New battery option: better power density!

This just popped up on RC Groups:

Foxtech claims 2570g for a 6s 30aH battery, with a 10C continuous/15C burst current rating. They are pricey at $560 each, but it’s nice to see someone make a jump forward with energy density. Hopefully they live up to the specifications.

1 Like

Impressive. So much so that I’ve just ordered two!

Two should be good for about 6 minutes of full power push. I will put them through their paces as soon as they arrive and let you know. Could be the future!

1 Like

Actually, that’s not much more than the typical price for other brands of 22 Ah 6S. The Bonkas are just a really good deal cause they are half that price. But these are exactly the same size and weight with 30 Ah!

The C rating is lower than the Bonkas. Plus, they recommend keeping discharge rate between 1C to 5C. So, full power with only two packs is really pushing it. Just warning you that you could ruin your investment really fast. I am anxious to hear what you think of them though. I’m tempted to try six packs as that would keep the discharge around 4C at full throttle and 1.5C for level flight. Four packs would put full throttle at 6C. Two packs would put full throttle at 12C. This is based on 360 amps which my batch 2 draws during takeoff when my batteries are full. After takeoff I typically climb with less than 300 amps.

1 Like

Glider pilot has already said correctly that you should be very careful if you only want to use 2 packs. I can tell you that when you 30 seconds full throttle (about 300A) give; is the pleasure ended because the cell connectors burn up … I would load such packs in any case with more than 60 A duration. a short-term load (less than 60 seconds) is possible with a maximum of 90 A

1 Like

@RichardG I’m eager to see what you find. I did a bunch of reading about these “semi-solid state” batteries and as far as I can tell these are cells coming from 24M and Kyocera, probably NMC chemistry. 24M is really targeting the bulk storage market, so they aren’t optimized at all for fast-discharge applications like ours. Still, with a 2S3P configuration like glider pilot mentioned would keep the discharge well under 5C.

I just emailed 24M to see if Foxtech is using their cells, and if so, what they recommend.

If you do get through to someone at 24M, I would like to see the full datasheet of their cells.
Did you come across any technical information that wasnt just a press release, obsured in marketing speak? It seems odd that only Foxtech have access to them, I cant see any such packs from anyone else.

It sounds like it was a pretty limited production run on a Kyocera line, so there may not be a ton of cells available to the hobby market. Also, I can see how other pack builders would be hesitant to put a pack on the market that is only rated to 5C, and even that 5C number seems a little optimistic based on what I read about NMC cells. We’ll see what 24M says.

What is really neat is that (according to a chart I found) they are already pushing 350 Wh/kg. That’s a pretty big jump over what is available now.

5C discharge would be enough of the cells had 10X the available energy.
I.e. 5C from a 35ah cell gives nearly 200 amps.
20C from our bonkas is still over 400amps though so the new ones need double the density yet.

I wonder if a viable solution could be built by mating these up to some big capacitors to make short high power bursts available. Like a power up mode in a video game.

1 Like

I would not recommend these packs because the maximum continuous current is only 150A.
Cycle life only 300 (under best conditions).
Not worth the investment compared to the Bonka’s.

@RichardG you will ruin the packs within seconds if you’re using only two of them.

If you run them in a 2S3P configuration you’re down to more like 3-4C at full throttle and 1.5-2C at cruise, which is pretty reasonable. For the light guys that don’t need full power, I bet you could fly a loooong time with six of these packs.

@mr.jadkowski Foxtech already changed the 10C/15C to 5C/10C and the 500 cycle to 300.
Such low C-rated high-capacity batteries usually have higher internal resistance so even with a discharge current of a few C the voltage drop and temperature rise will be significant.
The 30000mAh sounds alluring but I’m pretty sure the benefit will be rather small compared to the 22000mAh 20C Bonka’s, if there is benefit at all…
The packs are great for low current applications, not for ppg in my opinion.

1 Like

Hmm. So the batteries I ordered have changed spec before I even received them!

I will have to hope that they perform at least to their latest spec and then make a decision to either double down on my investment and get another pair or put them on the ‘expensive mistakes’ shelf!

Being forever the optimist, I hope that 4 packs in total will probably be the best Wh/KG pack that can currently be achieved – but at quite a cost.

That’s life at the bleeding edge I guess!

1 Like

@RichardG that’s the truth! Sometimes you get lucky and win big, sometimes you strike out. Do you have a way to run these on a test stand to take a look at heating and voltage sag at different discharge rates?

I can easily run a test at up 200W dissipation using my rather clever electronic load (Rigol DL3021) - but that’s only 10Amps at full voltage (22V). I’ll do that first to confirm that these cells do have something close to their rated capacity.

I could risk taking more current out of the BMS connection on just one of the cells, but the BMS wiring may not be up to that. If I do that, I can test up to 40A discharge on a single cell (and have some smelly cabling to contend with!). Or I can break the pack apart and get direct acces to the individual cell terminals.

Then, I have some high power (500W) resistors that I can configure to take 700W out of the whole pack, but that’s still ‘only’ 33Amps. I have a fluke thermal imager than can show me where hot spots are developing.

From then on, It gets tricky trying to take out 150Amps – that’s 3.3KW of power to get rid of!
What I need is a big cooling fan and something that can take this load…….!!

If only Paul Pdwhite would deliver my Christmas present of a Build 5 paramotor BEFORE christmas!! :wink: Hows it going Paul??

Many years ago many of them had F5B in the competitive area (model aircraft up to 6 kw peak). To test the competitive batteries, simple power consumers are used to measure peak performance. then several parts as in the link parallel closed depending on the application. The current was simply measured inductively.

It will be interesting to see how much of their claims hold up. Their website says: “there is no obvious heating during 7C discharge.”

Also: “The recommended discharge rate is 1C-5C to achieve the maximum discharge capacity”. So their only reason to keep the C low is to optimize the Ah (I would think running higher C would have a bigger impact on the life of the battery). If the batteries truly stay cool at 7C then this makes sense because heat is typically the biggest enemy for lipos. The only statement pertaining to battery life is charge rate: “charge with 1C current to improve battery life”. It’s unfortunate that they changed the life from 500 to 300 though.

If there is a big voltage sag, that can be cut in half every time you double the number of packs. So adding more packs not only protects the batteries from discharging too fast but it also increases your power because the total voltage doesn’t drop as much.

These packs also discharge to a lower cell voltage. That will make it so you will have less power at the end of the flight than at the beginning. We have that now with the bonkas but it will be more noticeable with these.

Look at that test methods:

All tests from that person](url-action-no-chooser:

He used a long steel wire(not chopper!) in a bucket of water for the 40 and 60 amp test and conected plus and minus on that.

In that following movie at 3 minutes he explain his 60 amp method:](url-action-no-chooser:

Brilliant! A coil of steel wire in a bucket of water!!
If I’m carefull, I can use it as a calorimeter to confirm the total energy taken.
And have a nice hot bath afterwards…!! Who knew testing batteries could be so much fun! :slight_smile:

I think the way that guy tests the batteries is the only way to compare the different batteries in a laboratory situation…

He often is surprised how good or bad the different and often expensive brands are performing compared to the others.

Maybe those tests can be used also to select the best 6 of 12 bonkas to be put together to 1 pack or the best fitting 4 of 12 etc :slightly_smiling_face: