New EV Supercar Project

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Zen1

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Hello All.

I'm currently working with a group of replica specialists who have been commisioned to produce an electric supercar. Me and a few colleagues are in China next week to visit some partners, and have an appointment with a well known cell manufacturer.

My question is this.

The car will be constructed of carbon kevlar almost entirely and therefore be very light. Who here would use 1 motor (driving the rear wheels),and who would use four (1 for each wheel)? why?? How many cells (therefore power) will i need to create a 0-60mph in 3-4 seconds with top speed 200kmph (approx) :?: with a race-like range? i am rather dunce-like at physics calculations - someone please point me to a EV speed/distance Vs cells needed chart for dummies!

Also - can anyone recommend a good controller system/accelerator pedal for a supercar?

Who makes the best motors??

Batteries??? Thundersky???

There might be some proper backing behind this project so any "Dream Spec-lists" with reasons are very welcome
Thanks in advance for any help anyone can give me
 
Thundersky for a super car is not going to be what you want.

Those cells are some of the worst quality as far as Lifepo4 goes, compared to almost any other manufacturer.

I've heard cells from PSI/BMI and Headway are good, they are somewhat large format, so easier to work with. If it were me, i'd stick to a central motor driving the rear wheels. You than can use mechanical gearing to your advantage.

Concerning this:
someone please point me to a EV speed/distance Vs cells needed chart for dummies!
Click to expand...
You will NEED to learn all about the different cell characteristics, and the differences between the chemistry's.

First thing you need to know is that cell count != power. Not all batteries from different manufacturers are created equally. For instance, Thundersky claims I think 3c discharge. For a 60ah battery that is 180 amps without hurting the battery. However, the reviews of Thundersky cells (that i've seen, things may have changed by now) show that drawing 3c from their cells will shorten their cycle life GREATLY, and also will not provide you anywhere near the claimed 60ah figure. When discharging at 3c 38ah could be drawn from the cell before running out of power, at 2c (120amps) I think it was 44ah, and at 1c (60amps) it was 51ah. This is on a 60ah cell. It should give roughly 60ah no matter how fast you discharge it (up to rated that is), with only small drops in available amp hours.

From that report I read on Thundersky batteries, it was easy for me to see that they are first of all over stating the amp hours that the cells can put out, and secondly are over stating the safe discharge rate the cells can handle.



I guess I need to know how far you are normally going to be going in a race to be able to tell you "you need this much energy storage in batteries to go that far, with the kind of speeds you will be going".

Keep in mind that an average EV gets 250-400 wh/mile at highway speeds. Your aero body will get better than average, not to mention if you go with lithium for some weight savings.
 
Hi Zen
Fascinating project. Could you give us more details of the performance requirements: Weight of the car minus drive train, minimum range, intended use (road or track), average speed requirement, etc?

Like tostino says, Thundersky are not high-performance cells - they're (relatively) cheap, but performance-wise are only really good enough for everyday runabouts. For a performance car you'll probably need to look at A123 cells or LifeBatt/BMI. The A123 cells are very small, and building battery packs from them is a specialist job. There's a guy on the DIY electric car forum who is offering to build packs complete with battery management system (essential) for a decent price right now: http://www.diyelectriccar.com/forums/showthread.php/a123-batteries-built-into-modules-3-29007.html

LifeBatt are just bringing out some new cells with discharge rates close to that of A123 (around 25C). These cells are about three times the size of the A123 cells and have screw terminals, which makes building the pack a much easier process.

As for drive layout, a single motor, rear-wheel drive configuration would obviously be simplest, but for performance, how about two motors, each driving a diff directly – front and rear. Good weight distribution, four-wheel drive, redundancy. Another advantage of using two smaller motors over a single larger motor is that they have less rotational inertia, so spin up faster.
 
In case you haven't already, you can surf the replicas and racers at http://www.evalbum.com/. Plenty of examples there.

Re lithium batteries: the proven race-capable cells are from A123 (google "killacycle"), but other makers are quickly rising (PSI, Headway).
 
My idea is to take a current chassis design, and then modify it to electric, and the one I have in mind is the T-Rek Three Wheeler. campagnamotors.com
 
Firstly, thanks for your input guys.

So TS batteries are not suitable for this application in your opinion. Do you think they are good price/quality wise for small E-city cars?

Headway are good? many complaints about them on this site - who to beleive?? many people seem to have agendas and motives for promoting or slating these companies.

Im visiting TS and Headway in next month or so and will report back what i see.

A123 seems the way to go to be sure, what do they cost compared to Headway/LifeBATT/pmi/bmi etc?

we will have to make up packs ourselves as they will be part of the monocoque itself.

we would like to be able to swith between straight drag-racing mode, and "Single stage Rally" settings (I'm assuming that this is down to the controller)

we approximate the monocoque and bodywork to come in around 300kg

How do lifebatt/BMI, A123, Headway, TS all compare for price??
Who leads the way in speed for charging (c rate)/ overall quality etc(in order) (EVERYONES OPINION PLEASE!)
While I see this is a new(ish) technology, its unstable and most companies are kind-of in "beta" mode so who's currently getting better/cheaper/more proffessional etc?

Thanks for the link to the guy doing packs on here Malcolm, but we will have to do that ourselves.

@ Tyler.

I'm very impressed with the builds on EVALBUM, who do the guys building those rate for cells?
so you think headway are getting their act together nicely?
thanks for the links to killacycle also - what a beast!
 
Up until recently, lithium mixtures have not been able to handle discharge at race values; so most of the racers have been using PbA. This is changing with newer lithium suppliers trying to catch up with A123.

ES member OATNET has documented converting a van using headway cells: http://endless-sphere.com/forums/viewtopic.php?t=8012

There is a second headway group-purchase in progress, http://endless-sphere.com/forums/viewtopic.php?f=9&t=9824&start=105. You may want to watch that topic for user reports.
 
A123 are the most expensive; PSI,BMI (Headway, LifeBatt, whatever) are in the middle and Thundersky/HiPower are the least expensive. Thundersky cells seem to be OK if you don't exceed their discharge ratings (3C). I think they've gotten a bit better lately, but expect a higher failure rate. The large prismatic cells make pack construction easier.

For really high performance applications, I've seen some large LiPo cells used on a drag bike, but I'd be afraid of those in an accident (fireball).

Yes, you can tradeoff between economy and performance by programming the controller.

As far as motors go, I'd suggest some kind of induction motor for that power level, but they are very expensive. Something like the ones from AC Propulsion. http://www.acpropulsion.com/tzero/index.php
 
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