BIG battery for eletric race car

[mateusleo]

Hello Folks,

My colleagues and I, maintained by our university, are trying to build and eletric race car for Formula SAE Student. We are actually struggling with the battery, because it's kinda hard to import stuff with government money in Brazil, also, its hard to find a company that builds us the pack. We firstly meant to use LiPo, with BMS ofcourse, but we couldn't find who would bult it. The voltage limit on this competition is 300V, we cannot draw more than 80kW from the battery, but we could draw as much as we could from capacitors, but those are out of our primary plans. Our motor is going to take average 60kW, so we need a battery that can supply something arround 150-200A continous. We also plan to have a pack that can be charged for more than 300V, and only charge it to this limit, so we get a more flat voltage slope during the discharge process. It needs to be as light as possible, which doesn't mean we want LiPo, we have agreed to sacrifice some weight in order to get a safely battery. For example, if using LiFePO4, we would make it 88 series (hypothetical) and only charge it to 300V(3,4V/Cell), not to 316,8V(3,6V/Cell).

Well, the main purpose of this post is get reference about companies that could build us the pack we need, any chemistry will be analised. It must be a reliable supplier, with good reputation. So, suggestions will be really appreciated.

Mateus.

 

[r3volved]

I would start by looking for wrecked EVs and hybrids with batteries intact. Often a 'bad battery' turns out to be a cell or some construction failure. Could easily trim out bad cells and rebuild a good working pack from one or a couple bad ones.

 

[mateusleo]

I would start by looking for wrecked EVs and hybrids with batteries intact. Often a 'bad battery' turns out to be a cell or some construction failure. Could easily trim out bad cells and rebuild a good working pack from one or a couple bad ones.

We can't buy used stuff, the university will only pay for new stuff

 

[Willow]

...you will want to - need to, charge your batteries to at least 3.6 volts - so you can top-balance them... LIFE cells simply are not even close to full at 3.4V.

There is no need to use such high voltage to make your car go fast. 300V region is more than deadly. The right setup at 100V will be just as effective - and you can keep the weight down...

You could use large prismatics such as the CALB cells (2-3C discharge).... or build a high AH pack of 18650 cells - samsung 25R or Sony VTC5 - for ample output.

Both are obtainable relatively easily.

 

[mateusleo]

...you will want to - need to, charge your batteries to at least 3.6 volts - so you can top-balance them... LIFE cells simply are not even close to full at 3.4V.

There is no need to use such high voltage to make your car go fast. 300V region is more than deadly. The right setup at 100V will be just as effective - and you can keep the weight down...

You could use large prismatics such as the CALB cells (2-3C discharge).... or build a high AH pack of 18650 cells - samsung 25R or Sony VTC5 - for ample output.

Both are obtainable relatively easily.

By checking the other teams, we more likely cant win with 100v, mainly because we will need alot of amps to keep with the same power as 300v. You'r right about the life, it might be better to charge them to 3.6 instead. We have contacted headways, they said they can build this pack for us, but it's gonna be really heavy. About 18650, that would be a really nice battery, the problem is that this is our first attempt and we do not have the skills to build a BMS for so many cells in series (70-80s). If someone can suggest a company that builds 18650 packs with BMS or sells the DIY packs with respective BMS thats would be a nice solution...

 

[athletic91]

Many many 6s 16ah multistar packs. Problem is hobby king will not stock the amount you require

 

[parabellum]

What is the capacity needed?

 

[Willow]

What about 2 motors, with 2 controllers - I'm thinking something along the lines of the Adapto Max-E, you'd be able to pull 30KW on a super light weight machine, given your battery pack is going to be much smaller (in the order of a maybe 200kg). Adapto is a complete system - with a simple BMS up to 24S if you use LiIon and 28S if you use LiFe. Controllers have field weakening so you can make the motor spin even faster than they would normally be driven. And they work as the charger to enable charging of up to 70Amps

...Hell, why not just use 4 motors, 4 Max-E's.... for your 60KW. 24S 60P 18650 cells (samsung 25R - 2500mAH) - for 100V 150AH - pack will be capable of peaks of 300KW.

Power to weight and efficiency are your big factors outside of aerodynamics.

M2C.

 

[mateusleo]

What about 2 motors, with 2 controllers - I'm thinking something along the lines of the Adapto Max-E, you'd be able to pull 30KW on a super light weight machine, given your battery pack is going to be much smaller (in the order of a maybe 200kg). Adapto is a complete system - with a simple BMS up to 24S if you use LiIon and 28S if you use LiFe. Controllers have field weakening so you can make the motor spin even faster than they would normally be driven. And they work as the charger to enable charging of up to 70Amps

...Hell, why not just use 4 motors, 4 Max-E's.... for your 60KW. 24S 60P 18650 cells (samsung 25R - 2500mAH) - for 100V 150AH - pack will be capable of peaks of 300KW.

Power to weight and efficiency are your big factors outside of aerodynamics.

M2C.

4 motors will require an eletric differential drive system to match wheels rpm, we can't draw more than 80kWh from the battery, and we are already processing the motor purchase, can't change right now. It's kinda hard to buy stuff with government's money in Brazil

 

[Willow]

elec. differential is handled by the Adapto.

Battery will be capable of outputting much more power than you will require - which is ideal.

 

[Ohbse]

Need more information!

What is the projected use case for the vehicle? How far and how fast does it need to travel to be competitive? How is it to be tested?

What is the motor you've already purchased? Controller?

LiFePO4 is definitely not the way to go with performance in mind. Specific power density is key and lipo will out perform LiFePO4 by a LOT. There is a varied spectrum of lipo chemistries that range from outright power to outright capacity and everything in between. Without knowing your energy capacity requirements it's difficult to recommend a solution. If you need to complete a 60 second sprint race and a drag race then you will require very little energy capacity compared to running a 40 minute road race. This can DRAMATICALLY alter not just your battery selection but also the shape and weight of the overall vehicle.

 

[Drunkskunk]

Perhaps contact Nissan, Honda, or GM in Brazil, and see if they will sell or donate a battery from the Leaf, Insite, or the Volt?
Since I believe those companies are already in Brazil, you might be able to avoid importing issues.

 

[mateusleo]

Need more information!

What is the projected use case for the vehicle? How far and how fast does it need to travel to be competitive? How is it to be tested?

What is the motor you've already purchased? Controller?

LiFePO4 is definitely not the way to go with performance in mind. Specific power density is key and lipo will out perform LiFePO4 by a LOT. There is a varied spectrum of lipo chemistries that range from outright power to outright capacity and everything in between. Without knowing your energy capacity requirements it's difficult to recommend a solution. If you need to complete a 60 second sprint race and a drag race then you will require very little energy capacity compared to running a 40 minute road race. This can DRAMATICALLY alter not just your battery selection but also the shape and weight of the overall vehicle.

I'll get the full information about motor and controller specs as soon as possible and bring them here, they'r in german...We have two main tests, drag race and endurance race. We don't mind about lipo or lifepo4, but our problem involves many stuff to do with the problems about buying a new battery, its hard to purchase stuff with the governments money, so we don't want a chemsstry that will last only 300~ cycles. Actually, those high rate 18650 are pretty interesting, but i'm struggling in finding a company that builds them. We need about 6kWh of energy to the endurance test and it must deliver good amps for the drag. We are forbidden to draw more than 80 kW from the battery, but our motor is probably taking only 68kW, so those are our limits. Less than 40kg would be great, but not sure if possible.

Perhaps contact Nissan, Honda, or GM in Brazil, and see if they will sell or donate a battery from the Leaf, Insite, or the Volt?
Since I believe those companies are already in Brazil, you might be able to avoid importing issues.

They'r in Brazil, they just dont sell/build or have any solid plans about EV's here. We'll get in touch anyway. But we don't have a solid stuff to show em, no company will sponsor a team with nothing hahaha. But, however, this is the begginig, i belive that when we get the motor purchased, frame build and stuff like that, we'll be able to get something from companies. We'll have to deal with importing anyway, so far we only found ONE company thats builds big battery packs in Brazil, but they work with low C rate cells, we enetered in touch and they seem very experient, also, they only work with safe cells. We asked them about A123 cells, because they are safe, relatively lightweight and 5C is not bad, we are waiting for the answer maybe this week.

elec. differential is handled by the Adapto.

Battery will be capable of outputting much more power than you will require - which is ideal.

If not asking too much, could you provide me the link for Adapto's page? Thanks

 

[mateusleo]

Anyone knows a company that builds custom or modular BMS?

 

[Willow]

yes

 

[mateusleo]

yes

Yes is a very mean answer hahaha

 

[999zip999]

Bro no need to worry.
Half an answer from half of a ?
Good luck as I was talking to a guy wanting an ebike for So. America and didn't know how to get it back home or to get one.

 

[mateusleo]

Where can i buy large amounts of samsung INR18650-25R cells? Other reliable brands with good capacity and c rate will work as well. We'll need about 800-1000 cells.

 

[CroArcher]

http://eu.nkon.nl/rechargeable/18650-size/samsung-inr18650-25r-presale.html

 

[Ohbse]

Where can i buy large amounts of samsung INR18650-25R cells? Other reliable brands with good capacity and c rate will work as well. We'll need about 800-1000 cells.

EVVA or Shenzhen E-fire Technology Development Co LTD from Alibaba. Excellent service, prompt quotes and legitimate shipping options meeting all legal requirements. Various payment methods available. I have no association with either, just had good experiences. Much cheaper than from EU.

 

[999zip999]

Some companies will spot weld in parallel strips for free or low cost. Then is ez to series. Make sure they have the gasket on the positive side.
Plus how is that sunthing battery doing ?

 

[CroArcher]

http://endless-sphere.com/forums/viewtopic.php?t=67661