Revised Comments in Italics, made 5/25/01
Revised Comments in Italics, made 5/25/01
In a gasoline car, a coil is used to generate a high voltage pulse to fire the spark plugs. The coil is wired through the ignition switch, so that power will only be applied to the coil when you want the car to run. In an EV, we use that coil wire to to activate relays and contactors to supply power to the motor, and other parts of the EV that we want active when the EV is running.
If you look at the schematic above, starting at the left you will see a battery. This is just a standard 12 volt car battery. (I'm going to try and find a deep cycle battery that will fit in the tray. An EV doesn't need the cold cranking amps a gasoline car needs, so a deep cycle battery is a better choice.) It's charge is maintained by the DC to DC converter that takes the main pack voltage and steps it down to 13.5 volts. Note that the step down is done inductively: the main pack voltage and 12 volt system are electrically isolated from each other.
Going from the ignition switch we put in a 15 amp fuse (would you believe that Ford doesn't fuse the main ignition wire?(actually they use a fusable link. It gives you the protection of a fuse, but isn't as easy to replace). We then run the wire through an inertial switch. Inertial switches are common in gasoline cars. The fuel pump in fuel injected cars runs at a very high pressure. If you were in an accident, and the fuel line was severed, gasoline could gush out of the ruptured fuel line onto the crash site. To prevent this, all fuel injected cars have inertial switches. In the event of a sudden change of inertia, such as when an accident occurs, the intertial switch opens killing power to the electric fuel pump.
In the event of an accident, we want to remove any power from the electric motor. What if the accident were to force the drivers foot down on the pedal? The intertial switch will kill all power coming from the ignition switch, and that, we will see, will kill all power going to the main contactors, which are what supplies power to the motor.
Next we have the charger interlock relay. Ever leave your lights on and kill your battery? I came close a couple of times till I got a car that "dinged" if the lights were on when you removed the ignition key. While it's true, it's impossible to make something fool proof-they are always coming up with a higher grade of fool! Still you try to compensate for human error. Knowing myself, I can imagine one morning getting up, hopping in the car and driving off- WITH the electric cord still attached to the car, still attached to the house.
The charger interlock relay prevents this. It's a relay that's normally closed, but the 120 AC current fed to the charger, activates the relay to open the circuit. This makes it impossible to drive off while your car is plugged into the wall.
Above the charger interlock, you'll see the motor controller cooling fan. In the process of controlling power to the DC motor, the motor controller generates a lot of heat. The hotter the motor controller gets, the more it degrades the motor controllers performance, and the harder it is on the controller's electronics. The motor controller needs to be kept as cool as possible, therefore as long as the ignition switch is on, a fan will blow air over the controller.
From this point there some uncertainty that's not shown in the schematic. There are two main contactors on either side of the battery pack. The contactors switch on the main battery pack voltage to the motor controller and other equipment (if you forget, go to The Electrical System also there's more detail on how the contactors are energized in Contactor Relays). Now as I understand it, there is a safety feature that prevents you from energizing the main contactors if your foot is on the gas pedal. Think about it. Suppose your foot was on the gas pedal, and you activated the main contactors? The car would jump forward! So, you don't want the main contactors to energize if your foot is on the gas pedal. There is a safety wiring with relays that prevents this, but I'll have to add it at a later date when I find out how it works (it relates to the KSI input on the Curtis controller, see Contactor RelaysT.E.N. 1/9/99).
There are two items left in the circuit. One is the electric vacuum pump for the power brakes. They don't say it, but I believe the vacuum pump has an internal power relay. I say that because instead of having just two inputs-power and ground, there's a power, ignition connection, and ground.
The other item is the relay for the heater core. The heater core runs off the main battery pack voltage, and is switched on by a relay. That relay is controled by two things: 1. a switch I'm going to attach to the hot/cold lever in the dashboard of the car, and 2. heater control logic. (I've thought about this some more. Basically there are two conditions you want met before you apply power to the heater core. 1. The fan is on, and 2. Air is being directed at least partially through the core, and it's not being bypassed (such as when the lever is in the extreme cold position).
Activating the fan can be done as simply as wiring the slowest position of the fan through the heater switch (I plan to use the old A/C switch as a heater switch: it's convient-already in the dashboard). Sensing the position of the Hot/Cold lever (and thus whether air is going through the core) is a bit harder. My primary idea is to use an LED sensor to detect when the switch moves off the extreme cold position. I'll probably update this again when I finalize the design.)
I've also added a relay for auxilary connections. That is, I don't know if I'll want to control more items through the ignition switch. Rather than tap more into this circuit, I'll activate a relay that will power on any other devices needing power when the car is on.
I'm planning on going over the electrical layout of the car, meaning where different components are being placed in the body of the car, in a future entry. Next, I want to give an update on the work done on Saturday.
Nature Abhors a Vacuum (Pump?)
Tim, I have a problem...
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