In previous posts, I showed the design and fabrication of the metal and wood portions of the battery boxes. My original intent was to have the lids push down on the batteries with small lengths of PVC pipe. I've seen this done on several conversions on the web. The main advantage of this method for me is that it simplifies the bottom of the box, especially how easy it will be to contain any spills. However, it greatly complicated the design and strength requirements for the lid. My original plan called for an angle iron frame and support members that would be very heavy and would require large bolts to hold it in place. These large bolts and heavy lid would have to be removed every time I wanted to check water levels or electrical connections. In addition, because of the placement of the battery boxes in the back of the car, it would be very awkward to reach some of the bolts. Finally, it was not clear to me that the lids could be removed with the seats in place. Too much effort!
So, instead, I opted for a different design. This one is also described by many converters on the web. Instead of pushing down on the batteries from the lid, I will use threaded rods with steel pieces laid across the tops of the batteries to pull them down from the base of the box, just like the starter battery in all ICE cars. I opted for 5/16" threaded rod and 1" steel box tubing in place of the usual M4(?) threaded rod and polypropylene battery straps or molded pieces that are used for starter batteries.
Since there is little space underneath the battery boxes (I'm trying to keep the batteries as low as possible without cutting into the floor) I welded nuts to the top side of the bottom frame.
The steel tubing was a little challenging. For the main box (6 batteries side by side) there was plenty of room for the tubing to run down the center of the batteries. There is a nice gap in the row of filler caps, and plenty far away from all of the battery terminals.
Since there are three tie-down places for this piece of tubing, I put the two slots on opposite sides. So, when installing the tubing I drop the tubing over the center threaded rod with the tubing pointing to the corners of the battery box, then rotate the tubing until the ends meet the two threaded rods at the ends of the battery box.
For the rearmost battery box the steel tubing was challenging in another way. In this case the top frame is angled "outboard" so there will be no issues with dropping the tubing straight down onto the threaded rod. However, in this box the batteries are laid end-to-end, and what I quickly discovered is that there is not room for the steel tubing between the battery terminals and the filler caps. Instead of opting for a smaller version of tubing (1/2" would probably work ok) for each row (there are 2), I chose to hold the batteries down by their edges instead. My plan is to have a single piece of tubing run along the common edge between the two rows of batteries, with "outriggers" welded in place to help keep the batteries from jostling out of place. Kind of looks like a TV antenna?
This welded tube structure will be held down in two locations, inboard from the very end of the box, so the span is not excessive. In these locations, there's a nice strong piece of angle to weld the nuts to.
The radiator box added another challenge to the hold-down scheme. The batteries are also laid end-to-end in this box, so the 1" tubing will not fit. So I bought some 3/4" aluminum tubing to lay across the batteries. However, this box is not as tall as the rear battery boxes (by mistake? Possibly.) so I've opted in this case to use my original intent of pushing the batteries down. These batteries will be loaded from the bottom so I will lay pieces of 1" tubing across the battery (side-to-side) which will contact the top frame when they are in place. I may have to add a piece of silicone rubber under these pieces of tubing so that the batteries are held snugly when the base is fully installed. A junk piece of steel tubing (welding practice!) illustrates the concept.
So, after slapping some paint on the newly-welded parts of these boxes I should finally be able to load them into the car!