was a constant discharge to 14V indicated with a load
of 40A. The stop point of 14V in this test is well before the batteries
fully discharge - the intent was to see how much charge the batteries
could push through while holding a decent voltage under high load. 40A
is a pretty typical load when racing so I think this test is a good
indicator what batteries will hold up well for that purpose. Once the
batteries hit 14V, they rested for 30 seconds and their temperature was
measured. Finally, they were once again charged back to full and the
charge put in was recorded.
Flight Test
The final test was an in-flight test where the battery metrics were
recorded with Blackbox. The purpose of this test was to show how the
batteries performed when the pilot does bursts of full throttle during
an otherwise constant load. Here is the procedure I followed:
1.Take off, fly in a circle using the OSD to keep a constant 20A discharge rate.
2.At 200mAh indicated consumption (on the OSD) do a full throttle pull-out for 3-5 seconds.
3.Descend quickly.
4.Continue flying at 20A in a circle until 700mAh indicated
consumption, or 55% of the labeled capacity for the bigger batteries.
5.Do a full throttle pullout for another 3-5 seconds.
6.Descend and land.
What I wanted to see in this test was:
1.How much effect different batteries have on the amount of power available in a climbout.
2.How each battery handled a full power climbout when it was near-fully charged vs when it was close to being depleted.
3.How much voltage sag each battery experienced in a climbout and how quickly it recovered.
4.How an inductive load on the batteries differed from a resistive load.
Again - the original intent of this test was to use some of the
ridiculous new N52 motors to really put the fear of god into these
batteries. Unfortunately that could not happen for this test because the
motors I am using are out of stock and I don't have the funds to change
out all of my motors. I intend to re-test this when I get some new ZMX
v2s.
Disclaimer
I wouldn't recommend anyone treat their batteries like I did in these
tests. The in-flight testing is probably fine but batteries in this size
really did not like the 20A full discharge and 40A stress test. Most of
them got quite hot, especially nearing the end of the 20A test, and one
even puffed slightly. Unless you like replacing batteries frequently, I
don't recommend ever discharging below 14V indicated on a 4S pack -
your batteries are telling you that they cannot handle the discharge and
you should listen. When LiPos are stressed like this, their internals
undergo chemical changes which permanently affects their capacity and
power delivery capabilities.
The Battery Lineup
There were five
1300mAh batteries
on the block for this comparison test. Dinogy sent us their new
Graphene 2.0 packs and Tattu sent us a pre-release version of their
upcoming "Pro Pilot" series of batteries. We also obtained a Turnigy
Graphene pack and a Bonka Graphene pack for comparison as well. Finally,
we have a normal Bonka 1300 75C pack to compare the new packs against.
Revolectrix sent us a very early version of their 1700mAh LiHV "GOPack" .
I really wanted to include this pack in the test but struggled on how
to do it - none of the other batteries were this big nor were they HV.
In the end, I decided to test this battery charged to standard LiPo
voltages (that's 4.2V per cell) and included a standard
Tattu 1800mAh 70C battery in
the test to compare against. As a result, this isn't a really fair test
for the Revolectrix. I wouldn't use these results to compare it to any
of the other batteries but I do find them interesting. I'm eager to get
my hands on one of their 1350 regular packs.
For more information on these batteries, check out our comparison
article, which will be linked at the top of this article when it is
released.
The Battery Test Results
The raw data for our tests, complete with the graphs we're posting below.
20A Constant Discharge Test Results
Temperature: Measured after discharge, hottest point on battery.
Charge: Amount of charge put back into battery after test.
Cell Variance: Difference between highest cell voltage and lowest in battery.
All of the
1300mAh batteries were very well matched in
terms of capacity. In terms of actual performance, the Dinogy and the
"normal" Bonka held about .3V less than the other packs throughout the
first half of the test, after which all of the packs were pretty much
equal. All of the batteries held their voltage quite well up until they
were almost entirely discharged - I was actually pretty surprised by how
close this was. All of the packs other than the Turnigy Graphene got
pretty hot near the end of this test. Definitely hotter than I am
normally comfortable with. I was actually really surprised when I
plugged the batteries into the cell balancer to find the opposite
indication, though - the
Graphene lipo battery was way
out of spec and the rest of the batteries were pretty well matched. I
guess with the lower price on the Turnigy Graphene you do not get as
precise of a cell matching.
I graphed the Tattu 1800 70C and Revolectrix GO pack separately to not obscure the 1300mAh graph. In this chart I included the
Tattu Top Pilot
as well for comparison against 1300 packs. Keep in mind that since the
Revolectrix is a HV pack, it was not charged to it's full capacity.
Given that, I think it actually did quite well - managing to keep
putting out consistent current all the way down to 12.8V - it actually
seems to perform like a regular LiPo throughout the discharge curve,
whereas I expected it to drop off somewhere in the 13V range.
40A Stress Test Results
Cell variance was not performed on this test as all cells were matched on all batteries.
Voltage was only averaged when?load was applied.
I think this test is the most indicative of what these packs would
experience while racing on a wide, open course. It's also where the
benefits of whatever technology that's in them starts to show. Every one
of the new battery packs kicked the ass of the "older" Bonka 70C by a
large margin in every measureable way. What's more amazing to me is that
all of the new generation of packs were able to perform close to, or
better than the
Tattu 1800 70C - that's amazing! It's
basically saying that these new packs can deliver to you the performance
of a 1800mAh pack in a 1300mAh pack and weight. They all discharged
over half of their capacity (actually - past where I would normally cut
off when flying - which is normally 800mAh for 1300 packs) at 40A.
That's pretty damned incredible.
The 1300s all performed pretty similar, again. The Dinogy once again
held the same voltage as the Bonka 70C at the low end - albeit
significantly longer before dropping off - and the other packs held a
higher voltage through the entire test. Voltage of most of pack was
always within swinging distance of each other, with the average voltage
over the test not varying by more than .07V between the lowest and
highest packs. The Turnigy Graphene pack again came down noticeably
cooler than the other packs. Maybe that's because of the extra weight
The Revolectrix pack again showed the best voltage holding capabilities -
staying noticeably higher through the entire test and delivering the
highest average of all the packs. When it comes to power delivery, this
is a damned impressive pack - but once again I can't say how much of
that is because it's a LiHV in sheeps clothing.
Flight Test
Results
For the flight test, I graphed the results of the performance of all
of the packs together during the two "burst" cycles of full throttle
climbs at 200mAh and 55% pack capacity. In order to better compare the
packs, I had to add a few data points to each calculation (up to a half
of a second of data) into the burst sections. This is because I could
not time each burst to be exactly the same as each other since this was
an in-flight test. If you download the Excel sheet above, the raw data
is available to compare the adjustments I did. I did not add increased
performance - just extended it for a few packs.
Average voltage and current measured from the start of 20A current draw until the end of the last burst.
Temperature measured 30 seconds after landing. Missing Revolectrix data - it was lost.
Keep in mind that during this test, the batteries are not the limiting
factor - it was the power system. All of the batteries in the test were
more than willing to give the 80A requested by the motors in the initial
climb. They then all performed similarly through both of the climbs
with a large initial voltage drop-off followed by relative stability.
Power decreased as the miniquad accelerated through the air and the
props unloaded. Variations in the air density during the climb or
angular changes in the quad can easily account for any of the variance
seen in these tests.
Of note is that other than the Dinogy pack, the newer packs all held
about .3V more than the "old" Bonka 70C on average throughout the entire
test. They also once again trumped the
Tattu 1800mAh
on voltage holding capability as well. This seems to be the running
theme of the test - all of these packs hold their voltage better under
load when compared with my "older" reference packs.
I had seen a lot of people talk about how inductive loads (basically -
loads that fluctuate rapidly with time due to the PWM motor drivers we
use on our brushless motors) affect batteries differently than resistive
loads. From the results in this test, I didn't really see any
difference between these types of loads. Perhaps I was not stressing the
batteries enough.
I'm really interested to see how these perform with better motors.
Thanks for the Sponsors
A big thanks to Revolectrix, Dinogy and
Tattu USA for
sponsoring this test by sending us sample packs of their upcoming
batteries. Our pocketbook isn't super deep so it's only by the
contribution of great manufacturers and vendors like these guys that
we'll ever be able to get comparison tests like this. Thanks again.
Source: http://www.propwashed.com/graphene-lipo-battery-performance-tests/
