Introduction: Build Your Own Electric Car!

About: Ordinary guy with no special skills, just trying to change the world one backyard invention at a time. See more at: On Twitter - @300MPGBen and at

(AUTHORS NOTE, July 9, 2017)
Hi Everyone, there' been a lot of views on this project lately! Thanks for coming by to read through it! Much has changed since I originally built this car, including the fact that there are a LOT of great commercially built electric cars available for sale, including used at good prices. When I built this car, pretty much the only electric car available was the $100,000 Tesla Roadster. Now, I'm driving a used Mitsubishi iMiEV electric car and power it with my Solar Garage! Please take a look at my other Instructables and at for the latest on my clean transportation adventures!)

The "Electro-Metro" Project.

Can't afford a Nissan Leaf? No Problem!

Build a cheap electric car yourself by removing the the car engine, replacing it with a forklift motor, and adding batteries.

I have plenty of videos about this project at:

The primary "build blog" for this project is at:
but watch out! That is a good read for when you have WAY too much time on your hands.

For a good intro to basic electric car construction, stick with this Instructable. (If you are more interested in electric MOTORCYCLES, please see this intractable:

For more in-depth construction information, check out the instructional Video DVD available at
I have now also converted that original DVD to a series of YouTube videos. See them in THIS playlist:

Step 1: Get a Car.

The first thing you need to do is get a car. They are not all equal.

I was looking for something lightweight, with no power anything.

Heavier cars need more energy to push down the road, thus limiting your range on batteries.

Things like power steering and power brakes run off the engine, which is going to be removed anyways, rendering them useless. Power windows and locks add weight and complexity to the vehicle.

I ended up finding a Geo Metro for sale, for $500. The engine ran fine, and the body wasn't too bad, but I couldn't drive it home because the clutch was messed up. Oh well, this conversion isn't going to use a clutch anyways!

Make sure the car doesn't have anything major wrong with it (other than maybe a blown engine!) You want to do a Conversion, not a Restoration!

Step 2: Remove Anything Gasoline Related

Remove anything related to the gasoline internal combustion system.

That means that you are going to take off:
Gas tank
Exhaust, muffler, cat
Coolant tank
Fuel lines and filter

and anything else you can think of.

Removing all the extra bits saves weight and cleans up the car, making it easier to paint, run wiring, and do everything else in the conversion.

If you remove parts carefully, you can sell them to help cover the cost of the conversion. I bought the car for $500, but then sold the engine, gas tank, and radiator for $550. Free car to convert!

Make sure to not alter any safety gear. In this case, I was careful to make sure the driver and passenger airbags remain intact and functioning.

Here I am removing the gas tank. I had never removed a gas tank before, and couldn't figure a good way to drain it. What a mess!

Here's a video of me literally lifting out the engine with a pulley and clothes line! Hard to answer my phone with my hands full like that!

Step 3: Adapter Plate

You did make sure to keep the transmission, right?

We will use the car's original transmission as a way to connect power from the electric motor to the car's wheels.

The trick here is how to attach the motor to the transmission?

We will make an "adapter plate" out of a chunk of plate aluminum which has holes in it to line up with both the transmission and the end of the motor.

I pulled the transmission out of the car, and flopped it on some tagboard, then outlined it in pencil and marked all the holes.

I then took that and the motor end cap to a local machinist who is also a hot-rodder and knows way more about cars than I do.

He cut an aluminum plate to the size and shape required, complete with carefully aligned holes. The center of the motor drive shaft and the center of the transmission driven shaft need to line up perfectly.

Before bolting the motor and transmission together with the adapter plate, we need to design a coupler that will mechanically connect both drive-shafts.

Step 4: Coupler

The coupler is a means of connecting the rotary power of the electric motor to the transmission to power the car.

While there are a number of ways to do this, including keeping the clutch and machining the flywheel, I chose to keep it simple and use a "Lovejoy"-style connector.

Lovejoy connectors have three fingers and a shaft-hole. Put one connector on either shaft, and a rubber "spider" between the two. Poof! you have a mechanical connection!

Lovejoy couplers are designed with a keyway and set-screw, but both the shafts on this project are splined! Splines are much stronger than keys, but much more difficult to machine!

For the transmission, I took the old (broken) clutch plate and ground off the rivets to get just the middle splined center out. The machinist cut off the ears, lathed a step in the Lovejoy coupler, pushed the clutch spline in there, and welded it in place.

The motor spline COULD have been more of a challenge, as I didn't have any part with a spline on it for the shaft to go to. Fortunately, the motor was double-shafted (one on each end) and the back end went to a drum brake, which was the parking brake on the forklift.

I took the drum brake apart, sure enough, it was the same spines on the back end. I was able to get the very center, splined section, of the brake out, and use it to make the motor half of the coupler.

Line up the motor and transmission, with the coupler halves between them (with the spider in there) and bolt both the the adapter plate.

Congratulations! You have an electric car drivetrain!!!


I ran the car all summer with this set-up, but a few weeks back, it failed. I don't think the issue was the style of coupler. I think the main issue was that I installed the transmission and motor in the car seperate from each other. Because of that, I never got a true center alignment and bench test.

I rebuilt the coupler (with a little help from some friends - OK, I would have been lost without them..) by welding both female splines to a piece of flat steel plate, rounding it off, and adding a tubular jacket.

Then, the new coupler, motor, and transmission were all mounted to each other, tested, centered, and tightened. THEN the whole thing got put it the car.

Been working great since then.

Watch the video - it will make sense.

The first three photos at the bottom are the original "Lovejoy" coupler. The last two photos are of the current one-piece "solid" coupler.

Step 5: Motor

What's an electric car without a big electric motor to run it!?

I bought my motor for $50 out of some guy's garage. He had bought a junky forklift to build his own automotive lift, and had no use the the motor and some other parts.

The motor was very rusty and greasy, but it did spin (not fast or easily) when I applied 12 volts to it.

Rebuilding an electric motor is very easy. There are only a handful of parts to it.
I degreased it, removed the coils and sprayed them with insulating epoxy, checked the bearings, put it back together, and painted it.

I also had the machinist put the rotor on his lathe and take a tiny bit off the commutator. That makes it looks new, and provides a smooth, conductive surface for the brushes to ride on.

I also replaced the brushes, purchasing new ones at a shop that specializes in forklift motors. $50 for the new brushes brings the total cost of $100 for a pretty decent electric motor.

Step 6: Batteries

The motor won't do you any good, unless you have some batteries to power it with.

This car uses 6 x 12V batteries, for a 72V system.

These are Deka Dominator true Gel-Cell batteries. They can not leak or spill acid, nor do they require watering.

I was fortunate enough to be able to get these batteries, slightly used, for $12 each - essentially scrap metal prices!

One downside of these batteries is that they are picky about charging voltage. I was finally able to find a 72V charger designed for these batteries, and got it used for $200.

If I had used the more typical deep-cycle flooded batteries, I could have used a different charger, or even 6 12V chargers, one on each battery.

Four batteries are in the cargo compartment of the car, and two are in front, where the radiator used to be.

For the rear batteries, I cut two pieces of bed frame to lay across the spare tire well, and ran a bolt through the end of each piece down into the frame of the car.

For the front batteries, a few friends came over and helped me weld in a metal tray for the two batteries to sit on. Then I cut two short pieces of unistrut, and ran threaded rod through holes in the tray to bolt the batteries down. I then insulated the front batteries with rigid styrofoam and re-installed the front bumper.

I went to the boat store and bought a "battery charger power inlet". This is a male electrical connection with a rubber cover. Since the gas tank was already removed, I installed the power inlet where the gasoline used to go in.

I added an additional circuit in my garage, just for the car, and have a 25' 12 gauge yellow extension cord with power indicator light in the end, just for plugging the car in with.

Plug it in at night, and it's charged the next morning, automatically.

Update! I later played around with more batteries. With a motor controller that supports higher voltage, I was able to run up to 144V (12x 12V batteries.) At that voltage, the top speed of the car was at least 73 mph, but I really had no cargo space.
Just so you know, Ford Ranger front coil springs fit the back of a Geo Metro, but you have to shorten them.

Step 7: Controller

The controller is an important part of the electric car conversion.

The controller is a solid-state electronic box that controls the power (speed) between the batteries and the motor.

My controller is a Curtis 400 amp peak PWM controller designed for use with series-wound motors. It can run on 48-72 volts.

The higher amperage your controller is, the better your acceleration will be. The higher voltage, the better top speed and efficiency of the car.

Also, keep in mind that amperage is also what defines range in a battery. Capacity is marked in Amp Hours, but draining a battery at double the amps will give you LESS than half the run time! Having a controller running higher voltage will use LESS amps to do the same amount of work.

What's this mean? Buy the highest voltage controller you can afford! 48 volt controllers are cheap, as they are used in so many golf carts. 100V+ controllers get expensive real fast.

My 72V controller seemed to be a good compromise of cost and efficiency. I bought it slightly used on E-Bay for $300.

Follow the schematics available through the controller manufacturer to connect the batteries to the controller and motor with heavy gauge cabling, such as welding cable, with solid, heavy-duty lug terminals on the end.

The controller requires a 0-5Kohm potentiometer as a "throttle". This could be as simple as a $3 Radio Shack part, or as fancy as a purchased, specialty part such as a Curtis PB-6

I split the difference and installed a 0-5K pot inside a free-from-the-junkyard forklift throttle control.

Run the gas pedal cable to the potentiometer, so that when your foot is on the gas, it sends a variable signal to the controller.

Update! I later switched over to running an Open ReVolt motor controller. It's the same one you can find here on Instructables at
That controller is good for up to 144V and 500amps.

Step 8: Other

Currently, the car is insured and registered, although the DMV is still requiring that I drag it in and PROVE that there is no engine in the car before they give me the emissions tesing exemption.

This car can go for 20 miles on a charge, and has a top speed of 45 MPH, the speed limit right outside my house. In town is all 25 mph anyways. My typical ride is 10 miles for going to work, grocery store, post office, etc, and back home.

If I doubled up the battery pack, I should be able to go 30 to 40 miles on a charge.

This project has cost me about $1200 total, including buying the car in the first place. If I would have done the machining myself, I would have only spent around $800 for everything. This car charges at my house through a renewable energy program. All electricity comes from wind, bio-gas, and other renewable energy sources.

I kept the back seat and can carry four people total.

The original driver and passenger airbags are completely intact and functional.

I mostly drive this car in third gear. Turn the car on - put it in third - drive. It's really that easy. There's no engine to kill, so you don't have to push in the clutch before coming to a stop. The motor has so much torque that I can pull away from a dead stop in fourth gear.

I still need to come up with a heater. (EDIT: Please see below) I think I will wear an extra thick coat and gloves for winter driving and have an electric defroster on the dashboard to keep it from frosting. The heat issue has been on my mind since the start of this project. The inefficiency of a gasoline engine is a blessing in a cold Wisconsin winter.

I did gloss over a few steps of this project.
I skipped telling you how many times I took apart, and put back together, the electric motor. How many times I lugged it back and forth to the machinist's. A friend and I were up til 2 in the morning one night fixing the control arm mount! Or how I had to literally shorten the motor because it was too long to fit in the car! But those things are for another story at another time!

I made sure to have an interlock, so I can't accidently drive away while plugged in. Make sure to have a nice big fuse inline of your main battery pack.

All the little challenges of a conversion like this are part of what makes it fun and interesting. In my case, I did a fair bit of experimenting of the best way to run the power brakes.

Winter Heat:
Sure, gasoline engines aren't efficient, but all that waste heat sure is nice in the winter. Since this car no longer has the original engine, it doesn't have the original heat either. The blower motor is still there and works fine for defogging the windshield.
Some EV converters remove the original heater core and replace it with a ceramic heating element that runs on their pack voltage. That sounded like a lot of work, and I was already sick of tearing apart the dashboard.

I already had a household (120V AC) electric oil-filled radiator. I just put that behind the passenger seat, and run an extension cord out the window to a timer.
The heat comes on automatically in the morning and heats up the inside of the entire car before I get in it.
The mass of the oil in the radiator stays hot for about 10 minutes or so after I leave. Most of my trips aren't any longer than that anyways.

I like that with this heat system in that:
1) I didn't have to buy a darn thing
2) The entire interior of the car is already warm - seats, steering wheel, everything!
3) This also helps keep the batteries warm.
4) All the electric power comes from the wall, instead of the batteries

The only down side is that if I am parked all day somewhere that I can't plug in, I don't have that same heat for the ride home. On the other hand, most of my trips are pretty short, so it's not the end of the world.

This heat system consumes about 5 cents worth of electricity per use.

One of the reasons why I chose this car to convert was that it has manual windows, manual locks, manual transmission, non-powered steering,pretty much manual everything - except the brakes. The first time I drove the car as an electric conversion, I found the brakes to be a little hard. (You CAN stop the car WITHOUT power brakes, you just have to push really hard!) It was just a low-speed test drive, but it was pretty obvious that I had to work on the brake system. Power brakes work on vacuum created by the engine. Without an engine to make the vacuum, the brakes just don't work the way they should. 
Some people say to find a different, manual, master brake cylinder and install that, or even just to punch a hole in a certain spot in the cylinder to convert it to manual. Neither of these sounded like great options. Really, I just needed an electric way to make a vacuum.
So, to start out with, I played around with an aquarium air pump, just to learn how the vacuum brake system works. After that, I starting looking around for a 12v air pump with a connection on the "In" end, so that it could be used as a vacuum pump. A friend of mine dug one up, along with an aluminum bottle that had a threaded connector already on it.
I connected the air pump to 12V+ power through a vacuum switch. The vacuum switch measures vacuum in the bottle - if there isn't enough vacuum, the switch turns on the pump.

Now the car has power brakes, just like it did originally, only it's driven by a tiny electric motor in a little pump, instead of by a gasoline engine. Compare this to newer versions of the Prius, where the air conditioning is driven by an electric motor. That way, you can have AC without the engine running!

Step 9: Now You Make One!