Convert Your Lawn Tractor to Electric Power

This versatile electric tractor is a super DIY project.
June 12, 2008
http://www.motherearthnews.com/diy/electric-garden-tractor.aspx
This lawn tractor uses no gasoline and hauls wood, plows snow and more.


KEN ALBRIGHT

Ken Albright of Columbia, Mo., converted a Case lawn tractor to run off battery power instead of gasoline. Mother Earth News interviewed him about the process.

Why did you decide to convert a garden tractor to electric power?
I bought 10 acres and needed some sort of equipment to help take care of the place. So I intentionally bought a used tractor that would probably need a new engine soon. I had already converted a car to run on batteries and really liked the result. Running on electricity does not directly produce any air pollution and is much quieter. The secondary pollution from producing the electricity is still much less than that from burning gasoline. And of course, there is the possibility of producing electricity with solar or wind power. Long range, I hope to charge the batteries via the sun.

How long did it take you to complete the conversion?
About 16 hours spread over a week.

How much did it cost?
About $1,100: the motor was $600; batteries, $300; welding, cable and miscellaneous parts, $200. The motor price was probably overkill. A good scavenger may find a motor for little or nothing from a floor scrubber, forklift or golf cart.

How long can you mow on one charge?
It is currently not set up to mow. I have been distracted with gardening and have not had the time to tinker with the mower. Its tasks for the immediate future are hauling wood (pulling a trailer) and plowing dirt or snow. When I'm using it hard, as in moving dirt, I get about 45 minutes of use before I start noticing a lack of power. Pulling a trailer full of wood, I get well over an hour of use. Like any machine, it depends on the effort required.

What parts are required?  
The basics are an electric motor, batteries, mounting brackets, wiring and switches. Some tractors may need a motor controller. If auxiliary systems such as lights are desired, a voltage converter may be required.

What kind of donor mowers work best?
I chose the Case tractor because it is driven by hydraulics. The motor turns a hydraulic pump, and that system does all the work. I chose that so there would be no need for a motor controller. The motor is simply on or off. Hydrostatic drive tractors and mowers would be similar. Straight mechanical drive, using gears, would require a motor controller to vary the speed. That would add to the conversion cost, but would likely also be more efficient. There are energy losses in hydraulic and hydrostatic systems.

Beyond that, you’ll want a strongly built and not-too-rusty chassis. The batteries are heavy. Many newer riding mowers have little metal in the frame and probably would not last long carrying the extra weight.

What are the basic steps in the process?
Remove the gasoline engine and associated parts. Mount the electric motor in its place. Find a place to put the batteries. Wire it up and turn it on.

What are the most difficult steps in the process?
The motor mounting and the battery placement are the most challenging. In my case, I needed to mate the motor to the hydraulic pump. I took the old bracket from the gasoline engine to a machine shop and had them alter it for me. At the same time, they extended the bracket to allow me to mount it on the tractor frame. This resulted in the pump ending up in the same position it started.

Placing the batteries was just a jigsaw puzzle process: lots of head scratching, measuring and sketching.

The wiring requires attention but is not difficult. In my case, I'm using three 12-volt batteries, connected in series to produce 36 volts. This is a good voltage to use because lots of golf carts, forklifts and other industrial equipment use this voltage. So, motors and control parts are readily available. I used the on/off switch (contactor or solenoid) from a golf cart. Knowing how to wire batteries in series to produce the desired voltage is important — doing it incorrectly could result in an explosion. Also knowing how to wire the switch is important. If a controller is involved, it gets more complicated. Likewise, if a 12-volt system for lights were involved. Basic knowledge of electricity and a thoughtful approach will prevent trouble.

Resources

Electric Tractors from Mother Earth News

Electric Tractors from Renewables.com

Solar-electric Mowers & Tractors

Converting an Allis-Chalmers "G" Cultivating Tractor into an Electric Vehicle

Electric Tractor Company

Electric Vehicle E-mail Discussion List

Books

Build Your Own Electric Vehicle by Bob Brant
Convert It by Michael Brown