ElectroClassic EV
Classic Cars Reborn into the Electric Future

Nice Racks

Here’s what I started with – these battery footprint templates, with exact to scale inner dimensions scribed onto the cardboard. The original plan was to take these to a metal fabricator, have a brief discussion about what type and thickness of metal would support the weight of the batteries, agree on specs, and then come back in a couple days to pick up the completed racks. After previously creating computer models of the battery bays, cardboard seemed a little too cowboy. Instead, I decided to capitalize on all of the rich data already in the CAD files.

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Of course, the CAD drawings were a means to build perfectly scaled trays to fit into the usable space, and to test out possible cell connection schemes as well. Everything Ron Kong at M&K told me about DraftSight was starting to make sense. All of the various elements can be put on separate layers, given different colors, and toggled on or off at will. Above is the motor bay rack design in red, with the battery and connection layers also visible.

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Here is the rack design for the fuel bay and trunk in red, including the exact dimensions that will be delivered to the fabricator. The blue object in the upper left corner is the ceramic core heater box and fan assembly, which fits perfectly in the remaining cubby. The teal object to the left of the steering column is the Elcon PFC 2500 battery charger. Also visible is the bus bar and cable scheme layer. All of these layers will be turned off except for just the rack and dimensions before printing out this CAD file for fabrication.

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It was word-of-mouth that led me to Aero Welding in Culver City. Formerly a Southern California aerospace fabricator, Aero is now enlisted by architects, designers, and the film industry to build sculptural structures for restaurants, elementary schools, public spaces, private residences, and movie sets. That’s proprietor Dave Hurley and his son Brian outside their shop in the picture above. On our first meeting, Dave spent a good half hour just telling stories and showing me photos of the variety of work they have done. Their portfolio is very interesting and definitely worth a look.

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Here is phase one of the battery racks, retrieved from the shop and test fit in the motor bay. I originally planned to use 1/8 inch thick 1.5 inch steel angle, but Dave assured me that 1/8 inch thick aluminum would be plenty strong if I used 2 inch angle. The higher price of aluminum could sting in higher volumes, but it wasn’t such an issue in this small amount. Pictured above is the motor bay rack conforming to the shape of the AC50 drive motor. The left and right trays were left unattached from the transverse support, so that exact fit could be determined before welding them in place. Otherwise, they risked being too wide and colliding with the swing arm support beams. They’re shown taped in position above.

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In order to give the motor bay rack space to spread out in the engine compartment, I removed the blower pedestal from the driver side cooling shelf using a cutting wheel. After grinding the remaining shards flat, I scuffed the area, masked it, and hit it with a couple good coats of rubberized undercoating.

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Phase one of the front battery racks involved making just the trays, so position and fit could be tested, and exact dimensions for the stands could be decided before fabricating and attaching them. I discovered that two mineral spirit cans held the trunk tray at the perfect height, giving the spare tire room to slip in and out while also allowing the batteries some headroom when the trunk lid is closed. The white object above is my proxy battery, cut from foam to the exact size of the lithium cells I will be using. With the trays in place, I recorded all the dimensions and produced CAD drawings that Aero will use to fabricate stands for both the trunk and fuel bay battery racks.

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Here’s a look at the finished trunk rack, easily installed via holes drilled in the trunk floor, and fastened in place with regular bolts and nylock nuts. Additional support for the cells will involve strapping them together and also to the tray. The measurements were so tight that the spare tire is left with just 1/8 inch clearance to slip in and out of the trunk well.

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The finished fuel bay rack has a vertical stand on each end with a foot that allows it to be bolted to the floor in two places. Since access to the underside of the mounting surface wasn’t possible, rivnuts were required to attach the feet. A rivnut is basically a rivet that is compressed into a drilled hole, resulting in a threaded sleeve. Only four cells will occupy the drivers side of the rack, while the passenger side is empty to leave space for the charger.

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Above is the finished motor bay rack, welded together as a single unit and bolted in its final position around the AC50 motor. Holes were drilled through the former engine cooling deck for the four rack corner mounting points. Four more holes were drilled in the back firewall above the transaxle to attach vertical corner supports.

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Here is a closeup of the rivnuts before the vertical braces were attached. All of the drilled holes were masked and shot with undercoat before the rivnuts were inserted. Just a heads-up – the rivnut hand tool looks similar to a standard pop rivet tool, but the force required to compress the rivnut is substantially more. Popeye arms with an anchor tattoo are not enough. I wedged a piece of wood under the lower handle and applied serious body weight on the upper handle before I sensed any motion. Another word of caution – make sure the rivnut is fully compressed in the drilled hole, or it will spin when you attempt to tighten a bolt into it. In that case, removing the bolt is just as challenging as drilling out the rivnut and unmangling the original hole. For that same reason, you want to avoid cross-threading the bolt. I pity the fool.

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Although there was enough room to vertically mount the Curtis controller and cooling plate on the front firewall, suspending it horizontally over the motor made better sense. Although it will obscure the motor, at least it leaves the flashy red adapter visible. The remaining open space on the firewall can now be used for the contactor, potbox, relays, and other electrical items. Shown above is the controller shelf bolted in it’s final position.

After all this drilling, I’m compelled to say how uneasy I am disfiguring the original classic Porsche body in any way. All I can do is exercise good taste and discretion regarding where and how those mods are made.  As battery technologies evolve greater power and smaller profiles, most of these racks could soon be removed. Maybe the next power source will come built into the motor. Maybe the motor will itself be the power source. This is really just the beginning.

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2 Responses to “Nice Racks”

  1. Hi,
    Do yourself a favor and mount the Kilovac contactor on the trunk side in the engine compartment. It buzzes and is annoying if you mount it on the firewall. When I moved it to the other side of the engine compartment it was much quieter in the passenger compartment. My 2 cents.
    Richard

    • Thanks Richard,
      I’m exactly at that phase where all of the EV electrical components are finding their place before all of the batteries go in and block all access. I will definitely take your advice.
      Mark


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