Electric cars, trucks, ATVs, NEVs - things bigger than a motorcycle.
jsaenz7   1 µW

Posts: 1
Joined: Nov 28 2020 1:46pm

Hi All!

This is my first post here, I hope it's somehow intersting even though it's pretty long. I'm converting my old 50cc ATV into electric and after doing a lot of reasearch I've come here to get some feedback if possible on some topics I'm stuck with.

Motor performance:
I'll probably go for 3kW mid drive motor from QS along with their EM 150 controller, attached you'll find the datasheet and the testing report they gave me. After doing some maths where I took into account the sprocket wheel relation, weight, aerodynamics, friction and max power of this motor I was able to get an estimate max speed of 75-80km/h.

However, this being an ATV I'm not looking for speed but for torque and acceleration, that's why I tried getting an aproximate acceleration time between 0-50km/h but I wasn't able, as I don't know neither the mean force that is being applied during the 0-50km/h time nor the angular acceleration of the motor axle.

Does anyone know any method of getting an estimated acceleration time for 0-50km/h? I would appreciate that a lot, as with this value I can understand the output performance given a battery input. In other words, this will help me decide how big my battery should be at first to get an acceptable performance.

Battery:
I believe 21700 cells from Smasung, specially the INR 21700 30T are the best batteries arround for my project. Each cell has 3Ah and rated 3,6V. So 20s to get 72V and then arround 10 and 15 in parallel to get somewhere arround 30 to 45Ah of capacity. This will end up being a 2,16-3,24kWh battery.

Moreover, each cell can provide a max of 35A discharge current, but for my case (max current draw from the controller is 150A) 150A/12p (let's say 12 in parallel instead of a gap bewteen 10 and 15) each cell will draw 12,5A, far less that it's max.

My concern here is not that I won't be able to give max power to the controller-motor, as with this cells I will with no problems. My concern is the entire capacity of the battery. Using only 12p will leave me with 36Ah aprox (2,59kWh). I've read on some sites that in order to get the range, I need to divide the battery capacity by the power from the motor. However, this motor can pull off up to 150A (11kW) yet it's nominal power is 3kW, so I'm not quite sure which power value I should use, maybe a central value like 7kW.

The fact that this is an ATV and it's going to be used to drive on the mountain with a lot of accelerations, I beleive that the mean power consumption will be more in the 11kW side than in the 3kW side, let's say 9000W. So that will leave me with 2590Wh/9000W= 0,287 hours of range, and this multiplied by the max speed of the ATV (75km/h)=21,525km.

Does this maths to get the range seem feaseible? Due to space limitation I won't be able to fix more than 15p on the battery. Do you have any recomendation here? Maybe another cell? I was hoping to get arround 35km of range.

Thank you!
Attachments
3000W Mid Drive Motor Testing Report.pdf
3000W Mid Drive Motor.pdf

thepronghorn   1 kW

Posts: 315
Joined: Mar 27 2011 8:07pm
Location: Bay Area, California

Your motor can't really sustain 9kW, but I also doubt it will take 9kW to maintain 75 km/h, so your range will probably be higher than your estimate.

For a 12,5A per cell peak discharge rate, you can go with a much higher capacity 21700 cell such as the 40T which will also help give you much more range.

tylerwatts   100 W

Posts: 156
Joined: Sep 14 2012 3:10am

That motor and controller can easily handle 9kw continuous, proven by countless others in the forum. So don't worry about that. Make sure your quad can handle the torque it'll throw out or you'll have to tune it to less torque to protect your drivetrain and safety.

Cheers
Tyler

HrKlev   100 W

Posts: 231
Joined: Dec 06 2019 10:24am