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Electric or hybrid tractor with 3 phase induction motor(s)

17067 Views 32 Replies 11 Participants Last post by  Kbeitz
For some time now I have been fascinated by electric motors, and after researching the various types I think three phase induction motors (invented by Nikola Tesla 130 years ago). They are very rugged and low-maintenance, needing no brushes or fragile permanent magnets, and only two bearings which may need lube or replacement as long as the windings are not damaged by overheating or deterioration. Until recently, only DC motors were practical for battery-powered vehicles, but with the advent of PWM VF solid state motor controllers, and DC-DC converters, it has become very easy to produce AC from DC.

Other advantages of induction motors are the capacity for very accurate speed and torque control, and they can be used as a generator when the shaft is powered faster than the drive frequency, so they can be used to replenish the batteries when coasting downhill and braking. And if a motor is designed for frequencies higher than 60 Hz (such as 400 Hz), the size and weight for the same horsepower is reduced by the same factor. So you can get a 5 HP 400 Hz motor about the size of a coffee can.

So far, only special purpose motors, such as used in aircraft and military applications, use 400 Hz motors, and as such they are very expensive and rare. A common three phase 60 Hz motor will run at higher frequency and RPM, but they are limited because the voltage must increase with frequency in order to get higher HP. So a 208/240V motor might only be able to run safely on twice that voltage, or at most 600V, which is the limit for what are technically called "low voltage" systems.

Also, there is a safe limit to the speed of the motor. A two pole motor runs at close to 3600 RPM at 60 Hz, and speeds higher than 7200 RPM may be unsafe and not very useful. A six pole motor is about 1200 RPM, and an 8 pole is 900 RPM. Lower speed motors are generally larger than their high speed equivalents, since they have higher torque for the same HP, and also the windings have more overlap, which needs more space.

I have addressed these problems by winding my own three phase six pole motor, from an old single phase 120 VAC motor, and I used less turns of heavier wire so that it runs at about 9 VAC at 60 Hz. Then I used a three phase VF drive and some step-down transformers to run the motor at up to 240 Hz, it which it ran at about 4800 RPM. But I don't know how efficient it was. It drove a decent size fan, but I didn't have a good setup for testing, and you really need a solid test table and some way of protecting the operator in case something breaks or comes loose.

I'll end this post here, and continue my discussion in following posts. I'd like to present some ideas and discuss their pros and cons. I can offer a fair amount of experience in electrical and electronic systems, but I'm not as much skilled at mechanical devices in general, or tractors in particular. Maybe we can collaborate on an exciting new project that AFAIK has not been tried before. :fing32:
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OK, so I'll present a few ideas and see if anyone has any interest, comments, or suggestions. Originally I wanted to develop a hybrid conversion package for FWD automobiles, by attaching electric motors to the rear wheels, and thus providing AWD capability, as well as an alternate source of power if the gasoline engine failed. But cars are very difficult to work on and there are issues with street legality and practicality. My 1999 Saturn already gets 35 MPG average and up to 45 highway, so I'm probably not going to improve on that very much. So I just did some preliminary design concepts and left it at that.

A friend, who is an aerospace engineer, has a sideline where he is developing simple farming implements and a multipurpose power module which uses a 9.6 HP diesel engine which can burn 50% vegetable oil, and he also has a press which can extract the oil from crops such as corn or sunflowers. He's targeting small villages in Africa as a way of "empowering" the people to be more self-sufficient, and utimately this will be important for people in the US as well, because of "peak oil" and economic instability.

He has been looking at DC motors that can be used as generators as well as power sources based on battery storage and renewable energy sources such as solar and wind. But there are some problems with brushed DC motors as well as BLDCs, with respect to efficiency and cost. I want to investigate the practicality of using three phase induction motors for this purpose, and perhaps making an electric tractor would be a good proof-of-concept project. Here is his website page on sustainable technology products:

He has something called an "EmPower Train", which is something like a garden tractor with the ability to pull various implements and carts linked together as a "train", and there is one concept which uses a simple track which allows the train to run unattended or by remote control.

I had conceived something like this a while ago, when I wanted to build a "train" which could travel up the hill on my property and then load it with firewood, so that on the return trip it might regenerate much of the energy used, by employing dynamic braking, charging the batteries or ultracaps. I thought it would be "cool" to have a train, but practically, it would not be able to negotiate the steep grade (15-20%), and reducing the grade to rail specifications (<5%) would have required extensive switchbacks and longer rail lines. So, another project mothballed.

In my next post, I'll try to present my latest idea as it applies to small tractors, and discuss some technical details about energy storage, efficiency, and practical ways to make something new and useful.:fing32:
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And I'll be eagerly awaiting! Interesting ideas, Paul!
Wow... You got my attention.
I love playing with electric, fuel cells, regenerative braking, Wind mills, Water wheels, DC, Ac, and whatever. I want to make an electric rider but I want to stay away from the expensive controller. I want my electric motor to run wide open all the time and change my speed with a transmission something like the Zero max gearbox. I'm also wanting a very heavy flywheel.
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You've got my attention as well! I've always thought about an electric garden tractor conversion in the back of my mind, but never had the understanding needed to develop the idea further. I took an electric vehicle class, but we only got into a basic theory and never played with different specs. I like your ideas!
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hey ps excellent post.check out the older lindsey tech. manuals have alot of books and papers on motor winding and such,from tesla himself.tried a few a former machinist im more set up for such applications.not hard to build jigs for spinning windings.or cutting shafts.and if you want to tackle a 30% grade simple weight and gearing can accomplish it.was going to do an articulated.but abandoned it after design to try a zero turn (like hustler zero) would buy one but the price tag is a big shocker to me.will post pics on her in the next month or so.just figuring out how to post pics.
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Although I think three phase induction motors are ultimately the best, there are other technologies that may have some merit. I found a 3200 watt servo motor on eBay for $150: That's about 4 HP, which is continuous power, so it's about equivalent to a 8-10 HP fossil fuel engine which has relatively narrow power/torque/RPM curve. The same type motor new is about $1200-$1600, and a controller is about $1000:

But you also need a power supply, and such a motor needs 180 VDC or more. But you can get that with an inverter and one or more 12V batteries. You can get a 2000W inverter for $150: A 12V 100 A-H battery is about $240:, and two of them will provide 2400 watt-hours, or about 0.8 hours running time at full power.

It's rather pricey for a 4HP conversion, but the components (except batteries) should last a lifetime with little maintenance. If you can find the motor and controller at deep discount or surplus like the eBay motor, this would be a reasonably priced project. I would consider doing this myself on my old Simplicity Broadmoor, but I really want to use a three phase induction motor.
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I just picked up two 3ph 2hp PM DC brushless motors to play with...
To many toys and life is short...
Very interesting stuff guys. I can see the desire to work w/ brushless 3 phase motors.

You guys clearly have a decent knowledge of this stuff, I wish my knowledge of it was deeper.
Here is what appears to be a good study of BLDC motors:

I like to use Microchip PICs for my projects, so here is an app note about BLDCs (made easy):

Here is part 1 of a multi-part video on BLDC control using a PIC:

Here are some videos about induction motors: (PIC VF drive) (homemade motor) (unwinding a motor) (Baldor motor mfg GA) (20kW BLDC hub motor design and test) (induction motor overclocked to 9000 RPM) (stepping motor at 9375 RPM) (7500 HP motor!)

Fascinating stuff. It can be addictive, following the related videos. But hopefully some of this will be helpful in determining your choice of motor and drive technology. I may make a video of my home-made three-phase motor I made several years ago, before I had a video cam. And I have some larger motors that I might rewind for lower voltage so I can overclock them for more HP. I also had a motor and generator from an electrical engineering college, but I gave them away:

DC Generator, 4000W

Universal Machine:

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Opps ... I found out my motors are Pm AC brushless motors. But they act like DC.
Opps ... I found out my motors are Pm AC brushless motors. But they act like DC.
I think they are really the same thing:

Actually, it can be argued that all motors are AC, since they must have a rotating field, but "DC" motors just have a mechanical means (commutator) to produce the AC. And in an extreme philosophical sense, it can be said that there is no DC, because it had to start from zero and eventually will return to zero, so it may just have a very long period. :)

And there is the homopolar motor, which runs on DC
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thanks for the links Paul, I got some more reading to do LOL.

Oh, and now we get philosophical too, I like that :)
I think they are really the same thing:

Actually, it can be argued that all motors are AC, since they must have a rotating field, but "DC" motors just have a mechanical means (commutator) to produce the AC. And in an extreme philosophical sense, it can be said that there is no DC, because it had to start from zero and eventually will return to zero, so it may just have a very long period. :)

And there is the homopolar motor, which runs on DC
Now I see why it's easy to get a shock from one of these motors.
Neutral is connected hot and to ground.
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90hp electric pulling tractor from last year, couldn't find video of it from January, was lots better:
Here is some technical discussion from the usenet newsgroup

I'm looking into a battery-powered small vehicle (tractor) design which will use a three-phase motor and VF controller, and I want to create the DC bus, or link, voltage from several 12V SLA batteries. I will need 360 or 720 VDC for 208/240 or 480 VAC motors.

I thought about using some of the inexpensive modified sine wave inverters available from Harbor Freight and other companies, where a 2000W inverter can be obtained for about $150. My first thought was to rectify the output and filter it, to get about 180 VDC and then use two or four in series for the higher voltages. But I think these inverters create their own DC bus using a switching power supply and then use high voltage transistors or IGBTs in a bridge which produces the modified sine wave.

I have searched for schematics but most of them are for simple inverters using a 60 Hz power transformer driven with a square wave, but that's not what I want. And other schematics are like the reference designs for UPS systems, which are probably similar to what I want, and they can have either modified sine wave or true sine (PWM) outputs. It's probably not hard to design and build my own, but if I can use off-the-shelf inverters then I'll be ahead of the game.

My next step is to open up one of the small inverters I have to see how they are made, and maybe discover and measure the DC bus voltage, but if anyone has the actual schematics for one of these, I'd appreciate a look at it. Otherwise, I'll let you know what I find.​


> You could also look for literature on DC-DC converters. You need a
> honkin' big one, and if you're designing from scratch, and to a point
> the higher the input voltage the better off you'll be -- the currents
> are lower, and the transformer turns ratio is less. But you're getting
> into some pretty serious power levels, which means that the design
> of the supply isn't trivial. If you want to focus on tractor-building
> and not power supply design, then finding some existing thing and
> hacking it is the way to go.

I think off-the-shelf DC-DC converters at the power levels I'm looking at
will be rare and hugely expensive. I'm sure I won't find any for as little
as $100/kW as the Harbor Freight units are. And this is now a
proof-of-concept design, and targeted to people who have tractors and want
to do a conversion. See my thread(s):

And I have an idea for a simple DC-DC converter. I can use a nominal 500VA
toroid and rewind it with less turns of much heavier wire, and drive it with
a 600 Hz square wave. It should be able to produce about 5 kVA, and such a
toroid is about the size of your fist and costs only about $50 and is much
more rugged than ferrite cores for higher frequency magnetics. I think it
will work out about the same size and efficiency as a high-tech 5000W
switching supply, but it can be much simpler to build.

> See the comments about just using battery voltage -- they're well
> meant and meaningful. In particular, keep in mind that if you rip
> all the wire out of a motor and rewind it with thicker wire, filling
> the space just as efficiently as it was filled before, you end up
> scaling the current up exactly as much as you scale the voltage
> down -- so all the efficiencies, maximum torques, etc., stay the
> same, just at a different voltage vs. current.

Actually, I did that very thing about 8 years ago. I pulled the original
windings out of a single phase 120V 3/4 HP fan motor, and rewound it with
much heavier wire (something like #18 or #16). And I converted it to a 6
pole three phase motor. It was designed to run on about 8 VAC so that a 12V
battery could drive it directly, and I wanted to be able to overclock it by
about 4x. I used a 2HP VF motor controller running on 240 VAC single phase,
and I used two step-down transformers to match the motor voltage. It ran OK
at 180 Hz with a fan load. And I made another motor that I drove using a
three-phase bridge and modified sine wave (rectangular wave) directly from a
12V battery, using a PIC controller.

Here is a picture of the stator:
It's probably not filled as tightly as the original windings. I wound by
hand rather than making belts externally and then fitting them in the
lamination slots.

My ultimate goal is to make a low-voltage motor that can be overclocked up
to 6x (360 Hz), and theoretically get 6 HP from a 1 HP frame. I have some
motors that I got cheap with the intention of rewinding them, but it's
difficult to do so with the heavier wire, and I am hesitant to rip out the
windings from these motors since they are new and unused. So, first I want
to use them as-is, and maybe overclock the 1.5 HP 240/480 4 pole motor to
2x, which is 3600 RPM, same as the gas motor in my tractor, and I was going
to use a 480V controller so I can get as much as 3 HP. The gas engine is
about 7 HP peak, while the induction motor should be able to produce 2x to
3x normal as peak, so it should be about equivalent. This is the tractor I
may use for this project:

> Of course, if you string 30 12V batteries in series then you have
> your 360V DC rail right there. Just don't lick your fingers and
> touch them to the end points to see if the thing is live.

30 batteries will be a problem. I'm looking at using 100 A-H SLA batteries,
so two of them with 12V-120V inverters should give me the 360V I need, and
2400 W-H which may provide up to one hour running time at 3-4 HP average.
Then I can go with 4 batteries to get 2 hours or twice the power.

I'm really focused on using a three-phase induction motor rather than the
more expensive and fragile BLDCs and PM or series wound brushed DC motors
that are the usual technology.​


> Essentially there is a 12VDC to 170VDC converter in there that turns
> on and off. This is followed by a full-bridge that switches output
> polarity at mid-point of the off-phases. That's pretty much it.

I found a 150 VDC bus in the 175 watt unit I took apart. And the switching
frequency is 43 kHz. The transformer is quite small, a little over 1" cube.

> Mind that super-cheapo versions sometimes save a few pennies or
> "boost efficiency" by only generating 160VDC and roaching that on
> top of the incoming 12VDC. Then the input and output are not
> isolated. This has resulted in some "interesting" experiences for
> some folks. "Yo, dude, why's there smoke comin' out of your camper?"

I had thought it was isolated. So that makes it riskier to use two of these
in series from separate batteries, as at least one of the batteries will be
about 150 volts above the other. I measured the resistance from the input to
the output and there is no direct connection. But from the schematic you
provided, that's probably because the output is bridged by MOSFETs, which
have high resistance until turned on.

> Here ya go:


That's very helpful. It looks like the 150V bus could be isolated by
removing some of the output components and the connection of the diode
bridge to battery +12V. But that defeats the purpose of using an
off-the-shelf component. I think I can make a simple DC-DC converter that
can produce, say, 1200 watts at 180 VDC for each battery, with isolation.
Then I can use two or four in series for 360 and 720 VDC bus voltages, for 3
HP and 6 HP. I could make them as modular components designed for series and
parallel connection, and have a way to produce a regenerative charging
current during dynamic braking (although that might not be very useful for a
tractor unless it is used for frequent up/down trips rather than, say, lawn
mowing where it needs power at all times. I could also add ultracaps for
surge power and energy storage, so the the battery would see only average
current within its more efficient range, but they are expensive.​


> I have a AC-Delco 2500W Msine inverter. No schematics, but it has
> 2 front end converters ~170VDC stacked for 340ish VDC.
> Which is then switched at 60 hz into AC. There is a common ground
> point, so there is +/- 170V to the output.
> Looks like this...
> <>

> Must have been a school project, uses a TL494!

That particular model was sold out, but they had others from 200 watts up to
6000 watts. The 900 watt model was the lowest price per watt, at $0.07. Most
of the others were about $0.10/watt, which is about what the Harbor Freight
units sell for. It does seem to be better to design this from scratch, and I
think it should be possible to make it for less than $0.05/watt.

A 200 VA toroid kit is just $63:
This is a toroid core prewound for 120 VAC 60 Hz, and has 0.23 V/turn. I
would just remove the primary winding and replace it with something like 10
turns of much heavier wire (probably actually four or more wires in
parallel), which would be about 23 VAC at 600 Hz. Maybe with a center tap
for 12-0-12. Then I would wind a secondary with 140 turns, for 320 VAC. A 12
volt square wave using a center tap design with just two power transistors
in push-pull should produce a square wave output with 320 volts peak, which
can be rectified to 320 VDC for the link voltage. This should provide up to
2 kVA, more than enough for a 2 HP motor. The battery draw would be 167
amps, however, so I should really design for about 1000 watts average for
each module.

In that case, I could even use the smallest (80 VA) toroid kit, which is
just $52, and should provide at least 800 watts for 1 HP, and a more
realistic 87 amps draw. I'm sure I could get the unwound cores for much
less, and even have them custom wound, for under $100. Then a pair of husky
MOSFETs like IRFB3077 at $3.50 each, a 5A 600V bridge and 470 uF 450 V
capacitor, controlled by a PIC or SG3526, and a few minor parts, and I'll
have a 1 kVA module that can be connected in series or parallel with its own
battery for the voltage and current needed. The whole thing should fit in a
2" x 4" x 6" metal box which will be a heat sink for up to 100 watts if it
is only 90% efficient.

Well, maybe that does come out as more than $0.10/watt. But if I made
thousands of them, the cost would go way down. And the biggest expense will
be the batteries, at about $200 each:
I couldn't find actual technical specs, but this seems to be the battery: Force Heavy Duty Brochure.pdf

It seems like a good battery, but actual A-H capacity seems to go down
sharply even at an 8 hr. rate compared to 20 hr. and 100 hr. rates. So I
probably need to design for no higher than a 4 hour rate for continuous
duty, so a 100 A-H battery would be good for only 25 amps. Yeah, battery
technology is really the kicker for practical EVs. Here is a pretty good

Thanks for the reality check.​


I did a little more investigation, and found some Lithium batteries designed
for EVs. Here is a 100 A-H battery for $150:

But it's only 3.2 volts so four of them are needed for the same W-H capacity
as the Lead-Acid. So about 3x the cost. Here is the spec:

But the good news is that it holds 3 volts even at 100A draw (1C), and can
even handle 5C surges. Here is more information from a US distributor:

Their home page has some interesting
information. They show about $10,000 for a complete system for an ordinary
car, for 100 mile range with a 500 pound battery pack, and an expected
lifetime of 200,000 miles (about 2000 charge/discharge cycles). A typical
small car is probably about 40 HP, so a 4 HP tractor might be only about
$1000 (although $2000 is probably more like it, since it probably does not
scale linearly). So 10 batteries will give 3000 W-H or 4 HP for one hour,
and cost $1500. The other components could probably be purchased/built for

Things may become even more interesting, and EVs more competitive, when
gasoline passes the magic $5 point (probably within a year), and if battery
technology can cut the present costs in half (which I think is very

And I'd also like to put a datalogger in my controller to determine how much
power and energy are actually needed for various lawn tractor needs. I have
a feeling that basic lawn mowing on a flat surface might take only 1 to 2
HP. And hills may average out if some regeneration is possible. Of course
there will be some tough jobs that require raw power, and for that a diesel
engine may be the way to go. I just bought a diesel lawn tractor with a 15
HP Kubota engine for $1000, and you can see it in action at, or go for a ride with me at


These are the sorts of technical questions that must be discussed for EVs. I learned a lot from my research, and there is still much to learn. EVs are very impressive for "short" time (pun acknowledged) demonstrations like the weighted sled pulling. But practicality will be determined by the ability to do the usual work of mowing a lawn or clearing snow and such, which involves a certain amount of power over a certain period of time.

Has anyone actually measured how much power it takes to mow an average lawn with various size mowers? This is difficult to do with a gas or diesel engine, but a battery powered vehicle can easily record the average and peak current draw (and power), as well as total energy usage. It can probably be estimated by knowing how much fuel is required for a certain job, and then estimating the efficiency (probably 40% or less) and calculating the BTUs (or kW-hr) of the fuel used.
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One thing you may want to research is VFDs (variable frequency drives.)

A VFD is often used to manipulate the speed of a 3 phase motor, and are relatively inexpensive. Most VFDs take in the 3 phase line, rectify it to DC, then modulate a 3 phase variable frequency/voltage out to the motor, including rotation reversal if required. If you could configure a battery bank or set up an inverter to match the VFD's DC buss voltage (need to find that out in the tech data) and make a charger, you'd have a very powerful setup.
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There are low volt induction motors currently available for golf cart use that have controllers that might work for you. The only problem is that your motors are wound for a higher voltage which means lower rpm. Also, I have read a post on another forum where a converted Simplicity 728 is pulling between 70 and 100 amps on 48 volts when in use(mowing), this comes out to 3,200 to 4,500 watts or 4 1/4hp to 6hp.
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Yes, I have a GE Fuji AF-300E11 that I used for testing my low voltage three phase motor. It is rated at 208/230V 3 phase 2HP but also works for a single phase 23V input. Its efficiency is supposed to be 94.8%, and it will work with a DC link voltage above 200 VDC, and overvoltage is 400 VDC. It can run a motor up to 400 Hz. There is a provision for an external potentiometer which can be installed on a foot pedal for an accelerator. It's a nice unit and I bought it new on eBay for about $60.

I also have an IDM CIMR-H3.7G2-E-10 which is a 10 HP 480 VAC 9A unit, but the controller section doesn't work, and it's just about impossible to get parts and service. But I plan to make my own controller and I can use the power components, although it's a much bigger enclosure than more modern units. I need the 480V unit so I can overdrive the motor to get 2x HP.

I might bid on this 4 HP unit:
or this 5 HP unit:
or maybe this 12 HP new unit:

I'm working on the DC-DC converter now. It will be about 1000 watts which will draw about 85 amps from a 12V battery and produce about 300VDC at 9.5A for the link voltage.
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There are low volt induction motors currently available for golf cart use that have controllers that might work for you. The only problem is that your motors are wound for a higher voltage which means lower rpm. Also, I have read a post on another forum where a converted Simplicity 728 is pulling between 70 and 100 amps on 48 volts when in use(mowing), this comes out to 3,200 to 4,500 watts or 4 1/4hp to 6hp.
Thanks for the link, but 18 HP is more than I need and 350A at 36-48V means a huge battery pack. And the $2000 price tag is daunting as well, although it's reasonable for the package. If they had a 5 HP unit for $600 I might go for it. But also I find much of the fun is the challenge of a novel design.

For a specific motor, higher voltage generally means higher speed, and higher current means higher torque. The speed of an induction motor is related to the number of poles (N) and the drive frequency (F), which determines the synchronous speed (120*F/N), and actual speed is about 10% less under load because of slip.

That's probably a good figure for the power draw on the Simplicity while mowing. But I'd like to see for myself. :fing32:
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