More Energy
Why does efficiency decrease with the more energy is added When converting from electrical to kinetic energy?
This is because i have recently done a investigation with a remote control car and found the energy put in and energy transfered to kinetic is significantly less each time it is charged for a larger amount of time (this is not the fault of the battery) and the only theory i can come up with to explain it is for the longer it runs the more energy escapes to sound heat and friction. (the more ideas the better and the more detailed the better aswell)
One reason is equation for heat generated due to current or power dissipated. It is
power = current^2 * resistance
In your case the resistance is constant so as the current goes up the power dissipated (heat) will go up exponentially.
You will also have to know more about your motor. The mechanical efficiency will be different at different rpms. This is due to magnetic losses in the motor.
You mentioned heat and typically as things heat up they add resistance to a system both electrically and mechanically.
Ambient temperature has effect on batteries also. That is why automotive batteries sometimes are rated in cold cranking amps and warm cranking amps. If your battery gets while charging unplug it immediately. If it is cold maybe stuck in the fridge it will not charge as well either.
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