DIY Electric Car Forums banner
1 - 20 of 31 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter · #1 · (Edited)
Hi All,
My name is Alex. I'm a big EV enthusiast and I have decided that I want to build a race car. I have little experience disassembling and reassembling cars but I am fairly apt with my hands and I'm fairly bright.
Here's a little bit about me, I am a student at a small university in upstate NY. I worked for two years for the University of Toronto on the original Surface and Google Glass with regards to notifications. I am going to major in Physics.

I have considered which car will serve as the basis for my car. I would prefer if I kept that private for now. Its a small car, perfect for racing.

The range I would like to achieve is around 80 miles at very high speed.

Parts:
Yasa 750 (H if available) x4 probably.

Battery pack ideas? Looking for Li-Ion

Rimac Battery Packs - if they are for sale.
Drive inverter?
Reinhart Controllers - PM250


Basic knowledge of EVs:

Energy goes in to the car from the grid through an adapter into a charger. The charger fills the pack. When you push down on the accelerator the controller allows current to flow into the inverter which converts the DC -> AC to spin a brushless motor. The motor usually connected to a reduction gear or gearbox spins the gears etc.

Is that correct? How does one program regenerative breaking?


That is really all that I have thought about.
I'm willing to push the limits financially right now. I would, however, like to keep track of the price of the parts.

Any and all help is greatly appreciated.

Best,
Alex
 

·
Registered
Joined
·
1,019 Posts
I'm sure you are aware that this will be expensive, and presumably you have a budget.

Forget about supercaps. Energy density is way too low for what you want. Modern batteries are plenty fast, and if you assemble a battery that gives the range you are talking about, you'll have lots of power on tap.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #4 ·
150 miles at very high speed ... Battery pack alone would be near 30,000$ for a civic size car ...
The car is a single seater. Looks akin to an F3 car. Space is going to be an issue, as is weight distribution. I know that the battery will be costly. I'm interested in seeing how costly. Do you know of any suppliers with battery packs that have a very high output?

A
 

·
Registered
Joined
·
512 Posts
Check out tekbattery.com since space will be limited they can make batteries in any shape you want .... Very good power outputs but expensive obviosly
 

·
Administrator
Joined
·
6,380 Posts
150 miles at very high speed ... Battery pack alone would be near 30,000$ for a civic size car ...
No not even close - triple it $90,000

150 miles is difficult and expensive - add "at very high speed" and you are getting close to impossible

Tesla's get 200 miles + at normal road speeds, at 120mph + that will drop to about 60 miles
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #9 ·
Check out tekbattery.com since space will be limited they can make batteries in any shape you want .... Very good power outputs but expensive obviously
Thank you for your help. From what I'm seeing, these batteries can only be charged at low voltage. I need to be able to charge them faster. This would work as a 12v for the electronics but not as the battery pack.

I am in the process of drafting an email to Rimac Autombili, what questions should I be asking about their battery packs?

So far:
Dimensions, price, weight, customization.

I know I need to know max output and continuous output. Can someone explain what that means?

Sorry if these are dumb questions, clearly I'm new to this.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #10 ·
No not even close - triple it $90,000

150 miles is difficult and expensive - add "at very high speed" and you are getting close to impossible

Tesla's get 200 miles + at normal road speeds, at 120mph + that will drop to about 60 miles
The 85kWh pack gets 260 at 320Wh/mi. That pack costs 30k (if I remember correctly) using 600Wh/mi I'd get 130 mi. Car has a low CD and I am hoping to keep it very light.

The issue is I wouldn't be able to fit an 85kWh pack in the car. If I'm lucky I can maybe fit a 65kWh pack. The car has maybe 140 in of usable length. Most of the space is in the back where the engine was.

It would be interesting to see if you can line the driver cell with batteries.

I draw the line at 90k for batteries.
 

·
Registered
Joined
·
4,458 Posts
No not even close - triple it $90,000...
That was my first thought.

A perfect combination of all-out race performance and street type range, at this point, isn't really going to happen. You're going to compromise one or the other.


...The issue is I wouldn't be able to fit an 85kWh pack in the car. If I'm lucky I can maybe fit a 65kWh pack...
For 150 miles in a fast race vehicle, you're automatically talking about the highest power density Lipo cells available, just to build a pack capable of meeting your goals, without weighing more than, and being half the size (or more) of, the vehicle you're putting them in. Your biggest issue then, is going to be cycle life. You go from the thousands of cycles road-going, daily driver, EVs talk about, to hundreds of cycles - meaning you start planning very carefully when and how often you'll use them.



...I draw the line at 90k for batteries.
You may not make it then. When researching the same thing for the Inhaler, I priced just the cells for a high-power Kokam-based pack at around $50K (much less range, but possibly more power than you're after?). That's not including connections, case - and most importantly BMS - you're not going to run these cells without a really good BMS, unless you just like the thought of roasting money over an open flame.

So, with great deals/partial sponsorhip, one $50-100,000K battery pack, if it's in your budget, fine. One or more a year, and you start to see why we only see occasional all-out performance demonstrations from the fastest, most powerful, EVs. It's a bit different than that 1200hp dino-burner that just wasted $200 in race fuel at the track.

To add insult to injury, generally, the faster you charge and discharge them, the lower the cycle life number gets...



Thank you for your help. From what I'm seeing, these batteries can only be charged at low voltage. I need to be able to charge them faster. This would work as a 12v for the electronics but not as the battery pack...
Those are 12v replacement battery packs made from lithium cells. YOu will charge your pack at pack voltage, with a charger made for it. How fast is dependent on how much $$$ you spend. The LiPo cells, with good BMS, can generally take a pretty fast charge rate - so it's a matter of how much charger you are willing to buy/can afford, and how much power you can safely tap from your source.



...I am in the process of drafting an email to Rimac Autombili, what questions should I be asking about their battery packs? ...

...Sorry if these are dumb questions, clearly I'm new to this.
We're here to help you learn. You might want to wait a while on that letter to Rimac, because if they get the sense that you don't know what you're doing you'll probably get a pleasant blow-off or no reply. Most companies are very busy and get bombarded with requests from well-meaning, curious, but out of their league enthusiasts; and they're also constantly thinking about liability, negative feedback/word-of-mouth from misuse, etc...
 

·
Registered
Joined
·
512 Posts
Tekbattery has all electric vehicule batteries and nuild packs to your needs i had researched them a lot a few years back but price turned me off i couldnt afford 20,000 in batteries back then and actually still cant lol
 

·
Registered
Joined
·
2,046 Posts
Space is going to be an issue, as is weight distribution. I know that the battery will be costly. I'm interested in seeing how costly. Do you know of any suppliers with battery packs that have a very high output?
Firstly, just about any battery with enough range to go 150 miles will have high enough output. Back of napkin calculation:

Single seat car with everything in it weighing about 1000 lbs (this will be very difficult) would get 100wh/mile at reasonable speeds. This means to get 150 miles range you would need a 15kwh pack. Since you are talking about higher speeds you wont get 100wh/mile. Lets double that so you would need a 30kwh pack. Lets assume 300 volts which means 100ah cells. If you used 100AH calb cells in a 94S1P arrangement you are talking about a pack that could realistically output 271kw (363hp) for perhaps 10 seconds at a time dropping back to an average of 81.2kw (109hp) or less the rest of the time. Such a pack would weigh more than 705 lbs (320kg) So for the driver and the weight of everything else you have only a 295 lb budget. Doesn't seem remotely practical. If you use Tesla's style batteries in a pack of 30kwh it would consist of 2133 cells (3.7 volts and 3.8 ah) have a minimum weight of 211 lbs (96 kg) Such a pack would be arranged as something like 79S27P and be able to do a peak output of around 78.9kw (106hp) with a sustained rating of about half that. The Tesla style pack would need to be larger to do the power levels you want. But at 211 lbs it would give you a weight budget for driver and the rest of the stuff of 789 lbs.

There are higher output batteries available. Cost is high. RC hobby LiPo packs are an example. A super lightweight minimal car will need a 30kwh pack to make 150 miles. Such a pack will cost around $904 per kwh so a 30kwh pack would cost $27114. It would however be able to put out all the power you need as you can dump these packs in less than a minute meaning they can do an average output of around 1.8 mw (2412 hp) and a peak of 3.6 mw (4826 hp). At least if you believe the advertising ratings. Oh and a 30kwh pack would weigh more than 275 kg (605 lbs).

In all cases I am quoting just the weight of the cells. These are unrealistically low numbers as it does not include the inter cell connections or mounting hardware or the cooling system that will need to be used.

I believe you have unrealistic expectations for your project. You can do the 150 mile range or the high speed but not both at the same time. But it doesn't hurt to shoot high and then back off to something that can be done. You might want to research the Formula E race cars. They probably have the performance level you are wanting and a pretty big budget so you can see what is being done for real.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #14 ·
You may not make it then. When researching the same thing for the Inhaler, I priced just the cells for a high-power Kokam-based pack at around $50K (much less range, but possibly more power than you're after?). That's not including connections, case - and most importantly BMS - you're not going to run these cells without a really good BMS, unless you just like the thought of roasting money over an open flame.
Okay. So what about swapping multiple packs around. Let's say that the price isn't a big deal. If I had multiple (5?) smaller pack with enough range for 80 miles, would I increase cell life? The way I think about it is that if I deplete one pack to 10% and I put it to charge (outside of the car) while the next pack is swapped in I would only be depleting at a faster rate.

What matters more, getting to 0 SOC or running through the SOC quickly?

Is BMS always separate from the battery module?
 

·
Registered
Joined
·
1,019 Posts
Here's what I would do, if I had your desire and your budget:

I'd stick with the four motor concept. I would drive them with four Rinehart controllers. Go with the PM150 series--there is no other controller available that will be small enough to fit four in your little car; it is by far the most power dense AC controller available publicly. Don't worry about it "only" being 150kW. That's a total of 800hp in your car.

As far as the battery goes, shoot for a 50kwh pack. That will give you a bit more than the 150 miles you need, but you'll need that size to get the power you need. Your best bet will be LiPo batteries rated at 20C. Discounting voltage sag, a 50kwh pack at 20C gives you 1000kw. With sag, it'll run your 4 motors.

The Rimac battery pack isn't going to cut it. They are LiFePo4 batteries, which is a great chemistry but it isn't that power dense. Rimac gets around it by having a bigger overall pack than you would be able to fit into your car.

In addition to talking to Rimac, I'd email Steve Tice at evdrive.com, who might be more likely to have things available (and which would eliminate the complication of importing from Europe). He'll likely try to sell you on using his motor as well, which might not be a terrible idea anyway. Although they are twice as heavy, they also have twice the continuous power rating, due to liquid cooling of the stator and rotor.

All of this is assuming you have money. Needless to say, to get the attention of evdrive, Rimac or anyone else selling super high end stuff you'll need to come to the table with money. You haven't mentioned your budget yet, but your 4 motor AC supercar is going to cost over 100K just in motors controllers and batteries.

Oh yeah, you'll need a reduction gearbox for each motor too :) If you can pull this off, it'll be epic.
 

·
Registered
Joined
·
4,458 Posts
Firstly, just about any battery with enough range to go 150 miles will have high enough output...
I don't think you can say that, that easily. "High enough output" is relative, and depends on the intended application. My idea of a high output pack used to be a LiPo pack that could supply a Shiva, without significant sag, for as long as my foot would stay down. Now, my idea of a high output pack is one that will provide enough voltage to spin an AC motor to 10K, without sag, and at drastically reduced current levels. Intended use, component choice, and vehicle specifications, all have a say in what constitutes high output. As usual, we're shooting in the dark here, because we don't have any of that, as solid data, to work off.

Anyway, your numbers agree and make the point that it's just not practical, at this time to try to accomplish both goals in the same pack.




Okay. So what about swapping multiple packs around. Let's say that the price isn't a big deal. If I had multiple (5?) smaller pack with enough range for 80 miles, would I increase cell life? The way I think about it is that if I deplete one pack to 10% and I put it to charge (outside of the car) while the next pack is swapped in I would only be depleting at a faster rate.

What matters more, getting to 0 SOC or running through the SOC quickly?

Is BMS always separate from the battery module?
You never want to go to 10% SOC, definitely not 0%, unless you like buying cells and building packs. The rule of thumb around here seems to be 20%. I generally figure 25% SOC with LiPo, just to give them a little extra margin.

As for 5 smaller packs, the same rules apply. How quickly are you discharging them, how often, and how fast are you re-charging each one? If having more lets you charge the others slowly, while one is in use - maybe. The problem I see is you're going to push a smaller pack harder for the same performance, so did you just eat your own lunch?
 

·
Registered
Joined
·
7,791 Posts
You never want to go to 10% SOC, definitely not 0%, unless you like buying cells and building packs. The rule of thumb around here seems to be 20%. I generally figure 25% SOC with LiPo, just to give them a little extra margin.
Heck, I'd go to 0% to win a race :confused: Done it a number of times. What hurts is hitting zero SOC 50 yards from the finish line while leading a 9 lap race at Laguna Seca :(

Zero SOC isn't zero voltage. The battery can take it. It's racing so I ain't looking to get 3000 cycles. I don't want to carry any extra battery mass than I need to finish the race.
 

·
Registered
Joined
·
4,458 Posts
Heck, I'd go to 0% to win a race :confused: Done it a number of times. What hurts is hitting zero SOC 50 yards from the finish line while leading a 9 lap race at Laguna Seca :(

Zero SOC isn't zero voltage. The battery can take it. It's racing so I ain't looking to get 3000 cycles. I don't want to carry any extra battery mass than I need to finish the race.
We (not specifically you and I) have had this type discussion here a few times. There's all-out racing, with Nitro Top Fuel and Funny Car drag racing at the extreme, where you leave nothing on the table. Everything is expendable, parts, fuel, oil is constant loss, etc, etc. Then, at the other extreme, there is bracket-level amateur racing, where vehicles and parts are expected to last for a season. It's all in what type of racing a person is engaging in and what the competition is doing.

9th lap at Laguna Seca, I assume in a championship series, where the bike is headed back to the shop to be gone over with the proverbial fine-toothed comb, and everyone else in contention is willing to risk it all - yes, leave nothing on the track.

I'm a grudge racer (formerly a street racer) and a part of the game there is to always have something left in it - never show your full hand. And, always be ready for the next sucker, errr, I mean challenger, to try you after watching you just squeak out a victory...

Again, it's all in what you're after and I am surprised at the tendency of such a science-based community to draw lines in the sand so quickly. :confused:
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #19 ·
Hi, I am back with a couple of questions.

https://www1.eere.energy.gov/vehiclesandfuels/avta/light_duty/fsev/fsev_ev_power.html

This article makes it seem as if an AC motor can only have a single speed transmission. Is it not possible to use multiple gears with an AC motor? If so why?

Do I have to do anything differently because I want to use an axial flux motor?

I'd like to create a parts list.

So far I have:
Motor
Drive Inverter
Controller
Transmission
Battery
Charger
Adapter
Car

What am I missing?


Thank you all for your help. I really appreciate it.

A
 
1 - 20 of 31 Posts
Top