# Daydreaming number crunching



## major (Apr 4, 2008)

Tomdb said:


> Drivetrain specs
> Motors 4
> total peak power 1.0 Mw (1000Kw)


Are you aware of this guy? Uses four 200kW motors. I think he has exceeded your budget estimate, but it is a nice car. Good luck getting $ backing. 

http://www.draysonracingtechnologies.com/home.html


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## Tomdb (Jan 28, 2013)

Im very aware of them. Ofcourse they have exceeded budget, they have a big team working behind them. 

This will remain a dream, unless some guy with crazy money wants a fast car.

However at my job we are working on a more obtainable sports car.


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## Hollie Maea (Dec 9, 2009)

You're in luck! Evdrive has everything you need, and would actually sell them.

http://www.evdrive.com/products/evd-motor-controller/

The motor in the seventh set down would be able to easily handle the 250kw per wheel (It's a remy core with oil cooled rotor so it doesn't melt a high power). Right now you would be limited due to the controller to a mere 600kw, but not to fear; the Rinehart 250kw controller is coming out shortly. They also have a VCU that will do all the torque vectoring for you.

And it won't even bust your 1 million dollar budget--for the 600kw system you'll only pay 80k for the motors and controllers. Add probably 10k each to get up to the 250kw controllers, so maybe 120k.

Your battery pack will probably cost 60k--maybe more if you have someone assemble it for you. I would go with 18650s so you can hit your weight budget, and fit them all in the car. LG has some 2.5ah cells that can output 35A (14C) so your 100kwh pack will be able to handle the power output. Also they are 48 grams each, so you'll be able to keep it under 600kg.

I would budget another 50k for the high power reduction gears, as those would probably have to be developed and some engineering costs will come in, but still that gives your whole drive train for a quarter of a million, leaving you with 750k to use for finding a car that won't get torn apart from a megawatt of power.


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## dougingraham (Jul 26, 2011)

The batteries are the problem. If you want a crazy fast car you have to use cells that can do 50C or more. Otherwise the vehicle will be overloaded with batteries. The RC hobby cells are about the most cost effective for these power levels. Hobby King carries a line of cells that are rated for 130C burst but 65C continuous. I suspect that if you treat the 65C as the 10 second rating you could use these. This means you can dump a pack in under a minute. It also means you are not spending tons of money to get the power levels you need.

I was doing my own daydreaming number crunching about drag racing. I built a spreadsheet to analyze the different configurations to optimize for a pack that could sustain 1000 amps at 192 volts and found the pack to do this was 3.6kwh, weighs 28kg and cost $3200. If you trusted the 130C rating it would be half of that. To get to the megawatt you would need around 5 of these packs. Knowing what voltage and current would let me look through the data and find a pack combo that just meets the requirements. In this case you need 20 of these particular battery packs placed 5 of them in series and 4 paralleled. Since the packs are 12S at 4AH this gives 16 amp hour at 222 volts (60S 4P of 4AH cells.) This would not be unwieldy to connect up using some bus bars with connectors on them.


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## Tomdb (Jan 28, 2013)

@ Hollie

Ev drive would indeed be quite a good choice of motor, i have indeed seen them and used thier weight/specs/price to ballpark some of the choices i made i my thinking.

The battery indeed i would go for 18650's but i would do the pack welding myself, investment is small enough to justify for a million dollar project. 
I have developed and researched into batteries a shitload (my job as development engineer), so the batteries are my smallest concern, so much choice. I have a few excel sheets for specing out battery packs, which give you pricing, weight, energy, configuration and preformance figures based off of your voltage and energy input.

Gears are indeed an expensive issue, but not overcome able.

Now the car ist the hard part, I set the weight limit for the compleet vehicle at 2000kg, 1000kg for just the chassis and body. This should be doable, however tires which will take the power and apply it to the road that is a different thing

@doug

Your reasoning is valid if you go for lightness, im going for weight (traction). 600kg for 100Kwh is 170 wh/kg and the cells do a max of 10c for 30seconds, these are very attainable figures nowdays, and with a good cell life too.

How ever for dragracing (lightness) you are right on the high preformance RC cells, however i would go with a kokam pack anyday over the rc cells just for cycle life.


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## dougingraham (Jul 26, 2011)

Tomdb said:


> How ever for dragracing (lightness) you are right on the high preformance RC cells, however i would go with a kokam pack anyday over the rc cells just for cycle life.


I contacted Dow/Kokam several years ago trying to purchase some batteries. I was unable to obtain a price from them. They wanted to engineer the battery pack for me. I had a catalog and wanted to buy X many cells of a particular model number (SLBP80460330H 100AH.) These were 5C continuous rated and 8C pulse which is really about the same as the prismatics we use today. I gave up after a few email exchanges. Now that Dow has sold off its interest in Kokam maybe things are different but I got the impression that unless I wanted a LOT of cells they were not really interested. The we only sell to OEMs syndrome.

Because of this I would be terribly reluctant to ever consider a Kokam product. It would even taint my buying or recommending an OEM EV that used their batteries. If you get the impression that I am still more than a little angry you would be correct.


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