Saturday, August 25, 2007

A spasm of Progress?

Yes, dEVoted fans, Karmann Eclectric has been sorely neglected for the past year, but another burst of energy came upon the scene with the return of Roy LeMeur from his midwestern sojurn. Yes, the National Electric Drag Racing Association NW Race Director is also a travelling EV mechanic, and the departure of wife and baby for my in-laws' for a week created a window of opportunity for real progress. Roy's schedule was fortunately in sync, and he spent a week at Casa del Donnaway to provide a boost to this project. Unfortunately, work demands kept me away from the garage for way too many hours, and we didn't make as much progress as planned, but it was a good time nonetheless.
Major tasks accomplished included routing, cutting, crimping and connecting all high voltage cables, re-mounting the Godzilla 003 motor controller on a new, improved and more precisely positioned base, placement of the main contactor, fuse and shunt, and installing the DCP dc-dc convertor, which was acquired in good used condition from Bob Bath of Grant's Pass, Oregon. A goodly portion of our time was spent debating the merits of competing cable routes, and dealing with my reluctance to drill more holes into precious antique German sheet metal... We settled on very few new holes in the end, and a graceful routing of cables that minimized their length while keeping the layout very simple.

Here's a closeup of the motor compartment cabling. You can see that the pack Positive and Negative enter through an existing oval hole in the firewall, and Positive goes to the main contactor, then to the Zilla. Pack Negative goes straight to the fuse, through the shunt, and then on to the Zilla. Note that I used 2/0 red and black cables for the pack cabling, but massive 4/0 black cables (with the nifty polarity-indicating shrink wrap) on the motor loop. This is because the Zilla will be pumping out a massive 1800 amperes at 170 Volts, while the battery pack will 'only' need to supply something on the order of 1275 amperes at 240 Volts. It's amps that eat copper, voltage means more insulation!

If you look carefully, you can see that the DCP dc-dc converter, though not wired in yet, is mounted on a piece of 1/2" yellow HDPE board. Besides providing me with another opportunity to minimize the number of holes drilled in the car, the board provides another degree of electrical isolation, and just makes for a nice touch, in my humble but correct opinion.

One the opposite side of the motor bay, what do we see, but a rare prototype Baby Optima Yellow Top! This battery never made it into production, victim of GM's 1990's episode of EV extinctions... The lead inside this unit is beyond rescussitation, but the case may yet prove useful, as it matches my color scheme, gets major EV trivia points, and fits perfectly atop the vestigial VW air cleaner stand. I plan to cut off the top, carefully extract the lead (and document the dissection), and then either rebuild it as a 12V accessory battery using Hawker Cyclon cells, or just re-task the case as the Zilla's coolant reservoir. A baby Optima with green fluid pulsing in and out? Now that oughtta be worth a few double-takes!! Besides, I'm more likely to use the higher-capacity nicads I already have as a house battery.

We also completed most of the pack interconnects, and let me tell you, that's no small task when 2oo individual cells are involved. I shudder to think about assembling a pack for the tZero, with it's 6800 individual lithium-ion cells, or the new Tesla Motors battery pack, which just had to beat the tZero with 6831 li-ion cells.

The packs may look complete, but they still need safety covers, which will also function as hold-downs. I plan to use thick Lexan plates, but have to review this strategy for NEDRA rule compliance.

Here's a look at the nearly-complete rear packs, along with their wiring diagram. We had to add some plate steel under the packs, because the sheet metal boxes, though quite strong at the corners, sagged too much in the middle, which would have put stress on the interconnects and cell posts, possibly causing poor electrical contact or electrolyte leaks. By the way, the interconnects, which are custom-fabricated nickel-plated copper stampings designed by John Lussmyer, have been doubled up in order to handle Big Zilla Amps.