Over the holiday I’ve been able to put in quite a few days working on the car. Today I finished up the high voltage cabling, wired all the low voltage circuits (+12v, ignition lines, hall pedal…) and spent some time building an interface cable for the Zilla (since I misplaced the original). At the end of the day, I lowered the car off the jack stands and took it for its maiden drive.
When I purchased my cells, they came with these copper bus-bar-ish connectors. They are bent in such a way that provides a little compliance between connections. This helps lower the stress on the cell’s binding posts.
They are basically four pieces of .02″ copper held together with some heat-shrink. They are sized to join two cells sitting next to each other with their wide sides touching. If the cells are position with their narrow sides touching, these connectors are too short.
(Note to cell manufactures – please locate your binding posts so that we can use the same length connector regardless of the orientation. Thanks)
For my last EV build I had to some slightly longer connectors to handle the narrow end orientation. Fortunately, I can re-use those for this project. However, I also need some special connectors for the front battery box. So, I ordered up a sheet of copper and started cutting…
I made a cardboard template as a guide. I located the holes in the template about 3/16″ further apart then the actual hole spacing to allow me to add the bend. Long ago I had free access to a waterjet cutter so cutting out shapes like this was a breeze. These days I have to pay for waterjet cutting, so it just wasn’t worth the expense for a few connectors. So, tin snips did the trick.
Over the last two weeks, almost every time I wanted to work on the car, it was raining. Since my car is outside, this makes it tough. So, this week I lowered the car back down on its four wheels and moved it into our covered carport. I hope it’s the last time I have to push the car by hand.
Note to self – avoid pushing the car over your foot.
After the move, I got back to work. The first task was to mount the two 2/O cable glands in the front trunk. It turns out that removing the gas tank wasn’t such a bad idea after all. It made the task of running cables to the front trunk MUCH easier.
Next I mounted the front battery box and filled it with cells. This would have been much easier if the my cells hadn’t gotten just a little swollen while in storage. It meant that I had to compress groups of cells between two aluminum plates squeezed with several pipe clamps while I applied poly strapping to keep them compressed. Then I could fit them in the box.
I’ll be replacing the poly strapping you see in the picture with strapping that goes all the way around the box. With the idea that it will hold the cell in the box if the car every was to roll over. However, there is so much friction between the cell I would guess that they are not going anywhere.
In addition to that work, this week I received a piece of .02″ copper sheet. I will be using it to make the weird cell connections in the front box. More on that next time…
There are a number of little things I need to do before installing the battery boxes. I am going to be installing a BMS board on each battery box and need a way to wire it to each of the cells. I decided on using simple DB25 connectors. They are inexpensive, but robust. They have good mechanical properties with their mounting screws and have decent current capacity (the contacts are rated to 3 amps). A little work with the Dremel tool and …
I also needed a way to secure the cells from bouncing once they are in the battery box. I decided to use poly strapping through some slots in the box. I will run the strapping all the way around the bottom of the box. I cut slots then ran thin strips of sand paper through them to remove any sharp edges.
The slots are a little hard to see, but they are there.