Engineer shares how to build an electric vehicle from the ground up -- Part 2: Specs, challenges, and future design

-July 14, 2011

Editor's note: In Part 1 of this two-part how-to article series, we looked at the core technology and design choices of this home-built electric vehicle (EV). In Part 2, we discuss some mechanical and structural challenges and solutions, the specifications, road-test results, and what will be next in improvements for this personal EV effort.

 
EV CarJohn Santini, vice president of engineering at TDI Power, faced many challenges during the three-year construction of this home-built EV, which, just like in any scientific effort, brought knowledge through innovation. Let's look at how the difficulties and problems evolved into a fully functional vehicle.

The goal of the project was to build a fully functional car which would be as lightweight as possible. Minimizing the size and weight of the motor and especially the batteries was key in this effort. The original goal was to be 1800 pounds; the final car weighs 2037 pounds complete. With smaller motor and batteries, the cars ultimate cost is kept as low as possible.

The following is a list of the major specifications for the vehicle as it is today:

Vehicle: 1988 Pontiac Fiero ... OK, so there's not much left from the 1988 Fiero. This is a ground-up EV project that will eventually become a plug-in hybrid. The concept is a series hybrid. However, Santini decided that he must use lithium-ion batteries. He is also focusing on low weight and high efficiency to minimize the size of the required battery.

Configuration: This is a three-wheeled vehicle (single rear wheel with tandem rear tires). Conventional A-arm suspension in front with rack and pinion steering. Air bag springs up front, coil spring in rear.

Chassis: Custom-designed space frame using one-inch-square steel tubing, 0.060-inch wall

Body: Custom fiberglass-on-foam construction

Motor: ABM three-phase AC

Drivetrain: A custom single speed direct drive with a gear belt and 6:1 ratio. The vehicle uses rear-wheel drive and has a solid rear axle with tandem wheels on a trailing arm.

Controller: The vehicle uses a Curtis 1238, three phase AC motor controller. This is the best in the business, in Santini's opinion.

Batteries: 30 cell lithium-ion pack; 100 V, 200 AH, LYP-200 made by Thunder Sky (20 kWH)

System voltage: 100 V

Charger: These are two model MER43-N54D01. They are telecom/industrial chargers made by TDI. Benefits include light weight and high efficiency. 110 or 220 VAC input, 54 V/80A (uses two, one on each half of the pack)

Heating system: Using a pair of hair dryers, switchable in series-parallel for hi/lo power

Instrumentation: Digital panel meters for volts and amps; the rest is "to be determined"

Top Speed: 68 MPH (109 KPH) geared, with a top end of 68 MPH

Acceleration: Does 0 to 60 MPH in 12 seconds

Range: 90 miles and full performance as a pure EV. Final vehicle will have a small gas engine and two modified car alternators to generate a continuous 15 kW.

Power consumption:  Uses 280 Watt hours/Mile. This is based on simulations and crude road tests. Santini has verified calculations on past projects. He is planning to find a good place to road test and get accurate actual numbers.

Odometer: 4130 miles as of July 2011

Seating capacity: Two

Curb weight: 2037 pounds

Dimensions: 186-inches long x 70-inches wide x 48.5-inches high

Tires: General Altimax 185/65R14

Conversion time: Three years (including many distractions)

Additional features: The motor controller has regenerative braking which works extremely well. The regenerative braking is set moderately aggressive so that Santini can drive the vehicle to work without ever using the foot brakes. The next step is a lightweight motor/generator to enable unlimited cruising on gas.

 
Weight
Since weight was such a critical part of the project, Santini maintained a weight spreadsheet to track the impact of various decisions made.  If weight was not as critical, he could have "converted" a number of compact cars, saving two years and a lot of expense.  However, the weight would have been closer to 3000 pounds and performance would likely suffer.  The most recent version of this spreadsheet is shown in here.

See John Santini talk about the internals of the self-built EV in this video:




Continue reading: Hybrid weight budget


Also see:


 
About the Author
Steve TaranovichStephen Taranovich is a free-lance writer with 40 years of experience in the electronics industry. He received his MSEE from Polytechnic University, Brooklyn, New York, and his BEEE from New York University, Bronx, New York. Steve is also chairman of the Educational Activities Committee for IEEE Long Island.

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