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DriveTrain Assembly
Now that I have resolved (or compromised) the issue with the RebirthAuto adapter I worked on assembling the whole drivetrain. When I put the drivetrain together before (see Motor placement for measurement below) I did not torque any of the bolts and the flywheel and clutch were not installed. The drivetrain was put together before to get a measure of where the motor mounts had to be for the Siemens motor, when it was placed in the car. For this assembly the first thing I did was put some anti-seize compound on the spline output of the Siemens. The spline on the Siemens looks like it has been heat treated so I have a concern about the spline adapter in the RebirthAuto adapter. That spline adapter is made of tool steel which is probably much softer the heat treated spline of the Siemens. Next I bolted the RebirthAuto adapter to the Siemens using some grade 8 bolts, blue thread-lock and some nord lock washers. The flywheel was next to be assembled. Using new flywheel bolts and some red thread-lock I bolted the flywheel to the adapter and torqued the bolts to 80 ft/lbs. The pilot bearing was tapped into place and then the clutch and pressure plate were assembled. These were previously spun balanced with the flywheel and were attached to the flywheel were the alignment mark was. The transmission had a new pivot pin and throwout bearing installed. The transmission and Siemens/adapter/flywheel/clutch assembly were aligned and bolted together. New grade 8 bolts and blue thread-lock was used to attach the transmission to the adapter. A new video that reviews the conversion process and this assembly can be seen here.
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DMOC Cable Swap
I had to modify the cabling output from the DMOC 645 inverter because of the way it will now sit on top of the Siemens motor. Because the motor is rotated 180 degrees from where it was originally designed by Azure Dynamics, two of the output cables that came on the DMOC are the wrong length. (See the Adapter Revelation below). They need to be swapped. I thought it would be easier to swap them than to make new cables. I took the cover off the DMOC and found the connections to the cables were covered in a thick heatshrink. It took me more than 10 min to cut though one connector's heatshrink. I could not tell how far the heatshrink went so I was trying to minimize how much I cut. Once I removed most of the heatshrink I found the bolt holding the wire connector was through the side of the capacitor mount. That meant it could not be removed without loosening the capacitor mount first. I finally got the bolt out. The rest of the heatshrink came off too - it was just a piece long enough to cover the cable connetion. Once I loosened the gland-nut on the cable feed through the cable came out very easily. I repeated the cable removal procedure for the other cable and then swapped the cable positions. I put the bolts in from the opposite side to make it easier to position the bolts and then tightened the gland nuts on the cables. Unfortunately I did not have any heatshrink big enough to cover the cable connections so I had to order some. Hopefully I will get that in a day or two so I can finish the job. Photos of the process are here.
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Battery Design Debacle
After reviewing the battery layout in the car I realized that I made a major mistake in the number of batteries. The DMOC/Siemens combination only works at 400V or less. The DMOC will permit charging to over 400V but will not run the motor until the voltage drops to that level. I had thought I could put cells together in a parallel connection to increase that capacity of the pack while keeping the pack voltage down. The problem is that all batteries would have to be connected together in parallel pairs to have a system that works. Having a subset of cells in parallel effectively makes larger capacity cells than the other cells in the system. So when all the cells discharge though running the car, the different capacity cells will discharge at a different rate. They will also charge a different rate. Having all cells in parallel pairs would drop the system voltage by a factor of two down to 246V which is too low for the DMOC and Siemens motor to operate. There is no room to increase the number of batteries by 40% to get the pack voltage up. My new plan is to use 118 or 120 batteries, all wired in series. That will give a charge voltage of 420V for the 120 cell system. When the charging voltage is removed, the pack voltage drops considerably. Also, when the DC-DC converter is connected there will be an additional drop in the pack voltage. I will have to experiment to see what the optimum battery number will be. The lower number has a couple of advantages. One, it reduces the weight of the battery pack by nearly 100 pounds and two, reduces the design constraint for the number of cells in the engine compartment. Unfortunately the reduced number of cells will reduce the driving range. The original driving range for the 141 cell pack was expected to be 100 miles. The new driving range will be 80 to 85 miles.
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Adapter Revelation
Part of the design for the engine compartment is fitting up the DMOC with the Siemens motor. I did not have a chance to place the DMOC in the engine bay when the motor and transmission where installed for the alignment and motor mount measurement. So while the engine and assembly is out waiting for an adapter solution I decided to see how the DMOC was going to sit on the Siemens in the way I had designed it i.e. with the DMOC parallel to the firewall. The DMOC will only fit in this orientation, because it is so wide. With the original placement of the motor and assembly the electrical connections for the motor would be on the side and there would be possible clearance issues with the hardware that is needed for the power brakes. Having the Siemens motor rotated 90 degrees puts the electrical connections on top where they would make the connections to the DMOC relatively easy. But as I have detailed below, the RebirthAuto adapter plate is not designed for that orientation. Just to see how the DMOC would fit with the motor I set the DMOC up on the motor with some wooden blocks (pictures). The motor in this orientation is actually rotated 180 degrees from the previous position. I realized in this orientation there would be plenty of room for the DMOC connection to the motor on the right side of the engine compartment. My revelation was when I placed the adapter plate up to the motor face and found it would work in this orientation. The Siemens motor has a alignment pin on the front face (photo). It turns out the RebirthAuto adapter is actually drilled for alignment in any of the 4 quadrants (photo). Someone had considered alignment in any of the 4 orientations, they just did not carry the idea far enough to provide connection to the Siemens bolt pattern in any of the 4 orientations. This means the adapter will work without any modifications. The Siemens motor in this 180 degree rotation only slightly impacts the design of the motor mounts.
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Adapter Reject
I got the final word from ReBirthAuto today. They are refusing to take any action to remedy the issue with the adapter and feel they have met their obligation for what was ordered. I don't know how they can see that since they did not actually make an adapter for a 1983 BMW transmission and they did not account for motor rotation of the Siemens. The lowest cost option for me now is to take the Siemens motor apart and rotate the drive face. People that I know that have taken this motor apart do not know if the water cooling will be disturbed with the rotation of the drive face. I will not know until I take the motor apart. Look for a video of that adventure. If the face rotation cannot be done without disturbing the water cooling then I will have to look at a more costly option of machining a new adapter plate. I have already been in contact with a company that does 3-D scanning. Making my own adapter from scratch may end up costing as much as buying another one from ReBirithAuto, but then I would own the design and I will know it will be done correctly.
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