Recently, several readers pointed us to some forum posts that chronicled a high school kid converting a Honda S2000 to electric power. Oh, and with 700 electric ponies of electric power. Electrically.
He's not the first to try this, but it is still a very compelling (and, to many, controversial) project.
Naturally, I was interested since so much of my high school years were sacrificed to onanism and bold projects that always managed to avoid completion. Clearly, this was a Car Hacker of a rarefied breed, and we needed to hear what he had to say. So, I dusted off my stalker skills and hunted down the builder, Juan Ehringer, and asked him a bunch of questions. I think you'll find his project and what he has to say about it fascinating and either inspiring or depressing, depending on your own self esteem
Jalopnik: So, tell us what the hell you're doing here. Give me a bit of an overview, please.
Juan: Basically I am taking a functioning S2000, and replacing the gasoline engine and gas tank with an electric motor and a battery pack. Of course it is a bit more complicated than that, but concept remains the same.
Jalopnik: Okay, now why are you doing it? What gave you the idea, and, beyond that, what made it actually happen? How long have you known this was a project you wanted to accomplish?
Juan: I had seen a video about The White Zombie on youtube in 9th grade and thought it was pretty neat. The idea of building an electric car didn't form until late 10th grade, when gas prices were rising and global warming was an increasingly present topic. When the time came to find a nice used car, I couldn't find anything that fit my bill: fast, stylish, efficient, and economical. I am a believer in saving money when possible, so I was having trouble deciding on a vehicle. Having to choose between efficiency and performance was tearing me apart. Once the price of gas went high enough, I found myself hyper-miling any vehicle I drove. I believe it was then that I decided to begin doing a little research on cars with electric drivetrains. The point at which I realized I was actually going to invest my time and money into this project is when a student in one of my classes told me that electric cars were inefficient and would never beat a properly tuned gas powered car. By then I had already done my research on electric cars and thought I might give it a try. I don't think I ever really expected to get this involved with the car and subsequently my state of mind on the entire topic has changed from "hahaha dude what if I built an electric car" to "oh crap I think I am actually doing this" and eventually to "I love electric cars as well as this project".
Other major influences include wanting to reduce my carbon footprint, save money on gas, and be remembered for something but the above story is pretty accurate as well.
Jalopnik: I've seen many folks asking this, often tinged with just a bit of jealousy: how are you able to afford to do this? You're a high school senior, these parts are expensive, etc. Time is easier to come by, I'd imagine, but still not easy. And, if it's rich parents, that's okay to say— many other kids with families of means don't do anything half as interesting. People are just curious about this kind of thing.
Juan: I've noticed a bunch of people ask this recently as well.
The parts are definitely expensive, but putting the car's total cost into perspective makes you realize that you aren't paying much relative to what is on the market. When my parents gave me a budget for a nice used car, I looked for a fast but efficient car and found that they all didn't meet my qualifications. With that in mind, I eventually was able to convince my parents to fund an equally expensive, but much more powerful and efficient, electric vehicle. My parents had agreed to pay for the main car components: motor, controller, and battery pack, which left me to pay for the remaining components. I have a job and run a little CNC business which allows me to pay for the remaining parts. I also worked at a machine shop for two years, during which I set some money aside each month to pay for a car once I got my license. In addition to the above, I find a lot of good deals on eBay and such which helps keep the overall cost controlled. One thing that people don't realize is that the cost of building this S2000 is less than purchasing a new commuter car from the dealership. Heck, the entire cost of the project (including the car) sums up to about 70% of the original s2000 price. Plus almost everything (excluding some plastic bits and connector and such) was built in the USA. Yay for local consumer expenditures.
Jalopnik: Where and when do you normally do your work? What sort of garage/tool setup do you have?
Juan: My family has a modest 1.5 car garage which is where this entire project has taken place. It is a little on the small side, forcing me to store some of the bigger things (hood, bumpers) outside; however I have learned to work within its confinements. Once you get used to its size, it's rather cozy. As for tools, I have the normal gearhead stuff, some pneumatic tools, a ratchet, a set of wrenches, nothing out of the ordinary. After working on this car I have found that you really don't need many special tools to accomplish any given job.
I have always been a fan of electronics and such, so I built a CNC machine in 10th grade for fun, and found that I really loved it. From there, I began engraving and carving things, and formed a small business machining things for people. My love for CNC only grew deeper, and I purchased a CO2 laser cutter further into the year. I keep those in my bedroom (they aren't very large) because the garage isn't air conditioned and the machines need to be near a computer. The CNC equipment is probably the most helpful tool I have for designing stuff.
I generally spend my weekends working on the car, but sometimes I find time to squeeze car work into the school week.
Jalopnik: Your projected HP ratings have been called into question on the various places this has been discussed. The overall power potential may be around 700 HP, but is that really what's going to make it to the wheels? Can you walk us through the math a bit here?
Juan: This is a little bit more complex than just some math.
Originally I had posted that the battery pack was capable of outputting about 700Hp, but it was interpreted as ‘the car will output 700 HP'. The 700 HP figure was found by the formula P = I * V , which was then multiplied by 85% to account for inefficiencies. This gives us a very rough power estimate for the pack.
A more accurate way of finding power would be to find the voltage sag of the batteries at a certain current and then find the peak power with that sag.
To find the sag, we need to find the resistance of the cells in parallel, then for the entire pack.
Each cell has an alleged internal resistance of < 2 mohm, so .002 ohms. I have four cells in parallel, so 1 / (1/ (.002)) * 4 = 5.0 x 10-4 ohms of resistance for each parallel set. To find the total pack resistance, multiply this by 104 (the number of cells in series). 104 * 5.0 x 10-4 = .052 ohms.
Since resistance = V / A , V loss = A * Resistance. Therefore the voltage sag = 2000 *.052 = 104v lost at maximum power, this doesn't include the resistance found in the copper bars. Subtract the volt sag from the traction pack voltage, and you get 239.2v. P = I * V, so 2000 * 239.2 = 478400kw.
Therefore, the peak vehicle power (from the controller) will be closer to 478400kw of power, or 641 Hp.
Multiply this by 80% to account for drive train inefficiencies = 512 Hp. With that said, I suspect that I will get around 600 Hp because in my independent test I have recorded around 1 mohm resistance per cell. Repeat all the calculations above and you get 52v sag, which results in a peak power of 582400 * 80% = 625 Hp.
To make it even more complex, you always have the increase of resistance when the cells heat up, but these cells seem to be most comfortable at 100° F. You also have wire resistance, bus bar resistance, lug resistance, etc. Keeping all this in mind, I would feel safest saying that the car will have between 500 hp and 600 hp in real world situations.
Jalopnik: Right, right, lug resistance. Numbers, good. Okay. So, why an S2000? What have you done to address the known weak points, like the transmission/transaxle?
Juan: Once I figured out that I was actually serious, I began searching for a car. I realized that I wanted something that was RWD (because FWD is for wussies), had a manual transmission, and had a large engine compartment to house the relatively long motors. The car also had to be lightweight and cheap. My car choices ranged from Miatas to CRX's to older Ford Focuses. My father's only request was that the car be manufactured after 2000, and have passenger / driver airbags. I searched for about 6 months or so, and contacted many people regarding possible donors but nothing worked out. Once I discovered the S2000 I realized how much more aesthetically pleasing it was compared to the Miata and kept looking. Eventually I found an S2000 nearby, called the seller, and talked his price down by explaining what I was planning on doing to the car. A week later I had an accident free 2003 S2000 in my driveway for $6000 cash.
Everyone who owns an S2000 knows that the Japanese decided to make the rear differential out of the weakest metals they could find so that it explodes once you pump more than 150 Hp into it. I immediately decided to take the differential out and sell it before I killed it with the new electric motors. There weren't many options available back then, so I chose to go with a ford 8.8 rear differential from a local guy off craigslist. From there I searched online and found that someone made a 8.8 ford to S2000 mounting kit but wanted some outrageous price. Realizing that I had a limited budget, I taught myself how to weld some front support brackets and cut an aluminum plate out on the CNC machine for the rear bracket. Axles, as well as the aluminum driveshaft for the project were generously provided by the Drive Shaft Shop.
Jalopnik: What are you planning to do with it once it's finished? Race, your daily driver, etc?
Juan: When the car is done I will drive it daily, but once in a while I wouldn't mind drag racing it or tracking it. I believe it will really be able to shine in the quarter mile so I need to make sure I take it to the drag strip once everything is buttoned up.
Jalopnik: Any estimates as to range when it's finished?
Juan: The range should be roughly between 80-120 miles at 80% DOD. How far one could get on a charge would largely depend on their average speed and driving habits. A gallon of gas has about 33.4kWh's of energy, so my car's 26kWh pack is the equivalent to roughly 2/3 of a gallon of gas. Having such a small amount of energy available at ones disposal makes the range very sensitive.
Jalopnik: What do your parents/family/friends think of what you're doing?
Juan: Everyone is very encouraging and supportive of my project. While only a couple of my friends / family understand exactly what I am doing, they all express copious amounts of interest. I originally told my mother that the car was going to be remote control like a small toy car and she believed me so I am not sure if she has caught on yet…
Jalopnik: Are you going to get any school credit for this?
Juan: Nope, it is just a fun project on the side! The interest my peers and teachers express for the car makes it worth it!
Jalopnik: What are your plans after you graduate?
Juan: I plan on going to college and pursuing an engineering degree. After working on this car for the past year has convinced me that I am most interested in automotive and electrical engineering.
Ideally, I would like to attend MIT, Berkeley, or Georgia Tech. We will see once admission results come out!
Jalopnik: What's your favorite car, if you could have anything? Jalopnik's buying!
Juan: This is a tough one. Likely a 458 because honestly how much cooler can it get?
If I had to choose something realistic it would be an Exige / Elise. Fast, efficient, economical, and simply awesome in general.