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Sun Sep 06, 2009 7:29 am Post subject:
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Computerpro,
This is definitely a board for crazy ideas and extreme goals. I can understand your private needs, but please do ask as many questions as you would like! I'm not much technically advanced on the welding, chassis engineering side of things here, but the electrical side I may be able to help.
The vehicle that I'm building, Amata, uses a 134 HP, 97% efficient, 100 kW motor in it, but it is powered by a fuel cell stack. Yours, I assume, is going to be built using lead-acid batteries or lithium-ion to produce the desired results? If this is so, a SUV will definitely be good - and bad. For one, the SUV will give you plenty of space for the batteries (which you will need), plenty of loadable areas (which you'll need), and a very flexible platform. However, it weighs a ton. Actually, it weighs about 4 tons, and with the batteries you can nearly add another!
The weight factor is a problem for electric vehicles powered by batteries. To propel an object forward in terms of horsepower, you apply the following math:
The distance the car must move is given by:
s = 1/2at^2 (Where a is acceleration in ft/sec^2, t is time, and ^2 is squared)
s = 1/2(10 ft/sec^2)(8^2 seconds)
s = 320 ft.
This is roughly 54.55 mph in 8 seconds, which requires s number of feet (320).
F (force) = weight/gravity * acceleration (here is where your weight comes in)
F = 4500/32.2 * 10 ft/sec^2
F = ~1398
Now you plug that into your HP requirement, which is:
1 horsepower (hp) is equal to 550 ft-lb/sec
hp = (force x feet / time * 550
hp = ((1398 force x 320 feet) / (8 seconds of acceleration x 550 ft-lb/sec))
This gives you your horsepower to accelerate your 4500 lb car to 54.55 mph in 8 seconds.
hp = 101.67
1 hp = 0.745699872 kilowatts
101.67 hp = 75.81 kilowatts
That 101.67 HP is also in a frictionless world, which we do not live in. You need to take into consideration the controllers efficency, motor efficency, even the efficiency of the high current wires! This brings your kW requirement up even more.
This is a substantial number for batteries to produce, and this is why electric vehicles tend to accelerate slowly. However, this is NOT to say you can't make a SUV dragster. Its just you need a lot of batteries 
Here are some links to help you along for now:
EV Roadster - http://www.teslamotors.com/
CalMotors - http://calmotors.com/
Best of all for you:
http://evalbum.com/
Please, if you have any questions at all, ask! Without the help of this board, I'd be completely lost in my ways! Most likely mentally slow too after breathing in fiberglass fumes that I didn't know were bad! (Thanks Graber for experimenting for us).
Hope this information helps. If you want, I will post a link to a spreadsheet which allows you to calculate the HP requirement of sustained motion through the air. You need to find the frontal area of your vehicle (the profile of it looking at its front in sq. feet), the weight (can be extremely approx.), rolling resistance (if you don't know this, just leave it), and the drag coefficient (most important). To get the drag coefficient, you would either need to A) Calculate it using a program such as ANSYS, or better yet, Wikipedia! The link to the drag coefficients of most cars is below. 
http://en.wikipedia.org/wiki/Automobile_drag_coefficient
Hope this all helps!
Michael |
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