Even at its rated voltage, a starter runs at an extreme overload, virtually a dead short. Doubling the voltage also increases the current flow, so if you're cranking in bursts of 5-10 seconds, it's a lot easier on the starter. A continuous duty motor with the power of a starter would need to be approximately the same size and weight of the engine. If the engine doesn't start after a total cranking time of 30 seconds, (six 5-second attempts, for instance) let the starter cool down for a minimum of 20 minutes before trying again.
Jerry
