Thanks Dave for your update.
I am now very confused by your comment that there is little difference in performance depending upon which load resistors you choose. Your graph clearly shows that 120v/1500watt/9.6ohm gives you much more delivered power than 240v/3600w/16ohm load?
If I look at a reasonable operating point below furl, I see at 18mph WS, that you get 2KW vs 1.2KW ..this is NOT insignificant.
As far as a contactor ..is it your intent to simply use a 3phase contactor to add more load at some voltage setpoint near the upper end ie 75v, to utilize that extra torque and possible reduce that 250rpm top end ( more power delivered, less noise, less vibration, less stress on mechanical parts)? Seems like a good idea to me after looking at your chart.
IMHO, a second set of 240v/16ohm elements would load even more than the 120v/9.6ohm, allowing you to use more of that torque with no chance of stall
" Each phase (10 coils wired series) measures approx. 4.5 ohms including the line resistance up to the load"
When you were using the 120v/9.6ohm elements, 1/3 of the power produced by the mill was dissipated as heat in the line wire and generator coils ..that is why for lower voltage systems, they use very heavy wire coming down the tower... but this is fine when the WS is high enough and the swept area big enough, that turbine efficiency % is irrelevant ..all you care about is how much power is "delivered"
I had asked you about TSR and did a few calcs off your graph data and I see TSR<5 at lower WS and TSR=5.5 at mid operating point ...if you send me the data set you used for that graph, I can do a plot of TSR for each of the loads you graphed ...it is important because it will show how loading effects the rpm and torque and ultimately the power produced. BUT, there is some point at which the TSR goes too low and you get into stall region (but not with these loads)
scorman@stny.rr.com
I can also send you my excel calculator which figures all this out
Stew Corman from sunny Endicott