Question about cheaper cells

EFOIL.builders Electronics (ESC, remote, batteries)
1

Hi!

I am currently trying to figure out, which cells I should use for my battery pack.
After reading through the forum I saw many successful builds with Samsung 30Q Cells.
The problem for me is, that these cells are really expensive (500€+ for 12s 12p pack)
Due to this I did some research and found a company near to my hometown, who would sell me used ebike cells for a very good price (0,4€ per cell).
The cells are Sanyo 18650 2200mah with a max discharge of 10A.

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I already bought 30 cells for testing, and I think they are in a very good condition. Nearly all of them have 2150-2220 mah of capacity and an internal resistance of <50 mOhm.

Now my Question is, if it is realistic to use these cells for an efoil?
My plan is to use a 63100 motor and a Vesc 6.
As we can see at @V_S build, it is possible to run this setup with 120A motor current.

If I am now building a 12s 15p battery pack, each cell of my pack would have to draw 8A.

Do you think this could be a cheap alternative to all the really expensive battery packs?

2

I am running 120A Motorcurrent with 85A Batterycurrent :wink:
That equals 5,66A each cell with 15p

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3

50mOhm is quite high this might produce a lot of heat inside your pack

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4

Average current is 30A on battery. Thats 0,2W each cell, or 36W / Pack
All i can say, my 16p 30Q stay cool

5

Sure because your 30q cells will be in the sub 3 mOhm area, not 50!

6

30Q and VTC6 are around 12mOhm. Lowest internal resistance is the Sony VTC5A with 9-10mOhm.

I personaly would not go for batteries with internal resistance higher than 20mOhm. My 14s11p VTC6 batteries can get 45°C after an average discharge of around 1C (33A)

7

Some example with 50mOhm12S12P at 30A discharge:

30A/12 = 2,5A cell
2,5A x 50mOhm = 0,125V voltage drop
2,5A x 0,125V = 0,3125W

0,3125W x 144 = 45W
So the total power in heat is 45W. This is like a medium soldering iron heating up your battery.

8

I have used a similar cell source, used ebike batteries. All tested and matched up to form an equal pack.
Mine are <35mOhm, the 12s12p pack does get warm (50degree?) during discharge but all acceptable.
My cells to compare the specs: LG LGDBMG11865 Cell Specifications | Second Life Storage & Solar

9

So you already fly with these cells?

10

Yes, about 35min flight time with inefficient chinese gearbox.

11

Hi.

I wouldn’t do it. It’s so labor intensive building a pack. And the dangers of cell failure in a KWH size battery is quite high.

Those cells will get hot! 70°C is 160°F! Wow…that will practically melt the plastic parts.

Just buy Samsung 30Q or Sony VT6. I prefer the 30Qs.

I pull 200A from my battery. I like to tow foil boards with my e-foil. I need the power.

:call_me_hand:

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