Hello,
I am considering building a 16s2p out of 20ah LiFePo4 those cells:
https://www.nkon.nl/de/eve-c40-40135-20ah-3-2v.html
It is about 0.5kg/kWh heavier, but I get a completely safe cell chemistry and easier assembly (no dot welding).
Any reason why that would not work or why alternatives might be better?
thanks
Daniel
Try and let us know;-)
I always wanted to try LFP cells.
The discharge curve is so much better.
Nominal Capacity 40Ah
Nominal Voltage - 51.2V
12kg it’s a little bit heavy, don’t you think?
12kg for a 2kwh battery isnt bad
If my numbers are correct cell weight (excluding BMS) for a cheaper 18650 cell (2850mah) would be 5.3kg/kWh, and for this LiFePo4 cell it would be 5.8kg/kWh
Also rated for like 6000 cycles.
For me size is the biggest problem.
And if you do not need the full capacity (for foil assist for example), they are pretty heavy.
But if they deliver to their specs, they would be really really good for a tow boogie
I would not count in them being any safer though.
If they come in contact with (sea)water, you will have thermal runaway, just as with li-ion.
no, as far as I know they are much safer? With a short-circuit thermal runaway reaches around 100°C and they do not burn.
Only possibility they burn is if you physically puncture them, and even then they often do not?
See for instance this paper on " Safety of LiFePO4/Graphite Li-ion pouch batteries under simulated external short-circuit (high rate) conditions".
Or does anyone have evidence to the contrary?
Thanks
Daniel
Maybe you are right.
But as far as I can read it, they observe a single cell of 3AH.
I would not count on the result being the same, if you cramp 32 20AH cells into a tight space made out of insulation foam.
It will be safer while handling on land for sure.
But unless you really mess up, you shouldn’t have any issues with li-ion there either.
if you have the space, go for it! LFP are indeed MUCH safer than any other currently available lithium cells. and 6-7 kg per 1kWh is pretty good as well.
Hi Daniel,
I use exactly this setup, 16s2p c40 cells for my efoil. I will share my build later, I have finished it earlier this year and was busy riding it. It’s based on Flipsky 75200 controller and 6384/63100 motor (tried both).
The batteries are capable of delivering 60A or more continuous current during more than an hour and only get slightly warm in an enclosed compartment without cooling.
They have suffered a short circuit due to a faulty controller, they were soaked in sea water due to poor battery compartment design and a faulty hatch, but they still work flawlessly.
So I clearly recommend them despite some extra weight.
The welded studs make assembly easy.
I load each 16s set separately using two 8A chargers, takes 3 hours on average.
Cheers,
Dmitry
Hi, could you please give us some more information? I’d like to use these batteries because I’ve heard they’re much safer from a battery manufacturer. Which grade A LiFePo4 C40 batteries did you buy? What brand?
Can you tell me if you use a BMS, and do you think it would work on a Flipsky 65220?
Hi, sure.
Judging from how I have abused those batteries, they are really safer than usual Li-ion.
I have the batteries from the chinese manufacturer EVE, here is the link: EVE C40 40135 - 20Ah - 60A LiFePO4 - 3.2V - A-grade
I use two 16-cell BMS, one for each of two 16S bateries.
I have checked the specs of 65220, my battery setup should be able to work with this motor.
What engine do you use?
I use 6384 and 63100, please see my first message.
Ok! How hot are they? What kind of protection do you use? Do you have any photos of your assembly?
Well, the batteries get lukewarm after the full session with multiple starts at full motor power, so no problems here. I protect them with just two 100A fuses.
My asembly looks really lousy right now, I didn’t make any photos of it, there is nothing to be proud of 
I’ll make a post about my build as soon as I print a new waterproof housing for the batteries.