# It doesn’t hurt to ask

Hello there!
After looking on lots of topics, I´m a little bit comfortable to make a new “newbie” topic: it doesn’t hurt to ask. It means the the most raw questions will be made here.

1- Why Efoils don´t use LiPO packs instead of LiIon ones?
2- How many Cs discharge can handle comfortably the most radical flyer (or surfer, or user)? I´ve seen 2C to 5C 21700 ones.

Best.

They pose higher risk for fires
They have poor energy density compared to the best cells (they give less runtime per weight and volume of battery)

Their advantage is high power density (they give more current per weight and volume) but this is not a priority for efoils since efoils run so efficiently with low power needed.

In order to build a powerful efoil a 30A capable cell in 12s4p configuration is plenty enough power (but still gives limited runtime, that’s why common packs can be 12s10p which can output way more current than will ever be needed).

The question regarding C-rate, i guess you misunderstand what that means.
C-rate is calculated by current per Ah so current output depends on both C-rate and size of battery.
A 20Ah 2C battery will output the same current as a 2Ah 20C battery but the 2Ah battery will only give you about 5 minutes of runtime on a typical efoil.

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Perfect, Larsb. So, I should presume that 2c on a 30Ah LiIon cells should do the trick, right?

Yes, it could work, but is marginal. This battery will max at 60A and a solid efoil battery should be able to output roughly 100A max.

Required start current on motor side can go to more than 100A and max motor current is battery current / duty cycle.

Assume:
Duty cycle at start 0.60-0.95
Battery current max 60A

Motor current max is then something between 60/0.6=100A and 60/0.95=63A for the 30Ah 2c battery

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This log has a few starts with 14S, FS65161 120kv, 100A motor amps, 75A battery amps limits. FR 6" 3-blade prop. The motor amps are the limiting factor for me, with a significant margin.

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Great data, i really have to get a logger

Seems the duty cycle for you at starts are about 60% at 14s, would be 70% at 12s (needed battery current also depends on battery voltage)

This means with a higher voltage battery at 14s a 30Ah 2C battery would be fine (with data from jkoljo board, wing and weight) as long as voltage drop due to battery internal resistance is not too high

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The eFoil packs should be used between 20% and 80% as any onther Li Ion device?

I wouldn’t necessarily say that. It will limit range and efoils having a low use battery i’d just use it with some small margin. 3-4.15V is what i run with limiting of current starting at 3.3V

(When i say low use battery i mean that average efoils aren’t used daily, i’d estimate max 100 cycles per year.)

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