Last update: Nov 17 2017
The car was worth $10K, the conversion cost $18K. Converting a gas car to electric is not an economical proposition. It only makes sense to convert a car that is special in some way - an exotic, classic, or hobby car. For economy, a used Nissan Leaf is king of cheap. Converting a car is like buying a boat to catch a few fish and have fun with friends.
This car does not currently have enough cells to compensate for voltage sag that occurs under long and hard acceleration. Shorter bursts of acceleration, like 0-40 MPH or 30-60 MPH, are similar to the performance with the ICE.
The 2.5kW charger adds 15 miles of range per hour. A full charge takes 6-7 hours. Doing a full charge requires returning home with no remaining charge. That never happens.
In this car, 3rd gear works well driving from 0-35 MPH, 4th gear works well from 30-55 MPH, and 5th gear is good for over 50 MPH.
OEM electric cars like the Leaf and Model S have one speed transmissions. They use AC motors that turn fast, reverse electrically, and provide good torque at low RPMs with liquid cooling. They use different gearing (around 9:1) than the typical final reduction in a gas car (around 3:1).
Maximum range is 40 miles with the current battery pack. This is enough for my needs. My typical trip is 5-10 miles and I generally charge the car ever other day or so. Batteries are expensive and heavy, so for a project like this it does not make sense to have more range than you need. Electric cars need much less range than you might expect. If you have a garage for charging and a gas car for long trips, you only need enough range for one day of typical driving. Electric cars start each day with a full "tank" and the typical commute is 30 miles or less.
I estimate the current setup makes 160 hp and 300 ft·lb. The turbocharged engine was specified at 230 hp and 235 ft·lb. With a few more battery cells the power could be raised to about 200 hp. As a rule of thumb you need about half the horsepower with an electric car to drive comfortably because full torque is available from 0 RPM.
There is air conditioning. Air conditioning is not a big issue since where I live, summers are usually mild.
The only other feature that no longer works is the cruise control.
Top speed is limited by the motor maximum RPM and the transmission gearing. I never attempted full speed. The calculation below gives an estimate of 79 MPH with the WarP 11 motor. With the WarP 9, the calculation is 105 MPH.
s = 60r / gfw
|s||Top speed in MPH|
|r||Motor maximum continuous RPM|
|r||Motor maximum continuous RPM|
|g||Transmission top gear ratio||0.738|
|f||Diff final reduction ratio||3.700|
|w||Wheel rotations per mile|
Continental ExtremeContact DW 215/45ZR17
AC induction motors that are available in the conversion market have the main benefit of regenerative braking, but they cost more and make less power than DC motors.
The table below shows the yearly savings, which varies with the cost of gasoline. The maintenace cost is the yearly average for 10-year cost of ownership items such as oil changes, air filters, coolant flushing, timing belt.
12000mi × $3/gal ÷ 25mpg
12000mi × $0.12/kWh ÷ 2.6mi/kWh
With AC motors capable of regenerative braking, there is additional savings in reduced need for brake service.
In short, I converted this car to electric for fun. I hoped this project would inspire my kids and show them that if what you want does not exist, you can make it happen yourself.
The choice of Subaru made the most sense for me. There is a strong and active Subaru community where I live. The area hosts several large Subaru clubs and there are two major annual car shows specific to Subaru.
I chose the WRX because of the World Rally Blue color and overall sportiness. World Rally Blue was only available on the WRX. Compared to the base model this car has sporty brakes, taller gearing, faster steering rate, and upgraded suspension. In order to have a car with these features (particularly the color) it is far more cost effective to start with the more expensive car and sell the very desirable turbocharged engine, than to upgrade a base model car.
In terms of the goals, this project is a great success. There has been tremendous interest in the car which has lead to quite a few interesting conversations and friendships.
Starting in 1st gear is awkward. Gas engines have little torque at low RPM, so it's easy to stomp the throttle and wait for the power to ramp up. Electric motors have maximum torque at all RPMs so stomping the throttle jolts the driveline pretty hard. The motor controller has a setting to prevent power from rising at an insane rate.
To start in 1st gear, you must hold the brake pedal hard and press the throttle just the right amount to load the driveline and suspension with just the right amount of tension. With the huge torque, this is a nervous guessing game. The feeling that you might break something creeps in. Once you launch, the car accelerates at a blistering rate, but that only lasts for what seems like a few car lengths. The acceleration is so fast that you max out the motor's RPMs instantly. Shifting from 1st to 2nd gear for maximum acceleration is also awkward.
In contrast, starting off in 3rd gear is smooth and satisfying. The torque to the driveline feels appropriate. The sensation of linear acceleration feels odd. We're accustom to accelerating quickly in 1st, then a little less quickly in 2nd, and so on. With electric, the car keeps right on pulling hard all the way to 35-40 MPH.
Converting a car is a major undertaking with difficult and expensive problems. The amount of work is similar to swapping a gas engine from a different model.
Not if you've got a good working gas car. Keep driving that until it is kaput.