Picture DSC05975 showing the hole (center of picture) that is located at the end of the plastic frame of each battery module that might be useful in aligning the stacked battery modules.
DSC05973 showing a 25/64" drill bit inserted through the pair of holes in the plastic frame of the battery modules. Since each module has these holes, when stacking the modules, the use of a plastic dowel rod that passes through each module could serve to help align the modules.
Steel Bus Bar Prototype
It is intended to eventually use all copper bus bars but steel is easier to fabricate as a prototype. The design criteria for the bus bars includes the need for the 8 mm Tesla hex bolts heads to be accessible for both monitoring and tightening with a torque wrench.
To test various design ideas, some 1.75" angle was purchased (McMaster Carr) and cut as shown in picture DSC05903. The 1.75" depth allowed the edge of the angle to rest against the back wall of the landing area which prevents any rotation of the bus bar connection when the M8 bolt is tightened (DSC05904).
DSC05903 showing the 1.75" steel angle that was cut with a band saw and filed to fit in the landing area of the Tesla (+) terminal of the battery module. The front to back distance is 1.75", the height of the horizontal leg is 1" and the length of the leg is 3".
DSC05904 showing the prototype positive terminal connection placed on the Tesla battery module.
Picture DSC05947 of the negative terminal connection that was fabricated from a piece of 0.1875" x 2.5" x 2.5" angle. Although the angle was 3/16" thick, it was used due to its ready availability. The final dimensions for the bracket were 0.1875" x 1.75" (deep) x 2.5626" (tall).
After bolting both terminal connections to the battery module, the fitment of the horizontal leg (9" x 1" x 0.125" ) was confirmed. The positive terminal (right side) was then MIG welded to the horizontal leg (DSC05970). Fitment was again confirmed and the final length of the negative terminal (left side) was then marked (DSC05976) with a sharpie.
DSC05970 after welding the positive (right side) terminal to the horizontal bus bar and reinstalling, the left side was marked for final length and position.
DSC05976 after marking the steel, the unmarked bottom area of the negative terminal connection was cut away.
DSC05979 of the negative terminal joint after being beveled on both sides prior to welding. The joint was butt welded with a MIG (MillerMatic 140 Autoset using 0.030" wire, wire speed 60, and 75% Argon/25% CO2) and the joint sanded smooth with a electric grinder and file.
DSC05981 showing the installed steel bus bar after all welding was completed. Some misalignment in the plane of the landing areas was noted and believed to be caused by the thermal changes of the steel during welding. Next time the connection will be made with a series of small welds, followed by allowing the metal to cool, before additional metal is added. Both green battery interface boards were also covered with clear packing tape to reduce the chances of shorting the bus bar to any of the fuses during trial placements.
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updated 7-12-2017
DSC05996 showing the bus bar after trimming the excess steel to create a more uniform 1" width. A consistent overall width of the final copper bus bars will allow a fiberglass cloth tube insulator to slide smoothly the full length of the bus bar.
DSC05995 showing final installation. The terminal landing areas were also reduced to 1" width (compare to DSC05981 above).
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After repeatedly using a hammer and vice, it was eventually possible to slightly bend the steel bus bar so that it more accurately seated on the terminals. A future solid copper bus bar will likely present the same challenges, so we will next instead try using a series of thin copper sheets that when combined together make a laminate of nominal 0.125" thickness. Each sheet will be more flexible and the laminate can then be covered with Kapton tape and/or a fiberglass sleeve to provide electrical isolation.
The designs described above can be used for both the 2 battery and 4 battery Tesla battery module packs,. A single bar would be required for the two module battery pack and three bus bars required for the 4 module battery pack. Note in picture DSC05984 that the M8 hex head terminal bolts (13 mm heads) on each module are fully accessible to a torque wrench with crows foot.
DSC05984 showing the potential ability of a torque wrench with a crows foot to tighten the M8 hex terminal bolts.
DSC05983 showing that if the torque wrench is not insulated, then it is very easy for the extension part of the torque wrench to short circuit the upper battery terminals.
