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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

http://i1155.photobucket.com/albums/...ckcorner-1.png

http://i1155.photobucket.com/albums/...yugobottom.png

http://i1155.photobucket.com/albums/...cornerview.png

http://i1155.photobucket.com/albums/...gosideview.png

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.

http://i1155.photobucket.com/albums/...dunderside.png

http://i1155.photobucket.com/albums/...underside2.png
http://i1155.photobucket.com/albums/...odderyugo6.png
http://i1155.photobucket.com/albums/...odderyugo5.png

http://i1155.photobucket.com/albums/...odderyugo4.png
http://i1155.photobucket.com/albums/...odderyugo3.png

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,

yugomodder 03-06-2012 07:50 PM

Note: edges will be rounded, this is not the most accurate model of a car ever.
This is what I think would be the most aerodynamic choice, but unfortunately it would severely limit space for batteries to go.

http://i1155.photobucket.com/albums/...oddernose1.png
http://i1155.photobucket.com/albums/...ddernose12.png
http://i1155.photobucket.com/albums/...ddernose11.png

I know it isn't the ideal nose, as it isn't blunt at the front. But my understanding is that a blunted nose works by increasing the pressure so that the flow adheres to the tail better. In this case there isn't a tail behind it, but rather the windshield, so I don't think that blunting it would help aerodynamically, but it would certainly give more room.

Next set of pictures will be of a nose design with more room, but still fairly aerodynamic.

yugomodder 03-06-2012 08:05 PM

Here are a few nose designs:

Squared
http://i1155.photobucket.com/albums/...quarednose.png
http://i1155.photobucket.com/albums/...uarednose3.png
http://i1155.photobucket.com/albums/...uarednose2.png

Rounded
http://i1155.photobucket.com/albums/...undednose3.png
http://i1155.photobucket.com/albums/...undednose2.png
http://i1155.photobucket.com/albums/...undednose1.png

And a hybrid style
http://i1155.photobucket.com/albums/...hybridnose.png
http://i1155.photobucket.com/albums/...ybridnose3.png
http://i1155.photobucket.com/albums/...ybridnose2.png

I think that the hybrid design should offer a significant drag reduction, but still allow room for batteries.

yugomodder 03-07-2012 03:26 AM

I just realized I haven't posted anything about a charger. I don't need anything super quick and I wouldn't want to charge the batteries too quickly or overcharge them. Does anybody have any recommendations? Something that I could plug into a normal outlet would be great. That should be about 1500 watts or so, which is more than quick enough for what I'd be using it for.

Also I've updated my hybrid nose design. This one goes up slightly over the windshield wipers, and is a little bit more blunt at the front.
http://i1155.photobucket.com/albums/...Hybridnose.png
http://i1155.photobucket.com/albums/...ybridnose1.png
Note: those sharp edges will be rounded, it's just very difficult to model this using sketch up.

Now looking at this an idea occurred to me. It's kinda along the lines of an aerodynamic top for it(I know this idea has been talked about previously and sort of dismissed, but hear me out) but in this case it may actually lead to a smaller wake area. The template tapers slowly at first, but then later speeds up. If it's just a few degrees for the first part I could build an aerodynamic top that is just slightly taller than the existing roof, but then taper it down, and the accelerating taper coming of the back end would leave a smaller wake than the current Kammback design. I'm not sure how this could affect CdA and I guess I could test it eventually, but for now it's just a though experiment and I'd like to hear some theories as to what the effect would be.

This is a picture of the current Kammback with the template overlayed. I think it matches fairly well.
http://i1155.photobucket.com/albums/...tefromback.png

This is a picture of the current Kammback with the template overlayed as if the windshield were slightly higher and the taper started closer to the front of the car. As you can see, the template in this case would go below my current Kammback.
http://i1155.photobucket.com/albums/...rontalarea.png

This last image is what the car would look like with a streamlined top according to the template.
http://i1155.photobucket.com/albums/...erlayednew.png

Now to me this seems like it would at least reduce Cd, but I'm not sure about CdA. Also I'm not sure how I would get the hatch to work properly in this configuration if there even is any aerodynamic benefit. I just thought it was an interesting thought experiment, and I would like to share it with everybody.

Note: The aerodynamic top adds 1.75-2inches to the height of the car, but the tail comes down to 3.75-4 inches below it's position at the other Kammback. This means the top would add about 2% to the frontal area which means if drag is the only concern it would have to have a Cd that is an additional 2% less than that of the original Kammback. You could possibly get some more headroom if you re-did the interior a bit but you would also have slightly less glass out the back to see through, so there are trade offs either way.

Now that 2% less isn't just two percent, if the normal Kammback nets a 6% gain, then 2% is 1/3, meaning the new Kammback must be at least 1/3 more effective. The original Kammback cuts about 2in off the height of the wake area, where as the new one cuts 6inches off the height of the wake area. If it's all about the amount of wake area then the new Kammback should give three times the Cd reduction of the original one. Now there are other factors, but that's promising. If the frontal area actually increases by about 2% and the Cd is reduced by about 18% (6%*3) that would give a total new CdA which is 84% of no Kammback (1.02*0.82=0.8364) and about 89-90% of the other Kammback.
The front part coming off the windshield may help alleviate any small separation that occurs at the top of the roof, along with providing smoother airflow from which to streamline which could possibly net a small drag reduction.
*warning all of this information is deduced through logic based off of numbers which may or may not apply to this or your situation. Your mileage may vary*

Please let me know what you think!

Daox 03-07-2012 08:02 AM

I'd completely forget aeromods for now and work with what you got to get it running.

You say you would like 25-30 miles of range. I'm going to tell you that is going to be really hard to do with lead batteries. You've been calculating your power draw at cruising speed. Unfortunately, thats not a very realistic way of measuring power usage. If you look at the other Yugo's page, it says he is using 440Wh/mile. I'd use this, or even 500 Wh/mile (which is what I used for calculating range on a possible conversion I was thinking about) to add some safety buffer. This means for you to go 30 miles, you're going to need 15 kWh of usable battery capacity. With lead acid, to keep DOD to 50% this means you'll need a 30 kWh pack. 30kWh of lead is going to be incredibly heavy. With lithium @ 70% DOD you'd need 21.5 kWh. With lithium @ 80% DOD you would need 18.8 kWh.

I also think you should consider something higher than 72V, especially if you're talking about going 45 mph. I've driven in a 72V EV before and getting to 45 mph is going to take quite a while, and pull a lot of amps out of the batteries. More amps means larger wires which costs more. More amps also means more losses to the peukert effect which means you get less capacity from your batteries (which means even more batteries). If you doubled your voltage to 144V, you would only have to pull half the amps to accelerate just as fast. This is easier on your batteries (lower C ratings) and allows thinner cable to be used.

Ryland 03-07-2012 08:50 AM

500 watt hours per mile is in the same range as a pickup truck uses, so while your car is pretty brick shaped I don't see that poor of range, but do you have any idea what kind of gas mileage it got as a gasoline car?
Most EV's that are based off small cars get around 300 watt hours per mile, but I do agree that sizing the battery bank size and the voltage as if you are going to need more is always a good idea.
I have driven a 48v electric car that could go 45mph but it drew over 600 amps and on a flat road took a while, 96v would be about as low of voltage as I would bother going with and the smallest, highest voltage lead acid traction batteries that I've seen that I would trust in an EV are 8v golf cart batteries, they tend to be the same size as the 6v golf cart battery that are also a good, common choice.

Daox 03-07-2012 09:32 AM

I like to use 500Wh/mile as a worst case to ensure I have enough capacity. Situations like cold days and needing electric heat, or are driving through rain and using wipers and headlights, or driving through bad road conditions like slush and snow. It all increases power used. Perhaps in Mississippi its not as big of a deal since they don't have the harshness of Wisconsin winters.

yugomodder 03-07-2012 11:32 AM

First, thanks for the replies!

Just to clarify the plan at the moment is:
1. Obtain and install new controller and batteries
2. Test to see if motor is up to the job, add cooling or replace with larger motor if it isn't
3. Find some sort of instrumentation to measure the draw on the battery pack at any given point.
4. Do A-B-A testing on modifications to try to lighten the load on the battery pack

The only reason for bringing up the aeromods at this point is just that I was thinking about them and figured I'd share. Maybe I should have posted that in the aerodynamics section.

I'll make sure to build the system to the max voltage the motor can take, if it's still too weak I'll rewire the batteries to the voltage of the new motor.


Tracking down mpg information was harder than expected. I've seen numbers from 30-45mpg. Probably a lot of this is due to variation in driving technique.

Looking at Greg Coleman's page, the wh/mi numbers seem off. He reports having "6 Deka MK Power M24SLDGFT 12 Volt GEL 73.4AH, 12.00 Volt, Lead-Acid, Gel" 6*12V*73.4Ah is 5,284wh. So even if he used 100% of the capacity to get 15 miles that's still just 350wh/mi not the 440wh/mi there or 500wh/mi. Several of the wh/mi figures seem to be off on that site. I saw a Honda Crx that said it used 18,000wh/mi (Michael Brooks' 1986 Honda CRX). This was most likely the impulse reading for watts at speed considering he has a 33mi range. At the same time there are other crx's that report 240wh/mi (Allen Grvoer 's 1986 Honda CRX) and 70miles range using lead acid (Victor Tikhonov's 1991 Honda CRX). Now the Yugo isn't as aerodynamic as a Honda crx, but it sure is more than a pick up truck.

The calculations I did before included cruising speed, as well as energy to get up to speed as if it were completely wasted at a stop (no cruising), which seems overly harsh to me. That would be as if somebody accelerated full out to speed then maintained that until just before each stop and slammed on friction brakes, wasting all the kinetic energy. On the other hand the 99mile range would be as if you could start out cruising with no slopes, crosswind, wipers, lights, etc. I did try to also take a margin of error on all my figures for size, weight, Cd, motor efficiency, etc.

Is there something else that would cause draw on the battery that I'm forgetting?


To clarify some of what I said before. I'm trying to build the battery pack so that the rate of draw is less than what the batteries are rated at. For example if they have a 115 min capacity at 75amps then I want to make sure that the draw is less that 0.5 C on the battery pack. That means it needs to have at least 2 hours of driving time. Now this doesn't have to be two useable hours of driving time, as I'm only looking at the rate. So if I have at least two hours of driving range, in order to prolong battery life I'd limit myself to just one hour of driving per charge. So if the full charge would give me something like 80miles of driving range, I'd limit my own range to 40mi, unless I ran out unexpectedly, in which case the extra buffer would be there even if it damaged the batteries to do so. Now my understanding of lead acid is that the more slowly you draw current from it the more charge you can use, and the longer they last. This is why my first priority would be to limit the rate of draw from the batteries, and then to limit the depth of discharge. I would actually normally drive less than 20miles in a day, but I figure if I could achieve 80 miles of range, and limit the current draw then the battery pack should last much much longer than one which depletes it self down in a matter of a few minutes of driving.

I'll try to find the specs on the golf cart motor to see what voltage it is. If it's less than 72 volts should I just abandon it and look for something that can take a higher voltage?

Also, I would be interested in making a lithium pack. I just don't know where to get lithium batteries with a BMS for anywhere near the price of lead acid. Now on the one hand I shouldn't need as many, and they should last much longer, but on the other hand the price is so high on everything I've seen. If you could point me to a good source I'd be glad to check it out.

I just saw your new comment Daox. Yeah it rarely gets cold here at all. It does rain for a few minutes at a time here and there though. Headlights shouldn't be too big of a draw because I'd be doing mostly daytime driving, but even so I'd gladly look into making some LED ones. A lot of places have to worry about the batteries being too cold and losing capacity because of this, but with temps over 100 in the summer I'd be more worried about keeping the motor and batteries sufficiently cooled.

P.S. found this here on Ecomodder about a guy with an electric Yugo. It's not extremely detailed as to what batteries, range, etc but I thought it was cool. http://ecomodder.com/forum/showthrea...ence-2738.html

Daox 03-07-2012 12:42 PM

I don't know the best place to get lithium batteries. If you google for places selling Thundersky or CALIB batteries, those are the ones people are using for DIY EV conversions. Last I compared, the price is about 2.5X more than lead acid. But, they weigh less than half as much, and should last almost 4 times longer than lead if taken care of. In the end, they end up costing less. They're also happier to give you at higher C ratings. Speaking of taking care of the batteries you'll definitely want a BMS. You can buy one or several people here are working on open source BMS systems for lithium (myself included for my PHEV Prius). So, if you DIY you can save a ton of money.

The best way to avoid high C ratings (and thus high peukert effect losses) is to increase the voltage. Many motors are capable of handling much higher voltage than what they are rated for. I think most of the guys are running forklift motors that are rated for 24-36V and they're running between 72V and 144V through them. I believe only permanent magnet motors shouldn't be run over their voltage rating (and amperage for that matter). For instance my mower motor was a 24V that I was running at 48V. It had absolutely no issues with bumping the voltage up.

For the Wh/mile that the Yugo has posted, its probably "from the wall". That takes into account his charger's efficiency.

Ryland 03-07-2012 03:16 PM

Quote:

Originally Posted by yugomodder (Post 291825)
I'll make sure to build the system to the max voltage the motor can take, if it's still too weak I'll rewire the batteries to the voltage of the new motor.

I'll try to find the specs on the golf cart motor to see what voltage it is. If it's less than 72 volts should I just abandon it and look for something that can take a higher voltage?

The higher the voltage the faster you will go, and some speed controllers can be programmed to limit the voltage to the motor as well, so you can take a 144v battery pack and have your speed controller limited to only give the motor 48v or 72v or whatever you want to set it at, or you can just tell your self not to go over say 45mph because at 45mph the speed controller will be limiting the voltage to the motor, the only time that the motor would ever see full pack voltage would be at full throttle.
I bought a new set of motor brushes for my motors and I was told by the engineer who designed them that they should be good for 160v in my 36v and 48v motor, I've also been told that my 36v golf cart motor should be fine running at 72v but that much higher then that and I should install this new set of brushes.
Any chance of taking some photos of your current setup? if your motor to transmission adapter is solid and well built you should have a handful of motor upgrade options too, depending on the motor that was used because there are only a few bolt patterns and shaft sizes that have been used for golf carts and there are two that are extremely common with a wide range of aftermarket motors that bolt right on.


My current battery gauge is a PakTrakr, the only people that I've talked to who don't like them seem to think that they should also act as a BMS instead of a battery gauge, but with the amp meter pick up it can give you amps and watts, along with pack voltage, state of charge, voltage of each battery and a whole pile of other info.

yugomodder 03-07-2012 03:33 PM

Thanks for the replies!
I'll look up those brands Daox. Yeah it seems like several people have said now that they could pump more volts through a motor than it's rated for. I guess it's like overclocking a computer, as long as you don't go overboard and you have the cooling you should be ok, right? For the wh/mi, that would make a lot more sense if it were from the wall stats.

That's exactly the sort of thing I was thinking Ryland. I can build everything so that it has the potential to do more, but just limit myself in order to prolong the life of the system. That PakTrakr looks great! That's all the sorts of info I'd like to be able to get. Unfortunately I cannot take pictures of the system at the moment, as it is still in Michigan. I do have a camera though, and pictures will be put up once it gets here. Yeah if the current motor fits, then it would make sense that being standardized other motors may fit too. I'll check what voltage the motor is rated at and then post here to see how many volts I should try to put through it.


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