Burnout Mode Engaged

After realizing that we had spare tires, all I could think about was doing donuts in the elEVen. Having never done a donut in the car, I decided to practice before hand. It looked more or less like this:


One difference is that I wore a helmet. As always, safety first.

In that same vein, we double checked all of the wiring and structural members to make sure that no short could occur, that all wheels would stay on the car, and that no oil would leak.

In our inspection, we found something wrong with the SCU. After 3 hours of debugging, we diagnosed the condition as dirty connectors between the motherboard and one of the cards. After cleaning the connectors, we fired up the SCU and sure enough the problem had been resolved.


We closed the SCU back up and soon we began the tedious process of remounting it back in the car.

The SCU was designed to fit into an electric school bus which has tons of space to mount components. Our Mercury Milan is a little more cramped making the mounting and unmounting process a more difficult. It is a three person job, with one person manning the hoist, another person making sure that nothing is in the way and the third under the car that aligns the SCU into its mounts.

Once every thing was back in, we went for a little drive up and down the street that our shop is on.


What follows are some pictures that we took before, during and after the first drive of this summer of the MIT EVT elEVen.

elEVen Status Update

The heat is rising in MIT's Electric Vehicle Team shop. After late nights of soldering, countless breaks for Monster, and hours of tedious coding, our Mercury Milan conversion - the elEVen - is nearly street ready. The elEVen conversion and rapid recharging were delayed due to a problem with the motor controller, as was discussed in Stephen’s earlier blog post. While that problem was being resolved, the team wasted no time in starting other projects to increase the safety, comfort, and robustness of the car. These projects - including the battery cooling system, the mount for the charger, the charging adapter, the motor controller wiring box, and all of the internal communications - have either been finished or are nearing their respective ends to where the whole car can be assembled. Once the car is put together we can begin working on rapid recharging, but until then, the engineers in us are eager to get the elEVen running and on the road.

Here is our status on each of the elEVen projects:

A New Cell Cycler

Recharge your electric car in less than 10 minutes! This has been the dream of many current and future electric vehicle owners. But imagine the batteries in your car could only handle this rapid recharging maybe 400 times - about the lifetime of a laptop battery, charging at a normal pace. Let's do some math: 100 miles (the range of the Porsche 914 BEV) x 400 cycles = 40,000 miles per car. Who would want a car with a battery pack that only lasted three years? [1] Not EVT! We wanted top of the line batteries that could handle our abusive rapid recharging and put up a fight for an acceptable number of cycles. Just in time, we came across A123, one of the industry's leaders in battery technology.

A hundred battery boxes later, we were ready to put our A123 cells to the rapid recharge challenge. In order to test our new batteries, Lennon Rodgers set up a station to rapidly cycle - charge and discharge - an A123 cylindrical 26650 battery, pictured here. After cycling the cell repeatedly, he hoped that even with the deteriorating effect of rapid charging on any type of batteries, the cell wouldn't lose much of its original capacity. His results are shown in the graph below.

Excitingly, after almost 1500 cycles, the cell barely degraded. So, 1500 cycles corresponds to 150,000 miles which is nearly the average lifetime of a car. [2] This is much more reasonable for a commercially marketable battery pack. Though this result is exciting for the possibility of rapid recharge technology, only one cell was tested which does not constitute a statistically significant sample size. Therefore I have spent the last few weeks setting up a new cell cycler. This cycler will rapidly cycle the same type of battery, a cylindrical 26650 battery and hopefully support the results from the first test.

Here are some technical details of the circuit. The cycler has two parts connected

to the battery through a set of relay switches: 1) a power source used for constant current charging at 10Amps and 2) a .25Ω resistor through which the battery can discharge. During the entire cycle, the battery temperature, voltage and current as well as the temperature of the resistor are monitored and constantly checked for dangerously high or low values. The data is sent through an Arduino-controlled circuit to a wireless ioBridge module which allows us to remotely upload data to monitor the status of the battery and keep a running chart of its capacity.

After a brief setback in which I killed a cell (thank you to Shane Colton for his assistance in soldering a new replacement cell), the cycler is up and running. In the time since it was turned on last Friday, July 30th, it has undergone over 300 cycles. It will take about a month to complete the goal of 1500 cycles, but the cycler is well underway and showing promising results. Stay tuned for the results on the second cycler test as a step on our way to rapid recharge technology.

[1] http://www.epa.gov/oms/consumer/f00013.htm

[2] http://www.arb.ca.gov/regact/grnhsgas/vmt.pdf

Manzanita Mounting Frame

The project I have been working on for the past week or two has been fabricating a mounting frame for our charger. Though it may appear so from the outside, charging a battery pack like ours is not as simple as plugging it into the wall. The power first has to go through an intermediate stage before it can charge the batteries. For this intermediate, we have the Manzanita Micro PFC-50 (seen below). It is a charger that can handle anything from regular charging all the way up to very rapid recharging.Since the elEVen's current battery pack is in the trunk, it would be ideal if the charger could be in there with it. However, there was very little room left in the trunk with the massive battery pack and new cooling shroud, so I had to work within the remaining space. The only place the Manzanita would fit was above the cooling unit. Keeping the dimensions of the trunk in mind, I came up with a design in Solidworks. The whole frame would be welded together, and the Manzanita would be easily bolted on. Here is a preliminary design I made.
After double checking everything to make sure it would fit, I began cutting lengths from a bar of hollow, square cross section steel using our cold saw. I then drilled the mounting holes in them, and handed them over to Pete, our designated daytime welder, to weld together. While he was doing that I cut four small triangles out of steel plate and put a hole in each of them. The idea was to weld the small triangles to the bottom of the trunk, and then bolt the mounting frame onto them. This would allow easy removal of the whole frame while having a small permanent footprint in the car and allowing for the cooling shroud to be easily removed if necessary. Once Pete finished the welding, he hit it with a shiny black paint job, and it was done. It fits perfectly too, have a look.

Wiring Party

These past few weeks I've been assigned to rewire the breakout box. Before it was a colossal mess but it did what it was supposed to, it got the car rolling.




This time I designed a much more compact wiring box that also incorporates the relay box and other small circuitry. It has one 0.5" cable that goes from the System Control Unit to the breakout box and it does everything else from there. It uses a d-subminiature as an input with two db-25 and two db-9 outputs. It is completely customizable to allow additional ouputs. It has a large 60 signal breakout board that centralizes all the signals that are going to the drivetrain. All of this is done in an enclosure about the size of just the original relay box.

Street Racing

So I was driving down the road the other day in my all electric Mercury Milan when a Tesla Roadster pulled up next to me. Feeling a little confident about my car, I challenged the Roadster to a race. Within 4 seconds, I was already at 180 kph! I blew that sorry Tesla out of the water!

Here's proof:

That's right, I did it with no fuel. Or battery charge. And I left the parking brake on. And my car was telling me to pull over. It's because I was being too awesome.

What? You think I'm lying? Okay! Okay! You caught me.

The slightly more interesting story is that I have started to integrate the CompactRIO, which I mentioned in my last post, into the car. As a test to see if it was working, I decided to control the car's speedometer and satisfy my need for speed at the same time. The next step is to try to convince the car that everything is okay. I hope to get this done by the end of next week so that the car will be ready for inspection and license plates following soon after.

Things are really starting to come together and I hope that you check back regularly for new posts about our work on electric vehicles.

A Luxury Vehicle - The Little Things

The little nuances are important when working with a luxury car (something you don’t think about until you are trying to maintain a luxury vehicle). The Porsche is a completed project that team has worked on in the past. Not only is it a beautiful car, it exhibits electric cars as a viable option. However, it is important that this luxury car look and run like a luxury vehicle. At the beginning of the summer, Pete one of the guys on the team noticed this creaking sound and decided it was creaking due to the suspension (the linkages, shock absorbers, and springs which connect the wheels to the vehicle). The decision was to look at the bushings on the suspension and make sure that they were well oiled.

This doesn’t seem like a big deal, but it can take up a lot of time. It requires moving the car and putting it on the lift. Then, we needed to start taking apart the suspension. This proved to be quite the task, in fact we ended up pulling out penetrating oil in order to disentangle rusted parts. We finally were able to pull the bushings out. We cleaned them thoroughly and spread oil on them. We than began putting all the suspension pieces back into the Porsche.

Good news – We got rid of that creaking sound, and I finally became a grease monkey (or at least I now consider myself in the club).