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Building a GEVCU
I built up a GEVCU 4.2 controller board that will be used to control the DMOC (pictures). The main processor on the GEVCU is an ARM Cortex M3 84MHz processor. It is packaged in a 144 pin LQFP device. This is the first time I have soldered a LQFP surface mounted device (SMD), but I found it was not much more difficult than soldering any other SMD. However, I have not done any SMD soldering for a few months and I did have some initial problems with configuring the ARM processor because of a soldering error. Paulo Almeida helped me out, via email. Many improvements have been made in the code over the past 6 months by Paulo, Collin Kidder, Charles Galpin and Michael Neuweiler. Once I have the drivetrain together I need to test the GEVCU 4.2 with my throttle and brake setup. The throttle is easy to test because it is used to spin the motor. The throttle is a duel potentiometer and will be connected directly to the throttle cable on the 320i. Two potentiometers are used as a safely measure. A hydraulic pressure transducer is use for the brake transducer and the signal is used to control regeneration or regen in the motor. Regen is a process where the motor is turned into a generator and the output is used to charge the batteries. Even with a lot of braking regen only leads to a 5 to 10% recovery of energy. The actual regen and throttle setup will have to wait until car is on the road for it to be fine tuned. The throttle and brake are 0 to 5V analog signals that have to be calibrated in the GEVCU code. These settings are accessed through a web page that is hosted by an embedded server in the ConnectOne WiFi device (pictures).
Once the throttle and brake are configured I then need to design all the circuits that will use the digital I/O on the GEVCU. One circuit will use one of the MOSFET outputs to control a precharge circuit for the DMOC. Because it has a huge capacitance it is necessary to precharge the DMOC with a low voltage, controlled current before applying the full battery pack voltage otherwise the high current inrush can fuse the contactor. Another one of the MOSEFT outputs will be setup to output a pulse width modulated (PWM) signal that will drive the tachometer in the instrument panel. One of the digital inputs will be for an enable switch for the whole system.
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Selling the ICE
I was able to sell the engine removed from the 320i on EBay. I made more than $100 on the sale over the cost to have the internal combustion engine (ICE) and components that were removed by Henry's Automotive. I found by searching on the internet there are many trucking companies that will transport items like engines and transmission for fairly low cost. The engine is being shipped nearly halfway across the country for very little money. Hopefully the shipper will do a good job and deliver the motor intact. The downside of selling items on EBay is the 14-day money back return policy. PayPal releases the funds to the seller only after that time has elapsed, if the buyer makes no claims. For other EBay sales there has never been an issue because UPS always delivers without issue. But in this case a trucking company is making the delivery that I have never used before. They are accredited and seem to have everything calculated and documented well. The ICE will be picked up by the shipper today.
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Washing the Engine Compartment
Taking advantage of the mild January weather I decided to roll the 320i out and pressure wash the engine compartment (pictures). That will make working on the electric conversion much easier (no grease!). The engine compartment will also need some painting since it will be shown off at car shows or to anyone that is interested in the conversion. I also took this opportunity to clean the grease off the transmission. Though this cleaning process I also got a good look at the engine compartment and what has to been done. The first modification will be to cut out the 12V battery mount. I probably will still have a small 12V battery somewhere but no need for the big cell that was part of the ICE. The old battery mount interferes with the area where the new batteries are going to be mounted. There is a bunch of heat shielding that also has to be removed. I have to decide if I am going to replace the fuse box. The fuse box is in the engine compartment and it has the old-style Bosch fuses - the ones that are not encased in glass. The old-style Bosch fuses are problematic and having the fuse box under the hood leads to corrosion problems. But moving the fuse box to inside the vehicle will require a lot of re-wiring.
Moving the 320i outside the garage is easy because the garage is sloped and so is the driveway. The problem is getting the car back in the garage. There is a 1" lip on the garage floor that is very hard to push the car over. To get around this problem I used an electric winch to pull the car back into the garage. That worked really well. The winch was connected to a rod that I had drilled and lagged into the garage concrete floor. The process of winching the car back into the garage will prove to be handy later in the conversion.
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Weighing the car
I got the Proform vehicle scale setup and was able to measure the 320i weight at each of the four wheels. I will post some pictures in the photo gallery. The total weight after the ICE removal is now 1776 lbs. With a spec curb weight of 2452 lbs that means all the of the removed ICE components weighed 675 lbs. That is just about what I expected for the ICE weight. It is interesting that the driver's side of the vehicle weighs about 40 lbs more in the front and only 5 lbs different between the left and right sides in the back. The front weight difference is probably due to the steering column and associated hardware. The 245 lbs difference between the front and the rear weight distributions now means I have to locate more weight in the front to get a balanced front/rear weight ratio. As I said in the EV Design article, some of the weight in the rear could be moved to the front, like the DC-DC converter. There also will be more components in the front that will add weight like the transmission.
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Conversion Design
Now the fun starts. The two biggest design problems are the battery boxes and the engine mounts. Batteries will be mounted in the engine bay, under the rear seat and in the trunk.141 batteries in all have to be mounted. The plan is to have 36 batteries mounted in the engine bay, 48 batteries mounted under the rear seat and the balance of 57 batteries mounted in the trunk. The critical aspect of battery placement is balancing the weight in the car. The BMW had nearly a 50/50 weight distribution between the front and rear wheels. The goal of the conversion is to maintain that ratio. The motor and all the other ICE components weighed approximately 600 lbs. The new electric motor and controller weigh about 300 lbs and the batteries weigh a total of 650 lbs. With the other EV components like the charger and the DC-DC converter I expect to add about 450 lbs to the weight of the car. That will put the curb weight around 2950 lbs. The max gross weight of the car is 3500 lbs so there is room for people and storage in the trunk. Check out the EV Design page for more detailed info on the conversion design.
The electric motor mounting will be difficult because the whole drive train has to be assembled and placed in the car to get an accurate measure of where the Siemens motor can be connected to the motor mount points. A spline adapter from EV West will be use to adapt the Siemens motor to the BMW 5-speed transmission. That adapter adds a couple of inches to the drive train length.