Battery Racks - Building
Once the layout was determined, I picked up the angle-iron I would need. Other people recommended 1 1/2" x 3/16" as a miniumum. I decided that the 3/16" thickness seemed a like a bit of overkill, and went with 1/8" instead. With the structure of the racks, and going with Orbitals instead of Floodeds, I think the 1/8" will be sufficiently strong. I started doing a strength analysis, but decided intuition would have to do on this one. It would be a fairly complicated calculation.
The angle iron comes in 20 ft. sections. This is slightly more than what I calculated I would need - perfect. To avoid the cutting charges at the local metal shop ($4), I bought some new hacksaw blades ($2 at Lowes) to cut the metal in the parking lot.
A hacksaw didn't seem that bad (at first), so the first several cuts ended up being done that way. After making about 10, my mind began to change. So I pulled out the circular saw and gave it a try. Wow! Almost like slicing butter with a hot knife!
To secure the racks, I'll be using the bolt holes that the seat belts used. I'll also use the holes for holding the seat-backs in. A basic brain-exercise determined that this will hold the batteries down, even in an accident. This is how I came to this conclusion: the seat belts would likely be designed to hold a large male passenger weight upwards of 225 pounds. Take two such passengers, and you have approximately the weight of the pack + racks. With the extra bolt holes, and having the car frame encasing the rack on the sides and the front, I determined that this would be a "safe" design. While only a full strength analysis could determine if this would maintain integrity in various crash situations, a logical analysis will provide a satisfactory level of confidence for this project. If the car was being built for a client, a more involved process would ensue.
To initially place the cut steel, small bolts would be used. This prototyping method ensures that everything fits properly before being welded together. There really is no other way in a tight design like this (well, I guess a trial-and-error method would eventually produce a finished product, but I don't have time for that!).
I formed the main supporting rack that bolts into the seat-belt and seat-back holes. Each of these will be supporting about 1/4 of the pack weight (approximately 100 lbs. each). After bolting them in, they feel pretty solid.
The battery layout ended up with the 5 rear batteries running lengthwise, and the foward-most 5 batteries widthwise. For the rear batteries, crossmembers were cut and placed in between where each battery will go. A threaded bar will bolt into each of these for a hold-down bar across the top of each battery.
I drilled the holes for the 7/16" threaded rod. After drilling a few holes with a drill bit that big, I began to wonder if there was a faster way. I tried first drilling with a bit about half the size, and then moving to the bigger bit. These are new drill bits, so that isn't the problem. Turns out that by drilling a smaller hole first, the larger hole goes very fast.
A piece of 1" x 1/8" steel will hold the batteries down. Making sure the holes on the steel bar lined up with the threaded rods took some careful measuring. My cardboard box mock-ups aren't perfect. I'm hoping Exide is more precise than I am.
I still have some work to do on the hold-down bar. It needs to be rounded on ends to look nice and also for safety. It is important to break all sharp edges with rounded corners to avoid cuts and scrapes. Lock washers are used on all bolt locations to prevent loosening of the bolts during vehicle operation.