ElectroClassic EV
Classic Cars Reborn into the Electric Future

Spatial Challenge

Before even thinking about installing batteries, the available space needed to be sized up. Substantial free volume was created in the motor bay with the removal of the gas engine and related apparatus, and a fair amount of new space opened up with the removal of the gas tank from the front of the car. The puzzle is to fit 36 prismatic lithium iron phosphate cells in that space.

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The first thing I needed was a physical representation of a lithium cell I could play with. Using some reliable dimensions for the CALB 180AH cells currently on my shopping list, I carved a dummy cell out of the packing foam that came with the AC50 motor. Battery placement is a spatial riddle, and the fake foam cell allowed me to physically visualize the form and fit of the battery pack. It became immediately obvious where a battery would and wouldn’t fit.

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Next I diagrammed the engine compartment and fuel tank bay, measuring and recording all possible dimensions on the drawings. As you can see just above, the fuel bay is a more complicated space, with many curves and bumps. I translated those numbers into an accurate computer model of the usable area in each space using DraftSight. At that point I could create computer models of the batteries and tinker with their placement and position. Although there was only one fake foam battery, I could now play with 36 virtual batteries and be confident of their exact dimensions and fit.

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After dividing the pack evenly on each side of the AC motor, while trying to cram as many cells as possible into the space, it was inevitable that no more than 24 would fit in the motor bay. Granted, there are many examples on the interwebs of a greater number being stuffed into the same area on a 914, but those are smaller batteries with a lesser amp-hour rating. Cells with a rating of 180 AH or greater begin to grow in size. I could have placed a few cells over the motor, but instead gave the battery pack a low profile to preserve room for the rain tray, the controller and other electronics, as well as maintain a low center of gravity. The placement of batteries on the right side will be a mirror image of the green cells on the left. The black filled area across the top is unusable because of the backward slope of the firewall. The two filled areas at the sides are where the rear axle swing arms jut into the engine compartment.

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The remaining 12 batteries will fit into the fuel tank bay and trunk thusly. My original hope was to keep the front trunk completely free, but that won’t be possible with batteries this size.  The next generation of batteries will likely be smaller and lighter, and the small rack for four cells in the front trunk can be removed. The blue filled box in the upper left is the planned location of the ceramic core heater box. The black filled objects are the fan box drain tube and the steering column. The black flared horizontal line is the wall dividing the fuel bay from the front trunk.

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The end result of the drafting diagrams were precise dimensions that could be checked against real-world volumes. An exact footprint of each battery pack was cut from cardboard using measurements from the drafting files, and then test-fit in each space. The foam cell could then be used to check vertical clearance, which is not accounted for in the 2D drafting files. Also notice the blower pedestal just touching the left side of the foam, which will be removed at a later date to create unobstructed space for the racks.

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Here is the footprint of the forward battery pack, straddling the fuel bay and front trunk. Notice how a perfect little cubby is left for the ceramic core heater box, as if it were designed for that exact spot. I call that magic. The next step is to choose and gather the raw material, take it to a metal fabrication shop along with the footprint templates, and have just the battery rack bases welded together. Fun is happening.

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5 Responses to “Spatial Challenge”

  1. Brems,did you leave space for any connector cables wires etc.? Also what are the usable positions you are able to place the battery in? All might not be possible . Did you account for that?

    • My design process included the necessary cables and connections, of course, not to mention the battery management system, charger, motor controller, DC-DC converter, and other electronic what-not. Unlike lead acid batteries, which must remain upright, lithium batteries can orient in any direction, even upside down.

  2. Mark. Awesome.
    Don’t forget….. don’t block the view of your beautiful motor!

  3. Word of advice: Add the positive and negative terminals to your mockup and think about how you will run cables. You will find that odd numbered groups of cells work better. Calb cells will come with copper buss bars which work great and will bridge from row to row of cells but only if polarity is correct. I had to rework my pack several times to get that to work out. 2/0 welding cable does not make tight bends easily.

    Don’t forget that you have keep Li cells in compression. They come with threaded rod and channels that I tossed and used steel banding straps instead because of space limitations….I have 94 100Ahr cells in my 300V pack in a ’71 914. Both trunks are full of cells as well as the motor bay. Make sure you maintain access to your motor and cells so you can torque connections. I just flipped my motor upsidedown so i can torque fron below. Google Dick’s 914 to see my car. You are doing a great job!

    Dick

    • Wow! You have a beauty packed with DC power. I’m running AC with a fewer number of cells, as you may have seen. I have a blog post in the wings that speaks directly to your advice, which includes connectors and cables. I’m springing for the braided/tinned copper straps to avoid any future vibrational insult to the battery terminals. I was told that the CALB cells are less prone to expansion and swelling, but I will probably strap them for added stability anyway. Regarding the battery and motor connections, I will be using Nordlock washers, so there should be no issue. Thanks for the encouragement Dick!


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