[NSRCA-discussion] Going Electric - Battery Questions

[Duane Beck]

> The ESC controls the voltage to the Motor, not the battery.

This is not strictly true.  The ESC controls the duty cycle during which the battery's voltage is applied to the motor.  This has the effect of controlling the average voltage, but as some fraction of the battery voltage, not referenced to some absolute voltage.  At 100% duty cycle, obviously the full battery voltage is applied.  At 50% duty cycle (1/2 throttle, more-or-less depending on the ESC and your throttle curve), about half the battery's voltage will be applied to the motor.  If the battery's voltage sags less under this load (because it has a higher C or lower internal resistance), then the motor will try to spin faster (based on its KV).  Spinner faster with the same prop (load) means more torque is required and, with electric motors, current is proportional to torque.  So, for the same throttle position, you end up with more voltage, more current, and more power (proportional to the square of the voltage increase).  You can get the same power output as the lower C battery by reducing the throttle, but you're effectively reducing your usable throttle range - and thereby making it more sensitive.

Duane