THE ELECTRICAL SYSTEM: JUNE 10, 1998
Now let me spend some time on the electrical system. Below is a schematic/block diagram of the main electrical connections in the car.
The main battery pack consists of 15 8 volt batteries. Current plan is for 10 batteries in the hatchback area, and 5 under the hood. The main battery pack is fused and then connections are made to the E-meter, charger, DC-DC converter, and heater core. What is not shown is that each of these circuits is individually fused. The next connection is to a relay that is energized by the ignition switch. From this relay the power goes to the motor controller (the box with the cliped corners and B-, B+, etc. inside) and the motor.
On the negative side of the battery pack, the first connection is a shunt. A shunt is a piece of metal of known resisitance. When the current flows through it, the amount of current flowing can be determined by the voltage drop over the shunt. This information is monitored by the E-meter, which keeps track of power consumed and battery pack voltage. The battery charger will be on board and plug into a 120 VAC household outlet. Not shown is a charger interlock: the AC to the charger will also be run to a relay that will do two things: 1. It will open the ignition switch circuit, so that you can't try to operate the car when it's being charged. 2. It will complete a 12 volt circuit to energize a relay attached to the DC-DC converter circuit. The purpose of this is to energize the DC-DC converter while charging the main pack, to insure that if the 12 volt battery is run down, it will be charged up with the main battery pack.
The next connection is to a relay which is a twin of the relay on the plus side: it is also energized by the ignition switch and completes the negative side of the circuit for the DC-DC converter, the heater, and the motor controller. That round cylindrical thing below the controller is the electric motor.
What is also not shown in this schematic is the full ignition switch circuit (I did this later. If you want go there it's 12 Volt Electrical System and additional details on the contactor relays are found at Contactor Relays). Using the wire from the ignition switch that use to run to the coil, we run it through a fuse, then to an intertial switch. The inertial switch is a safety device: if the car is in an accident, the inertial switch will open, cutting off all power to the motor. Next it runs through the charger interlock relay that was mentioned above. Then it runs to both the main contactor relays. Another connection will be made to the vacuum pump for the power brakes.
Loose ends: One point that I haven't mentioned is this: the 12 volt system and the 120 volt system are to be kept totaly seperate. The 12 volt system is grounded through the car's frame. If the frame was live with 120 volts and you came in contact with it, you could be seriously hurt. The presents a problem when it comes to powering the E-meter. Since it's in circuit with the 120 volt battery pack, an isolated DC-DC converter must be used if it is to be powered from the 12 volt supply. As far as turning on the heater goes, I will mount a switch on the dash board. It will be wired through the ignition switch (only want the heater on when the car's on) and it will go to a relay that will switch the 120 volts on and off to the heater.
You might think since this is an electric car, that the biggest problems are electrical: they aren't. Chip Gribben told me he wired his car in one weekend. The biggest problems are mechanical: removing the gasoline engine, making mounts and brackets for the electric motor, welding battery boxes, installing battery boxes, etc. There will be nothing more to write about till something mechanical gets done: the engine is removed.