Battery Box, Cell Measurement Progress and 12v Pack

The battery box is coming along nicely, I haven’t welded anything substantial in almost 2 decades however I’m starting to get use to the welder and develop some basic skills that are making the process easier and better as I go along.  I started by cutting all of the steel angle to length along with any 45deg angles on the ends and cleaned up the pieces ready to weld.  I used my cut sheet and sketchup drawing to fairly quickly assemble those parts into the fairly complex “box” shown below.  I’m still cleaning up the welds but it will be ready to paint shortly to protect it from the elements.  After painting I will rivet on the aluminium skin that will form the remainder of the box followed by a generous coat (or two) of rubberised undercoating to protect and insulate the box.  Finally the rigid foam insulation will go inside the box and I will be ready to install the box semi permanently in the car.  It will be removable or at least “lift able” to give clearance for transmission work.

To speed up the Cell Measurement process I picked up a 2nd PowerLab 6 that ties into the first and lets me control both with a single software interface and only a few mouse clicks.  I’ve decided to leave the cells empty at the end of my cycle testing instead of charging them back up.  The cells arrive at 30-50% SOC so I’m putting in a fair amount of energy before the discharge cycle, this lets the charger measure/calculate the IR of each cell.  Then it automatically discharges the cell and I can record the capacities.  Once assembled into my 12v packs I will use my new dc/dc converter boards in a 50 or 100A configuration to charge/balance the cells (or without the balance taps hooked up to simply charge the cells as a group).  The charging process with the PL6 isn’t 100% efficient and although I’m using regenerative discharge which puts energy from the test cell back into the 12v pack I still have to put energy back into the 12v battery on a regular basis.  By eliminating the recharge process where I top the cells back up and leave them full I now find it almost unnecessary to recharge the 12v battery as it is using the energy in the cells when they arrive to make up for the energy wasted in the charge/discharge process.

Some people have had issues getting their PL6 to charge/discharge above 10A, this is because some of the presets are limited to 10A if you pick one of the “high power” presets you can set it up to 40A.  The custom preset for the PL6 I’m using can be downloaded here.  A123 19000 mAh High Power

I’m using my “defective” A123 cells (anything with low capacity, questionable IR, or soft casing) as a 50.75Ah 12v battery, I’ve been using this pack for a few months to power my charger (now chargers) for testing the remaining cells.  I also use this pack to drive the car (yes as the traction pack, not the 12v system battery) when I need to move it in and out of the garage as well as jump start both my Infiniti G35 and Ford F150 when I had battery issues and very cold weather.  Basically for a pack of defective cells it is working flawlessly, I keep it above 10v and below 14.4v and beyond that it just works.  I have a few hundred shallow cycles on this pack along with some 100% discharge cycles and it works well beyond my expectations.  I believe the main pack in the car once complete will operate simply and reliably for many years.


3 Replies to “Battery Box, Cell Measurement Progress and 12v Pack”

  1. So, at 350lbs, between that and the electric motor, the weight distribution of the car is staying pretty even, it sounds like. Have you been keeping track of the total weight and load distribution as the component list has changed?

    I think the original weight distribution of the 944 was 50.7% front/49.3% rear?

    Loving the progress and the pictures. It’s making me nervous about converting my 944 though. You obviously have a level of knowledge regarding electronics that I will only one day wish to hope to aspire to.

  2. The weight balance will move to the rear slightly, however the change won’t be drastic. I haven’t visited the exact weight balance for awhile but I’m not far off the early numbers. It should be 51-53% rear / 47-49% front.

    The electronics is my comfort zone, I’ve had to branch out in many other areas to get this far in the conversion.

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