We kicked off the official start of the 4th Annual EVTV.me Electric Vehicle Conversion Convention with the opening keynote speech by Jack Rickard. This year, as last, the session part of the convention is being held at the A. C. Brase Arena in Cape Girardeau, Missouri. I thank them for free wifi and available laptop & phone charging access!
We have 131 registered attendees and 36 electric cars this year. The car bringers (co-hostages as Jack calls them) have special shirts with numbers on the back that match the number on their car. We are encouraged to talk with the builders about their component and design choices.
Jack had the first time and all-time attendees stand and be recognized. The furthest attendees were from 3 guys from New Zealand. Coming from Thailand, I could challenge them - Google Maps says I came about 400 miles farther but it depends where in New Zealand they live...
Jack flashed back to the beginning of computer BBSs and the Internet and compared it to the growth curve of electric cars. He's realized that 90% of the people at the show have been in the computer industry and are not necessarily "car guys". With the proliferation of microcontrollers in modern cars, we geeks are in a good position. We can design hardware and software that integrates well into existing cars, and we can also extract data from and send control commands to the data-enabled components we're buying and installing in our own cars.
This is a very self-selected group but about half drive their own-built electric car and about 90% are working on an EV project. About 20 people have a store-bought electric car along with their own-built EV, such as Tesla, Ford Focus, Nissan Leaf and Coda.
Due to the exponential growth of the human population, we need to move more and more people around all the time. These vehicles largely run on fossil fuels and there will be no end to the supply of gasoline, but the price will skyrocket as it becomes harder to find. This is a big impetus to the rise of non-fossil-fuel vehicles.
Jack discussed the standard product adoption curve: the early adoption phase represents up to 2.5% of the market. For new vehicles worldwide, that's about 375,000 per year. Electric cars are selling at about 120,000 per year, so we're not even in the early adoption phase yet, so there is a lot of market space available for innovative people and companies.
Jack pointed out that as modest as we are about our knowledge about electric vehicles, people regard us as the local expert in the field, and we are key in the dissemination of the benefits of EVs and also keeping the car companies in line.
Next session: Jack Rickard on the Basics - Why to do a conversion and how to get started with the initial planning.
Jack started out by discussing the two show specials, is CALB SE Series 100 AH batteries are going at $75 each. He has made a deal with UQM and received his first shipment of 10 UQM PowerPhase 100 motor and inverters. These come with no factory warranty, no product support or documentation. UQM will sell this to you for $15,000 but Jack's price is $7,000 each and he can order 20 more if needed.
Several of the speakers who initially committed to the show have dropped out, so Jack is having to step in. Eric Kriss was initially supposed to give the basic conversion session but was unable to make it.
To do a good conversion you start out with the car of your choice and spend $25,000 to get it rolling on electrons alone. If you try to save money, you're not going to be happy with the result. This is only fair when you look at other hobbies such as boating. 4-line BBS systems in the '80s cost over $20,000 and you can't drive it down the street.
By the time you have purchased all of the components and designed your battery boxes, you've completed 80% of the project. The rest is just installation and wiring. Building an EV is very personally satisfying.
There are two major criteria: range and performance. You've got to seriously look at your daily driving needs and design your pack size accordingly. Battery technology does not let us go 500 miles yet. You also have to decide if you're looking at drag racing, performance driving, highway driving, or sedate around-town driving. You need 1 watt-hour of energy per 10 pounds of vehicle to go one mile of mixed driving. Determining the weight of the car with this formula times your desired distance gives you the target kilowatt-hour size of your pack. You should always put extra padding on this as you don't want to take the batteries all the way down to get the desired mileage.
DC series-wound motors are the cheapest way to get your car rolling, as they're simple motors with simple controllers. DC systems have lower voltages (120 - 144) and very high current but a relatively low 40 - 44 lithium batteries. AC systems are gaining market share in EV conversions due to dropping prices, more product choices and the small benefit of regenerative braking. AC systems have much higher voltages (300 - 335) and lower amperage, but that voltage requires about 100 lithium batteries in series. This is important in a space-constrained vehicle. The new CAM series batteries have different form factors with quite similar capacity so you can pick the one that fits best.
Car choice comes down to weight, quality (rust-free, paint, interior, etc.) and personal style. The more unique and sexy the car, the more attention you'll be getting as you silently cruise down the road or come out of the grocery store with your melting ice cream.
Jack talked about the genesis of EVTV. He bought a shipment of Chinese batteries which came with no documentation, so he tested them to destruction to find out their performance characteristics. He then tried to figure out what to do with the remaining batteries, so he asked Brian to put them into a car. This was the first Porsche Speedster build, which went 110 miles and a top speed of 95 mph. He was amazed that without knowing what they were doing, they made this great car - why aren't other people or car companies doing this? About this time, Chris Paine made the Who Killed The Electric Car movie and the US government announced the financial bailout. The rising price of gas and the result of his car gave Jack the impetus to start the videos which led to more car builds which led to an online store selling EV components.
Next session: Fundamentals of Electricity and Magnetism by Ralph Tate, Southern Illinois University
SUI offers a Bachelor's Degree in Automotive Technology, and has expanded its focus into alternative energy vehicles. They've done two conversions so far, the second is a 1990 Miata. The third conversion starts next month, a PT Cruiser.
Ralph teaches his students about energy, right from the basics. He discussed energy and power, coulombs, volts and watts. A gallon of gasoline contains 36.6 KW of power, which is about half the size of a Tesla Model S battery pack. Gasoline engines run at about 18% efficiency but electric motors are about 85% so a lot of the power in that gasoline is thrown away as heat.
Ralph then talked about charge and force, attraction and repulsion, and conducting elements which have one electron in the valence shell. This electron can leave and rejoin the atom without too much difficulty, leading to current flow. An ampere (amp) is one coulomb of current per second. Battery charge is indicated in Amp-Hours, so a 180 AH battery has 180 * 3600 = 64,800 coulombs.
Voltage is a difference in potential through a circuit. A volt is 1 joule per coulomb. Resistance is the opposition to current flow, measured in Ohms. When resistance decreases, current goes up towards infinity. This is the explanation for the real-life scenario of a short circuit shooting sparks everywhere.
Magnets! Magnets generate lines of force from the North to the South poles. We can create machines the exploit this force, causing rotation. A Tesla is the unit of flux density and is equal to one Weber per meter squared. Only some elements exhibit magnetism - they need to have non-paired electrons that spin in their orbits. Lodestone was the first naturally magnetic material discovered. Ferrite, Alnico and rare earths (grossly misnamed) are other classes of materials. Neodymium has a very strong capacity to be magnetized and is hard to demagnetize, and is awesome to play with.
New magnets are made using electromagnets by running a current through a wire. Wrapping a wire around a core gives an even stronger electromagnet. By putting a looped wire between the N and S of a C-shaped magnet and running a current through it, the wire will turn. We have just invented the DC motor. There is a saturation limit of flux density, dumping more current into the motor gives no additional rotation.
Lunchtime!
Next Session: Batteries
Jack is going to do without his usual LiFePO4 battery intro talk. They are available, predictable, stable, long-lived and almost affordable. This session will be on long-term and temperature testing of lithium batteries by John Hardy and David Bogard.
Note all of the test results below are for Lithium Iron Phosphate (LiFePO4) chemistry batteries. Other lithium chemistries like Lithium Cobalt Oxide (LiCoO2) and Lithium Manganese Oxide (LiMn2O4) will not behave the same way.
John has a metal shed in his back garden at home in England to do battery testing. He uses an Arduino board to run the code for the tests, switching relays on and off to the charger and load resistor and collecting voltage and amperage values. He stressed that any testing apparatus must draw the minimum current possible, down to the nanoamps or it will have a detrimental effect on the cells under test.
For test 1, he tested Headway 10AH cells and had a failure at 600 cycles, but no drift in the rest of the cells. Test 2 used shunt balancers and he destroyed his pack in less than 100 cycles. Test 3 used CALB CA 40 series batteries and he halted the test at 2000 cycles because there was no drift and 80% of original capacity left. He's working on test 4 right now, charging at faster rates. The preliminary data gives similar result as Test 3 but the cells lose capacity slightly faster. More data will be forthcoming.
He also tried using dielectric grease but it actually caused the temperature at the battery terminals to raise about 5 degrees C higher than terminals with no grease, so it's not a good idea. He found that a small number of cells are subject to self-discharge and will go out of balance with the rest of the pack, so it's important to identify these cells and replace them. He recommends you buy a couple of spare cells for replacements. He says to bottom balance them to within 5 millivolts and record each value. Let them sit for three days to a week. Most cells will bounce up slightly, and any cell that has drifted down should be discarded.
This testing validates Jack's theory that a bottom-balanced lithium ion battery pack will work beautifully for thousands of cycles if you don't use a BMS, don't over-charge them and don't over-discharge them.
Dave Bogard was up next, showing the results of his 8 AH battery life cycle testing with temperature variation. You should go back a couple of weeks to see his video report in Jack's EVTV episode. His basement testing lab is something to behold! This session is a recap of his testing methodology, raw data and analysis. He also used an Arduino, specifically the Mega 1280, a switched relay board, two power supplies and 3 fan-cooled high wattage resistors. Be sure to use a snubber diode across the relay coil terminals to avoid a voltage spike back to the Arduino signal pin which can reboot or damage the Arduino.
He tested 6 identical Headway 8AH cells in 3 packs of two cells, at 0 degrees C (in a small bar fridge), ambient (18 degrees C) and 55 degrees C (in a toaster oven). He initially tried to charge and discharge at 8 amps, but it was too hard on the cold battery so he changed to 4 amps. He built a discharge / rest / charge cycle scenario against the 3 packs.
He did initial calibration with 47 test cycles and identified a bad battery which was swapped out. He ran all batteries at ambient to 100 cycles to confirm they were behaving similarly. Starting with test 101, he subjected them to their test temperatures. The cold cell quickly started falling behind, ending up with about half of the charge / discharge capacity of the other two, and this is permanent damage. The heated battery performed a little better than ambient. This confirms manufacturer claims to avoid charging and discharging at low temperatures, but warm ambient and hot temperatures are OK. This is good news for electric car owners in Phoenix, there is no risk of shortened capacity or lifecycle.
Next Session: Hacking Electric Vehicles for Fun and Profit
Given that I'm a computer geek and crave data and control of bits of hardware, I've been looking forward to the next two sessions.
Collin Kidder presented this session on reverse engineering CAN bus messages. CAN bus is the standard for connecting microcontrollers in modern cars, so understanding how to connect to this bus, read data and put new commands on the bus is key to the future. CAN actually stands for Controller Area Network, not Car Area Network as some people think.
Collin's goals for CAN bus communication includes getting more info out of the car than the manufacturer is willing to divulge, using parts from wrecks in your own car, and just because!
What data is flowing on a CAN bus? Temperatures around the car, tire pressures, voltages, amperages, remaining range, door lock/unlock, window up/down, etc. What gets in the way? Lack of standardization of data messages and intentional manufacturer obfuscation. OBD II standardized the data required for emissions testing, but not much beyond that. J1939 is used in heavy trucks but not passenger cars.
Reverse engineering requires the understanding of how to convert from different number bases, including decimal, hex, octal and binary. There is also the concept of Big Endian and Little Endian (Intel) ordering of the binary bits in the packet. Some numbers are represented with a negative sign which normally takes the form of 2's Complement binary representation. Floating point numbers, such as 3.14, take a very different form and a lot of computing power to manage, and for this reason floats are multiplied by say 10 or 100 before transmission, then divided back out at the destination. Binary Coded Decimal is also sometimes used. Bit shifting and bit operations such as Not, Or, And and Xor are used frequently to mask out the data you want from a larger data packet. If none of this makes sense, take a 2nd year Computer Science class! Been there, done that, taught that.
CAN bus is a single long cable with two wires, and is a serial bus like USB. One wire is the + signal and the other wire is the - signal, in a differential format. Each device just connects somewhere on the wire, in parallel with all other devices. Both wires can float up and down in voltage but only the difference between the two wires determines if the bus has a 1 (recessive) or a 0 (dominant) on it. Recessive and dominant is used to see if two devices are trying to talk on the bus at the same time - this is called the arbitration scheme.
CAN has a well-defined message frame format, with different fields in the frame representing different information. Embedded inside the frame is the actual data, like the pressure of the front left tire. The ID in the frame is key, it identifies the specific frame format for a single type of data, this way tire pressures aren't confused with battery voltages - they will have different IDs. There are two ID types, standard and extended. Priorities are also encoded in the ID, since ABS signals are extremely important, engine RPM is medium importance and cabin temperature is low importance. Masks and Filters are applied as frames come across the bus, allowing you to focus on only the frames you care about, not the 3000 frames per second as you're driving down the road.
So how do we start playing with CAN? You need a device that you can wire to the two wires, software to read and interpret the frames. The Kvaser Leaf Light is quite good, but costs $350. You then use the free CAN King app. The Komodo CAN Duo runs $450 and has screw terminals for each connection to the CAN bus and a free app to drive it. The Microchip CANBus Analyzer too is not isolated, but does a good job for $100. The Salae Logic device is a general purpose logic analyzer that understands CAN. BusMaster is a very powerful and free app but only supports the expensive dongles. Vehicle Spy Pro requires its own dongle which is very expensive at $2500. Vector CANalyzer is the gold standard but costs $5000. Collin is writing his own, specifically designed for reverse engineering, and hasn't decided how he will release it or what it will cost. EVTV's own GEVCU can be used too, more in the next session on GEVCU.
Now how do you reverse engineer a car? You need to search following the characteristics of the expected data. RPM is a large number. Temperatures change slowly. Triggered events just fire one frame as needed. Just capture frames as your expected message should be coming through. Analyze them later, looking for relevant changes. Guessing is powerful. Keep notes to correlate data to real events. Watch for counter values, endian, offsets and scaling factors. Plot data to visualize how it changes over time and compares with another data stream like commanded torque and reported torque. Keep the wheels off the ground when testing motor controllers!
Collin then explained his steps of deduction to decode the magic byte in the Coda motor controller torque command. It still amazes me that he was able to figure this out!
We were running about an hour late so dinner showed up just before the last session was about to start. Everyone ran for the food, so the session will be postponed until tomorrow.
I will leave you with pictures of the vendor area and the components they brought over that are available for purchase from the evtv.me store. I don't think some of those motors are going to be accepted as carry-on luggage!
Lonestar EV Performance is here with their design for a dedicated electric drag racing electronics and drivetrain. The video they took of their motor with a GoPro must be seen to be believed. That's a plasma field during the heavy acceleration.
Hi Performance Electric Vehicle Systems brought a selection of their motors and controllers.
Below are some of the EVTV components for sale.
And I'll leave you with another of Jack's upcoming projects, this beautiful wooden speedboat, with a jet ski drive system, just waiting for an electric motor and battery bank.
That's it for today, we've come back to the shop to put some more work into the Smart car. More from the show tomorrow.
No comments:
Post a Comment