Optima AGM D31T Trial Fitting - Part 1

One of the goals of this conversion (if one puts aside the goal of the EVGrin) is to use this car as a test platform for different configurations and components.  This particular 1992 BMW 325i was chosen in part due to its availability, but also, it represents a much more significant choice in that the drive train appears in many BMW models and 10+ different years of BMW construction.  Thus, all of the efforts with this build should transfer very smoothly to later versions of this car, including even the BMW Z3 "rocket ship". 

Each iteration of this build is being tested  both for facility of fabrication and eventually for overall efficiency in turns of physical effort and expended ducats.  One of the background initial goals also includes the desire to see how many of the original operational BMW parts can be utilized within the build itself. 

The final test of the build will be in the application of the EV for a daily 70 mile work commute.  To achieve this final test point will demand the use of about 45 CALB-180 batteries in the final battery pack.   For initial trial work a total of eight Optima Yellow Top –8050-160-FFP-D31T batteries were purchased from Amazon.com.  These cells are rated at 75 amp hour capacity, and by comparison to other EV Album projects, this 7.2 kilo watt pack should allow for about 18 miles of range and should be sufficient to test out each of the various systems.  Additionally, if Murphy’s law presents itself, then the destruction of this AGM battery pack will not be nearly as painful as the destruction of lithium iron phosphates.

 

Battery Specifications:

 

YellowTop; Deep Cycle Battery; Grp. D31T;Cold Crank Amps 900;Crank Amps 1125;Res. Cap. 155;Ampere Hour 75;Threaded Terminal;L-12 13/16 in.;W-6.5 in.;H-9 3/8 in.  The T indicates a stainless steel threaded post.  59.8 pounds per battery.  Terminal configuration:  3/8"-16 UNVC-2A stainless Steel stud. 

(Note added 3/3/2016)

The studs have about 5/8" of exposed threads and they are fully threaded right down to the metal terminal surface.  But, the terminal surface is actually elevated slightly above the plastic battery case.  Consequently the absolute overall height from the plastic case to the top edge of the studs is really about 13/16".

Full data sheets can be found at:

 

http://d26maze4pb6to3.cloudfront.net/4713/4583/5068/YELLOWTOP_Full_Specs_Sheet.pdf

 

With that said, a similar build (1995 BMW 325) that also utilized Optima Yellow Top batteries is that of Robert Nicol  ( http://www.evalbum.com/2896 ) .  He used a total of 12 batteries, and he placed six of the cells very nicely in the car trunk, above the plane of the wheel well.  He located the remaining six cells under the hood.  Examination of the 1992 BMW 325i wheel well, suggested that with a little modification, it might be possible to actually recess six cells within the wheel well itself.  This has been confirmed and will be described below.

 

 

Picture DSC00664 showing the initial placement of the Optima D31T batteries prior to wheel well modification.

 

The initial trial fit of the Optima batteries can be seen in picture DSC00664, and it was apparent that the center spare tire mounting bolt (visible in picture DSC0665 below) would need to be removed, and that the curved surfaces at the left side of the wheel well would also need to modified.

 

 

 

Picture DSC00665 showing the spare tire hardware mounting bolt prior to its removal.  This mounting bolt in part prevented the full six batteries from fitting symmetrically within the wheel well.

 

 

 

Picture DSC00669 demonstrating the space provided after the removal of the spare tire mounting bolt.  A sheet metal disk will later be welded to seal off this opening.

 

The removal of the mounting bolt and all sheet metal modifications described in this post were performed with a Craftsman 4.5 inch sander/grinder using a 1/16" (1.6 mm) metal cut-off blade(Picture DSC00686)

 

 

Picture DSC00686 of the sander/grinder that was used for the metal modifications.

 

 

 

Picture DFSC00672 with the proposed initial cut lines marked on the metal surfaces. This area is towards the front of the trunk.

 

 

 

Picture DSCF00673 after removal of the top triangular sheet metal portion, and after the completion of the vertical releasing cut, and after the curved cut was made at the base of the wheel well. (seen at the top of the picture).

 

 

 

 Picture DSC00675 showing a vice grip holding the partially bent curved surface adjacent to part of the straight bottom cut.  There are no releasing cuts and thus the curved section will not bend properly to lie flat against the bottom surface edge.

 

It was important when bending the sheet metal to provide releasing cuts at various points in the metal.  Without them, the metal buckled and it would not bend smoothly and it could not lay flat against the adjacent cut  surface.

 

 

Picture DSC00678-B after initial removal of the triangular wedge top portion and making the releasing cuts (vertical cut at the left and bottom horizontal cut).  This picture is the area at the rear of the trunk adjacent to the bumper.

 

 

 

 Picture DSC00679 showing the approximation of the metal surfaces.  A gloved hand is holding the bottom of the sheet metal for demonstration.  The three releasing cuts (two in the center area and one at the far right)  were required to allow the initially curved metal surface to bend back upon itself. 

 

 

Picture DSC00683 showing the successful initial placement of the six Optima Yellow Top batteries in the wheel well.  The red terminal at the upper right and the black terminal at the upper left would be the outputs. 

 

 

Picture DSC00684  showing the available space created after the wheel well modifications and prior to final welding.  Note that the center sheet metal portion remained intact and is structurally sound.

 

The last picture (DSC00684) also shows the difficulties presented in attempting to MIG weld the sheet metal.  Previous welding of  0.125 and 0.25 inch thick steel plate when fabricating the motor mounts (described in previous posts), although perhaps not very pretty, was rapidly learned and successful.  It was found to be much more difficult to weld the sheet metal (measured to be only 0.036 inch thick).  The electric arc blasted holes very easily and rapidly through the sheet metal, and the proper amperage and welding wire feed rate has not yet been worked out.  The bolt and washers visible to the right of the brown welding attempt, was used to hold the two sheet metal edges adjacent to each other and in the same plane.  It may turn out that oxy-acetylene stick welding will prove more successful in this welding effort.  More on that later.

 

The hope will be to add additional sheet metal patches to fill in the current openings and upon completion have welded joints that are both structurally sound and water tight.  Since the batteries are recessed in this design attempt, it may be possible to later reinstall the original trunk floor carpeting and thus create a pleasing finished interior appearance.