An Electric Scooter Community on a Mission to Stamp out Transportation Mediocrity.

Discuss the Xiaomi mijia mi M365 original and pro versions in this forum. Topics include hardware, software, hacking, riding, and everything in between.
#21571
People use batteries with bigger voltages to make the scooter faster and more powerful. I know the max speed and current that can be pushed trough the coils is limited by the voltage. More voltage = more pushing power to overcome the resistance of the coil. Thats all fine an simple.
The problem starts when I read about electric motor workings and basically only the current is what determines torque and voltage doesnt even appear in the equations. Then we get a situation like this: 36v*30A=1080w and 72v*30A=2160w, but they both have the same current, so acceleration would be the same?! That cant be right. Where does the extra kilowatt go? It cant be just lost to heat, if anything, higher voltage should be more efficient, not less.

I understand the motor is controlled by pulse width modulation, so 72v with 60A per pulse at 50% duty cycle would equal 36v*30A on average, so we would get the same result as just using normal 36v battery. That solves the mystery for me for the same power output from a higher voltage battery.
But now I want more torque and, as I understand, the only way to do that is to increase Amps. To increase Amps beyond what the classic motor can eat at 36v we need to increase the voltage.. lets say I want double the torque, so double the Amps: 60A. To push 60A I need double the voltage, so 72V, 60A on 100% duty cycle. 72V*60A= whooping 4320w ! But since im "only" getting double torque, where the hell does the extra 2000w go?

#21575
If you double the voltage for a brushless motor you double the torque, and quadruple the power in theory.

If the motor is not built for twice as much voltage it will heat up and finally burn through.
But don't just think about the motor, think about the whole powertrain: battery - ESC (with software) - motor
By overvolting you can increase the battery voltage but you have no control over the ESC.



#21587
365GUY wrote:
Sat Jun 20, 2020 6:32 am
Your planning on going up to 72v battery ?
Are you going with a Flipski type esc ? I’m sure you know the stock M365 has 63v caps so you can’t push 72v through it unless you want to use it to make some burnt toast.
Yes, the controller needs to be changed, of course, I know. Thats not what im asking here To view images REGISTER or LOGIN for full access.

#21597
Torque, acceleration and top speed are all a product of your battery, controller and motor.. obviously. ( you knew that)
I guess what I’m saying is if your wanting more torque everything else increases to. These are not like cars where changing a rear differential can change the amount of torque it creates.


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