Fiat Spider Conversion Completed
The first conversion of the Fiat Spider is completed! All target parameters were achieved, including 0-60 acceleration below 6 seconds (compared to the stock Fiat's 10-11 sec), and a 100 mile city range. The top speed was tested to 85 mph. With the EMotorWerksSmartCharge-10000 charger, refilling the battery pack takes 3.5 hours from a regular household dryer outlet (30A 240VAC). This can easily be cut in half by installing one additional breaker into the electric box of a regular house - 30-min job for a competent DIY'er or an electrician.
The First EV Conversion by the EMotorWerks Team - Fiat Spider 124 Convertible
- by Valery Miftakhov, May 2011
I myself contracted the 'EV bug' long, long time ago - maybe because of my High Energy Physics background or maybe because my father started teaching me all things electric (and later, electronics) at the tender age of SIX. ;-)
I remember though that my first encounter with the soldering iron was not very fortunate - as I grabbed its hot business end with my bare hands when I was about six. My mother reacted in a non-traditional way and insisted that the best way to avoid accidents like this in the future is for my father to teach me how to use that stuff. So there it went...
Anyway, I've started thinking about electric cars a few years ago when I first heard of Tesla motors. Obviously, being right out of my grad school I could only look at the $120K sports beauty but the idea got planted. In fact, now, 7 years later, Julia (my wife) and I are in line for Tesla Model S delivery sometime in ...2012 or 2013. But after thinking about it a bit more we have decided that we can't wait that long and be at the mercy of someone else's plans and timelines. So we were going to just do it ourselves. Soon after (late 2010) we bought our donor car - a 1977 Fiat 124 Spider. Always had a soft spot for Italian cars and the right kind of California rust-free, bright-red beauty just came along...
Our target EV performance parameters were:
The rest of the Team EMotorWerks (Henry, Andy) have joined our pursuit not too long after. After doing a TON of online research on forums, and reading a "Build Your Own Electric Vehicle" book, we have tentatively decided on the following "Big3":
With the battery being the weakest link, the total max electrical power that we can get from this setup comes to ~170kW. Taking into account the drivetrain & motor efficiencies, this means ~170 wheel horsepower - which is ~double the original car. What's more important, however, is that the torque at 1000A is ~300 ft*lbs and the sub-6s 0-60mph is virtually guaranteed with at least one gear shift (from 2nd to 4th, for example).
After the most daunting choices have been made, we have spent a lot of time taking a TON of courses on various maker's subjects like Strength of Materials, CNC design & manufacturing, Plasma Cutting, CNC Mill operation, Welding, Hardware design, high-power electronics, switching power supplies, etc, etc. TechShop Menlo Park is awesome for that kind of stuff! And with 1 CS and 2 Physics PhDs on the team, it was reasonably easy sailing ;-)
The conversion itself split into the following 7 major types of tasks
1. Procuring the componentsNot as easy as it sounds. While there are a lot of companies selling those, getting a compatible set of 30+ types of components one needs to convert a car is not particularly easy. Some of the companies do offer kits that are supposed to work together but (1) they are generally underpowered for what we wanted to achieve and (2) are overpriced as they always include stuff that you don't really really need. So we spent some time researching and shopping for just the right connectors, just the right cable, etc, etc. Majority of misc components were bought from EVSource, motor and controller from RebirthAuto, and batteries direct from CALB office in LA. Generally, the experience with the above vendors was great, with the exception of having to wait for over a month while our controller was being assembled by EVnetics team...
Total component cost at this point - ~$15,000:
2. Building a high-performance EV charger from scratchWhy would we do such a thing, one might ask. Turns out that this is an area of particularly fat margins if you are really after high performance (i.e. short charge time in case of a charger). And we were definitely after high performance. The typical US household has a 240V dryer hookup with a 30A breaker. A smart charger capable of fully utilizing such a line would set you back for at least $4-5K which was definitely not acceptable when the total cost base of all other parts combined is $15K. Also, thinking about the future conversion services, we did not want our customers to have to spend that kind of money on a decent charger. We felt that we would be better off doing some R&D in-house and passing the savings to our customers later. Therefore, we have decided to do it ourselves. And we made it fully open source!
All the fun details are available on another page of this site but the summary is as follows:
3. Designing & making a motor-transmission couplingThe main task here is to build a small (something like a 3" diameter, 3" long) part that accepts motor shaft on one side and connects to the flywheel on another. This is probably the most complicated part of any EV conversion - for 3 reasons: (1) very tight tolerances for the 6,000-rpm part to avoid vibration and resulting drivetrain destruction, (2) it needs to be custom-made for the [normally irregular] shape and design of the stock flywheel units, and (3) it needs to be made of extra-hard material (such as stressproof carbon steel) to withstand the torque loads from a big electric motor.
After unsuccessfully trying to find a machine shop that would design & build this for us, we have decided to do everything ourselves. For some reason, everybody wants to charge you a few thousand bucks on anything custom. So we said screw it, especially given that we want to do that again and again with our future conversions. So we sat down, learned a bunch of CAD design tools, done a lot of measurements and a couple of versions of the final design before we got it right. Took us probably 30 person-hours total. We have CNC machined the first copy of the finished design out of aluminum - fine for initial motor break-in (<300A) but likely not good enough for full power. For the latter, we have also machined a copy out of stressproof 1144 high-carbon steel (the same material the motor shaft is made of).
We wanted to keep the clutch system for 2 reasons: (1) the clutch disk has stress-soaking heavy-duty springs that will help absorb torque spikes from the huge electric motor when we floor the gas ;-), and (2) you need to shift at least once if you want faster 0-60. Generally, the idea is to drive in the city mostly in 2nd gear, on the freeway mostly in 4th According to my calculations, the above setup will result in in ~5s 0-60 time (including allowances for all losses in transmission, rear diff, tires, etc). Some other converters opt for a clutch-less system but that means you need 2-3 seconds to shift gears as you need to wait until your synchros in the transmission adjust the transmission RPM to the right value. Too slow for my taste...
The last component of the coupling system is the adapter plate between the motor and transmission bellhousing. The length of the coupler and thickness of the plate has to be precisely matched to get the 'critical distance' right (the distance between the edge of the bellhousing and the outer surface of the flywheel). If you get that wrong by just a couple of millimiters, you either won't be able to shift or will be slipping the clutch all the time and hence not have much power delivered to the wheels. The plates were CNC machined on the TechShop's Tormach mill out of 5/8th inch thick aluminum.
4. Designing & making a Motor mounting systemApart from designing and building the charger, mounting systems were the most creative part of the conversion - I felt a bit like an artist making something out of raw metal that would then have a predetermined function and form. As a result, welding and CNC machining are probably my favorite fab skills now. Also, the guys from Online Metals and Santa Clara Metal Supermarkets are my best buddies now ;-)).
Anyway, the task here was to design the mounting system to connect the motor to the stock engine mounts. The benefit of the stock mounts is that they (1) isolate any vibration from the motor/transmission assembly, and (2) they absorb at least a part of the motor torque reaction when you floor the gas. A few converters who used rigid mounts for their motors had them snap off after a few hundred miles due to stress so using the right mounting system was rather important.
The construction itself consisted of an additional back plate attached to the rear of the motor, and welded brakets connecting the back plate with the front coupling plate. Then the brakets were bolted onto the stock engine mounts.
So far, everything is holding up great. In idle tests, I can see the motor rotating about 1 degree or so - or 1cm on the outside circumference - pretty sizeable deflection that would otherwise have to be absorbed in the rigid components. We will probably have to further reinforce the mount with some kind of a cross-bar to better withstand the torque once we lift the motor break-in power limit...
5. Designing & making an under-hood mounting sub-frame and boxes for battery & controllerAgain, more art here as we decided that we want to fit in the absolute maximum number of components under the hood to ensure the stock weight distribution does not change much. You have probably already guessed from the photo on the top of this page that there is not a huge amount of space under the hood of that tiny car ;-). An additional complication was the construction of the vehicle frame - essentially sheet metal rolled into a boxed structure for rigidity. Unfortunately, thin sheet metal is not so fun to weld things to (ask me how I know...).
So we had to get creative. In the end, we welded a separate sub-frame tightly matched to the hood dimensions and bolted it to a few structural elements found under the hood - such as a cross-bar, front frame element, and the piece of the frame holding the firewall. Then we mounted everything else (batteries, controller, etc) to that sub-frame. To maximize the utilization of highly curvy interior space, we ended up splitting the cells into 4 cell groups, which let us fit 22 battery cells (out of 60) under the hood. And the controller. Most of the batteries and the controller were mounted in an aluminum semi-closed box that in turn was bolted to the sub-frame.
All in all, we estimated that we lost 400lbs when we ripped all the gas engine components from under the hood (engine itself, radiator & cooling system, etc.). Then we put back in: (1) 180-lb motor, (2) 35-lb controller, (3) 160 lbs of battery cells, and (4) ~60 lbs of a frame and heavy-duty wiring - for the total of ~440 lbs, or +40 lbs over stock. Success.
6. Designing & making an in-trunk mounting sub-frame for batteries and chargerThis was a much simpler task than under-hood mounting as most of the surfaces and shapes are way more rectangular. We did have to do a small number of modifications, though - (1) remove the fuel tank, (2) remove the spare wheel and the mounts, (3) remove all exhaust piping, and (4) board up the holes that appeared.
Once that was done, we have designed a simple battery mounting rack out of the angle steel stock to hold the remaining 38 cells. Then on top of the batteries we have added some mounting brackets for our charger (also containing DC-DC converter to get 12V supply for all the car systems and temperature control circuits & logic, etc.). I'd estimate that we still have space left for 30 or so cells should we wish to upgrade in the future.
So far, the weight reductions in the back were: (1) the fuel tank with full fuel - ~100lbs, (2) exhaust system - ~50lbs, (3) spare wheel and mounts - ~50lbs, (4) stock lead-acid battery - ~70lbs - for the total of ~270 lbs. Weight increases are: (1) 38 cells - total 270 lbs, (2) mountining system - ~30lbs, and (3) charger - ~30 lbs.
So net weight increase in the back ~60 lbs. Total weight increase for the car: ~100lbs, with virtually unchanged weight distribution which is awesome for preserving agile handling of the car. The suspension was changed over to the stiffer sports shocks & springs to further improve the feel.
7. Replicating various accessory systemsNot as much fun as the previous tasks but needed to be done.