MORE PLANNING: JUNE 10, 1998
Let me give some more detail of the systems on a gasoline car that are affected by a conversion to electric:
A gasoline car has an internal combustion engine that burns gasoline. The energy from this process turns the engine as well a generating combustion gasses and heat. The heat is dissapated through a radiator and the exhuast is fed to a catalytic converter to reduce pollutants, then to a muffler to quiet the sounds of combustion and finally released to the air in the back of the car. The speed of the engine is regulated by the amount of air that is allowed to enter the carburator (throttle body for fuel injected cars).
An electric car has an electric motor that converts electric power from batteries into rotational motion. There is no combustion-hence no exhaust or pollution. While there is heat that is generated, no special cooling system is needed except a fan for the motor controller. The motor controller is a device that controls motor speed by regulating how much power goes to the motor.
From this it is clear that the conversion process starts with removing the gasoline engine, fuel tank, exhuast system, and cooling system. To complete the process an electric motor must be mounted and coupled to the transmission. The batteries must be mounted into the car in such a way that they pose no hazard to the car's occupants. This means keeping battery cabling out of the passenger compartment, securing the batteries so they don't become projectiles in a crash, and venting any hydrogen gas generated.
Now, specifically for the Escort: EVAmerica sells the hardware to mount the electric motor to the transmission, and couple the motor to the clutch. The Escort gasoline engine mounts at two points: 1. It mounts to the transmission. 2. There is a motor mount on the right hand side of the engine bay. I'm on my own here: I will have to design and have fabricated a motor plate that will attach to the electric motor and a bracket that will bolt onto the existing motor mount on the right side. I was going to add a bracket to mount the AC compressor and drive it off the motor's tailshaft, but upon closer inspection I've discovered there's no way there will be room for the fan the AC needs, so the AC gets chucked.
The batteries provide another challenge: how do you make space for the batteries without taking away all the cargo room in the car? Some people just do that and live with it: they build a battery box in the hatchback area, and sacrfice that space to the batteries. However there is a way to save some of that space. In the floor of the hatchback area, there is a recessed area for the spare tire. This recession dips about 8" below the floor of the hatchback area. Using the help of a welder, I plan to cut out the floor of the hatchback area, and the recessed area for the spare tire, and recess my rear battery box 8" down into the hatchback floor. The battery box will still stick up some, but nowhere near as much as if it were resting on the floor of the hatchback area. The battery box will have a welded frame, with the enclosure itself made of plywood (3/4" on the bottom, 1/2" on the sides and top). What about the spare tire? It will rest on top of the battery box.
Since the batteries will not be totally outside the passenger compartment, there is a need to deal with some concerns about the batteries. When being charged the batteries can give off hydrogen gas, which is very explosive. A ventilation system is needed, wired into the battery charger, that pump out the hydrogen gas from the battery box. Another concern about the batteries is that they don't perform well in cold weather. For this reason it would be good to insulate the battery box so they can keep the heat they generate.
Not all the batteries will be in the hatchback area (I hope to fit 10), some will be in the engine compartment. They too will be in insulated boxes, but ventilation is less of a concern since they are outside of the passenger compartment.
Speed control: how? In the gasoline car, a cable is attached to the gas pedal. The cable runs to the carburator and opens or closes the throttle valve, allowing more or less air into the carburator. In an electric car, we keep the cable, but run it to a potentiometer. The cable moves the potentiometer to vary its resistance. The motor controller reads the resistance and adjusts the power it sends to the motor proportionally.
For the electrically minded, let me explain how the motor controller works. The motor controller switches power on and off to the motor at a very high speed, typically around 15 KHz. It controls the power the motor gets by the percentage of time it stays on in one cycle. If you want very little power going to the motor, the controller might be on only 10% of the cycle. If you want a lot of power going to the motor, the controller might be on 90% of the cycle. This is called Pulse Width Modulation or PWM. The constant switching of power on and off doesn't disrupt motor operation. It happens at such a high frequency that the motor only sees an average current.
What about the heater? If you are familar with automobile heaters, you know they use the hot water from the engine, run through a heater core, to provide heat for the passenger compartment. No gas engine, no hot water. The EV solution for this is: an electric heating element. An electric heating element replaces the heater core. On the downside, this consumes some energy that otherwise would have been used to move the car. On the plus side, and electric heater produces heat pretty much instanteously, you don't have to wait for the car to warm up to have heat.
The 12 volt battery used to start the gas engine, is still needed to power headlights, turn signals, brake lights, horn, etc. The problem is how to keep it charged up? With a gas engine, an alternator is driven by the motor to keep the battery charged. In an EV, an alternator could be used, but it is more efficent to use a DC-DC converter. The DC-DC converter takes the main battery pack voltage (120 volts) and isolates it and steps it down to 12 volts. Since an alternator runs at about 14-15 volts and puts out 50-60 amps, it's still possible for the battery to become discharged using a DC-DC converter. For example, most DC-DC converters are rated for no more than 40 amps, and produce only about 12 volts at that point (a heathly "12 volt" battery actually has a potential of about 13 volts). My solution is to add a relay, so that when the main battery pack is charged, the DC-DC converter will come on, and charge the 12 volt battery.
Most modern cars have power brakes & power steering. Both are run off the gasoline engine. Can both these systems be saved? The answer is "Yes," if you want to. For power steering you can put a pulley on the tailshaft of the motor and run the power steering pump. The only problem is, unlike a gasoline engine, the electric motor doesn't "idle." The gasoline motor is always running whether the car is moving or not. The electric motor only runs when you need it. Therefore, sitting at a dead stop you will have no power steering in an EV. My decision was to remove the power steering rack, and replace it with a manual rack: I'd rather deal with manual steering than the problems associated with EV power steering.
Since the weight of batteries load an EV to near it's maximum gross vehicle weight, it's important that the power brakes work well. However, the power brake system relies on vacuum from the gasoline engine in order to work. The EV solution? An electric vacuum pump. It is paired with a pressure switch to turn on the pump when the vacuum drops, as well as a reservoir. The reservoir is basically a chamber to hold vacuum (it holds the absence of air) so that you will have good braking, even if you need to press the brakes for a long time.
With 10 batteries in the hatchback area, each weighing around 60 pounds, the rear suspension is going to need some help. The minimum you can do is put air bags in your rear coil springs. This will help keep the rear from "dragging." A better solution is to order new heavy duty coil springs. To do this, you measure the current ride height of the car (unloaded). Typically this is the distance from the wheel well to the ground. Then measure the ride height of the car, fully loaded. The supplier can fabricate custom springs for you, based in the change in ride height information.