[jonboy]

The source of the ultimate amount of energy input to the spring is from the motor that is compressing or stretching the spring. The problem was stated that the motor loading the spring stalled. Bad for the motor but what is even worse the power or energy out from the motor is Zero. Max motor power output is usually when the speed of the motor is loaded down to about 1/3 of max RPM as I remember it. Therefore the trick to get the max power available from the motor into the spring is to keep the motor from stalling which means a smaller spring constant. You could take it to an extreme in a frictionless vacuum environment but we are dealing with the real world here so get a “weaker” spring and plan on greater travel for loading it. Good luck!