Sunday, November 13, 2005

A Battery of Cells.

That's right, my car doesn't have a bunch of batteries, only one- but it's made up of 280 individual 1.2 volt cells. These are no ordinary lead slugs, no, but nickel-cadmium wet cells. BB-600 spec, to be exact in US military parlance, as these batteries were originally purchased by Uncle Sam as starting cells for tactical jet aircraft. These little babies are rated to deliver 1800 cold cranking amperes, and each cell contains at least 34 amp-hours of juice. Nicads have many advantages over lead-acid cells, not least among which is their ability to fully recover from complete discharge. As a matter of fact, proper storage technique calls for running down the cells and shorting them out with a jumper! These cells have been proven to deliver beyond their rated capacity at 30 years of age, so why did Uncle Sam discard these cells after only three years on a shelf? Heck if I know, I guess that complete reliability is paramount when defending the free world, but I'll be happy to reuse castoffs like these anytime, for 1/464th the original cost, thanks to fellow EV'er Tim Humphreys, who scored of a truckload of these units in a surplus auction.
How to fit them into the Karmann Eclectric? Well, thankfully my battery boxes were designed for the maximum space possible, to fit even the 10 7/8" tall T-105 6 volt battery, that old reliable golf cart battery. The 9 1/4" bb600 cells fit quite nicely in my boxes, so snugly that one would thing they were designed for them all along...

The front battery box, shown above holding 64 cells (@ 220 lbs, once wired) was built by Doug Weathers for his Ghia, but when he decided on a different battery model, this one was surplused. The front pack is offset to the passenger side because the steering column passes too close on the right (and provides weight balance). There's room for a 10-cell stack on top of that filler plate if necessary. I like the clean look it has right now, but one thing to consider for optimal weight distribution is to get more batteries further forward. There's room in the trunk to mount a larger number of these cells atop a flat plate, rather than sunken into the gas tank void, as shown.
The main battery boxes are in the rear seat area. Here we have several options. Since the nicads have to be watered on a regular basis, easy access would be a plus. As shown here, 76 cells fit on each side with unfettered access. What you can't see is that an additional 25 cells per side are hidden from view. Additional trimming of the body wil be required to provide access for maintaining these cells, or I could just put filler in those inaccessible spaces. 101 cells per side, plus 64 up front gets us within 14 cells of our 280 unit goal. Well, it so happens that ten cells fit perfectly within each quarter panel, giving six cells spare.

With a simple box added to each rear quarter panel, 20 cells will be easily accessible for maintenance. And don't worry, even the quarter panels can be ventilated for proper Hydrogen management.

This shot also shows how the rear seat sidewall interferes with maintenance of the outermost cells of the lower rear pack. Enlarging the front pack and keeping the rear packs to 75 or 76 cells apiece would provide for not only better balance (ironically at the expense of a slightly higher center of gravity), but also eliminate the need to hack up my rear seat, and perhaps also reduce the need for small packs scattered throughout the car. Stuffing small cells into every available niche would seem advantageous, but it increases the chances for trouble with balance of charge due to temperature variations and numerous long interconnects. A single massive pack is better for battery management. Of course, compromise is the name of our conversion game, more to come after some head scratching...

The Gamera 9 is Born!

Who is Gamera, you ask? Why only a fire-breating turtle, hero of Godzilla knockoff movies and Guardian of the Universe. Okay dorko, so why'd you name your electric car motor after a Japanese movie monster? Well, it's green and short for one, it means business at both ends, it breaks stereotypes about the slowness of it's species, and since I matched the color of Zilla controllers, why not continue the naming convention? Long live the Gamera Nine!

Gamera 9 artwork courtesy of Andy Chung

So, the legendary motor finally came to life this week, unveiled before the gawking hordes at November's Oregon Electric Vehicle Association meeting. Well, the horde only consisted of @ 20 fellow EV geeks, but it was a great treat for Jim Husted of Hi Torque Motors to come on up and demonstrate the motor's innovative features to the club. Besides shortening the body to a compact 14.25 inches, (leaving less than 1/4 of airspace between the motor body and the ghia's rearpost portions) Jim threw in another first-of-it's-kind feature, series/parallel shifting within the same motor. That's right, The four field coils can be run as matched pairs, or one right after the other. At 12 volts, the effect was immediately apparent, as the motor drew 30 amps idling in parallel mode, but cut back to 18 amps in series. Series windings allow greater influence from the field coils, resulting in increased torque and lower amp draws, but at reduced speed. I still don't have a full understanding of the theory behind this, but I've sure seen the results in Wayland's drag racing, and now my motor will have a bit of the magic as well. The Adjustable Brush Ring assembly was run through it's paces as well, demonstrating the amazing tunability of a DC motor with 15 degrees of variable brush timing. At 12 volts and full advance, the motor started complaining and spitting carbon sparks, but at 170 motor volts and high rpm, it'll be very thankful for a little advanced treatment....
Here's a little wisdom from the Maker:
(Jim Husted writes)
"Wire size and turns are not the only things that effect coil / armature
relationships. How the fields are plumbed play a key role also. Jay Donnaways
motor is plumbed to be operated in either series or parallel."

In series the motor runs 1200 RPM @ 18 amps 12 volts, 0 load.

In parallel the motor runs 1850 RPM @ 30 amps @ 12 volts, 0 load.

"Every EV motor I’ve seen so far has been plumbed parallel, which gives you
higher speed, but less torque. Jay’s motor should put to rest whether going to
series will be beneficial or not. I believe that being able to switch the
fields to series would benefit those that face long or steep uphill drives.
Even if one could only get a 10 % improvement would that not be the same as what
some are getting out of regen? What I do know is that Prestolite used a two
speed motors (motors wired for both series and parallel) for years. If you were
going up a ramp the unit stayed in series as switching it over to parallel would
bog down the motor as torque dropped and the amps would skyrocket. I believe
this applies the same for anyone facing the same issues."

After the excitement of Gamera Nine's unveiling, this weekend's task was to 'dry-fit' the motor into Karmann Eclectric, seeing how well it slid into place, and how much trimming of the body would be required to do so.. Well, the good news is that practically none at all was required. The bad news, as you can see, is that I got a bit carried away and cut a big'ol slot for the motor shaft to slide through, which turned out to be rather unecessary. Of course, when I wind up installing some sort of accessory on that tailshaft, that slot will need to become much larger. Till then, the motor shaft will be visible, but reside below the stock decklid latch.

Installing the motor was fairly straightforward, but simplified since I left off the flywheel and clutch for this first test-fit. The extra clearance required by this hardware will indeed require me to lift the body whenever removing the motor, or go ahead with my earlier plans to make the rear valance removeable. Any new car, or motor for that matter, is treated with kid gloves until that first scratch, which I promptly inflicted with a little slide over my floor jack, removing @ 1/4" of powder coating from the motor's underbelly. Time to mix up a can of touch-up paint. Fortunately, I've already got the code for Zilla Green...

Thank you Jim Husted, burning rubber can't be far off now!