Electric Miata


In the Fall of 2007 I bought a 2000 mazda miata with the intention of converting it to a battery electric vehicle (BEV). The plan was to buy parts and supplies and do a bit of research over the Winter and Spring, and begin the conversion process in the Summer of 2008.

I'm a college math teacher so I don't have a lot of commitments in the Summer -- I should be able to put 20 to 30 hours a week into this project. I've worked out my plans pretty well at this point (including a lot of contingencies in case some things don't work out the way I hope...) Almost all of the parts I'll need are either ordered, or have arrived. Probably the two most critical items are the electric motor and the controller for it. Both have been ordered, but both have pretty long lead times and I'm a bit worried they won't get here by the end of the Summer.

The overall picture is this: I have a short (6.4 mile round-trip) commute, and we have a another car in the family (an old Volvo station wagon) that can do all the longer trips, so the limited range of an all-electric vehicle is not a problem for me. It is possible to get ranges in excess of 50 miles out of a BEV but that comes at a price -- either literally a high price tag for expensive light-weight batteries, or a penalty in terms of the final weight of the vehicle (what some enthusiasts call a "lead sled," a car that's carrying more than half of its own weight in lead-acid batteries!

Since I can afford a very limited range, I'm hoping to end up with a car that, once converted to electric, will be only slightly heavier than it was stock. A lot of the design of an electric conversion revolves around ones choice of batteries, and almost all batteries stink! It takes hundreds of pounds of batteries to store the energy equivalent of a gallon of gasoline. The lead-acid batteries that serve as the starter batteries in cars are the oldest and still one of the best technologies around. For use in an EV you want the kind that are known as "deep-cycle" (a.k.a "golf cart") batteries -- these are constructed more ruggedly in a lot of ways, but they involve exaclty the same electro-chemistry as the batteries that everyone's got in their gas-powered cars.

Perhaps foolishly, I decided that I didn't want to use lead-acid batteries right from the start. I decided to go with something a bit more exotic, a so-called "flooded" nickel-cadmium battery. This is basically an industrial-strength version of the familiar ni-cad rechargeable batteries that you can buy at the drug store. The particular batteries I've obtained are called BB-600's. They are military surplus batteries that were never put into service but exceeded their shelf-life. My cells were manufactured in 2001 and declared surplus in 2005, but these cells are well known to last in excess of 20 years! The problem is that they are used in aircraft and in that application folks tend to be overly conservative... for pushing my car around they should be fine. My hope is that by the time these batteries die the next generation of lithium ion cells will have become affordable.

The main components of my conversion are:

The so-called donor vehicle. A black 2000 Mazda Miata that I got for $7500.00.

200 BB-600 cells, purchased for $10 each from Bob Rice, president of the New England Electric Auto Association.

A WarP 9 motor, this is a series-wound DC motor that is suitable for a much larger car than my Miata. They're made by Netgain Motors Inc. in Lockport, Illinois. Guess who the Netgain distributor in Connecticut is -- that's right, Bob Rice.

A Cafe Electric LLC Zilla 1k HV motor controller. This sort of controller is actually suitable for racing and will be somewhat under-utilized in my car with the BB-600's but I'll have an upgrade path in the future if/when better batteries become available at a reasonable price.

A Manzanita Micro PFC-20 charger. This is a real cadillac of a battery charger. I could have picked chargers that would cost less than half as much. What the PFC-20 has going for it is extreme flexibility; it can be configured to charge pack from 12 volts to 360 volts so I'll be able to try lots of different configurations of the cells in my battery pack and the charger can adjust. Also, if those wunder-batteries ever come on the market...

Those are the main components. There's lot's of other smaller, ancilliary things, but those are the big things. Batteries, a motor, something to control the flow of juice from the batteries to the motor, and something to put the juice back into the batteries.

I'll be keeping a log (I refuse to say "blog" --- AAaargh! I just said it!) throughout this adventure.

A few links:

NetGain Motors, Inc. makers of the WarP 9 motor.

Cafe Electric makers of the Zilla Controller.

Manzanita Micro makers of the PFC-20 charger.

The Yahoo BB600 user group.