Thursday, July 29, 2010

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.


Wednesday, July 28, 2010

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.

Friday, July 23, 2010

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.

Saturday, July 17, 2010

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.

Thursday, July 15, 2010

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).

Thermal management of the battery pack

One of the projects I'm working on this summer is the thermal management of our battery pack during rapid charging. Charging the battery pack in less then 11 minutes generates a lot of heat within the pack. To remove that heat and cool down the cells during rapid charging I've designed a cooling shroud to force air through the closely spaced battery cells inside the pack. To overcome the pressure drop inside the pack we're using three centrifugal blowers.

Wednesday, July 7, 2010

Breanna's Blog #1

After much resistance, I have decided to finally begin my blogging for the summer. My blog posts might not seem quite as relevant as other team bloggers, but hopefully they will give a bit of insight into how our team works and functions as both a research group and student group.

Despite majoring in Course 2, before this summer began I lacked the hands on experience that is associated with such a degree – basic shop training. The first thing I want to post about is how I learned to use this equipment.

In the beginning of the summer, Steven Lam a fellow EVTer was designing and constructing an oil sump. In order to build specific sides of this oil sump he needed to use a milling machine. When Steven was working on it, he took me under his tutelage and taught me how to use the milling machine. By the end of this instruction, I knew how to change the mill bits for the various sizes and types of holes needed to cut into this aluminum and understood how the various planes of the mill worked and how they could be used to finish creating a design.

However, this lesson didn’t even begin to cover everything you need to know to use the milling machine. I needed to gain a lot more knowledge and experience before I could use the machine by myself, without being under some supervision. The options were reading a manual, helping my fellow EVTers machine stuff, and/or attending a machining class. Luckily, our team had a shop training class that weekend. After a 3 hour training on the mill machine, I felt comfortable to use a machine basically by myself (of course, I would still need to appeal to one of the senior members on my team to double check my set-up before I began to mill). In addition to this newfound skill, I also had joint ownership on “EVT bling” with Dianna.

SAE J1772

Normally, when your car runs out of fuel, you pull into a gas station and fill up. Most cars run on regular, though some cars run on premium, diesel, etc. If you have an electric car, you probably have to drive home to charge up you vehicle, and likely use a custom made charging port for your car that you plug in to a normal wall outlet. Well, all of that is changing. Enter the SAE J1772 standard outlet.

This plug will be the new “regular unleaded” for EV’s. It is being used on the new Nissan Leaf, the Chevy Volt, and even Tesla is likely to take advantage of it. On top of that, charging stations are being built around the country by several companies, most of which will use the J1772. Having a uniform standard is important for large scale production, and is a necessary step if EV’s are to become mainstream.

This may sound great, but here’s the most exciting part: we’re getting our own J1772 port. I have been in contact with Tim Rose, the managing director of REMA EV, a company which makes electric power connections. They have been kind enough to donate the port along with the appropriate connectors, and if all goes well we’ll be getting one for the elEVen very soon and one for the Porsche in a few weeks. When it arrives I will be figuring out a way to install the port where the fuel filler cap used to go, and soon after we will hopefully have a way to charge the elEVen’s batteries.

Thursday, July 1, 2010

Talking to Batteries

EVT has worked a lot with the A123 26650 cells: we've cycled them, rapid-charged them, drilled into them, built packs out of them, all in a few semesters. At the beginning of this summer, we even charged the whole eMoto pack in 11 minutes and 30 seconds! This spring we got a shiny NEW toy: an A123 Prismatic Module.

The A123 prismatics have a much higher energy density than the 26650's and they come in a sweet pack arrangement. We have some single cells that we've been testing, and Lennon and Shane have built a rig to cycle one prismatic 1,500 times at a 6C charge/discharge rate. More updates on that later.
For the past few weeks I've been working on using an Arduino and an MCP2515 chip to talk to the BMS built into the Prismatic Pack. It talks over a CAN network, much like the systems in the Porsche or the elEVen. I've found that using the Arduino allowed me to start communicating in CAN easily in only a day or two, and now I can intelligently talk to the module, polling it for voltage and SOC information and telling it to actively balance itself. In the picture you can see the Arduino board sitting on top of the module, and the cable running over the top that connects the two together. The next step will be to output the battery data to a screen and create a system for talking to multiple packs, like we'll have on the next EVT motorcycle.

Say hello to the newest member of the EVT fleet, a blue Lifan motorcycle. This is the same frame that eMoto was originally converted from, and soon it will hold the above prismatic module and a shiny new motor. Last week Lennon, Randal, and I traveled down to Providence and bought the 2-year-old gas motorcycle from a guy who had never ridden it. When we returned, Randal and I ripped the combustion components and twelve volt system out (the lights and fairings had already been removed) and Will has begun designing a new frame to mount all the electric components. Look out for updates on the new frame and another new addition to our team.