Have you ever wanted to own an electric car? or have you ever wanted to drive a Porsche 911? I wanted both, so I decided to build one. This blog is here to document my journey as I convert a 2002 Porsche 911/996 Carrera 2 from a gas guzzler to a completely electric vehicle - not a hybrid!

Tuesday, January 29, 2013

Dashboard Indicators

Life's been busy the past few weeks, but in the few minutes I've had available, I've been working on a few circuits to make the dashboard experience better.  The dashboard has a temperature gauge, oil pressure gauge, and fuel gauge that currently just flash red while driving because the sensors are missing.  Its taken a lot of work to obtain the correct schematic for the model year 2002 996 C2.  Without it, I was working in the dark trying to figure out which wires did what on each of the two massive engine wiring harnesses.

I've decided to map the gauges as such:
Gas Fuel Gauge: 0-4/4 = Battery State of Charge - driven by OrionBMS SOC output (0V-5V)
Oil Pressure Gauge 0-5 Bar = Pack Amperage 0-500Amps - driven by OrionBMS output (2.5V-5V)
Temperature 100F-250F = Motor Temperature 100F-250F - driven by motor temperature thermal diode

I had to craft a few custom circuits to convert the outputs of the OrionBMS and motor's thermal diode to the input requirements of the ECU.  Here are some sketches and a picture of the circuit that drives the Oil pressure and coolant temperature gauge.

So far I've built up the Amperage and Temperature circuits.  I've debugged and tuned the Amperage circuit, however, the Temperature circuit is giving me trouble.  I'm going to try a single ended op-amp in place of the dual-supply part I have in there now.  Both the circuits use one op-amp to multiply the input by a number, then a second op-amp to subtract a fixed offset.  I've only done limited testing in the car so far.  I need to finish debugging the Temperature circuit before I hook it up to the motor's embedded thermal diode and the car's ECU.

1 comment:

  1. Hi Kurt, how did you solve the issue with the fuel gauge?
    It requires a resistor normally and as far as I know it is not possible to change the soc signal just to drive it in a range of f.e. 2.5 to 4.5V as other bms are able to do it.