Tap, Stack, and Rack: LEAF Vectrix Batteries

The next step in the Vectrix battery upgrade with the Nissan LEAF cell modules is to figure out how to hold them together in the motorcycle.

Since I started off with an entire Nissan LEAF battery pack, I had a few of the components that originally held the modules together inside the pack. That included the threaded rods, nuts and bolts, and flat steel plates the cells mounted to. I was hoping to reuse as much of these materials as I could; not only does it save money, but it’s less materials to go out to the scrap bin as well.

To start with, I cut one of the bottom plates from the battery pack down to just one cell module wide. These plates originally held four stacks of cells on either side of the battery pack. A cut-off wheel in an angle grinder zipped through the steel pretty easily. The plate already has threaded holes in it – 6mm – for the long bolts originally used. The rear section of the battery pack had a set of long threaded rods (also 6mm) but the threads were only on the ends. If I cut the rods short, for my 18 module battery pack, the threads would be gone on one end or the other. Also, I don’t have any equipment for machining threads on to rod. In addition, metric parts in the United States are still oddly expensive at any local hardware store. Threaded rod measured in fractions of an inch is cheap, but in mm it’s pretty pricey, and that’s only if you can find it.

Interestingly enough, quarter-inch is just a hair larger than 6mm when it comes to threaded holes. And since I DID already have a 1/4″-20 tap, all I needed to do is just tap RIGHT THROUGH the existing 6mm holes – no other drilling or machining needed at all. Once I tapped out the four holes in the plate, I could thread cheap 1/4-20 threaded rod in place. Since the finished battery itself will be 24 inches long, I cut the threaded rod to 25.5 inches to allow for the end plates, the nuts and washers, and some room to get all the cell modules in place before compressing them. Again, an angle grinder with a cut-off wheel works great for cutting metal, including the threaded rod.

I had also ordered a Cycle Analyst, which just recently arrived by mail. I opened it to take a look and it’s pretty straight-forward. The main two things I need to decide are where I want to mount the display itself, and how I want to mount the ammeter shunt on the negative end of the battery pack.

Once my basic plate-and-threaded-rod was together, I could start stacking the cell modules onto the framework. I had already done sort of a mock-up, loosely assembling the cells with the original smooth rods, making sure I had enough spacers, and that I had the cells in the right order. There are “Right-Handed” and “Left-Handed” modules. The polarity is opposite between the two and I needed to make sure that they alternated so that the bus-bars and electric connections would all correctly place the cells in series.

After assembling the cells, I made sure they were all straight and square (I used a nice large old carpenter’s square to check this) and then tightened down nuts on the back end until the pack was back to the original 24 inches. Before I originally disassembled the LEAF pack, I counted how much space was taken up by 18 modules all squeezed together, and it came to exactly 24 inches. I figure that by now recompressing 18 of them to 24 inches, that the cells are held together nice and solidly in the exact same way as they were in the LEAF.

Once the modules were together, I put the bus bars with their orange plastic insulators on top, snapped them in place, and installed the terminal bolts and the center tap screws. Oddly, I accidentally broke a bit of the orange plastic while installing the terminal bolts. Right after I did it, I realized that the first bolt I put in spun the whole bus bar clockwise, which was to the OUTSIDE of the plastic, where it hit and broke the relatively brittle insulator. On the rest of the terminals I installed the bolt on the end of the bus bar where if it did spin, it would push the bar to the INSIDE where there was considerably more material to resist any breaking. Of course, it was only just that one bus bar that moved at all. The orange plastic covers still snapped over all the terminals just fine when all was said and done.

So, what’s next?
I need to figure out where the ammeter shunt for the Cycle Analyst will go. It needs to be on the negative end of the battery pack. Part of the reason I designed the pack with + to the front and – to the back was knowing this and that I would have a little space at the back, but not the front. I also allowed a little extra threaded rod with the idea that maybe I can mount the shunt right on the rod going through the battery pack. That should hold it in place well, and it will be in a convenient location between the battery and motor controller.

I’m also hoping that my new friend, Nick, can stop over this weekend and lend a hand. With him and the chain hoist, it should be pretty easy to put the entire pack at once into the cycle.

‘Til next time, stay charged up,
-Ben