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Toyota MR2 EV

Toyota MR2 EV front view with new paint job
Toyota MR2 EV front view with new paint job
Toyota MR2 EV side view with new paint job
Toyota MR2 EV side view with new paint job
Toyota MR2 EV rear view with new paint job
Toyota MR2 EV rear view with new paint job
Toyota MR2 EV front compartment
Toyota MR2 EV front compartment
Toyota MR2 EV rear compartment
Toyota MR2 EV rear compartment
motor and transmission in car.
motor and transmission in car.
Toyota MR2 trunk with batteries.  Still have space for cargo.
Toyota MR2 trunk with batteries. Still have space for cargo.

This is the main page for my Toyota MR2 EV conversion project log. The car first ran on September 4th, 2007, and I am currently using it as my primary vehicle for around-town driving. My EV Specifications page summarizes the details of the car. My EV Project Timeline chronicles major milestones in the project and my EV Project Expenses page documents some of the major expenditures. I'm starting an EV Maintenance Log to record repairs and modifications, and I have recorded some of my EV First Impressions based after driving the car for about 1000 miles.

In the pages below I cover the what, why, how, when, and who of my conversion experience building an MR2 electric car, as well as providing some background into my thought process. I have created many links to related web pages and information on my EV Reference Material page, to avoid duplicating information that other people have already provided in better form than I could. In the time since I put up this website, I have contacted, or been contacted by the owners of Other Electric MR2s. Of course, all information in here is based on my own experience, and may not be the whole truth, the full truth, or contain any vestige of truth at all.

Update! August 16th, 2008: Finally got my Battery Monitoring System to "hardware complete" and updated the web page with screenshots, data, etc. But still need to get some schematics and perhaps if I am feeling gregarious code listings up there too, but the system works!

Background and Reference Material

Look at the EV Background Page for a short discussion of what an EV is, whether or not one would work for you, why you might want to build one instead of buying one, and a compilation of reading suggestions and links.

Look at the list of EV Reference Material that I compiled while doing some of my research. While not exhaustive, it should be a good start.

Analysis

The EV Performance Analysis page goes into a fair bit of mathematical analysis of the performance characteristics of an EV Conversion. Example numbers from my conversion. Also provided are some rule-of-thumb considerations for those of us who can't stand math.


Toyota MR2 arriving home
Toyota MR2 arriving home

Finding My Chassis

There are many EV Chassis Selection considerations to be thought through when selecting a car to convert. Not the least of these are weight, aerodynamic drag, your intended use, and battery carrying capacity. I wanted my EV to be a decent performing, small second car with as much range as possible. I don't need much cargo capacity but I insist on enough to carry a full load of groceries and still have a passenger. After going through the process and considering about a dozen different car models, I settled on the 1985-1989 Toyota MR2.


Toyota MR2 engine being lowered out
Toyota MR2 engine being lowered out

Stripping down the MR2

There is a huge amount of crap in an internal-combustion powered car that you won't need if you convert to electric. Over the course of a month, I pulled out over 500 pounds of stuff from the car, including the engine, gas tank, exhaust, and cooling system. My EV Weight Change Page has a detailed log of the weight change on the project. I was able to sell the engine and some of the other take-off parts to recoup a little money, but not a whole lot.


Toyota MR2 transmission prior to rebuild and modification
Toyota MR2 transmission prior to rebuild and modification

Transmission modification

There are three things I have done to the transmission to reduce inertial weight and increase efficiency. The first thing I did was to replace the flywheel with an aftermarket aluminum one. The second is to use a lighter weight oil to reduce friction. The final thing was to make internal modifications to the transmission to reduce friction and rotating weight. See my MR2 EV Transmission Modification page for more details.


motor and transmission assembly, ready to be installed
motor and transmission assembly, ready to be installed
motor and transmission assembly installed into car.
motor and transmission assembly installed into car.

Motor and Adapter plate

I am using an advanced DC 9" motor in my car. I got ahold of this motor from a local EV enthusiast who buys and sells all things EV related. The motor (pictured with adapter plate) is a bit shopworn but has very low "mileage" on it. Since this electric motor and the original transmission of the car are not designed to fit together, An adapter is needed to mate the two together. Look at my Motor And Adapter Plate page for more details.


Chassis Work

There were a bunch of Chassis Modifications that needed to be made to the MR2 body as part of the conversion. These changes were necessary to allow the EV Battery Racks to fit into the engine compartment and front compartment, and to make a place for components of the EV Charging System. These sorts of changes are, of course highly dependent on the choice of car body, motor, type and number of batteries, and a myriad of other factors. My MR2 needed several moderate modifications. Other (larger or less aerodynamic) car bodies or pickup trucks might not need any modification at all.


Motor and rear battery rack finished and installed.
Motor and rear battery rack finished and installed.
Front battery racks, done and installed
Front battery racks, done and installed

Battery Racks

Since the original chassis was not designed to carry seventeen batteries, I needed to make some EV Battery Racks to support and contain them. There are two main areas in the car that get batteries installed: The engine compartment has 10 batteries, and the front compartment has seven batteries installed.


passenger side motor mount frame bracket tacked in place.
passenger side motor mount frame bracket tacked in place.

Motor and Transmission Mounts

I want to get as many batteries into the car as I can. of course. The engine compartment has room for ten batteries of the type I want (more than half of the amount I need) above the motor and transmission assembly. The only issue was that the transmission assembly needed to be moved down about two inches to allow sufficent clearance for batteries above it. I have detailed the work on realigning the transmission/motor assembly on my Custom Motor Mounts page.

Body work and basic repairs

This MR2 was pretty solid structurally when I bought it, but it was well worn out. The brake system was leaking, and needed a complete overhaul. The clutch and its hydraulics were also shot. There were several dents and dings on the body that needed to be repaired, the worst being a moderately sized dent on the passenger side rear quarter panel which according to the prior owner had been caused by a soccer ball. More likely it was the soccer player, but whatever. I straightened out and bondo-ed up all these spots, and primered them. I will take the car to a body shop to have it painted in the near future.


Struts with new springs and shocks installed
Struts with new springs and shocks installed

suspension upgrades

The Toyota MR2 is a small, lightweight, mid-engine sports car. Its curb weight is 2265lbs stock. The maximum GVW is about 2800. However, the completed EV conversion of this car is likely to come around 3200lbs. (Update: car weighs in at 3140lbs according to the scales at the local dump!) Add in another 500lbs for a full load of passengers and cargo, and it is obvious that the suspension is going to need attention. Details are on my EV Suspension System page.


Curtis 1231C 500A motor controller
Curtis 1231C 500A motor controller

Controller and other electronics

EV Electronics are necessary to control the motor, charge the batteries, and power the 12 volt accessories in the car. The major components in a typical conversion are a Motor Controller, Onboard Charger, and DC-DC converter. There are also several contactors, circuit breakers, gauges and such that should be installed, but the exact configuration depends on several factors. Modifications and extensions to the original circuits in the car will also be necessary. Follow the link for more details

Power brake system

Virtually all modern cars have a power brake booster. Since an EV conversion is almost always going to be considerably heavier than the original gas setup, it becomes even more important to have a power-assisted EV Braking System. Since power brakes derive their "boost" from engine vacuum, this vacuum source needs to be replaced in an EV conversion. This is a straightforward process. EV Power Brakes are powered by a vacuum pump instead of by engine vacuum. This vacuum pump runs off the 12 volt circuits of the car. Follow the link for more details.

Battery installation

The EV Traction Battery is what powers the car. My car is designed for a pack of seventeen Trojan T-875 8v golf car batteries, for a 136v system. As it turns out, those batteries, with the terminal type I need would have been a three-month special order. Having just finished the car, I did not want to wait for those batteries to be made, so I purchased a set of seventeen Trojan T-105 6v batteries off the shelf (same type as my original ones), for a 102v system instead. The lower pack voltage impacts my top speed and acceleration, but does not substantially affect range. Despite the lower voltage, the car is still accelerates adequately and is able to reach highway speeds.

Test Drive!

The first successful drive took place on Tuesday, September 4th, 2007. I drove about a mile around the neighborhood. Over the course of the next several days of driving it, I replaced the EV Traction Battery (used one was exhausted) and discovered a few (thankfully minor) things that need reworking. See my EV Maintenance Log for details on repairs, rework and modifications to the car now that it is running. See my EV First Impressions page for some thoughts after about a hundred miles of driving.

Performance Improvements

I got the car running on September 4th, 2007, but I had not done everything I wanted to do to ensure maximum range. My EV Efficiency Improvements page covers the things have done and will be doing to try and improve range.