Build an Electric Car: Wiring
As shown in the wiring diagram, there are four basic systems in an electric car: the propulsion system, 12 volt system, charging system and the driver’s displays and controls. The propulsion system uses high voltage to power the electric motor, in this case 96 volts. The 12 volt system powers the accessories such as the radio and lights. The onboard charging system uses 120 VAC household current rectified to DC power to charge the batteries.
The driver’s display and controls are pretty much the same as in a gas car. Although not shown in the illustration, the clutch pedal and mechanism are the same and the power brake system is the same except an electric vacuum pump supplies vacuum for the power brakes. The accelerator linkage is now linked to the potbox. Instead of a fuel gauge there is a voltmeter and there is an ammeter that measures the propulsion system amperage.
The propulsion system’s battery pack is split between the front and rear of the car. Since high current, up to 300 amps, will be used in this conversion heavy duty 2/0 welding cable capped with heavy duty lugs is used for connections. In addition, a 400 amp fuse is placed in the circuit. To prevent corrosion a thin layer of Noalux is applied on each battery terminal.
On the 12 volt side, 16 gauge wiring is used throughout the vehicle, except the wiring for the 12 volt battery which is heavier. The existing ignition wire, 12 volt accessories, and components including the vacuum pump, and contactor are wired to a terminal strip. When the ignition key is turned to start the car, the contactor closes the circuit in the propulsion system. Although the circuit is closed, current will not flow to the motor until the driver accelerates.
Also wired into the car is a charger interlock which is a safety relay that opens the contactor while the car is charging. This prevents the car from being driven off while the car is still plugged into the charger.
The charger is an onboard transformerless unit with built in GFI (ground fault interruption). Input wiring includes 10 gauge household wire that is wired from the charger to a 110 VAC outlet under the front bumper of the car. Output wiring includes a positive lead from the charger to the top of the battery pack and a negative lead from the charger to the bottom of the battery pack. The charger has a built in ammeter so amperage can be adjusted according to the available current at the charging location. This means the car can be charged anywhere where there is available electricity.
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Next step is Final testing
Build an Electric Car: Installing the Battery Box
Since 10 of the batteries will be located in the rear section of the passenger compartment the batteries will need to be stored in a protective box. This is to prevent fumes from entering the passenger compartment when the batteries are charging and to protect occupants of the car in an accident. The box also keeps the batteries warm in cold weather. Because of the limited space in the front of the car, battery boxes were not installed.
Mounted on the side is an explosion proof brushless fan that ventilates the box when the batteries are charging. The fan is wired in series with the fan in the battery charger so when the charger is on the battery box fan is on. A marine grade ventilation bilge hose is attached to the fan and routed to the vent on the underside of the car.
The box is constructed of marine grade plywood and painted with water repellant paint. Metal banding is secured around the box so the weight of the batteries will not break the box apart in an accident.
The box is securely mounted with bolts to the frame of the car. For ease of installation the box in this conversion fits in the trunk. However, with careful planning, some cutting, and a little welding, the battery box can be sunk into the floor of the trunk to regain storage space. Before the batteries are installed, a layer of baking soda is spread on the floor of the box and the air bags in the coil springs are filled with air.
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Next step is wiring the car
Build an Electric Car: Installing the Components
EVs require very few parts so installing the components is relatively simple. Below is a photo showing the major components installed in the car. As you can tell they don’t take up as much room as the engine. The rest of the space will be filled with batteries. Not shown in the photo is the compact battery charger which is mounted at the opposite side of the new motor compartment.
Ideally, the components should be placed close together to keep wire lengths short. The controller requires sufficient cooling to work properly so it should be placed in the airstream or mounted on a heatsink with a thermal joint compound for heat conduction. The potbox should be mounted on a sturdy surface and the accelerator cable should be routed in such a way so as to prevent kinks or pinching. Since there is a slight spark when the contactor closes it should be placed below the top level of the batteries. Each component should be kept away from water splash. Some EV convertors mount all their components on a board that is hinged to allow easy access to batteries and the motor.
PVC pipe is mounted under the car as a conduit for the wiring that runs to the rear battery pack. The wiring harness that runs inside the conduit includes heavy cables that connect the battery packs, a charging wire for the positive lead of the top most battery, wires for the battery box fan, and extra wires for future expansion.
To support the weight of the rear batteries, air bags are installed in the coil springs to support the weight of the rear batteries. The vent in the rear spare tire well is ventilation for the battery box. The spare tire will be stored on top of the battery box.
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Next step is installing the battery box
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Electric Car Conversion Manual
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