More Battery Box Work
I finished painting all the battery boxes with the bed liner material. I had to touch up some of the sides of the rear seat boxes. Once all the painting was done I could start on the next phase of battery box preparation - the lining of the insides of the box with rubber sheeting. This is done to provide both a thermal as well as a electrical insulator layer. The material I chose was a Buna-n rubber, medium strength, 1/4" thick. The rubber comes in different hardness, I chose the 60A which is medium hard. That seemed like the best compromise for stiffness and elasticity. It is available in 12" wide sheets in many lengths, which is perfect because all my battery boxes are 12" tall. The material can be found from many sources, I bought some from both McMaster Carr and Ebay. The price on Ebay was 20 to 30% less than McMaster Carr, but there is a limited selection that had an adhesive back. I am not sure how important that is, except for assembly purposes (it is possible to apply your own adhesive). The battery boxes were designed to use this 1/4" rubber sheeting. I first installed the rubber sheets in one of the rear seat boxes. The material can be cut with a box cutter, but it is not easy - pretty tough material. After I got the material on both of the long sides I decided to test the fit of the batteries. Until now I could not do that measurement. I could slide two batteries side-by-side very tightly in the middle of the box but, unfortunately, I found I could not slide two batteries at either end. It looked like there was only as small offset that was preventing them from being inserted (less than a 1/16"!). Probably the box has a very small dimension variation at the corners because of the fabrication technique. This is one of the problems with battery boxes. The batteries have a fixed size, so if the box is too small the batteries cannot be inserted. Also the thickness on the rubber sheet can vary +/- 0.031". Fortunately with the rubber sheeting there is an easy solution. The material is available in 3/16" thickness. I ordered one sheet to test it out and it worked! Batteries can be inserted at both ends of the box. The still are very tight, but that is what is desired. Another part of the battery box preparation is to install a silicon heating pad in the bottom of all the boxes. The heating pad is designed to heat the batteries when their temperature drops below 0C because they will not take a charge at that temperature. The pad does not get very hot and is just designed to warm the batteries. I found a Chinese Ebay vendor that offers custom size heating pads. They not only can customize the pad size, but also the wattage and voltage of the pad. I chose 400W and 400V because I plan to power the pads with the battery pack voltage. This seemed the most simple electrical solution, with the wattage of the pads they will only draw an amp of current. I plan to use 22AGW wire so the wire will act as a fuse if there is a short. I also plan to have a high voltage 5A fuse in circuit as a failsafe. Each of the pads will have a thermistor - I don't plan to control the temperature but rather just have a upper limit for control. All the pads will be wired in parallel so they see the same voltage. The pads will sit on some of the rubber sheet material on the bottom of the box. This is done to prevent the heat from the pad being conducted away by the battery box. With all the sides of my boxes being insulated there is no reason to heat the box. The heating will be directly into the battery cases.
Other work on the interior of the car has progressed. I was able to remove all the underlayment material and install new underlayment. The next step is to install the new carpeting. That should happen soon, but first I need to finish running all the wiring to the engine compartment. Now I have heaters in all the boxes there are another 4 cables to run. I also want to get the rear seat boxes fully installed before the carpeting goes in.
No news on the Siemens spline adapter from EV West. Should arrive any day.
video of all this fun can be found here.