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A motor/generator (as well as a transformer, or other electromagnetic device), has a characteristic impedance, which can change with RPM or frequency. It appears that this motor/generator is well matched to the 150W 220V lamp, which has an incandescent resistance of 220/0.68=323 ohms. At the same RPM, the generator probably puts out about twice the voltage, or 440 VAC. Thus the generator has an internal impedance about the same as the lamp. Maximum power transfer occurs when the impedance of the source equals that of the load - this is known as impedance matching.The maximum current in this case would be 440/323, or 1.4 amps. But it may be higher, as the impedance is an estimate, and may vary with RPM. Ultimately it will be limited by winding resistance at low RPM and inductance at high RPM. A 12V 24W lamp has an incandescent resistance of 6 ohms and nominal current of 2 amps. It probably has a cold resistance of 1/10 that, or 0.6 ohms. So it is practically a short circuit, and the generator will be limited to 2 or 3 amps. The lamp probably saw power of 20V * 3A = 60W for a short time, and survived. Also note that the load caused the motor to slow down to perhaps half RPM, also reducing the power delivered.

I just had a idea, ceiling fans have multiple poles so they run at a slow speed. They should be really good for slow speed alternators.