# Electric tractor Design



## TractorDesign (Dec 21, 2010)

Hi as part of my mechanical engineering design course,

We have been asked to design an electric tractor that is powered by Wind energy.

The details are as follows: 
The tractor will be used on a small scale forestry and pasture farm.
We have a budget of €25,000 
We have decided to design a tractor with 35hp ~ 25kwh
To be able to pull a load of 2,000kg

We are modelling the tractor similar to this one http://www.northerntool.com/shop/tools/product_200445936_200445936

What we need help on is battery choice, size, cost and amount as we are struggling to find solid information dealing with this.
Is there any way you can help?

A NiMh battery seems to be the best value at the moment.

Thanks
TractorDesign


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## major (Apr 4, 2008)

TractorDesign said:


> What we need help on is battery choice, size, cost and amount as we are struggling to find solid information dealing with this.


Just steal Woody's  http://www.diyelectriccar.com/garage/cars/243 

http://www.diyelectriccar.com/forums/showthread.php/woodys-tractor-project-39910.html 

A member called Jim Dear (no relation to John Deere) also is into tractors. And I have a small (& rusty) one. http://www.diyelectriccar.com/forums/showthread.php?t=44430&highlight=etractor 

I don't think anyone here has done exactly what you have in mind, but use the info section http://www.diyelectriccar.com/forums/showthread.php?t=669 and search feature and you can find a lot of basics which will apply.

Regards,

major


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## Jimdear2 (Oct 12, 2008)

Tractor Design,

Not to state the obvious, but whatever tractor you convert you will need to be sure that it has a full frame not a tractor where the engne is part of the chassis.

You might take a look at this youtube of a converted Massy Harris 20 tractor, an older tractor but in the size range you are looking at. He has a number of other videos of the tractor as well. I think he might have a website also.

http://www.youtube.com/watch?v=3F9qmHY5YzQ

His youtube user name is SlungBlade.

You can also see quite a few other EV tractor efforts by just searching electric tractor on youtube.

Since you appear to want a usable farming tractor you are going to want the most energy dense batteries out there. In that case I'm pretty sure you would want lithium. 

If you are going to want working hydraulics you are going to have to research the tractor carefully. I would look for one that uses an external hydraulic pump rather then a internal transmission driven type. you can drive the pump with a separate motor that way.

If you are going to go with wind power recharging you re going to have to have a LARGE fixed storage battery to keep the tractor battery charged and running when their is no wind. A working tractor has to be able to keep going when the work need to be done. Figure at least 2 days worth of storage capacity to recharge the tractor from. (A REALLY BIG BATTERY).

Hope this helps you get started.
Jim


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## PhantomPholly (Aug 20, 2008)

If the source of the Wind Energy is a part of your budget, you are sunk.

Unless, of course, you use a vertical turbine attached to the tractor!


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## TractorDesign (Dec 21, 2010)

Thanks for response, very helpful. The use of wind as our source of energy is only on a practical level. The tractor would be designed to be plugged into a grid, the grid is powered by wind energy combined with other forms of energy so the "no wind factor" won't matter.

However we will be calculating wind farm performance etc etc.

Also we wont actually be building the tractor we only have to develop a design solution. 
The budget is for the tractor and its parts not the wind energy/grid system


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## TractorDesign (Dec 21, 2010)

Ok after a bit of research it turns out for the horsepower comparisons for an EV vs a Fuel vehicle are quite different due to ev efficiency and so our decision to choose 35hp may be too much for what we need. Can anyone confirm this?

Choosing a motor and controller is our next task however this will be based on the hp needed. 

Was looking at series wound motors:
http://www.cloudelectric.com/category_s/531.htm

Also http://www.evmotors.com.au/products/appguide.html

For motors...any thoughts?

Regards
Tractordesign


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## Woodsmith (Jun 5, 2008)

I suppose as a pure design excercise there is good and bad.
Good is that you can chose the best components, bad is that you are reliant on new stock so it costs more.

If you were to be actually building the tractor then you can make great savings with components from a fork lift truck. That would give you the traction motor and the hydraulic pump motor too plus a whole load of other miscellaneous part and cost less then the retail price of a single motor.

The down side is that you don't really know what you will have until you have found a lift truck to break.

One of the problems of a tractor is that you really need a lot of energy to get it to do a proper day's work. Pulling and powering impliments in dirt and mud is hard work and difficult to calculate a realistic energy consumption figure for.


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## Yabert (Feb 7, 2010)

Hi

I think you need to design around the originale diesel RPM engine. Because this one is relativly low (2000-2500 rpm) I think a DC serie motor will be fine with high torque at low rpm. Take the peak torque of the diesel engine and find a DC motor with similare torque.

For exemple a Warp 9" and a Warp 11" motor are rated at 70 lbs-pi and 135 lbs-pi respectivly (95 Nm and 183 Nm). Also, this kind of motor can give more than two time this torque at higher amperage.



> A NiMh battery seems to be the best value at the moment.


No. Go direct with Lifepo4 cells.

And because you don't need high speed, I think a moderate voltage battries pack will be ok. Something like 83v and 300Ah (26 series) will give you a 25Kw/h batteries pack. The main advantage of low voltage is a less costly battery management systems, less wires, connection and chance to blow something.
At the right of this page you can see europeen suplier of cells:

http://www.ev-power.eu/?p=p_55&sName=lifeypo4-big-cells-(3.2v))

You only need to integrate 26 cells under the hood of your tractor.... Good luck!


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## major (Apr 4, 2008)

TractorDesign said:


> We have a budget of €25,000


Hi Tract,

So I guess you are in Europe. They use 72 volt lift trucks over there. I'd see about using the electric system from a fork lift directly. But suggest you look into a Lithium battery. The tractor application is much like that of a forklift. Heavy vehicle, slow speeds, towing capacity (load carrying) and hydraulic accessories. And for this budget, you may be able to get new components from a forktruck company or their suppliers.

Regards,

major


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## Duncan (Dec 8, 2008)

Hi Tractor,

I suggest that you first look at your duty cycle - ie what you want the tractor to do,
petrol or diesel are amazingly energy dense fuels - you will not be able to match a diesel tractor running at full power all day.

Look at the fuel consumption of a tractor doing the jobs you want to do - how many kg of diesel does it use a day?

each kg of diesel is about 46 Mega-joules of energy, about 12 kwhours - but a small diesel in a tractor is probably only going to achieve an efficiency of about 10 - 20% - call it 16% (makes the numbers easy) 

So use 2 Kwhrs for each Kg of diesel used

If your target uses 20 kg of diesel in a day then you should aim at 40 Kwhrs of battery

For a tractor weight is good (within reason) - when you have decided on the kwhours needed look at the weight and cost of the batteries - you may well be best with Lead Acid

Once you have decided on your battery requirements then you can look at motors and controllers


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## TractorDesign (Dec 21, 2010)

Ok back again, 

So we have not made much progress, we have tried to find information on the fuel consumption on tractors as advised above but there is limited information available.

We have been told the power is to be 25kW.

After much research we found the battery that offers us the best option (taking price and effectiveness into account) is Lead Acid. We have researched this thoroughly and are sticking to this decision.

The next part that I can't get my head around is how the tractor uses this 25kW. We have sourced an AC motor. Again we have chosen AC due to much research. 

http://www.everything-ev.com/15-kw30kw-ac-induction-higher-speed-motor-p-461.html

What we need to work out is how many motors we need? One for set of wheels, one for the P.T.O and one for the front loader? Do we need a smaller motor for the P.T.O and for the front loader? 

How many batteries do we need to facilitate this? The amount of batteries that amount to 25kW or do we need more?


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## KenB (Apr 6, 2009)

Since this is only a design exercise, why not try an electric-hydraulic system? Using the electric motor to pressurize the fluid, you could have hydrostatic drive, hydraulic motor for the PTO and traditional hydraulics for the loader and other implements. Much simpler than multiple electric motors.

Ken


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## Duncan (Dec 8, 2008)

Hi Tractor design

you need to do some homework, 
Kw - kilowatts is a measure of power
Kwhrs - Kilowatt hours is a measure of energy

Your battery will need to be sized in Kwhrs - to do your work between re-charges
The amount of power needed to do the work is in Kw

A battery will normally be able to deliver its energy in less than 1 hour

30Kwhrs battery can deliver 60Kw for 1/2 an hour - 

with lead acid batteries there is a thing called the Peukert factor which means that you get less out if you take it too fast

Number of motors
You need to know what you are going to do with your tractor,
For some jobs the PTO is used with the tractor stationary 
- for other like mowing the PTO and the main motor are used together

When mowing you don't need much power for the travel motor but a lot for the PTO
when ploughing you need power for the travel

If you use a tractor gearbox you get all of this and you only need one motor

Please check that AC motor - does it include the controller?
The most expensive part of an AC motor is the controller - the actual motors are simple and cheap


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## jeremyjs (Sep 22, 2010)

Agreed if you go A/C you'll be putting all your money in the motor and controller; and not as much so the batteries. Personally I'd want to do the opposite of that. Put as much of the money as you can into the batteries and use a relatively cheap/big DC forklift motor/controller. You don't need the regen, high RPM or any of the other benefits of the a/c motor; because those things are completely wasted on a tractor.


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## dtbaker (Jan 5, 2008)

why are you stuck on using wind to charge? In typical small farm it would be way easier to use a PV canopy, and just leave the tractor in the field for a couple days if you run out of juice. A friend of mine in Maine did this with a small tractor: see http://www.solarcarandtractor.com/Home.html

It is unlikely you would need or want to pay for regen from an AC motor, even with minor downhills, chances are that if you are 'working' you won't need regen braking. The DC motor/controller is far less expensive and simpler to build.

choosing FLA for battery pack is not terrible, especially for a tractor where weight is good for traction. BUT you have to be careful with the fairly high self-discharge of lead if the tractor is not in daily use... you might consider a few PV panels just to keep the pack charged.

economically, I think you will find that LiFePO4 cells like thundersky or CALB will yield a lower cost per hour of use over the life of the pack...but require 2.5x the initial investment. So whether you go Li or FLA depends on your start-up funds available versus long term operational economy.


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