New battery option: better power density!

I contacted Foxtech and wrote I was confused about their maximum 5C continuous statement and 7C test without obvious heating.
I wrote the 7C was well above the 5C continuous so presumed the test at 7C was a short one and therefore not long enough to heat up the battery.
They confirmed the short test and also that 5C is really the maximum continuous discharge current.

I know the 30000mAh sounds good but most of the capacity profit against the 22000mAh Bonka’s comes from the fact these new ones can only be discharged with a lower current and to a lower voltage.
Those lower voltages are not usefull in our high power applications so these new packs are really not worth it in my opinion (for our purpose).
Would be nice if someone could do a capacity and voltage sag test at high current on one of these packs, compared to a higher C pack with less capacity. I’m pretty sure what the outcome will be :blush:

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I find the whole thing as a joke. the companies write incredible “c” rates … how did they do a long-term test, often with only awg 10 cables? anyone who claims that the awg 10 cable can withstand more than 150 A permanently is a magician. I’m just surprised that many people here don’t understand the basic principles of electricity? but there is worse that clearly shows how the cheap lipo manufacturers lie to you. protect yourself from an xt 90 connector with a thermocam if it is permanently loaded with 150 A. you can watch it melt and then go up in smoke. something does not fit together … write 5 C and then use the plug with 3 C … be careful if you want to fly with material that is unsuitable for it.

I agree… C ratings are always hyped up. The only way to know the true C rating is to test it yourself. The Bonkas can’t handle anything near what their C rating claims. Foxtech claims a much lower C than Bonka but they might be more honest with their numbers too. The only way to know is to try it but I definitely wouldn’t stress the battery above what the manufacturer claims… specifically since those claims are always hyped.

Now also 22AH 5c available
https://www.foxtechfpv.com/foxtech-diamond-6s-22000mah-semi-solid-state-lipo-battery.html

Than you can put 2, 6s packs in series 3 in parallel 12S3P (6 batteries in total ~11.4kg) for 1.5 kg more compared to the 2, 6S packs in series 2 parallel 12S2P (4 bonkas ~10kg).

This means so you get 2 times 22Ah extra for 1.5 kg.
THIS IS 50% MORE!!!

By full throttle ~ 300 amp for batch 3 with 180kv motor and 22x10 prop you will pull 300/3=~100 A per battery.
compared to the battery specs we can pull 5 C x 22A = 110 continues per battery so this should be no problem at all when you have 3 in parallel. (than is 330A ).

For batch 4 150KV motor can we put 2 6s batteries in parallel and 3 in series = 18S 2P ?
this is 4.2 *18S = 75.6V (I know it above the lethal 50V )
Or is this to mucht for the ESC, BEC, and motors?

Here is an idea that I’ve been kicking around for a while: running a pair (or two pairs) of these in parallel with a pair of Bonkas. Because of the difference in IR, the system should draw more power from the Bonka packs during times of high load, but because everything is connected in parallel more power will have to come from the Foxtechs once the load drops. Theoretically that is how it should work, but in practice is another question. @RichardG, maybe you can try this with the two packs you ordered? It would be interesting to see current readings from each series battery pair at full power and cruise power.

@bartremes the openPPG draws more like 300A at full throttle, not 100A. And I’m pretty sure 18S would smoke the 150kV power system.

different packs can be used in parallel. very important here !!! when starting, both systems must have the same voltage. as an example 4.15 - 4.20 volts … one pack would have 4.05 volts and the other 4.2 volts would charge the weaker pack when plugged together. however, this cannot be controlled and is dangerous. if both systems are the same at the start of the volt it is not a problem the voltage drops the same for both. I’ve been doing this in a trike for a long time. here i use sony cells 18650 and samsung 21700 at the same time. in flight i can see the Volts per every single 5 S -pack on 12 single displays exactly. the difference ends up being less than 0.1 volt.

the display is of course only an additional option. and because I am interested in what happens in the cells. the esc and the on-board computer naturally take care of the security of the system.

Hmm, interesting. So the Bonkas provide the current and the Foxtechs provide the capacity.
There would be all sorts of odd current flow dynamics going on there!

I would be most concerned that when the Bonkas run down, the only limit to the re-charge current from the Foxtechs would be the cells internal impedance.

I still haven’t received these Foxtech packs yet, and I don’t have any Bonka packs to experiment with.

I still don’t have a Batch 5 paramotor for that matter!! - delivery early December we were told! Where are they??@pdwhite

I don’t think you’d have to worry about the Bonkas “running down” any more than the Foxtechs. What will happen is that as the current draw increases, The Bonkas are going to supply more current than the Foxtechs because of the increased IR of the low-C packs. However, as the Bonkas discharge more, the resting voltage of the Foxtech packs will be slightly higher than the Bonkas and that will compensate for the increased IR and current coming from the Foxtech packs should increase. The “extra” current coming from the Bonkas under high draw is going to have a finite time limit, then the power coming from each pack should equalize. So the Bonkas should supply some short-term burst power (like for takeoff), but in the end the voltages should stay equal and both packs should be exhausted at the same time.

This is all theoretical… someone will have to test it to see how well (if at all) it works.

Yes, as long as the packs are run at significant draw all the time, then current always flows out of both packs and all should be well.
My concern is that as the Bonkas are supplying most of the current, they will discharge faster than the foxtechs. If a large part of the capacity is used taking off, and the motors are then switched off for a bit of free flight, then the Foxtechs would be re-charging the bonkas without current limit (other than IR). This may be fine, needs investigation.

I am of the opinion that if you load cells in the range of 2-3 c the different internal resistance means no problem. it is important that the capacity must be pretty much the same! that means 20000mah brand x and 20000mah brand y in parallel at 2-3 c load and start volt is no problem. 16000mah brand x and 20000mah brand y in parallel doesn’t work well. the difference in capacity automatically shifts the c load.

Connecting battery packs in parallel will insure the the voltage stays the same between the packs. The voltage between the packs must be at the same level before connecting them in parallel or the high one will charge the low one at a rate higher than the packs can handle. Bonka and Foxtech have the same full charge voltage of 4.2 so if both are fully charged there won’t be any issues upon connection. The extra capacity of the Foxtech comes partially from its ability to be discharged to a lower voltage of 2.7 vs 3.5 of a typical lipo. So, if you run them in parallel until they are down to 3.5 then you don’t get the extra capacity of the Foxtech. If you run them down to 2.7 then you will destroy the Bonkas. Again, the voltage will be forced constant between the packs.

The rate of discharge will be the rate it takes to keep the voltage the same between the packs regardless of internal resistance. However, higher resistance will make the voltage sag more during current draw and the ”sagged voltage” will equalize between the packs. Then when you let off the throttle and the voltage sag goes away your packs won’t be at the same resting voltage causing the high pack to charge the low pack at a rate potentially higher than the packs can handle (if there is a significant difference in the resistance).

I don’t think we can assume the Foxtech has lower resistance just because of its C rating because the technology isn’t even the same. True both are lithium based but one is semi-solid state.

The Foxtech packs would work fine for OpenPPG with the given C rating if you had enough of them in parallel. The question is how many packs would be enough? 6 packs might be enough. That’s how many Bonkas I fly with. The extra flight time of the Foxtech would be nice but I don’t think it’s worth the extra cash to invest in 6 of them to find out.

here you can see the prices for the molicel 21700 for end customers depending on the number of pieces. my milling machine is already running for the frames and brackets. I will not mill the copper connectors myself this time, but have them lasered in Germany. if I had known earlier how cheaply it is possible to solve. i would have saved myself a lot of time and broken cutters on the cnc. pictures of the new battery as always on my facebook page. the long-term test of the molicell is complete, so i am using this cell type for powerppg and thermik ppg. i will also use the cells for the yuneec eppg from 2009 about which i will make a report soon. I have the possibility to supply an original of the series that was delivered to test pilots worldwide with new cells. Of course, we will also make a comparison on the test bench and when flying, make 2009 technology and 2020 technology.

I have now received two of the Foxtech Diamond 30AH batteries – taking 5weeks to arrive. I have been putting them through their paces to see if they live up to their spec.
They do!


I have given one of the batteries 6 charge/discharge cycles so far. Using an electronic load with a battery testing capability and voltage logging.


1/ Charging at 10A then discharging at 10A.
Resulted in 30.7AH current and 672WH power.So, their spec of 30AH and 666WH is correct.

2/ Charging at 20A and discharging at 10A.
Resulted in 30.6AH and 670WH. So no obvious capacity degredation or lesser capacity due to greater charge rate.

3/ Discharging at 30A(approx.)
Driving a constant 660mOhm load power resistor gave out 27.5AH and 590WH of power.
So the delivered power has reduced with increase in load.


The picture shows the three 2Ohm power resistors in parallel giving 220mOhm resistance. A fan was needed to keep them cool!

4/ Then, the big one! Discharging at 150Amps.
This was done using a 0.15mOhm steel wire put into a 12L bucket of water. This gives 146A at 22V.
The steel wire used was measured at 77mOhm per meter. (but increases when hot!). So 2M would be 0.154Ohm.
I measured two lengths of 4Metres and put these in parallel to produce a 154mOhm resistor.
These two coils where wound around a former as shown, then put into a plastic bucket containing 12 litres of water.

We have got 600WH of energy in the battery, that gives about 11 minutes of discharge at 150Amps

The water temperature started at 11.6 degrees. It was a cold evening!
Nervously, the switch was switched and the current flowed.


Current measured on a current clamp meter showed 151A at the start – nice!
My thermal imager was showing the cabling getting a bit hot.
The 4AWG cable through the switch was fine and barely got warm
The Diamond battery pack has a 10AWG cable from it. This is too thin for 150Amps.
After 3 minutes when the cable had built to a temperature of 160 degrees, I switched the battery off as the cable would be overheating the battery.

I quickly set up a fan to keep the wiring cool and switched back on.
The wiring from the battery stayed at about 70 degrees with the fan running.
This ran for a further 5 minutes.


Then the cable into the XT90 connector popped out! I’m not sure whether it was bad joint or the heat had melted the solder. This was the connector fitted to the battery pack by the manufacturers!
I managed to get enough contact with the cable rammed back in to continue.

I ran another 3 minutes until the battery voltage dropped to 15V.

The rise in temperature of the 12Litres of water was 52DegC- 11.6 Deg C = 40 Deg C
Using P = (4.2 X 12L x Temp)/3600, means that 560WH of energy was delivered to the water.
This is probably less than actual, given there was no insulation of the bucket and the water would have cooled slightly during the interruptions.

Unfortunately, my voltage logging was also messed up by the interruptions, so I didn’t have enough data to do a proper current and watt/hour calculation from the logs.

5/ A discharge with 8AWG cable on the battery
I stripped back the battery and replaced the 10 AWG cable with 8AWG.
I replaced the XT90 connectors with XT150 connectors.


I filled the bucket with 14L this time and again ran the pack at 150 amps.
After 3 minutes the 8AWG cable reached 70 degC. Switching the fan on reduced this to 50 degrees C.
This ran into the 150mOhm load for 14:39 minutes:seconds with no worryingly hot cabling.
The battery reached 60 deg C. The 14L of water got to 46 deg C.
The rise in temperature of the 14Litres of water was 46 DegC-11 degrees C = 35 deg C
Using P = (4.2 X 14L x Temp)/3600, Energy put into the water = 571 WHours.

From the voltage log, power = 576WHours. A remarkably close result!
And accumulated current = 28,500 mAH

6/ Charging at 20A and discharging at 10A.
One last cycle to see if the two 5C discharges have reduced the batteries capacity at all.
Resulted in 30.433AH and 666.264WH. I include the decimal points here because this is so weirdly close to the spec of these batteries. So no significant capacity degredation after the high current discharge cycles.

Conclusions.
The spec of these battery packs makes them the highest energy per weight ratio of any battery I have tested or am aware of.

At 10A discharge they have their specified capacity of 30Ah/666Watt hours.
At 30A discharge they drop to 88% capacity.
At 150A they drop to 86% capacity - 576Watt/Hours and deliver 28,500mAHours

At low currents they give 260Wh/KG which looks to me to be a record breaker for a lithium battery!!
Even the mighty tesla cells only come in at 250WH/Kg

Note: I’m afraid the OpenPPG battery comparison speadsheet OpenPPG Battery Comparison - Google Tabellen has some wrong capacity claims for some of the batteries.The NCR18650 cell = 224WH/KG not 259WH/Kg.

The next best cell I have tested is the Sony VTC6 which comes in at 225WH/Kg at light loads, 210WH/KG at full load. The Molicell P42A is also a contender having a slight edge at 230WH/Kg according to the data sheet- but I haven’t tested it at working current - yet!

The 10AWG cable and the XT90 connector from the battery are not fit for purpose.
Changing to an 8AWG cable with a XT150 connector is adequate as long as there is some cooling taking place. 4AWG or two 8AWG cables in parallel would be even better.

If you want the best batteries, don’t mind paying and don’t mind ripping these batteries apart to change the cabling, it looks like these ones have the edge!

Maybe I should invest in 4 more to make a really powerful six-pack!!

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Thank you richard for testing so well!
Very cool datas and a great testsetup.
How did the voltage change over the full test?
And how fast has the temperatur of the pac changed to 60 c ?
As you cooled the cables you also cooled the pack itself
If you would double the cables you could do another testrun without any cooling.
In the real scenario the pack will be on your
Back without that perfect ventilation and 2 to 6 over each other heating up each other!

What if you would double the load and use doubled cables per battery as you recommendet and put the 2 batteries over each other like in real use?

And most importand would be that you dont cool anything becouse you can not do so in real use…you would need those 2 packs you have now with big distance - so that they dont heat up each other and 2 vans blowing ideal on the opened pack like it was now to have the same situation for the battery…

And if you use your set in summertime the temperatur could easy be 30 c in the shadow.

And if the sun shines on the black batteries they will be warmer than on a desk in a 20 c surrounding…

Have no idea how to simulate that situation but the bonkas are reflecting silver and those are black so this could have also an effect as it takes time to start and even in flight there will be not much wind on your back between the backplate and your pack even when flying.

Thank you for building that great testsetup and sharing your results!

All the best

important for all those who consider safety and their life important: if you solder thicker cables with battery packs, the cables will be less warm yes that’s right. but checks whether the arresters from the pack are also strong enough. very often these are too thin in cross section. that means if a pack is then loaded with 5 c duration over the entire flight time, the arrester will begin to glow and in the worst case ignite the electrolyte as it leads to a short circuit in the layers. if a pack could realistically withstand 5 C discharge, the manufacturer would have used 1. awg 6 cables and 2. minimum 150 A plug. if the packs were constantly loaded with 150 amps for 12 minutes, they would be thermally destroyed! that’s fact! therefore be careful and use a system that is also suitable. on the ground it is not a big problem if something burns. in flight it’s the end.

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@bratwurst

You are right safety fist.

The packs where constatly loadet with 150 amps and he prooved that they did not be destroyed.

Or do i misinterpret his numbers?

Regarding safety - is that kind of testing the packs not the best safety you ever can get?

That becouse you can simulate the loads in a laboratoy situation…

So it should be possible to find out if the connections between the cells are to weak or get too hot ideally with thermalimaging…

Much better to test every battery like that bevore using it in the air first time to find out how it can handle those big loads.

Didnt he do that?

a constant test is not possible with a resistor because the voltage drops and therefore the current decreases. so i wrote in 12 minutes for the whole discharge. yes of course an experimental setup on the floor in the workshop is the best thing when it comes to safety. It only becomes dangerous if people are now of the opinion “ok. 150 A is possible” now I’m flying with such a pack I want to use a light setup by weight and only gain a little height for thermal flight. you have to consider that a new pack has a good performance. if it gets hotter than 55 degrees celsius several times, the chemical composition changes somewhat. that means the inner resistance gets worse and the capacity decreases. that means after 20 cycles, the pack becomes noticeably hotter than the first try. this means that the conversion is even more noticeable. It is a doom-loop. this is the reason why lipo can often no longer perform the service after a short time. this is dangerous for people who do not fully understand the background when flying with it. that’s why I always repeat not to use a system based on manufacturer values ​​but after extensive tests under real conditions. and the most important thing is to have a 30% reserve at the temperature. only then will I describe a battery as suitable for man-carrying. to fly a pack that already reaches 60 degrees celsius with 5 C load is tired of life. the same applies if the cables and arresters are not designed for this. imagine using 2 packs in parallel. one of the plugs fails. the pilot does not notice it and remains at 200A. if he is lucky the other plug will melt. if he is unlucky, the lipo ignites beforehand through the arrester, which begins to glow. i often think many believe flying with eppg is a game where you can get out at any time. this is only possible if you fly very low only on the sports field ok. if you fly properly at great heights or longer distances you can’t just say: ok my battery is starting to burn, i’ll land you quickly … some will understand. some not. warnings have been written enough. opportunities as well as how to fly safely. Many here build the li-ion batteries themselves are proof of this.

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So to have a good cutaway for the battery could be the best …

Here is the voltage graph of the discharge into 150Ohms. Because this is a constant resistance load, this graph is relatively flat as the current reduces as the voltage reduces.


The demand from a motor ESC will be more of constant power demand rather than constant resistance. So in the real world, the tail end of the discharge will have greater current demand on the cell, not less. The voltage graph would be much steeper.

I think I need to run the 150Amp test again with the battery opened out to let me see how hot the tabs on the cells get.The Bonkas would have a similar problem. Do they? Has anyone done these sorts of tests on the Bonkas??

I think that with the props running, there will be plenty of air cooling to keep the cabling and batteries to 60 degrees C.

OK, now you got me thinking about emergency eject mechanisms for a burning power pack!!

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