Battery Boxes Received

I received the aluminum battery boxes I had fabricated by New Hampshire Precision Metal Fabricators in Londonderry, NH, who are about 20 miles from my house.   They did a fantastic job on the fit and finish of the boxes.  There is one box for the front of the car, two for the rear seat area and one for the trunk.  They had given me one of the rear seat boxes before it was welded to check the size of the holes I had cut in the rear seat deck.  Those boxes were 1/4" wider than I had originally modeled.  The reason for the discrepancy is that I plan to line the inside of the boxes with neoprene rubber sheeting for both electrical and thermal isolation.  Here in the northland you need to worry more about keeping the batteries warm than cool.  I did not catch outside dimension had grown because of the sheeting on the inside of the box.  My friend that did the CAD drawings forgot to inform me of that change also.  However, the increased size of the box was not a big deal.  I just cut more metal out of the rear seat deck.  The only tough spot was the back right corner.  The box just fits before a support rail.  On the one side the weld at the bottom of the rail was too big to get the box in so I had to use a cut-off saw to cut away part of the weld.  That was almost the 1/8" that kills battery box designs.  The second rear seat box only took about 30 min to get the hole cut to the correct size, because I had the first one to measure from.  Another issue with a battery box was with the box for the front of the engine compartment.  Brackets were designed to attach the box on the inside of the area where the radiator once resided.  I has assumed the radiator was in the center of the engine compartment but after I got the box I found the area was not in the center.  It is displaced by over two inches to the left, looking out from the engine compartment.  So one bracket fit because it was 1 inch outside, but the other one did not because the 1 inch overlap interfered with the rest of the metal around the radiator area.  I had to have the bracket removed and a new one welded in the correct place.  Fortunately NHPMF did that rework for no charge.
I also did some more battery discharging using another grid tie power inverter.  I got a second one on Ebay for very little money.  It is 1200W which is half the wattage of the first one I got that had failed. It can only can be used up to 50V input, but that is good for smaller groups of batteries.  The inverter work without any issue and I discharged the rest of the battery pack.  Now I have to build the bottom balancing systems.   I have a design that uses a MOSFET to vary the load on the battery, so that the battery voltage can be precisely tuned.
A video of the battery boxes can be found here.


0 #1 Alex Vieira 2014-08-08 14:09
Hey Ed,
Do you mind sharing how much you paid to have your battery boxes made? I'm not quite to your stage of converting my Boxster, and I'm trying to decide if I learn to weld myself or farm it out. Looks great so far!

Thanks for taking the time to share your work with others!


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