1983 Porsche 911 SC Targa

Saturday, November 17, 2012

Battery Boxes, part 3

The first 12 cells are mounted. It was a bigger chore than I expected avoiding all of the potential interference issues. The rear crossbar (the one with the clamp) will be welded in place once the second box is completed and mounted.

Here is a close up of the cross bar mount.

There is only 3/4 inches (19 mm) of clearance between the motor and the battery box.  If there is any rubbing I will switch to a stiffer racing style motor mount.

The cells are mounted below the rear motor mount bracket.

The box sticks out beneath the bottom bumper and valance. This is mostly a cosmetic issue, but if mounted too low, dragging could be an issue driving up the drive way. From most angles, they box is not visible, but if you are low enough, or far enough away, it will be visible under the rubber bumper. Painting the rack black should help it blend in.

A clearance issue with a curved part of the frame forces me to offset one of the mounting points.

One corner of the box is close to a tie down plate on the frame of the car.

The boxes were skinned with sheet metal.

Tuesday, November 13, 2012

Electrical Odds and Ends

My electrician brother was visiting from out of town. I took advantage of his skills and we wired up a dedicated charging outlet in the garage. Sharing a plug with the clothes dryer would get old fast. We wired up a 240 volt, 30 amp circuit using a NEMA L6-30 twist lock outlet.

I ordered bunch of odd parts that I will need to complete the project. 
 The proximity sensor will be mounted near the motor tail shaft and will sense the motor speed. The signal is sent to the motor controller to limit the motor RPM and drive the tachometer in the instrument cluster.

The electrical terminals will be used to connect up the 12 volt systems. The translucent insulated ring terminals are marine grade.  A professional crimper can run $300, but for occasional use, a compound ratcheting crimper can be had for $35. The dies in the jaws are color coded to match the terminal insulation, and cover a range of wire sizes. The crimp quality is much better than you get with a combination stripper/crimper.

The rubber mounts will help isolate the controller from the jarring automotive environment.

The accelerator pedal position sensor is a potentiometer – the resistance of the device changes as the input shaft rotates. The throttle linkage connects to the potentiometer through a ball joint and a control arm. 

Adjacent batteries will be connected with braided straps. The braid is flexible to minimize any stain on the terminals of the battery. M8 bolts, and Nordlock washers fasten the braided straps to the battery terminal. Nordlock washers are a marvelous invention. They are a pair of washers with sloped steps that must slide past each other, expanding the thickness of the washer pair, in order to loosen the bolt. This mechanism prevents vibration and thermal cycling from backing out the bolt over time.

Longer connections are made with 0/2 AWG welding cable. The cable is 0.63 inches (16 mm) in diameter. 1,235 strands of 30 AWG copper makes for a flexible cable. The cable is sized based on average current draw and is rated for 190 amps at 90 degrees C. The terminals must be crimped with a hydraulic crimper.