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yugomodder 03-06-2012 04:36 PM

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.

Daox 03-06-2012 05:12 PM

Welcome to the site. You have a pretty well composed idea of what you want to do, thats very good!

I have some info for you:

Never never use starting batteries for an electric vehicle. :) They can not handle many cycles of any decent DOD. They will simply die very very quickly. Yeah, they can put out crazy amperage, but they're just not meant to be drained much at all. You need deep cycle batteries.

Depth of discharge for lead acid batteries is usually kept to 50% to ensure maximum life. This means your 4.3 kWh is now 8.6 and your 9 kWh is now 18. This is a huge benefit of lithium as it can go to 70 or 80% DOD and still survive many more cycles than lead.

Most motors are rated at continuous output. Their peak power can be significantly higher. I had a series wound motor on my electric riding lawn mower that was rated around 1.2hp. I was pumping about 5hp through it while in use. It did get hot but it did its job for over a year like that. If I would have put some cooling on it (a blower fan or something) I think it would have lasted just fine. Unfortunately I didn't and on a very warm summer day it did overheat. I also don't think you want to mess with combining a few different motors. It'll just be a big headache. I'd suggest finding a decend sized motor that weighs a good amount.

I would definitely look up the open revolt controller here on ecomodder. It was designed by one of our members. If you're handy with a soldering iron it is insanely reasonably priced controller for $600. It will handle up to 144V and 500A.

yugomodder 03-06-2012 05:19 PM

Some of the batteries I looked at are 6V 75Amps for 115min(from Advance auto). That would suggest to me that a discharge rate of over 0.52C may be bad for the batteries. Is this true? If so, to handle a 9kw load it would be necessary to have 20 batteries. 20 batteries would weigh about 900lbs, which is a lot of weight for a small car. Now some of this would just be replacing ICE components, but much of it would be extra weight added to the car. Now logically 4 people in the car should weigh somewhere around 600lbs and the ICE components should weigh a couple hundred pounds so the weight of the converted car with no people in it shouldn't be much heavier than a fully loaded ICE version, but I'm still concerned about the extra load on the suspension. The other thing is that the batteries are about 7"by10"by12". In a fairly small car where would I put 20 batteries this size? There will be some room under the hood, and possibly in the back but will there be enough? I'm going to do more research on what other people have done regarding battery location in EV conversions.

There's also the problem of system voltage. In order to achieve 48 volts I'll need 8 batteries per string, and if I need at least 20 batteries that means I'll need 3 strings of 8 batteries. Now 24 batteries is a lot of batteries, but it should also decrease the discharge rate leading to better cycle life. On the bright side, having 24 batteries in addition to improving the number of charge/discharge cycles should increase the range of the vehicle. I don't really need more than 25-30 miles, but if it's extra cold or windy the range could come in handy. Now going 45mph according to the calculator is going to draw 9.3kw with a motor a little less than 80% efficient (about 7.2kw/0.8). So if the battery pack is giving me 20.7kwh(24* 6V * 75Ah * 115min / 60min/h) it should be able to handle 45mph for 133min, about 2.2hrs. That means a discharge rate of 0.45C and a total theoretical range of 99mi with no starting or stopping, heat, ac, windows or anything. Obviously that won't be the case, but even if all the energy starting and stopping was 100% wasted, a 2600lb vehicle going 45mph has 66wh of kinetic energy.(however around 80% efficiency 66/0.8 about 80-85wh is put in) So even if you stop 100 times from 45mph abruptly with no coasting that's just 8kwh of energy meaning you still have about 12 left to drive on which gives a range of 60mi. Now driving like this would obviously be detrimental to both the car and battery pack with such large bursts of energy demanded from the battery pack and draining it near 0% capacity, and I don't expect to do anything like that any time soon, this is just a thought experiment. If it holds true though there may be a promising bit of range and battery life. If I could achieve something around 60mi of range and 500 charge cycles that would mean the battery pack would last about 30,000miles, which would not be too bad.

As a side note, how many charge cycles do you think are possible if you only use about 30% of the battery on a daily basis, and never exceed a discharge rate of over 1C?

yugomodder 03-06-2012 05:28 PM

Thanks for the warm welcome!
I didn't see your post before posting my reply.

Yeah normal automotive batteries aren't meant to be discharged, they're mostly just meant for instantaneous power. That's why I was considering the golf cart batteries.

Yeah I have been looking in to lithium. The problem I've had is that lithium batteries tend to be pricy and seem to require a BMS. I've found some that seemed promising at first but after reading some reviews most people said they were a scam. They were ultrafire 18650 cells on Ebay. Good lithium cells are supposed to exceed 2000 charge cycles though, which would be awesome and it seems like they'd eventually pay for themselves, I just don't know what type to get. If you have any recommendations please let me know.

Yeah setting up multiple motors is going to over-complicate things as first. If you have an idea as to where to get a good sized motor I'd be happy to check it out. I think I want to get the instrumentation, battery pack, and single motor in first before I play with aero-mods and eventually multiple motors. Those are far on down the line though. If I could get a basic setup going that would be huge progress. I'd like to avoid making it too difficult that I have to postpone it.

That's an interesting story on the electric lawnmower. It does get very hot here in Mississippi, in the summer days can average over 100 so a cooling system would definitely be beneficial.

I'll make sure to look up the open source controller. It would be really cool to build it myself as long as I have the capability to do so.

Ryland 03-06-2012 05:45 PM

Greg Coleman' 1991 Yugo is a the only Yugo that shows up on EV album but he has a lot of info and over 13,000 miles on his conversion.
The motor I have in my electric car is rated for 6hp (5kw) and is more or less a golf cart motor as well, but if you push it hard while going up a hill I've seen it draw nearly 50,000 watts, so I don't see 4 7kw motors being able to do the same amount of work, I would stick with the golf cart motor, maybe upgrade to a slightly large one if you can and add some cooling to it.
I also would stay away from Gel batteries, our local EV club has had a handful of members use Lead Gel batteries and found them to be very short lived and disappointing flooded deep cycle lead acid batteries seem to give the best performance.
Other then that take a look around at the EV Photo Album: Our Electric Cars on the Web and see what other cars that are the size of yours can do.

yugomodder 03-06-2012 06:09 PM

If I can get a basic set-up going where I can test changes scientifically without ruining my equipment I'll start making aerodynamic modifications. The Yugo being as boxy and un-aerodynamic as it is certainly has room for improvement. The cd is horrific, but the frontal area is small, so if I can improve the Cd without increasing the frontal area I should be able to achieve a much smaller CdA leading to better battery life and range.

I would be up for some fairly radical aeromods, even if that means changing body panels, I've done projects with fiberglass before (all be it not body panels) and know people that can help with welding. Unfortunately the front end of the yugo is not only blocky, but it sloped downward directing air directly under the unstreamlined underside, which other than directly into a rotating 26in unaerodynamic wheel is about the worst place for air to go. I don't think that just a simple grill block will give me the results that I'd like. I figure that If I change the Yugo from diverting 50% of the air under the car and 50% over to 90% over/ around the side and 10% under as well as adding a full belly pan(no ICE parts to deal with) and a slight diffuser that should net me a huge aero gain. (now by huge I don't mean 60% or something but it may net me up to a 25% gain) Now 25% may seem unreasonable, but by my logic as per the 65+ efficiency mods, even a simple grill block should give me 5%, a simple belly pan should give me another 5%, and a simple diffuser at just a few degrees should also reduce drag by a few percent. Now, not having ICE parts underneath the car to have to work around should allow me a few more percentage points gained for the belly pan, the same thing would go for the diffuser, and diverting flow cleanly over the top and around the sides, as well as a much smaller amount cleanly underneath should make a fairly large difference aerodynamically. The Yugo is a fairly small car, so adding a short boat tail would also be an option. I figure I could mount it on the hatch, which is already cut towards the front of the car, and as per the template streamline it back a couple of feet, then cut the flow off cleanly. That should give me at least as much gain as a simple short kammback would give, but not as much as a full boat tail, but it wouldn't adversely affect the ability to use the hatch. I have these things modeled in Google sketch-up and I'll post them once I have the image posting privileges.

At the moment I'm only working based off of information from others, which may or may not fit my situation. But if I have some good instrumentation and can do some tuft testing I should be able to significantly reduce the drag for the car. I'm not going for a basjoos-like cd of 0.17 but if I can take it from 0.4 to 0.35 or 0.3 that would be awesome.

I read somewhere on this site that somebody did a study which took an extremely streamlined car like the sunraycer and made the windshield completely vertical doubling the drag from 0.12 to 0.24. Then by angling back the windshield to something like 60 degrees it was down almost to 0.12 again. I'll give the guy who posted it credit as soon as I find who did. I figure that there is a similar effect (probably not as dramatic though) with the very front end of a car. I'd be interested to see a test of angling the front end from completely vertical, leaning back until it hit the angle of the windshield incrementally and seeing what the change in drag would be. Now I'm going to need room for batteries, so I probably won't be able to slope the hood/angle the front all the way to the angle of the windshield, as it may not leave me with enough area to put batteries. I should be able to at least angle it back and smooth the transition a bit. I'll be posting different configurations shortly.

yugomodder 03-06-2012 06:15 PM

Thanks for the reply Ryland!
Yeah I had looked at his yugo on there, but it was still difficult to see where all the batteries go etc. There is some good info though. That site has been very useful and interesting. I'd love to be able to modify something light and aerodynamic like a Honda Crx, but I figured I already have this, so I might as well use it.

Wow, I had no idea that a golf cart motor could draw that much without frying. I'll definitely add a cooling system and see what I can do with the current motor, then if it's not enough upgrade it to a single larger motor.

Thanks for the information on the gel batteries. I had always heard that the gel batteries were longer lasting which is why I was looking at them. I'll look into some quality flooded lead acid batteries and see what kind of a battery pack that would make.

yugomodder 03-06-2012 06:26 PM

Props to aerohead for digging up this info:
(quoting him)
"I stumbled onto some tasty little numbers when re-visiting Walter Lays wind tunnel work of 1933.
Lay tested a 'pumpkin seed' model car,which for all intents and purposes IS the 1987 GM Sunraycer,with matching Cd 0.12.
By installing a completely vertical windscreen with square edged header and A-Pillars he doubled the drag to Cd 0.24! Hucho refers to this in his book(s) when mentioning that no amount of boat-tailing will reap benefits if the forebody isn't 'clean'.
What's remarkable about Lay's research,is that by tilting the windscreen back only to 50-degrees from vertical,all the turbulence was killed,and the car was as low-drag as if it had the 'ideal' compound windshield.
Of course,this is only at zero-yaw,and the 'ideal' windshield WOULD have an advantage in a crosswind,but it kinda drives home Hucho's point,that most contemporary automobiles have adequate forebodies,from which to streamline from."

yugomodder 03-06-2012 06:42 PM

Here are pictures of the unmodified template which I am working from. As you can tell it's not the most geometrically accurate model of a car ever, but there aren't a lot of people dying to model a yugo. I'll post modified photos shortly.

yugomodder 03-06-2012 07:32 PM

These pictures are of modifications made to the underside and rear of the car. All of the white areas have been modified.

Modifications include, making a single level for ground clearance rather than higher lower in different places, full smooth bellypan, rear diffuser going up to slightly below bumper level, slight kammback, sides which are flat in this model but would actually taper with the kammback and the edges would be radiused,

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