Understanding Motor and controller

[dario_ds]

I know that ebike motor is a three phase motor working on AC produced by the motor controller drawing it's power from the battery. Motor :
I have a hub motor rated as 350w at 36v. A lithium ion cell has a nominal voltage of 3.6~3.7 volts (3.6 volts considered for ease of calculation) and 4.2 volts when fully charged. So a 10s lithium ion battery would be 36v nominal voltage and 42v when fully charged.
Using Ohms law if I calculate the resistance (R) of the load, the motor, I get, R=(VxV)/P= (36x36)/350= 3.703 ohms. If the same motor is used on a fully charged battery i.e. 42v the power consumption is P=(VxV)/R= (42x42)/3.703 = 476.389 watts drawing 11.343 Amps And if I use lithium phosphate battery that has a fully charged voltage (12s) of 43.8v the power is 518.097 watts drawing 11.829 Amps.
Is a 350w motor designed to handle that much of power?

Motor Controller :
My motor controller is rated 36v/48v with lower cutoff voltage of 29v/39v. How would the controller know what voltage battery I am using 36v(10s) or 48v(13s) ?

 

[spooknik]

Hello!

I'm by no means an expert, i've just been tinkering with this stuff the last few weeks and reading / watching a lot. I had a similar thought to yours so I can chime in and maybe it will help :wink:

If the same motor is used on a fully charged battery i.e. 42v the power consumption is P=(VxV)/R= (42x42)/3.703 = 476.389 watts drawing

I believe you are not taking the controller fully into account. The controller takes the current available from the battery and converts it to phase current for your motor. So whatever the battery can deliver regulated is by the controller. The controller can be set to only provide a certain current to each phase.

Is a 350w motor designed to handle that much of power?

Normally a 350W motor is rated for 350W nominal, but peak can be a lot higher. It would be helpful if you knew the rated amps and voltage for your motor. On my motor, they give a nominal and peak amperage. It works out to be 250 W nominal and peak around 500 W. This is safe because the peak current is only for a short time and it doesn't overheat anything. (Further reading here if you're intrested) Sometimes motors are underrated and their design can take a lot more power, but I wouldn't venture into that territory unless you know what you're doing.

How would the controller know what voltage battery I am using 36v(10s) or 48v(13s) ?

Usually this is programmed into the controller somehow. Along with the cut off voltages to prevent underdischarge. It might help to know the model of your controller.