1995-12-09

Battery Box Build

I haven't found much to read about battery boxes. Bob Brant's otherwise excellent book doesn't go into the details and all of the information or pictures I found dealt with pickups, which is a much different (easier!) animal than a family sedan. After months of thinking about the battery box I finally hit upon a break through, or perhaps had a breakdown...you decide. First I sketched out some rough diagrams and measurements on paper, then I used my Mac to render the idea so I could play around with some "what-ifs" and not burn up a bunch of supplies. Here's the concept rendering:

The Concept

On the drafting board everything has this nice geometry and rigidity (or flexibility depending on what you need) that seldom shows up when the jigsaw and drill come out. Bob Batson makes some really nice battery boxes out of polyethylene, using a handy plastics welder to make the seams. I shopped around for prices (parts & tools) and decided to see what else I could do. Here's what I came up with:

The Material

Cool, eh? Ahem. Let's approach this scientifically. The water containment device pictured above consists of an eighth inch semi-rigid polyethylene material integrated with a fiberglass mesh backing. A slightly used unit was found in the recesses of the garage. Tests were conducted using heat, cold, stress, and battery acid and the material performed favorably. Only concerns were methods to shape and secure said material.
I borrowed a device which heats a wire pressed down on a Teflon coated surface, like a giant seal-a-meal. It was 24 inches long so I did some creative engineering to handle the thirty inch bends. An ample amount of pop rivets with reinforcing washers took care of joining the ends. The box is insulated with "tongue and groove extruded polystyrene foam".

The Result

I'm in the process of making an inner box which sits inside the foam. I have also over designed the enclosure's dimensions just in case I decide to use the next size up in batteries.
Still up in the air is the front battery placement. It doesn't seem like there is enough contiguous space for one box, especially an insulated one. The goal is to have all of the batteries insulated to help maintain their performance throughout the winter. The insulation I'm using is an inch thick, which means an extra two inches of width, height, and length to any battery box. So if I make two or more battery boxes, then it really adds up. Here are the dimensions of the two 12volt batteries I'm considering:

       Battery    Length   Width   Height
       -------    ------   -----   ------
        5SHP       13.56    6.75    11.5      (inches)
       27TMH       12.75    6.75    9.75

It may be that I'm limited to using the smaller battery in order to make the front battery placement work out with insulation. I'm making some fake batteries out of cardboard to play around with placement.
Also being planned for the boxes is some small heat source to warm up the batteries whenever they are being charged.