I have finally installed the Fuel Gauge Driver Plus from EVWorks in Australia. The Fuel Gauge Driver Plus or FGDP is a State of Charge device. SOC is the EV equivalent of a fuel gauge. What's really nice about this one is that it can actually drive the existing fuel gauge. It also has a couple of other nice features: 1) it can drive the tachometer as an ammeter and 2) it has a low State of Charge warning indicator.
Here's a picture of the Fuel Gauge Driver Plus from the EVWorks web site:
Here's a drawing of the device showing the inputs and outputs:
Here's the wiring diagram that I put together for the FGDP. The 914 fuel gauge has a low fuel warning light that I decided to use as the indicator for the low SOC warning indicator. The problem is that the FGDP only puts out a +5V 5mA output signal only capable of driving an LED. To drive the existing 12V lamp in the fuel gauge, I used the +5V 5mA output to drive a 2N2222 transistor and a 2.2KOhm resistor to switch on the lamp. I decided not to use the low SOC warning ind as a means to switch to a "limp-home" mode as I will be the only driver of this EV. I can also switch from the ammeter from the FGDP to a real tachometer of the motor speeed from a RechargeCar WarP Speed Sensor on the WarP 9 motor.
Here's the FDGP, low SOC warning ind circuit, and 12V power momentary switch in a plastic enclosure. The enclosure is located in the front trunk and the device is on the most positive leg of the traction pack cable just before it connects to the emergency breaker and positive contactor.
Here's a closeup of the fuel gauge. You can clearly see the low fuel light is lit up as the orange ind.
And another closeup of of both fuel gauge and tachometer: