Ass suggested above, there should be 6V of output with a 20 ohm resistor connected, or a little over 300mA short-circuit current. It is hard to get a good measurement while spinning by hand. One method I have used is to use the chuck of a variable-speed electric drill as a roller on the tyre. For comparison, I measured internal resistance at 6.5 ohms and inductance 86-108mH, varying with wheel position.