[EV CELLS] Where to buy high capacity cells?

[gabriel_ribeiro]

Hello guys,

my name is Gabriel and I'm a brazilian student of electrical engineering in the Federal University of Itajubá (UNIFEI). I'm also a member of a Formula SAE EV Team named Cheetah E-Racing. For this year, 2019, we are looking forward to change our battery cells. Our electric motor parameters are located below:

Nominal tension: 72 V
Peak current: 280 A
Nominal current: 83,4 A
Nominal power: 6 kW
Maximum power: 20 kW
Total energy needed: 9 MJ

So, as seen above, we are looking for high discharge rate and capacity cells, properly manufactured for electric vehicles. Unfortunately, in Brazil, we have little to zero availability of those batteries.
Could you, please, give us some recommendations of possible suppliers or cells/modules/packs?

Thank you very much for your attention!

 

[Marv1337n]

Well what capacity do you want?
You'll need a good balance between capacity and current because 85A/280A is pretty heavy.
For the most capacity, go for Samsung 50E, for a better current rating choose Samsung 40T.
What about LiPos? No hassle to assemble them and they offer great current ratings. Pretty light too.

 

[gabriel_ribeiro]

Well, since we are talking about a formula vehicle, the mass is pretty important. Since the capacity and discharge rate depends on each other I'll give a range of values that would work for us.

The desired cells would have 35~70 Ah of capacity and peak discharge rate of 5~10 C, with the nominal tension being around 3.2~3.7 V.

We are a bit afraid of using LiPos because it is quite unstable with over/undercharging and we have never ever worked with it. But it is still an option for us.

EDIT: forgot to say we are looking for prismatic cells.

Thanks!

 

[Marv1337n]

Well, since we are talking about a formula vehicle, the mass is pretty important. Since the capacity and discharge rate depends on each other I'll give a range of values that would work for us.

The desired cells would have 35~70 Ah of capacity and peak discharge rate of 5~10 C, with the nominal tension being around 3.2~3.7 V.

We are a bit afraid of using LiPos because it is quite unstable with over/undercharging and we have never ever worked with it. But it is still an option for us.

EDIT: forgot to say we are looking for prismatic cells.

Thanks!

Every battery will burst into flames when you overcharge it so that isn't really an argument.
You can counter the discharge with a simple low voltage cutoff, problem solved. I've got these voltage alarms: https://www.ebay.de/itm/4x-Lipo-Ala...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649 they monitor each cell and will warn you when one gets too much discharged (you can set the voltage point for that in 0.1v steps).
Get a high quality balance charger and don't charge it unattended and you're golden. You won't get better discharge rates than from a LiPo, fact. They're also super light and you can get all sizes and voltages. Need more capacity? Just add a parallell connection, need more speed? Just add a new series connection. You really don't have that freedom with other cells because you need expensive hardware to reconfigure your battery pack.

 

[gabriel_ribeiro]

Thanks Marv!

So, could you recommend me some sites/stores which sell LiPo batteries?

I got pretty excited about the 40T, even though it is not LiPo.

 

[Marv1337n]

Thanks Marv!

So, could you recommend me some sites/stores which sell LiPo batteries?

I got pretty excited about the 40T, even though it is not LiPo.

The 40T seems pretty nice even though I haven't built a battery with them yet. 35A at 4Ah is just great for a round cell. I'd suggest HobbyKing because they're pretty cheap and got all sorts of voltages and capacities. I've bought 3x 6s 20000mah Multistar LiPos from them. https://hobbyking.com/de_de/turnigy-high-capacity-battery-20000mah-6s-12c-drone-lipo-pack-xt90.html

 

[Punx0r]

Is there a requirement to use new cells? If not, salvaging batteries from hybrid or electric vehicles can be a good (and inexpensive) means of obtaining large-format and, most importantly, high quality OEM cells.