Thread: Electric Yugo
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Old 03-06-2012, 05:36 PM   #1 (permalink)
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Electric Yugo

Hi I'm new to the forums. I've been a lurker for a while but now figured I had enough information to start asking questions.

Here is the background story. I've been looking at converting a small compact car to a short range electric vehicle for city driving for a while. I talked to a lot of people about this and ended up with an old Yugo that somebody else had been playing with. It isn't here yet it's up at my grandfather's house so I am not able to take pictures of it at the moment. What's special about this Yugo is that it has already had an attempt at a conversion. All the ICE parts have been stripped out and replaced with a golf cart motor, a resistor to control the speed, and a couple of old worn out car starter batteries. As you could probably guess the range was not great. My grandfather says it did about 2 miles at 30mph.

Goals of project:
Create an electric vehicle that is usable in city driving
Learn about EV components, design, and instrumentation
Learn about modifying a car's body to make it more aerodynamic and or safer

I figure that the first modification that I need to make is to get a proper motor controller and some fresh batteries. I've been looking at 6 volt gel golf cart batteries. The price looks descent but I'm not sure if they're up to the task. I know that they won't have the same power as a starting battery, and that if I try to discharge at too great of a rate I'm probably going to wear them out too quickly. Would it be correct to assume that if I have enough batteries that the discharge rate doesn't exceed 1C that they should last much longer?

I went ahead and punched in some numbers for the Yugo into the "Aerodynamic & Rolling Resistance calculator." The frontal area from what I could find on Wikipedia and other miscellaneous internet sites seems to be about 19.43 square feet so I rounded up to 20. The drag coefficient seemed to be extremely hard to track down. I got numbers all the way from .32 to .4, .32 couldn't be right for a car like the Yugo, so I just went ahead and put in .4. I don't know what shape the tires are in so I put 0.015 as Crr. Now the reported curb weight for the Yugo is between 1800 and 2000lbs. Removing the engine, exhaust, etc should take some weight off, but the batteries are going to be heavy. I'm going to need hundreds of pounds of them. Is the suspension going to be able to take the extra weight? In any case I used an input value of 2600 pounds for the calculator.

The values it gave that seem important to me are 3420 watts at 30mph and 7181watts at 45. It isn't necessary for the car to be able to go over 45mph, but I think I should build the battery pack so that it could handle the draw if it needs to. So assuming a motor efficiency of just under 80% the draw on the battery pack would be 4300 watts at 30mph and 9000watts at 45mph. For a discharge rate of under 1C I would need at least a 4.3kwh pack at 30mph and a 9kw pack at 45mph. Now this obviously doesn't account for draw during acceleration and a buffer zone on the battery. I'm not sure how much of the capacity of the batteries I can use without negatively impacting their life. Could anyone that knows please tell me?

Next thing is that to even reach 30 mph I'm going to need at least a 4kw motor, but to get there in any descent amount of time it's going to have to be larger. I doubt that the golf cart motor is larger than a few kilowatts, so I'm probably going to have to replace it with something larger. I found a brushless DC motor that is 48V 7kw peak for about $100. Now that's the peak rating so I wouldn't want to put that stress on it for more than a few seconds at a time so I'll probably need a few of them. I figure if I get 4 that's 28kw of power, and if about 4kw is gone in wind/rolling resistance that's still 24kw available to accelerate the 2600lb vehicle. That isn't exactly going to make a blazing fast car, but it should be more than enough to make lane changes and pull out of a parking lot without fear of being hit by oncoming traffic. The problem I have is that I don't know how to mount these motors. It might be possible to do some sort of chain drive to the drive shaft, but if possible I'd like to look at the idea of hub motors. I'm not sure how the system would work, but figured that somebody here might have some input. I've heard that Hub motors can cause the wheels to have too much weight leading to poor handling, but these aren't gigantic motors, they're about 5lbs.

For controllers, there are controllers specific to the motors that cost about a hundred dollars each, I'm going to need 4 of them which shouldn't be too bad.

The next thing that I'm hung up on is a way to read the state of charge of the battery pack. I'd really like to be able to see the instantaneous draw on the battery pack as well as the amount of charge left in the battery pack. That would allow me to calculate range as well as test modifications at different speeds to see a change in load. That would be extremely useful for aerodynamic modifications. I could do fairly quick A-B-A testing that way.

As far as planned modifications go I have drawn some out, as well as modeled some in Google sketch-up. I will post images of the modifications I've made once I have enough posts to do so. *warning* mod's are not 100% accurate, neither are models. I just thought that it might help me visualize the changes.

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