Why Electric?

Why Electric?

I have been designing and building electric machines for years. I have also used the electric machines to do many jobs for myself or a neighbor. I have a unique insight into the efficient design of these vehicles. 

The most important thing to consider when building an energy efficient machine is that heat, noise and friction are wasted energy. The closer you can build without one of these three things, the more efficient the machine. (Unless the machine is supposed to make heat, noise or friction).

 I don't want to drone on about tradition and being stuck in old ideas. “ I think that most people get where I’m going with this”. I build electric utility machines. I started out designing and building human powered machines, so I know a little about energy efficiency. 

Let's talk about basic philosophy.

“Any Problem can be solved with enough horsepower.” 

Some designers like to throw horsepower at a problem. I have found that in building human power or electric machines, they need to be built around a fixed horsepower rating. I have a loose horsepower rule of thumb. 

Human power is ¼ to ⅓ horsepower. 

Battery power is up to 1 horsepower. 

AC 120 volt is up to 2 horsepower. 

Keep in mind that electric horsepower is a different rating than gas horsepower. This can be super complicated. Another rule of thumb is to double the electric horsepower of a motor to find comparable output to gas. (More on this later)

The guts of the idea.

I want to do a task. Let's say that the task is moving dirt or softening the ground for planting a crop. I  will compare tilling the ground using gas engine power versus electric energy . 

  The main thing to remember is that anything that is not contributing to the work of tilling or plowing is wasted energy.

Gas Engine.

 Engine and Drivetrain loss. By its nature, a gas engine makes a lot of heat and noise. Much of the energy from the small explosions inside the cylinder are lost in heat friction and noise. The average gas engine wastes about  80% . (We have been throwing this energy away for years.)

 We already know that the gas engine is wasting most of the energy that goes in. The next loss is transferring the circular motion to the implement. 

Here is something that I find interesting. Cars and trucks originally had the engine in the front with the rotation of the engine being 90 degrees offset from the rotation of the wheels. Once the auto manufacturers turned the engines so they were turning the same direction as the wheels and eliminated drive shafts, the gas mileage of the vehicles went up considerably. 

The point is that changing the direction of the source rotation will waste energy. 

The gas engine must always turn at a certain rpm to stay running. Now we have clutches and torque converters along with drive shafts. This is sapping more energy from our original five horse power engine output. 

One more thing to consider.

Spinning or rotating an implement is another waste of energy. For example: The spinning blade of the gas engine rotary type lawn mower wastes a large amount of energy. The rotating tines of a rototiller also sap energy.  A sickle type mower or reel type mower can cut grass with a fraction of the energy used by a rotary mower. 

 A plow being pulled through the soil will do the same work as a rototiller with a fraction of the energy usage. 

I think that I have shown the waste that happens with a gas engine machine. Let’s now look at: 

“Electric design.” 

My wife changed our incandescent light bulbs to LED bulbs. Our  house is lit the same at night, we just use 75 percent less electricity for lighting. This is a great comparison for electric motors to gas engines. LED bulbs create very little heat. Just in case it is not clear, (less heat means more of the energy goes to create light).

Most electric motors are about 85 percent efficient. This is kinda the opposite of a gas engine. My electric walk behind tractor uses a 1 horsepower 12 volt permanent magnet motor. Most people would shake their heads and say “That's not enough power to do anything!”. My walk behind tractor will actually plow faster than our old 5 horsepower rototiller. 

“It is not the amount of Horsepower but what we do with the power”.

My 1 horsepower motor is comparable to 2 to 3 Horsepower gas. The output shaft of the motor is connected directly to the input shaft of the transaxle. There are no clutches or drive shafts. The motor is either running full speed or it is off. The speed of my tractor is controlled by transmission gearing. The permanent magnet motor can also be reversed by changing the DC polarity to the motor.

The tractor motor only moves the tractor. This means that any attachment that goes on my tractor has its own motor. No drive shafts or clutches. All my attachments will have the same direct drive efficiency as the base tractor. 

Why Walk behind?

I like to walk. I even enjoy running once in a while. It is great exercise!. Another great thing about a walk behind tractor is that I don't waste power moving my 180 pound body. I also use my arms to raise and lower the implements. 

Another benefit is that I don't have to climb out of a seat to open and close a gate. If I had to climb on and off a tractor to open a gate I would just leave the gate open, then the chickens would get out and tear up the yard. 

I have noticed that there seems to be a “Domino effect” when it comes to machine simplicity. By defining the purpose of a machine and designing within power limits, we can use less energy to perform a specific task.

 We need to get creative with implement management. Here is an example: the front loader on my “Walk behind tractor” is raised and lowered by my arms. (Simple right?) I get good exercise and I have one less lever. 

  Here’s where it gets complicated..

Let's say that I don't want to use my arms to raise my loader. I will need to have front wheels to support the heavier loader and the hydraulics. I would need a seat or a standing platform. The heavier machine will now need a larger motor which will need more batteries. I now have a four wheel electric tractor. I no longer get any exercise when I work, my yard is a mess because I leave the chicken yard gate open while I am working. 

The given information was mostly estimated (I probably weigh closer to 190 lbs) . I am trying to show a whole new way of thinking. The exact numbers can be argued by those people that love to do those things. If we would have been thinking this way 100 years ago, we would probably have a planet without global warming, an over supply of gasoline and a whole bunch of healthy, happy people…    Think about it.