7/22/2016 Update: All of the tests were re-do75ne with the introduction of two new batteries and some brand new RS2205 motors on the Krieger!

This article is the first in a two-part series where we test the new LiPo battery packs coming out in 2016 (many of which are labeled “graphene”). This article outlines the 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!

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.

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.

But do these batteries actually have graphene in them? Well that’s tough – an important physical property of true graphene is that it is only 1 atom thick. What this means is if you tear a battery that uses graphene in the electrodes apart, you will not be able to “see” the graphene, even if it is there. The only way to detect it is in a lab. The other tricky thing about graphene is that other carbon structures, like graphite, regularly form what can be referred to as “shards” of graphene inside of their structure. Graphite is regularly used in LiPo construction. What I’ve just constructed here is the excuse that Turnigy and other battery manufacturers use to be able to claim their batteries “have graphene” without actually changing anything about the battery chemistry.

In some discussions with the vendors behind these batteries, I have been told directly that there is no graphene sheets in these packs. As John from Revolectrix put it – “if there was really graphene in the packs, we would not be selling in the RC hobby market, Apple would have it first typically”. I think I will lean in this direction of believe until proven otherwise, but the jury is really still out – According to the contacts I spoke to, the LiPo factories are remaining pretty tight-lipped about what has changed with these new 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.

Preparation

Break-in

Before testing any of these batteries, I “broke them in” first. I’m not convinced this is necessary for LiPos – the reason I did it was more to bring the new batteries down to the level of the Bonka 75C pack I had laying around which I am comparing them to – which had about 10 cycles on it. I also believe (this is just a seat-of-the-pants observation that I’ve had – nothing scientific) that batteries perform differently in their first few cycles than they do for the rest of their life. The break-in consisted of a few discharges on my load cell at 18A down to 60% of their capacity and a few moderate flights on each.

Equipment

Load cell

I constructed a water-cooled resistive load cell very similar to the one Joshua Bardwell recently used to do his battery tests here. It’s basically just a long length of steel wire wrapped around a wooden core that is dunked into a 5 gallon bucket of water. The battery leads are shorted through the extremely long coil. When power is applied, they act like a giant water heater. Discharge rates can be altered by moving the attachment leads of the battery up and down the coil. This contraption worked fantastic – thanks to Joshua for the tip and tutorial on how to make it.

In-flight Testing

The Krieger with onboard logging used in these tests.

The Krieger with onboard logging used in these tests. Note: this picture is from before the red bottoms were installed.

One thing I wanted to do in this test which wasn’t touched on in some of the other reviews I have seen is some in-flight metrics. I opted to use the onboard Blackbox datalogger for recording purposes. The flight controller I use on most of my miniquads – the BeeRotor F3, has a shunt resistor for current sensing ability on the PDB and a built in OSD so I could monitor battery metrics in flight. Unfortunately, the shunt resistor only worked with Cleanflight’s 3.3V ADC to provide sensing of up to 90A. To fix this, I purchased a new shunt resistor with half the resistance from Digikey. Once installed, this upped my flight controller current sensing range to 0-180A. The downside is it significantly reduced the resolution of the recording – the flight controller is only able to sense current in steps of .8A. That’ll have to do though.

The testing miniquad

When it came to picking the actual mini-quad I’d do the test on, I settled on my tried-and-true Krieger. Mostly because it is the only quad I have that fits 6″ props and it already has 30A ESCs installed for some real abuse. Here are the specs I settled on for the test flights:

ShenDrones Krieger 225
LittleBee 30A ESCs
Emax “Red Bottom” RS2205 2300kV Motors
DAL 6045 tri-blade props (with airmode disabled..)

The numbers

A lot of the data generated for these tests were generated by uncalibrated voltage and current sensors. I do not professionally work in the electronics industry and do not have the money to spend on the professional equipment needed to generate properly calibrated tests. I did my best to calibrate my sensors using the tools that I have on hand, but I know for a fact that some significant error remains. As such, the actual raw numbers that you see in this test and the attached spreadsheet are useless when compared against other tests or judged by then numbers themselves. If you see 16.2V – it does not mean 16.2V exactly, but probably somewhere between 16.1V-16.3V. The relative numbers is where all the value lies in this test – the battery performances in these tests should only be compared against the other batteries I also measured. This is why I included an “older” style LiPo batteries in this test.

I also want to note that the voltage recorder I used had some noise, especially in the flight tests. I attribute a lot of this to ESC backcurrent. This data was sampled at 125Hz, which I downsampled to 5Hz to reduce the noise.

The 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, as shown under a decent load. 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 Lineup

battery lineup

Note: This picture was before the 7/22 update (which added 2 more batteries to the lineup)

There were 6 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, a Bonka Graphene and a Luminier Graphene pack for comparison. 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” (‘GO’ stands for “Graphene Oxide” – this is their next generation technology targeted at the high performance market). 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 75C 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.

Battery Description Weight Price
Bonka "Normal" 75C 1300 Older release by Bonka – compared favorably to most last gen batteries 153g $29.95
Bonka Graphene 85C 1300 Graphene offering from Bonka 167g $39.99
Dinogy Graphene 2.0 75C 1300 Graphene offering from Dinogy 152g $30.99
Dinogy Graphene 2.0 75C 1500 Larger graphene offering from Dinogy 178g $34.99
Luminier Graphene 80C 1300 Graphene offering from Luminier 167g $34.99
Tattu Pro Pilot 1300 Upcoming battery series from Tattu 162g $44.99
Tattu 75C 1800 Older release by Tattu – the best higher capacity pack I had on hand 201g $49.95
Turnigy Graphene 65C 1300 Graphene offering from Turnigy 176g $25.38
Revolectrix GO Blend 435 1700 New upcoming LiHV with "Graphene Oxide" technology 201g N/A

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.

Results

The raw data for the first set of tests, which includes the results from the Revolectrix pack, can be downloaded in excel format here. The results posted below are from our second set of tests, done on 7/22.

20A Constant Discharge Test

Battery Avg Voltage Temperature (C) Charge (mAh) Cell Variance (V)
Bonka 75C 1300 14.063 53.7 1200 .14
Bonka Graphene 1300 14.226 49.3 1211 .03
Dinogy Graphene 1300 14.117 53.6 1194 .02
Dinogy Graphene 1500 14.182 59.3 1511 .05
Luminier 80C 1300 14.254 50.6 1280 .2
Tattu Pro Pilot 1300 14.192 52.1 1178 .08
Tattu 75C 1800 14.127 55.3 1711 .13
Turnigy Graphene 1300 14.228 46.4 1158 .22
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. None were what I would call overrated. 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 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 75C and Revolectrix GO pack separately to not obscure the 1300mAh graph. In this chart I included the Tattu Pro 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

Battery Avg Voltage Temperature (C) Charge (mAh)
Bonka 75C 1300 13.817 54.2 590
Bonka Graphene 1300 13.975 49.3 682
Dinogy Graphene 1300 13.812 53.2 685
Dinogy Graphene 1500 14.024 56.3 908
Luminier 80C 1300 14.097 44.9 711
Tattu Pro Pilot 1300 13.989 49.6 680
Tattu 75C 1800 13.88 52.5 911
Turnigy Graphene 1300 14.027 48.3 775
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 75C 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 75C – 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(ish..). 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 75C 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

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.

Battery Avg Voltage Avg Current (Amps) Avg Power (Watts)
Bonka 75C 1300 11.775 83 989
Bonka Graphene 1300 12.262 93 1141.12
Dinogy Graphene 1300 12.371 89 1086.72
Dinogy Graphene 1500 12.228 102 1241.37
Luminier 80C 1300 12.47 98.81 1232.30
Tattu Pro Pilot 1300 12.187 91 1115.95
Tattu 75C 1800 12.133 96 1169.18
Turnigy Graphene 1300 12.476 96.9 1208.97
Average power delivered during first burst at 200mAh of capacity.

Battery Avg Voltage Avg Current (Amps) Avg Power (Watts)
Bonka 75C 1300 11.504 85 974.54
Bonka Graphene 1300 11.93 94 1079.05
Dinogy Graphene 1300 11.846 96 1136.61
Dinogy Graphene 1500 12.08 98 1181.59
Luminier 80C 1300 12.106 89 1082.38
Tattu Pro Pilot 1300 11.989 92 1101.57
Tattu 75C 1800 11.945 95 1129.08
Turnigy Graphene 1300 12.007 94 1129.66
Average power delivered during second burst at 500mAh of capacity.

The real determining factor in this test was the first second or so of the burst, when the quadcopter wasn’t moving quickly. At that point, the numbers pulled by the motors are similar to those on static thrust stands – which, for this power system, nears 35A per arm. Once established in the climb, the props unloaded and power decreased. Since I did this test in flight, it was hard to get a 100% reproducible scenario. Variations in the pitch of the quad and the state of the air it was moving through could have had effects on the test. This can be see in the variance between the 1st and 2nd bursts.

Nevertheless, you can see some patterns emerging. For instance, the new graphene packs all held more than .3V more than the “old” Bonka 75C on average throughout the entire test. They also all matched or beat the performance of the Tattu 1800, a pack that has a 35% capacity advantage. 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 and deliver about 20-30% more power on the bleeding edge.

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. I am also very impressed how each of these manufacturers are very interested in improving their batteries for the miniquad racing market. They were all interested in the results of my testing and asked me to provide any feedback on the batteries I could come up with. Props to these guys, seriously:

Revolectrix

Dinogy

Tattu

One final note is that I spoke to Mark at Dinogy about the voltage sag performance I saw and he wasn’t surprised. He said the sample pack I had received had some issues that were still being worked out in the factory. He suspects the next shipment of Graphene 2.0 packs will be better. If you have a Dinogy on pre-order I wouldn’t worry too much. I’ll update this article if/when I test the next shipment.

References

http://www.revoblends.com/chemistry/4587282020 – Great article by Revolectrix explaining how LiPo batteries are manufactured.
Joshua Bardwell’s battery tests – Thanks to Joshua for some of the tips used in the testing on this page.
Article on LiS batteries – a potential upcoming development for LiPos
Another article on Silicone/Graphene hybrid LiPo packs
Another article on Si LiPos – this article contains discharge graphs very similar to what we are seeing with these new LiPos. Some are speculating this is the tech behind them.
Trade article on Graphene doping process
The RCGroups thread on the Turnigy Graphene packs – A treasure trove of community investigation into these packs and the technology behind them.

 

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