On Craig's list I happened to find someone selling a "Fun Racing Rider Mower / Go Cart" about 5 miles from my house, for $35. There are links in the ad to his project pictures and a video clip of his boy riding it a couple years ago:
So I got it on Sunday, and I have already removed the 10 HP gas engine (which seems to be in great shape), and I replaced it with a 2 HP 3 phase electric motor. I have not actually applied power to it yet, and I need to adjust the drive belt because the drive pulley is smaller (or I could use a larger pulley. This mod still uses the 5 speed transmission, which had been modified with a 12 tooth sprocket (originally 8) for a speed boost. My new motor is 3450 RPM, similar to the gas engine, but I'll use a VF controller so I can run at slower speeds or even faster. :thThumbsU
Eventually I might remove the transmission and drive the rear axle sprocket with a direct chain drive, but for that I might need a different motor with higher torque and lower RPM. I figure a 9 tooth sprocket and a 1750 RPM 1.5 HP motor will give about 12 MPH and 22 lb-ft torque on the rear axle, which is a bit low. But I intend to use this more as a utility vehicle and fun project, so it should be enough. It should be more efficient without the transmission. And I could use a 1 HP 850 RPM motor which should give 6 MPH with 35 lb-ft torque. On 12" diameter tires that should give about 70 lb of thrust.
:fing32:
Today I actually applied power to the machine and was able to ride a short distance. I had problems with drive train inefficiencies as well as the fact that my long extension cord on 120 VAC, and a 500VA step-up transformer for the drive power, so the fact that it worked at all was an accomplishment. Here is a thread on power and torque losses where I added my observations in light of what I experienced:
Neat project, interesting choice of motor.
I'm not really familiar with your tractor but looking at both your videos I think the belt is on the wrong side of the idler (tensioner)
The pedal seems to be down on the tractor which should loosen the drive belt and apply the brake, when the pedal is up the belt should be tight.
Is the idler a V pulley or a Flat pulley?
I determined that the drive belt was too tight, which pulled the pedal down and activated the brake on the transmission. I put a smaller pulley on the motor but even more effective was making slots in the motor mounting plate so it could be adjusted to the proper tension. I also made adapters so I could connect the motor drive directly to the 240 VAC line, through an extension cord. And I saw that the left front tire was flat, and both front tires were in pretty bad shape, so I replaced them with some 8" wheels I got on clearance from Harbor Freight for $5 each. They have a round cross-section so they should have less rolling resistance and easier to steer.
So, I was able to apply power, and I was able to ride both forward and reverse without stalling, even with the motor speed set very low. I need to reset the motor parameters to get the correct RPM readings, and also add an external control like a joystick for forward and reverse. I still think there is a problem with the transmission. It is difficult to shift, and there is a lot of free play so it seems to take several revolutions of the input pulley to start moving.
I think my next step will be to get free of the umbilical cord and run off battery power. For an initial trial I may just use a couple of 120 VAC inverters through bridge rectifiers and capacitors to get about 300 VDC bus link voltage. The inverters I have are only 175W and 300W respectively, which is just over 1/2 HP, but I think it will be enough to move slowly for a short distance. Even if I use small 12 A-H batteries, they should give 288 W-H, which is enough for 15 minutes at 1.5 HP. That will draw 46 amps which is a lot for such small batteries, but I think starter motors draw as much as the CCA rating, which is 200-420 for those I saw at Tractor Supply Co.
Finally, today, I finished the DC-DC converter which takes 12 VDC from the battery and provides 320 VDC for the three phase motor controller. I used a 17 A-H SLA battery protected by a 30 amp circuit breaker just to be safe. I was able to operate the vehicle at low speed, with battery currents of 15-30 amps, which corresponds to 180-360 watts, or about 1/4-1/2 HP. This was really just another proof-of-concept test, so now I may be ready to mount things more permanently and increase the size of the wiring in order to run at up to 1 or 2 HP. The DC-DC converter will be capable of using two or three batteries, 24 or 36 volts, to keep the current down around 50-60 amps. That should give about 1 HP per battery. Here is a video clip of my "slow ride":
I think this may have never been done before, at least for lawn/garden tractors and rider mowers, although the technology is not really "cutting edge". If anyone would like more details about the project, and suggestions on how to implement it on a tractor, please let me know. The electronic circuitry is fairly simple and the parts are not expensive. You can get the other major components like the motor and the controller for well under $100 on eBay.
nice project !
where did you found the vf controller that accepts DC input? we use them at my office to drive 230/400v 3 phases motors , but with a 230 v ac input only , I guess it's also possible to use a 12vdc-> 230ac converter to feed a vfc ?
Almost all VFDs will accept DC. They are essentially switching supplies, such as those in computers and many other modern electronic devices, and the first thing they do is rectify the line voltage to DC on a capacitor bank. It's often called a DC link. This particular drive will work on 200-400 VDC. Some of the larger drives are designed for 480 VAC motors, and they use a 400-800 VDC link. I just recently bought a used 7.5 HP Toshiba drive on eBay for about $75. The 2 HP Fuji/GE unit shown was a surplus new unit which I bought about 8 years ago for about $50.
This thread sure has piqued my interest in moving forward on an electric rider. Great stuff Paul, I wish I understood this stuff like you do. Genius:congrats:!
I think this may have never been done before, at least for lawn/garden tractors and rider mowers, although the technology is not really "cutting edge".
About 5 years ago, I wanted to run some 3PH equipment in my garage. I only had a 1PH supply. I heard you could use a VFD. Being inquisitive I also discovered that they convert to DC first and therefore can be supplied DC only. I immediately thought of a GT. My thought at the time was to get 16 batteries and a 208V/3/60 motor. I guess I'm still waiting to come across 16 batteries.
I also have a few inverters including a 1500w modified sine wave. Never thought to put them together. Thats a Eureka moment. Can't wait to see your "permanently" install.
The motor is three phase 2HP 240 VAC (it can be rewired for 480). A VFD has a DC link which runs at about 1.4 times the RMS voltage. Mine will work on 200-400 VDC. I made an inverter which is now configured for 12 VDC to 320 VDC, but the same components should work on 24 or 36 VDC, and the output can be 320 or 640 VDC.
Originally I used a 400W modified sine inverter, and a doubler circuit gave me about 300V and I was able to run the motor, but could not get enough power to move. A larger converter probably would have worked. Actually, inside the converter, there is a 150 VDC bus. You could use two converters in series to get 300 VDC, but the output is not isolated so the batteries would be at a high voltage. Or you could get a 240 VAC unit.
If you can get some UPS units you can disconnect the circuitry and drive the MOSFET gates with a PWM signal. I did that with a 650 watt unit, and by using a higher frequency you can get twice the output voltage at the same current for twice the power, with 24V input. But the MOSFETs in the one I have are only rated 55V, and they need to be twice the maximum battery voltage with some safety factor.
I was able to wind my own special toroid on an old Powerstat core. But ideally it could be done using a ferrite transformer, and maybe 100kHz. You can probably use a 12V or 24V high power switching supply, and turn the transformer around, with different MOSFETs of course.
The motor is three phase 2HP 240 VAC (it can be rewired for 480). A VFD has a DC link which runs at about 1.4 times the RMS voltage. Mine will work on 200-400 VDC. I made an inverter which is now configured for 12 VDC to 320 VDC, but the same components should work on 24 or 36 VDC, and the output can be 320 or 640 VDC.
Originally I used a 400W modified sine inverter, and a doubler circuit gave me about 300V and I was able to run the motor, but could not get enough power to move. A larger converter probably would have worked. Actually, inside the converter, there is a 150 VDC bus. You could use two converters in series to get 300 VDC, but the output is not isolated so the batteries would be at a high voltage. Or you could get a 240 VAC unit.
If you can get some UPS units you can disconnect the circuitry and drive the MOSFET gates with a PWM signal. I did that with a 650 watt unit, and by using a higher frequency you can get twice the output voltage at the same current for twice the power, with 24V input. But the MOSFETs in the one I have are only rated 55V, and they need to be twice the maximum battery voltage with some safety factor.
I was able to wind my own special toroid on an old Powerstat core. But ideally it could be done using a ferrite transformer, and maybe 100kHz. You can probably use a 12V or 24V high power switching supply, and turn the transformer around, with different MOSFETs of course.
Or you could avoid all that and just use a 48v DC motor and off the shelf motor controller, or just wire it direct and use the belt drive/hydro trans on the mower you choose to convert. 48v is a good choice for projects this size because all you need is 2 lead acid bats to give decent run times and keep amps low enough.
If all I wanted to do was make something that runs, I would probably use a DC motor and controller and direct connection to 24 or 48 VDC from batteries. But, I am trying to evaluate a concept whereby a standard 3 phase motor can be used for drive power, using a standard AC motor controller, and a simple DC-DC converter which allows the use of only a few batteries and safer low voltage levels, and low current power wiring which minimizes use of heavy copper cables from the battery pack to the motor.
Perhaps I am a bit "different" in that I enjoy the process of designing and building something unusual. And there are some benefits to my alternate design, some of which I will be quantizing when I install my datalogger which will keep track of the voltages and currents over a period of time to determine how much is actually needed for various performance demands.
If all I wanted to do was make something that runs, I would probably use a DC motor and controller and direct connection to 24 or 48 VDC from batteries. But, I am trying to evaluate a concept whereby a standard 3 phase motor can be used for drive power, using a standard AC motor controller, and a simple DC-DC converter which allows the use of only a few batteries and safer low voltage levels, and low current power wiring which minimizes use of heavy copper cables from the battery pack to the motor.
Perhaps I am a bit "different" in that I enjoy the process of designing and building something unusual. And there are some benefits to my alternate design, some of which I will be quantizing when I install my datalogger which will keep track of the voltages and currents over a period of time to determine how much is actually needed for various performance demands.
Nothing wrong with trying new things, the reason I go for DC motors is that I don't know enough about AC, 3phase AC motors to make them work.
I think most of the commercial EVs like the Tesla and Leaf use AC motors, there must be a good reason why they do.
Cars are a bit different from tractors, but many of them use DC motors. I think it's important to learn as much as possible about all types, and weigh the pros and cons. My goal now is to determine the actual power and energy use under various conditions, so I'll have to connect my datalogger to the rig and to a computer and let it collect data at 3 samples per second, while I run with a videocam. Then I can correlate the current and voltage readings to what I am doing, such as climbing a hill or accelerating.
Yesterday, I tried to go for a run and my DC-DC converter malfunctioned. A transint voltage suppressor shorted out. But I thought I had fried my VFD, so I took it all apart and slowly applied voltage, and it was OK. The DC-DC converter also was OK after I removed the TVSs. I do have overcurrent protection built in to the gate drive, and it seems to work well. I really need to make sure I keep the wiring clean and take care to mount everything solidly. The control terminals of the VFD are uncomfortably close to the DC bus link, which has a large metal tab which can be removed for a link reactor. I think I'll replace it with a smaller, insulated jumper, and put a plastic shield over the terminals. I had used a shielded cable for the 320 VDC to the drive, and some strands of the shield were just about touching the control terminal block, which also has an exposed metal link.
A bit more progress to report on my project. I modified the DC-DC converter to run off 24 VDC (two batteries), with 300 VDC output, and after a few problems (including a blown MOSFET from my Part 3 ride), I got it working again. I had to change from the 30A breaker to a 40A, mostly because of high inrush and inadequate time delay, because it draws only about 2.5 amps with the motor off and 5 amps running with no load. Once I got things stabilized I went for a ride, and even on small hills the current draw was generally 15-20 amps, or 1/2 to 3/4 HP, input power. But it was a "short" ride because I had a "short" in two of the MOSFETs. Maybe because I was wearing "shorts"? :dunno:
Anyway, here is a 10 minute movie of my latest (mis)adventure:
After more than a year of inactivity on this project, today I finally made a little more progress by connecting a modified 1000W automotive inverter with an output of 270 VDC, to my 3 phase VFD and motor. It proves the concept works, although I might need a bigger battery (the one I used is an old 17 Ah SLA with a date code around 1999), and maybe a more powerful inverter. I also think I need to do some mechanical work on the tractor because the transmission seems to have a lot of loose play, and there seems to be a lot of friction and about 100 watts of losses, even in neutral. Probably not bad for a 10 HP gasser, but a battery powered vehicle needs to save energy wherever possible.
I decided to take some of the tractor apart and do a good cleaning and inspection. I pulled off the hood and seat assembly and found some rust, but nothing too serious. However, I found that the brake seemed to be inoperable, and I think it may be missing a part. I wire brushed most of the deck where it was rusty, and it looks much better, especially after a quick spray with gray primer. There are two metal pins that seem to function as caliper brake pads which would press against the disk, but they are too short to make contact. The actuation lever has a bent portion that would push on these pins if they were longer, or if there were an extra part like a real brake pad with pins to match the pins already there.
I looked at my owner's annual and found that the missing parts are two fiber brake pads and a backing plate. They were in stock at http://www.searspartsdirect.com and cost a total of about $18 plus $9 shipping, so they are enroute for delivery next week.
Hi this is Peter McDonald with TriVector and i found this forum on Google. I noticed some comments about our new electric tractor that need clarifications. Let me know if you have any questions.
Hi Everybody,
Just found this and want to pass it along to those who may be interested.
http://www.trivectorev.com/Trivector/Home.html
Pix and vids on their site...
Cheerio,
John
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