The idea here is that I would like to keep the car between 95% charged and 15% charged. And, I would like the actual % charged to be shown on the original fuel gauge as “F”/100% and “E”/0% respectively. The dash / instrument cluster has a white back-light bulb for the fuel-gauge, and I am replacing that with a multi-color LED so I can run it white while all is normal, and then orange -> red when I start going into the last few % of capacity. Everything looks original, and still everything is just better than original.


The battery pack itself is split into a rear pack of 2 sets of 6 cells, and a front pack of 3 sets of 6 cells (makes 30 cells = ~95 kWh). The front pack creates the “bottom” 3 x 60V, and the rear pack has the upper 2 x 60V. In between I’ve run two 4|0 cables (the biggest I could reasonably find), one for the overall positive terminal of the pack to the front switch box, and one for the “halfway voltage” between rear pack and front pack. That halfway cable then connects to the front battery, and the negative terminal of the pack comes back from the front to the switch-box.


To make it all work, I have added a Hall-sensor for the battery current that can go -1,000 to +1,000 amps (so I can measure charge and discharge), and a 0-500V high-voltage sensor to provide a safety-shield between the raw pack and the control circuitry. Each of these sensors then produce a 4-20mA signal to go back to the PLC.

The assembly of it all looks like this in CAD:

The positive high-voltage cable passes through this assembly using a 1″ thick copper rod. The wire comes in from below and bolts into the rod, rod w/ power goes through the black sensor, and there’s a cable on the other end to go back down to the actual positive terminal of the battery pack.

The second, shorter copper rod only has a wire going down on 1 side, and it connects the negative of the charger-setup to the negative terminal of the battery pack inside the front disconnect-box.

On the top of the copper bars are cut-ins to wire up the charger-setup connection(s) as well as the DC/DC converter that mounts over top of this monitoring setup.

The physical setup as I built it looks like

It came out very close to the concept, and it looks like it’ll do the job just fine. The big wires will be properly lugged, crimped and cut once this thing is mounted in the actual body of the car, and not on my cheat-sheet of plywood….