Electric ATV Conversion Project

I’ve been following the electric vehicle scene for many years and I decided it was time for me build an electric vehicle of some kind.  I thought I would start off small, and I had seen very few electric ATV conversions on the web so it seemed like a good first project that I could work on with my sons.  I don’t think anyone has built one with the same performance and features.  In addition to the electric drive conversion, I also set it up so that I can attach and power electric implements, making it more useful than just something to drive around.

ATV Before Conversion

I bought a used 2004 Polaris Sportsman for this project which was in good running condition.  I wanted something in good shape considering all the time that would go into the conversion.  The shot below is what the ATV looked like before I started any work.

The main reason I chose this ATV model is that the engine and transmission are separate units, which you will see later made the conversion quite a bit easier.  In some ATVs the engine and transmission are contained in the same housing, and this would have made adapting the electric motor drive much more difficult.  The specifications of the stock ATV are as follows:

  • Engine:  single cylinder 4-stroke 500cc, peak HP=38@6600RPM, peak torque=33 ftlbs@5400RPM (at crankshaft)
  • On-demand all-wheel drive
  • Electric winch
  • Transmission:  2 forward speeds and 1 reverse speed, plus continuously variable clutch drive between engine and transmission
  • Towing capacity 1200lbs
  • Dry weight: 700lbs, GVWR: 1200lbs
  • Full specs can be found here


Here is my engineering team for this project, having one last “ride” on the ATV before taking it apart:

From some of the photos below you can see they were gung-ho on taking it apart, but later on when it came time to do the more time consuming design and assembly it took more cajoling to get them to stick around.

The picture below shows the original continuously variable clutch drive between the engine crankshaft and transmission input shaft.  This is the same kind of drive commonly used in snowmobiles.  The previous picture above shows the clutch pulleys removed from the engine and transmission, and this makes it fairly clear that to convert it to electric, it was “simply” a matter of driving the input shaft of the transmission with the electric motor.  The two-speed gearbox used in this ATV was ideal since it would have a low speed for any maneuvering or pulling jobs, and a high speed for getting around on the road.  The transmission ratios between the input shaft and axle for Low, High and Reverse are about 26:1, 10.5:1, and 16.5:1.

I found out there is a good market for used parts for these ATVs, so all the parts we removed will be sold and useful to someone else.  Basically everything related to the engine including fuel tank, fuel system, exhaust, cooling system, air filter, etc. all came out.  The complete dis-assembly took the three of us about 3 hours.  We also took out some of the original electric system related to the engine ignition, but left in all wiring necessary for the electronic console that displays gear selector, odometer and also controls the on-demand front wheel drive.  The 12V battery was left in, which will be charged from the main traction battery pack as I will describe later below.  The total weight of all the removed components was about 100 lbs.

The Electric Drive Components

The main components of any electric conversion are the traction (drive) battery pack, electric motor, and motor controller.  There were many smaller components used in the conversion that I will describe later below.  The two main choices I considered for the battery were lead-acid and lithium.  The main advantage of lead-acid is a lower initial cost.  However, the cost of lithium batteries has dropped considerably over the last several years to the point where in the long run the cost of using a lithium battery is lower than lead-acid.  Lithium cells can be recycled at the end of their life, but they can also be used for other less demanding electric storage applications when they no longer have sufficient capacity for an electric vehicle.  There are other pros/cons to consider when choosing a battery and this issue generates a lot of discussion on the electric vehicle conversion forums.   More about the basics of lead-acid vs lithium can be found here and here.

After quite a bit of research I decided to use lithium iron phosphate (LiFePO4) cells.  LiFePO4 is the chemistry of the cathode material used in the lithium ion cell.  The main reason I chose LiFePO4 is that they are very safe and do not have any problems with thermal runaway and fire like some other types of lithium chemistry cells.  In past years there were some laptop fires caused by lithium cells, but these were a specific type of lithium chemistry (LiCoO2) combined with poorly designed battery management systems.

After taking measurements of the frame and figuring out where all the cells and other components would be installed in the ATV, I chose 100Ah cells made by Calib Power Inc.  These cells have a nominal voltage of 3.2V, weigh 3.2kg(~7lbs), and are 142mm x 67mm x 218mm (~5.6″x2.6″x8.6″).  The cells have a maximum discharge current rating of 800A for short periods of time, so a single cell can provide about 2.5 kW of peak electric power (~3.3HP).  In most electric vehicle applications the general rule-of-thumb is that the battery pack should be designed so that the vehicle is drawing less current than 1 times the Ah capacity of the cell (1C) the majority of the time to maximize battery life.  So for my 100Ah cells that would be a current of 100A.  Each cell looks like the photo below:

I wanted to have a significant amount of battery capacity to allow the ATV to have a good driving range and also because I would be using the ATV to drive electric implements.  So the total number of cells that I ended up installing in the ATV was 32, which gives a nominal battery pack capacity of 10.24 kWh.  To maintain good battery life, the cells should not be discharged to less than 20% of their full capacity, which means the battery pack in the ATV has a useable capacity of about 8 kWh.  I’ll translate this to what this should mean for driving distance later below.  Since each cell weighs 3.2kg, the total weight of the battery pack is about 102kg (225lbs).

The motor I decided to use is made by High Performance Electric Vehicles, model AC-20.  This is an AC induction motor specifically designed for electric vehicles, and is shown in the picture below.  The motor weighs 50 lbs and is 6.5″ in diameter x 12.5″ long.  The motor has a continuous rating of 13HP and peak rpm of 6500, and with the motor controller I am using a peak rating of 37 HP and peak torque of approximately 75 ft-lbs.  Unlike the original engine, the peak torque is available at zero rpm and the torque curve is fairly flat over a wide rpm range and then slowly decreases at higher rpms (which makes electric motors actually more suited to power a vehicle than an engine).  So in comparison to the stock engine that was in the ATV, the electric motor produces about the same peak HP and a little more than twice the peak torque.

The motor controller that I used is made by Curtis Instruments, model 1238-7501.  It has a nominal input voltage range of 72-96V, a 2 minute current rating of 650A, and a 2 minute power rating of 74kVA.  The controller is programmable and can be set up to use in many different applications.  For electric vehicle applications it has the benefit of allowing regenerative braking, electronic forward and reverse, and has multiple safety fail-safe features.


I completed the project in 2012 but have not been able to add to the writeup on the conversion here lately.  You can find more information about the project at the evalbum.  The project was also featured in the February 2013 edition of Current Events, a publication from the Electric Auto Association.


16 Responses to Electric ATV Conversion Project

  1. WarrenCY says:

    Cool project…want to convert a mx-5 next!

  2. Gordon says:

    Did you finish your project? I am looking at converting my Polaris Sportman 400 and would like to know how yours works.

    • Hi Gordon. Yes I finished the majority of the project last February but have not finished my write up here yet. The only things I have remaining are to attach the air cooling system that I have built, and build a guard around the synchronous belt that runs between the motor and transmission. I also plan to finish the electric snowblower attachment over the next several weeks.

      I would be happy to answer any questions you have, and also send you a bunch of pictures I took during the conversion. The performance of the machine exceeded my expectations. I am willing to bet that it would take any ATV in a drag race – it certainly outperforms the original stock machine.


  3. Robert Y. says:

    Great project and nice intro write-up. I’d love to see the write-up on the completed production (at least what you’ve done so far). Anything you’d do differently, if you we’re to build another? Is there room on the finished build to put the recharger on board, so you can plug it in anywhere you go?
    Thanks again for taking the time to share!

  4. jamie says:

    How much did u end up spending?

  5. christopher bellamy says:

    Love your project and im going to build an e-atv myself for hunting and work around the farm. The atv im using is a 2001 polaris 500 HO I was able to pick it up for $400 so i don’t have much in the atv it self. im planning on a 48v system becuase i really dont need speed.Range and torq is the main thing im looking for and for it to be quiet to slip in and out of my hunting area. Is there any thing you can tell me about converting this polaris that might make it easier or anything you wish you would of done different. Do you think a 48v system would work good on the polaris using the drivetrain thats already in the atv. what kind of range to you think i could get using a 48v system with a 100 to 200ah battery.Any help would be appreciated.

    • Hi Chris. Thanks for the interest in my project.

      Overall I am very happy with how the ATV turned out. The performance is great with very high torque and it has plenty of capacity for longer rides. I go for offroad rides with some friends that have gas ATVs and they are always amazed at how helpful the extra torque is for slower steep climbs, etc. I can do several hours of snowplowing in my neighborhood and still have capacity left. I would say the only negative is the extra weight, but there is no way around that right now with current battery technology. I would assume that your range would be directly proportional to the battery pack capacity, and I don’t see any reason a 48V system could not work. My pack is 96V and 100ah and I get about 30 miles range driving at lower speeds and starting with a battery pack at room temperature – my garage is warm in the winter. I am also using an AC drive system which is slightly more efficient than a DC system. The belt drive I am using to connect the motor to the transmission works much better than the chain system I used for a few weeks initially. Feel free to ask questions as you work on the project.

      • Pat W says:

        Great project! I also just got a 96 Polaris sportsman that had been converted to electric (36V but think I will expand to 48v) with a similar engine/transmission set up. I was wanting to replace the noisy sprocket and chain for a belt drive similar to yours. It looks like I would be a to use the same belt and pulleys and was hoping you might be able to list the size/models of the pulleys and belt so I know I would be getting something that has been proven to work. FYI, the separation between the center of the motor sprocket and transmission sprocket is right around 10″ with wiggle room. Any info would be greatly appreciated. Thanks!

        • Hi Pat.

          The belt drive will definitely be quieter, but it is also somewhat more expensive. At the time I did the conversion, the belt, pulleys and bushings were about $US300. They are made by Gates and I bought them through McMaster-Carr. Here is a list of the components I used:

          – 1x polychain 8mm pitch 21mm wide carbon belt (product # 7904k139)
          – 2x polychain 4″ OD pulleys (product # 7970K16)
          – 1x taper-lock bushing, 7/8″ bore for mounting pulley on electric motor shaft (product # 57095K159)
          – 1x taper-lock bushing, 1 – 1/2″ bore for mounting pulley on transmission shaft (product # 57095K167)

          The parts you may need could be different than what I listed above. You would need to go on the Gates website to calculate the correct belt length based on the exact distance between the motor shaft and transmission shaft in your setup. You will also need to be able to adjust the distance to correctly tension the belt. Alignment of the pulleys is also more critical than sprockets on a chain drive to prevent wear of the belt.

          Since you already have a sprocket on the transmission, I assume you have adapted the shaft with a keyway. When I did my conversion, I removed the inner shaft from the variable speed pulley that was on the transmission and cut a keyway into the shaft. This shaft fits over the splined shaft that comes out of the transmission and is 1 – 1/2″ OD.

          • Pat W says:

            Thanks! This is great information. It looks like this should work, but I might have a little work to figuring out the pulley on the transmission shaft. I actually didn’t do this conversion, just bought it converted and I am trying to upgrade it. So, not really sure where the current connector came from. It does go over the splined shaft with a bolt holding it on and can be easily pulled off with the bolt removed. Looks like the sprocket has a 2″ ID and is held on to the connector that goes over the splined shaft by 3 bolts.

  6. Basith Penna-Hakkim says:

    This is so cool! I am going to do this for the Honda TRX250X. 😉

  7. Todd says:

    I have a Suzuki King Quad 500 axi, any ideas on how to convert? What are the pain points? How much of the transmission can I keep? How much money do you estimate the project to cost?

    • Hi Todd.

      The biggest reason I used the Polaris for this conversion project was that the engine and transmission were in separate cases, so it was easier to remove the engine and leave the rest of the drivetrain intact. I am not familiar with the Suzuki so not able to provide any guidance, but even if an ATV does not have a separate engine case it would be possible with more work to convert it. Depending on the motor you choose you may still need some form of transmission to allow for gear reduction prior to connection to the drive axle. I have actually considered an ATV v2 project where I connect two separate motors to front and rear differentials, which would simplify the mechanical drivetrain and allow for efficient all-wheel drive.

      The primary challenge (not really a pain point, since I consider challenge something to look forward to) was being able to fit all the components (batteries, motor, charger, motor controller) into the ATV frame without making significant modifications. The biggest cost in any EV conversion project is batteries, and to get the same range as my ATV (~50km) you would need to spend $2000 – $4000.

      For now I have moved on to a new EV conversion project – an electric 1968 mustang fastback.

  8. Ralph Allen says:

    We like hunting but conven atv’s are too loud. Our thoughts are stripping engine, tranny and drive train and going with electric hub motors a battery pack for stealth mode but with a small gas genset to to keep everything charged up while running around to and from. Then switching to electric only when stealth is needed. Do you think this could work?

    • I considered hub motors for this project and also for a car project I am working on right now. Unfortunately, hub motor technology is still developing and it would be more difficult to build up a system with hub motors. Using the existing differentials and half-shafts also makes it easier to keep the motor up and away from most of the water, dirt, etc.

      If you have a charger mounted on the ATV, then yes you could potentially extend your range using a small generator, perhaps mounted to your back rack. My ATV gets about 30 miles of off road range with ~8kWh of battery pack capacity, so roughly 3.5 miles per kwh. So a 1kW generator would need to run for about 1 hour to give you 3.5 miles of range (without accounting for charger losses).

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