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 Building an EV
"SELECTING A VEHICLE FOR CONVERSION"
www.EV-America.com INTRODUCTIONThe decision to convert my first EV in 1987 was very simple. It was a 1973 VW which was in the process of being converted to electric. I helped its owner complete the conversion, and then I purchased the vehicle from him. After I purchased the vehicle, I invested $1500-$2000 into the vehicle for new brakes, tires, PMC controller, and paint job. My purpose for the VW was to demonstrate the feasibility of EVs and to learn from the experience. Later, I found the VW limiting because of the space available for batteries and the location of batteries within the passenger compartment. Consequently, after a couple of years of driving the VW Beetle, I was itching to try another vehicle And this time I was going to select the vehicle based on an engineering evaluation. After proceeding through the selection process, I determined that "selecting a vehicle" to convert to an Electric Vehicle (EV) can be as simple as 1 - 2 - 3 :
STEP 1. DEFINE THE PURPOSE OF THE VEHICLE
These are important questions that must be answered. My purpose for my second vehicle was finally selected: To demonstrate that EVs can be larger vehicles which serve a useful function. And my criteria became: A vehicle designed for the extra battery weight. Battery weight represents fuel weight; the more fuel you carry, the greater your range. A vehicle that allowed all batteries to be located outside the passenger compartment. This makes it easier to restrain the batteries in designing for an accident. I felt it was a safer design. A vehicle that allowed components to be easily replaced for testing new EV components. I did not want to bury components in inaccessible places. A small passenger compartment to limit the heating requirements in the New England winter. STEP 2. EVALUATE THE VEHICLES MANUFACTUREDOnce you start to evaluate the different vehicles you find there are three classes:
Each of these classes have their own characteristics with respect to aerodynamic drag, curb weight, Gross Vehicle Weight Rating (GVWR), passenger compartment, and available space for batteries. Table 1 lists typical vehicles under each of these classes and their range using various lead acid battery packs (6V and 12V). Range is a function of battery weight because the battery represents the fuel. Typically it takes 15-20 lbs of lead to achieve 1 mile in range. A Rule of Thumb is that 1/3 of the EVs weight should be batteries; the other 2/3 represents dead weight (i.e. frame, suspension, body, motor, etc). If you could decrease this dead weight to 1/2 leaving 1/2 for fuel, you would have superior performance. TABLE 1 - CLASSES OF VEHICLES
Notes:
Other ConsiderationsOf course, there are other considerations, including:
Front Wheel Drive(FWD) vs Rear Wheel Drive (RWD). In addition, the high voltage, high amperage EV controllers and motors can produce greater torque and horsepower than the original engine in the smaller FWD vehicles. This can produce a problem. There are two distinct limitations for FWD vehicle. During "launch"(initial take-off from a standing start) all cars tend to pitch up (front rotates up relative to back.) This is because the center of mass is above the force being exerted by the tires against the road. In a RWD, this pitch tends to plant the driven tires more firmly against the road, thus enhancing traction. In a FWD the effect is opposite. The force pressing the drive wheels against the road is reduced because of the pitch. If power is applied while the car is in a turn, RWD is much more stable. If the rear wheels spin, the car over-steers. If the front wheels spin, the car under-steers and may easily spin out.
Availability of Spare Parts / Age of Vehicle
Manual Vs. Automatic Transmission
Power Steering
Power Brakes Curb Weight Curb weight is the weight of the vehicle parked at the curb. No passengers and no payload. If you want to have 1/3 to 1/2 of the finished weight in fuel; then the initial curb weight of the vehicle should be less than 3000 lbs. The Geo Metro is one one the lighter vehicles with a curb weight of 1695 lbs. Consequently, an 800 lb battery pack seems ideal, except that GVWR and weight distribution become a major problem. GVWR and Distribution This is the most important consideration in any vehicle, because this directly affects the safety of the vehicle (Refer to "Safety First" in the September 1997 issue). As previously stated, converting an existing vehicle to an EV will add 800 - 1400 lbs in curb weight. Check the Gross Vehicle Weight Rating (GVWR) of the vehicle including the tires presently on the vehicle to see if it is designed for this increase. The GVWR and each axle rating are located on the drivers side door jamb. If the GVWR of the vehicle is exceeded, then the vehicle frame, suspension system, and braking system may be beyond their design value. Although the Geo Metro can perform with an 800 lb battery pack, the payload capacity of the vehicle is 600 lbs. Payload equals GVWR minus curb weight. With two people in the Geo, the available payload decreases to 300 lbs. Consequently, an 800 lb battery pack can lead to braking and handling (See FWD vs RWD above) as well as a long term fatique problem with the unibody. Therefore, the lightest vehicle is not always the best vehicle. You must also consider where the EV components will be located. Where will the batteries be located; they are the bulk of the additional weight. Will the charger be carried onboard or offboard? How will this change in weight distribution affect the vehicles handling? In the 1973 VW, the majority of weight was on the rear wheels; this was great for snow.
If my criteria was different, a different type of vehicle may have been selected. For example, if the most important criteria was acceleration to 50 mph. Then, the selection would be based on a vehicle with minimum weight and a low drag coefficient, i.e. a sports car. STEP 3. SELECT ONE OR TWO MANUFACTURERSIt actually became easier as each decision was made. Here I searched through the available literature ( Consumer Reports, Changing Times, Motor Trend, etc.) that provided detailed information on the weight and features of the different light-weight trucks available. Much of this information is now available on the internet. These trucks varied in weight from 2555 lbs to 2900 lbs for the standard bed model; the long bed models add another 200 lbs. The lowest weight was the Dodge Ram 50 at 2555 lbs and the Toyota at 2565 lbs. Both of these trucks had an excellent reputations. When I considered light-weight trucks, I evaluated the VW Rabbit P/U Truck, an oversize Rabbit. It had the advantage of being light-weight (2200 lbs) as well as front wheel drive to minimize drive train losses. It's disadvantage was that it had not been in production for 10 years and body rust was a problem in New England. By doing this evaluation, my search was clearly focused. This eliminated time wasted looking at vehicles that did not meet my criteria. My second EV conversion was a 1987 Dodge Ram 50 pickup converted in 1990 to 96V. This truck had a 5-speed overdrive transmission, power brakes, and rear wheel drive. The batteries are beneath the bed of the vehicle and the weight is over the drive wheels. This significantly improves their handling in snow. Its maximum range is 50 - 70 miles. Its maximum speed is about 65 mph. My third EV was a Bradley GT II originally built as an EV. Surprisingly, this vehicle met my requirements developed in Step 1. This EV has been upgraded to the FB1-4001A Advanced DC Motor and Curtis 1231-8601 controller so that it will perform as a sports car. My fourth EV was a GMC S-15 truck (same as the Chevrolet S-10). The advantages of the S series are:
We have since converted a number of vehicles (Dodge Caravan, Saturn , and more S-10s for electric utilities, U.S. Air Force, and Curtis Instruments. CONCLUSIONIn conclusion, consider the long term use of your EV. Here is a vehicle that you are going to invest thousands of dollars and approximately 100-200 hours of your time. Don't buy a vehicle just because it is available at a cheap price. You want to enjoy the vehicle and be proud to show it. Consider value not just initial cost. It is important to state that a good conversion even after used for a few years can be sold, usually at a price greater than the cost of the components. A number of my S10 customers sold their EVs for $10,000 - $12,000 after driving them for a few years. How many internal combustion vehicles actually retain their value? We sold our S15 GMC for $20,000 after showing and driving it for 4 years! However, this EV was a really sharp vehicle and the workmanship was outstanding. It is still on the road with a very happy owner after 4 years! Bob Batson
Electric Vehicles of America, Inc.
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