Low-Voltage System

Low-Voltage System

On the low-voltage side, the idea is to blend the existing ignition, lighting, and accessory wiring with the new instrumentation and power wiring. There are six main components on the low-voltage side:

• Key switch • Throttle potentiometer • Ammeter, voltmeter, or other instrumentation • Safety interlock(s) • Accessory 12-volt battery or DC-to-DC converter • Safety fuse(s)

Every EV conversion should use the already-existing ignition key switch as a starting point. In an EV, the key switch serves as the main on-off switch with the convenience of a key—its starting feature is no longer needed. You should have no problem in locating and wiring to this switch.

In Jim’s 1987 Ranger and Paul Little’s Porsche conversions, they mounted the throttle potentiometer (Figure 10-23) on the driver’s side fender well (Figure 10-24, top). Figure 10-24 (bottom) shows it mounted in place and wired up.

Instrumentation wiring is simple; just be sure to observe meter polarity markings— the plus (1) marking on the meter goes to the positive terminal on battery. The ammeter is connected across the shunt(s) already wired into the high-current system. The voltmeter goes across the battery. The best solution is to wire the voltmeter so that it is

Figure 10-23 Electric Porsche throttle potentiometer (Cour tesy of CoolGreenCars.net).

Figure 10-24 1987 Ford Ranger throttle potentiometer positioning (top) and mounted and wired throttle potentiometer (bottom).

always on, giving you a continual readout of battery status. You don’t have to worry about draining the battery because a modern voltmeter’s internal resistance is high enough to cause only a miniscule current drain (an order of magnitude less than the battery’s own internal self-discharge rate). The battery indicator or state-of-charge

Figure 10-25 1987 Ford Ranger ammeter and voltmeter instr umentation (top) and impact cutoff switch (bottom).

meter also goes across the battery, but it should operate only when the key switch is on, so wire it to the on-off side of the main contactor (away from the battery). The temperature meter wiring is not particularly critical; just observe proper polarities and grounding, and make sure the thermistors are securely attached to whatever you are measuring. Jim utilized only ammeter and voltmeter instrumentation, with a range switch mounted on the 1987 Ranger’s dashboard (see Figure 10-25, top).