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Old 08-04-2011, 10:30 PM   #1 (permalink)
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Help, What car for E.V. Conversion?

Hi everybody,
I'm looking for a car that would make a good candidate for an E.V. conversion. So far I've looked on eBay and Craigslist. I've found some old Honda CRX's which seem to have fairly low weight and drag. (on the wiki it had one of the lowest drag areas Vehicle Coefficient of Drag List - EcoModder)

I've also looked at some old sports cars. I thought that they might be aerodynamic enough to make a good E.V. but I'm not sure. I've found a 1978 Chevy Monza, and a 1980 Pontiac Sunbird which both seem to have a kammback type shape. My worry is that the roof slopes down too quickly, and there may just be turbulence all along it. Does anybody here know what the drag coefficients are for these vehicles?

I was also thinking of possibly using a diesel generator as a range extender. I could use biodiesel or normal diesel if need be. That would allow me to take the vehicle as far as I want. I was thinking if I make the generator's output a few kilowatts higher than the energy needed to maintain 60mph, the excess energy could go into the batteries to help on hills and things.

I also think that some aeromods are necessary to help reduce the energy required to run the car. I was thinking of a belly pan, rear wheel skirts, and smooth hubcaps, but I'm not sure what else to do. Could you guys help me out with ideas?

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Old 08-05-2011, 08:25 AM   #2 (permalink)
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I'm not real sure why you need help. It sounds like you have a bunch of good ideas already.
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Old 08-05-2011, 10:14 AM   #3 (permalink)
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My worry with a car like a CRX is first off that they do not handle having extra weight in them very well and are really sensitive to how well they are balanced.
My other worry with the CRX is that you could be taking a gasoline car that gets some of the best gas mileage off the road, so if you do convert a CRX please start with one that someone already pulled the engine on, not with a nice running stock CRX HF
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Old 08-05-2011, 12:38 PM   #4 (permalink)
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Volkswagen Rabbit. There are many EVs based on it out there, kits are available, and even a book telling you how to do it. Check out Convert It: Amazon.com: Convert It! (9781879857940): Michael P. Brown, Shari Prange: Books. There is also a kit available for the Porsche 914, but they are rarer and more expensive. You can make a great sports EV out of one, though.
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Old 08-05-2011, 04:41 PM   #5 (permalink)
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Thanks for all your replies,

Daox, thank you, but I need help with some of the finer details, as well as some other areas which I am not very familiar with. I've learned a lot from research and calculations, but I have never actually built an E.V. so there are bound to be tricks of the trade I don't know.

Ryland, I'm hoping to find one with the engine and transmission shot or gone, but with the brakes, body, etc still good. I wouldn't want to take a good thing and mess it up. Plus it should be cheaper to get one that has the engine broken or missing. Do you know how the CRX is balanced, because I was thinking that if I keep track of what weight I take from where, and replace it with batteries, motors, generators, etc that the vehicle could end up the same weight distribution and it wouldn't affect the suspension. Would it be ok if the vehicle ended up lighter as long as the balance was the same? Or should it end up pretty much the same weight? I'm going to do some research myself on the weight distribution, as well as the weight of parts I would like to remove.

Patrick, thanks for the advice. I'll be sure to keep a lookout for Volkswagen Rabbit with a broken or missing engine. On the sports car idea, the ones I was looking at are quite a bit under 1k, and look like they'd be fairly aerodynamic, at least at low Reynolds numbers. My problem with them is that I don't know how aerodynamic they'd be at 60-70mph. I would really like to have an old sports car as an E.V. because it would be really cool, but it has to be practical too. I tried searching the internet, but the only figures I got were 0.5 for the coefficient of drag on both of them, which seems very unlikely.
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Old 08-05-2011, 04:50 PM   #6 (permalink)
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Have you seen BenNelson's DVD on how to build your own electric car? He sells them and it'll give you a very good idea of what you'll need to do with your own car.

Electric Car Instructional DVDs

For issues you need help with along the way, we're always here to give help.
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Old 08-05-2011, 04:56 PM   #7 (permalink)
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We don't have enough info. For example, how much range are you seeking? That leads to what battery tech you plan to use and if it's lead acid and longer range then you need a base vehicle with a higher load capacity, like a small pickup, but then if you need four seats you'd want something else and....
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Old 08-05-2011, 05:18 PM   #8 (permalink)
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Thanks Daox, I'll check that out.

Frank Lee, I'm thinking of getting about 40mi of city range in the vehicle. I was able to use the "Aerodynamic & rolling resistance, power & MPG calculator" found here Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com to estimate how many kwh I need for the range. I found that with the CRX it doesn't take much energy to go 45mph compared to other vehicles. I think I'm going to try to wire my own Li-ion battery pack.(i know it'll probably take a few thousand cells and it'll be difficult but that will get me the pack i want) If I build the pack/packs myself, I can make them lay flat. I was thinking I could mount them on the underside of the car, placed correctly to get the balance how I want, so that the front to back weight distribution stays the same as stock, but I may possibly lower the center of gravity. I'd then put a belly pan over them to protect them. I was thinking of using a diesel generator as a range extender because I could use biodiesel or normal diesel if need be. The all electric range would cover my normal city driving, and the range extender would allow me to go as far as I want in it. I was thinking the generator could go where the engine normally goes, to try to keep the weight distribution similar, the weight down, and allow lots of airflow through. All the generators I was looking at are air cooled, so I think it would be advantageous to place it in a high airflow area. I also used the calculator to find out the amount of energy needed to maintain 60mph in a stock CRX. I was thinking that if I make the generator a few kilowatts more powerful the extra energy could go into the battery pack, and drawn out if winds pick up, or you have to go on hills, or just need to go faster. I then calculated the amount of gallons per hour to find out kWh per gallon, and in turn miles per gallon. It looks pretty promising so far, but has to be tested to find out for sure. I think the Honda CRX, or an old 70's-80's sports car would work well for me because if they take less energy to run, I don't need as many batteries, and in turn not as much weight is put onto the frame. I will have to research the weight of all the particular parts of the car to find out how much weight is taken from where, and how to replace it to keep the weight distribution the same. There isn't as much information available on the old sports cars as there is on the CRX, so if anybody knows anything about them, please let me know.
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Old 08-05-2011, 05:26 PM   #9 (permalink)
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I think you should look at our discussion on "range extending generators".

I've had the notion that if the base vehicle doesn't have the capacity for carrying a heavy battery pack, that it certainly would still be able to pull a battery trailer...
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Old 08-05-2011, 05:29 PM   #10 (permalink)
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40 miles is going to require a pretty decent battery pack. You're looking at at least 16 kWh. Lithium is definitely the way to go though. I don't think I'd recommend doing a lead acid car unless you can get free/cheap batteries and don't need much range.

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