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Drive train coming soon
I have not been doing much work on the conversion for the past month. For a couple of weeks I was building and testing GEVCU 4.2 boards that I built for my friends Collin, Charles and Michael. They now have updated hardware to work in their conversions. Then I was travelling to Japan for my day job and last week I was on vacation for a few days. This week I will be travelling to San Diego. I hope to have time to meet with the guys at EV West while I am in San Diego. For my conversion all the drivetrain components are ready. A new racing clutch was received from Summit Racing. The flywheel clutch face was resurfaced and the flywheel and clutch plate were spin balanced by Lindskog Balancing. The 5-speed transmission had all new seals installed. The motor adapter for the Siemens motor is being shipped by RebirthAuto sometime this week. The adapter will make it possible to assemble the drivetrain and place it in the 320i to design the motor mounts. Photos of the adapter plate can be seen here.
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Cutting the first metal
To prepare the engine compartment for the front battery box, the battery mount for the ICE lead acid battery had to be removed. The mount was actually welded to the frame, probably to get a good electrical connection to the frame, as the frame ground connection was part of the battery mount. Because it was welded, I had to use a cut-off wheel saw to cut the welds. This was the first cutting of metal on the 320i. Pictures of the process can be seen in the photogallery. The new battery box for the Li-ion batteries will take up an area between the two wheel wells at the very front of the engine compartment, in a place where the ICE radiator was once mounted. The front battery box will hold 36 of the CALB 60 cells. I used cardboard to make a model of the battery box to verify how it will sit and will be mounted. Fortunately the way the hood is mounted allows room for several inches above the box, which will be needed to bring the cables in to connect to the batteries.
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Testing the GEVCU
Now the most involved part of building a complex electronic board begins - testing its functionality. As described elsewhere on this site the GEVCU has many functions and input/outputs. Testing the board first involves loading the GEVCU firmware. Using an Arduino IDE (integrated development environment) the latest version of code from Collin's github repository was loaded. I found that version of code would not compile. Collin sent me a new version that would compile. Once the code is loaded a Serial Console can be run in the IDE and connect to the GEVCU. It is possible to control the GEVCU though a USB connection - the same one that is used to program the ARM processor. The test begins with checking that all the inputs and outputs are functional. The Serial Console can read the raw input values from the analog ports or the logic value of the digital inputs. The first test of the analog inputs found that one channel was not working. That was traced to a resistor that was not soldered completely. The first test of the digital input channels found all to be working. The next test was of the MOSFET digital output channels. I don't actually test the full current capacity of the output- if the MOSFET is working it should just be capable of delivering the current. Using a LED for a current sensor all eight channels of the MOSFET digital output were found to be functional. The analog inputs have to be calibrated for the throttle and brake transducer. That is done through the embedded web server on the WiFi module. Screen shots of the GEVCU web site are shown here. Accessing the web site also demonstrates the WiFi unit is functional.
The most involved testing is for the functionality of the CAN bus. That is done by communicating to the DMOC 645. Since the GEVCU main function is to control the DMOC this is the best test. For bench testing I use a program called ccShell3 that can connect to the DMOC via a serial port. ccShell3 will show all the DMOC parameters and can be used to determine if the CAN bus communication from the GEVCU is working. The commands available in the Serial Console allow control of many aspects of the DMOC. To enable the DMOC the first digital input is used. Setting the bit high enables the DMOC and then the Siemens motor can be controlled to spin through the throttle input. Although all of the commands are available though the Serial Console most of the setup is done through the GEVCU website.
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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.