Don't worry about stall at cut in, you won't.
Use the test coil to find the number of turns for the cut in speed you have chosen.
If you have chosen a prop with nominal tsr of 7, you would probably take the cut in speed as if it was tsr8 at 7 mph wind speed. As you load the prop the tsr will fall as speed increases. You need to check the loading to make sure you don't fall below about tsr5 at full output.
If you are a good at calculations you may possibly be able to predict the output from load testing one coil, but I have never found it a useful thing to do.
It is much better to measure the resistance ( or calculate it) of the test coil. From that you can predict the winding resistance of the complete machine.
Knowing the open circuit voltage, battery voltage and winding resistance you can then predict the output and see how it compares with the prop power.
If you cut in at 200 rpm for 12v, at 600rpm the o/c voltage will be 36v. You have 24v in excess of the battery so the current into the battery would be 24 divided by the winding resistance. This current x 12v gives you power out.
Power lost in the alternator will be current^2 x winding R. From this you can find the input power ( output + losses) and compare this with your blade power.
Flux
